**3. Past tomato-breeding programmes in Ghana**

Tomato-breeding programmes in Ghana can be traced to the 1950–1978 when cultivars like OK, MH and Wosowoso were developed. A major tomato-breeding programme led by the National Research Institute (NRI) in UK also carried out a study from 1994 to 2000. Post 2000, tomato improvement programmes focussed mainly on screening tomato germplasm for both biotic (particularly the TVLCD) and abiotic stresses as well as mutation breeding; however, none has led to the release of varieties. Robinson and Kolavalli in 2010 stated that since the NRI tomato-breeding work ended in 2000, there have been no breeding programmes and no systematic seed multiplication in the country [26]. Again, a 2013 publication indicated that the varieties developed during the 1950 to 1978 together with farmers' selection in tomatogrowing areas have led to the development of large tomato ecotypes in Ghana [27].

parental line [32]. The five induced variant lines used in the previous study were also analysed for lycopene, total antioxidant properties and other quality factors such as pH, total soluble solids (TSS) and total solids. Similarly, 10 F5 tomato-breeding lines were characterized for variability in physico-chemical properties (colour, pH, total titratable acidity (TTA), TSS and vitamin C). The lines used include wosowoso (parent variety), cherry yellow, roma variant (a prolific trait), wosowoso variant (stripped, prolific and big fruit), roma variant (bicoloured fruit), *S. pimpinellifolium* parent, roma variant (hardened and big fruit), roma variant (yellow skin), roma variant (red skin) and wosowoso variant (big fruit, and deep red color). The lines varied in the various physico-chemical properties measured [33]. In addition, fruits of F4 lines derived from crosses between some varieties of *S. lycopersicon*, cherry red, cherry yellow and roma, and wosowoso with a wild tomato, *S. pimpinellifolium,* were analysed for physicochemical properties, and variation was seen among the lines for the traits studied [34].

Review on Tomato (*Solanum lycopersicum*, L.) Improvement Programmes in Ghana

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53

In 2014, five introduced fresh market tomato varieties from the USA and Crops Research Institute of Ghana (CRI) were evaluated for genetic variability, adaptability in Ghana as well as plant and fruit attributes. The varieties included Heinz, Shasta, Op-B149, Op-B155 and CRI-P00. With the advent of molecular markers, this study used 15 Simple Sequence Repeat (SSR) primers (**Table 1**) to determine the genetic diversity existing among the five introduced fresh market tomato varieties [35]. In order to establish the genetic diversity that exists in the germplasm collected in 2015, all the accessions (in exception of Rano) were evaluated in field as well as molecularly characterized using 12 SSR primers. The SSR primers include Tom 8–9-F, Tom 11–28-F, Tom 55–56-F, Tom 59–60-F, Tom 67–68-F together with seven primers listed in **Table 1** [36]. In the same year, 20 tomato genotypes were evaluated in the greenhouse as well as the field at the University of Ghana Forest and Horticultural Crops Research Centre (FOHCREC), Okumaning-Kade in the Eastern Region of Ghana to determine the genetic variability in agronomic and fruit-quality traits. There was variability in almost all the traits studied [37].

The various findings of the germplasm evaluation for morphological and agronomic traits together with the variability that exists in the germplasm can be explored in the development

Cultivars such as OK, MH series [38] and Wosowoso [39] were developed in the 1950s. Agble [40] also began breeding for processing quality traits, shelf life and heat tolerance lines by making crosses between local accessions with heat-tolerant and nonripening gene (norA) from exotic accessions. Nonetheless, due to lack of continuity, no variety was released despite the

The NRI focused on pure line selection of local landraces in the Brong Ahafo region of Ghana with the aim of releasing pure lines of good open-pollinated varieties. Six varieties consisting of three local and three introduced varieties were used in that study. These varieties were selected based on farmers and traders (fruit quality, good taste and longer shelf life) preferred traits. As part of this project, a tomato breeder seed production trial was then established at Wa in the Upper West region with the five selected varieties. The research was, however, not very successful because there was no long-term impact due to lack of sustainable seed distribution systems to ensure that the resource-poor farmers have access to the developed varieties [42].

of new varieties.

positive outlook [41].

**3.2. Breeding for fruit quality**

#### **3.1. Germplasm collection and genetic diversity studies**

Germplasm is required for the commencement of any breeding programme. Consequently, the Council for Scientific and Industrial Research-Plant Genetic Resources Research Institute (CSIR-PGRRI) and the National Agriculture Research Programme periodically collected a number of tomato accessions from all the 10 regions in Ghana. The 2012 tomato germplasm collection by the Council for Scientific and Industrial Research-Crops Research Institute of Ghana (CSIR-CRI) included accessions from two districts in Burkina Faso (Kougoussi and Yako), Asian Vegetable Research Development Centre (AVRDC), Rural Development Administration (RDA), National Institute of Horticulture and Herbal Science (NIHHS) and Republic of Korea. This was funded by the Korea Africa Food and Agricultural Cooperation Initiative (KAFACI) project [28]. Recently, 13 accessions were also collected from Afari, Akumdan and Akuawu in the Ashanti region. The recent germplasm collected included accessions such as 'Atoa', 'Daagyine', 'Local 1', 'Power', Pectofake 1, Petomech, 'Akoma', Pectofake 2, Powerano, 'Bolga', 'Dwidwi' (cherry), 'Local 2' and Rano [29]. Most of the locally collected germplasm and introduced accessions have been evaluated for various agronomic and morphological traits as well as the establishment of genetic variation that exists within this germplasm. The Savanna Agricultural Research Institute evaluated three tomato varieties (ICRISIND, Petomech and Tropimech) for various agronomic traits. Variations were observed in plant height, days to flowering, number of fruits, fruit size and fruit weight [30]. Again in 2013, SARI evaluated the following accessions: S 22, Naywli, Bebi yereye, LBR 7, Keneya, LBR 17, Abhijay and Petomech for variability in various agronomic traits [31].

*S. pimpinellifolium* possesses some desirable traits that can be utilized to improve cultivated varieties; however, the size of the fruit is a hindrance to domestication. In order to improve on the size and other desirable traits, a group of researchers at the Biotechnology and Nuclear Agriculture Research Institute (BNARI) of the Ghana Atomic Energy Commission (GAEC) irradiated the seeds of *S. pimpinellifolium.* The variability of the elemental composition of five mutation-induced variant lines (M3 population; BV-27, BV-40, BV-21, BV-23, BV-10/27) of *S. pimpinellifolium* and the parental line was studied using Instrumental Neutron Activation Analysis (INAA). The results showed a significant variation in the concentration of elements (Na, K, Ca, Mg, Cu, Mn and V) in the pericarp, pulp and seeds of the variant lines and the parental line [32]. The five induced variant lines used in the previous study were also analysed for lycopene, total antioxidant properties and other quality factors such as pH, total soluble solids (TSS) and total solids. Similarly, 10 F5 tomato-breeding lines were characterized for variability in physico-chemical properties (colour, pH, total titratable acidity (TTA), TSS and vitamin C). The lines used include wosowoso (parent variety), cherry yellow, roma variant (a prolific trait), wosowoso variant (stripped, prolific and big fruit), roma variant (bicoloured fruit), *S. pimpinellifolium* parent, roma variant (hardened and big fruit), roma variant (yellow skin), roma variant (red skin) and wosowoso variant (big fruit, and deep red color). The lines varied in the various physico-chemical properties measured [33]. In addition, fruits of F4 lines derived from crosses between some varieties of *S. lycopersicon*, cherry red, cherry yellow and roma, and wosowoso with a wild tomato, *S. pimpinellifolium,* were analysed for physicochemical properties, and variation was seen among the lines for the traits studied [34].

In 2014, five introduced fresh market tomato varieties from the USA and Crops Research Institute of Ghana (CRI) were evaluated for genetic variability, adaptability in Ghana as well as plant and fruit attributes. The varieties included Heinz, Shasta, Op-B149, Op-B155 and CRI-P00. With the advent of molecular markers, this study used 15 Simple Sequence Repeat (SSR) primers (**Table 1**) to determine the genetic diversity existing among the five introduced fresh market tomato varieties [35]. In order to establish the genetic diversity that exists in the germplasm collected in 2015, all the accessions (in exception of Rano) were evaluated in field as well as molecularly characterized using 12 SSR primers. The SSR primers include Tom 8–9-F, Tom 11–28-F, Tom 55–56-F, Tom 59–60-F, Tom 67–68-F together with seven primers listed in **Table 1** [36]. In the same year, 20 tomato genotypes were evaluated in the greenhouse as well as the field at the University of Ghana Forest and Horticultural Crops Research Centre (FOHCREC), Okumaning-Kade in the Eastern Region of Ghana to determine the genetic variability in agronomic and fruit-quality traits. There was variability in almost all the traits studied [37].

The various findings of the germplasm evaluation for morphological and agronomic traits together with the variability that exists in the germplasm can be explored in the development of new varieties.

#### **3.2. Breeding for fruit quality**

**3. Past tomato-breeding programmes in Ghana**

52 Recent Advances in Tomato Breeding and Production

**3.1. Germplasm collection and genetic diversity studies**

Tomato-breeding programmes in Ghana can be traced to the 1950–1978 when cultivars like OK, MH and Wosowoso were developed. A major tomato-breeding programme led by the National Research Institute (NRI) in UK also carried out a study from 1994 to 2000. Post 2000, tomato improvement programmes focussed mainly on screening tomato germplasm for both biotic (particularly the TVLCD) and abiotic stresses as well as mutation breeding; however, none has led to the release of varieties. Robinson and Kolavalli in 2010 stated that since the NRI tomato-breeding work ended in 2000, there have been no breeding programmes and no systematic seed multiplication in the country [26]. Again, a 2013 publication indicated that the varieties developed during the 1950 to 1978 together with farmers' selection in tomato-

growing areas have led to the development of large tomato ecotypes in Ghana [27].

17, Abhijay and Petomech for variability in various agronomic traits [31].

*S. pimpinellifolium* possesses some desirable traits that can be utilized to improve cultivated varieties; however, the size of the fruit is a hindrance to domestication. In order to improve on the size and other desirable traits, a group of researchers at the Biotechnology and Nuclear Agriculture Research Institute (BNARI) of the Ghana Atomic Energy Commission (GAEC) irradiated the seeds of *S. pimpinellifolium.* The variability of the elemental composition of five mutation-induced variant lines (M3 population; BV-27, BV-40, BV-21, BV-23, BV-10/27) of *S. pimpinellifolium* and the parental line was studied using Instrumental Neutron Activation Analysis (INAA). The results showed a significant variation in the concentration of elements (Na, K, Ca, Mg, Cu, Mn and V) in the pericarp, pulp and seeds of the variant lines and the

Germplasm is required for the commencement of any breeding programme. Consequently, the Council for Scientific and Industrial Research-Plant Genetic Resources Research Institute (CSIR-PGRRI) and the National Agriculture Research Programme periodically collected a number of tomato accessions from all the 10 regions in Ghana. The 2012 tomato germplasm collection by the Council for Scientific and Industrial Research-Crops Research Institute of Ghana (CSIR-CRI) included accessions from two districts in Burkina Faso (Kougoussi and Yako), Asian Vegetable Research Development Centre (AVRDC), Rural Development Administration (RDA), National Institute of Horticulture and Herbal Science (NIHHS) and Republic of Korea. This was funded by the Korea Africa Food and Agricultural Cooperation Initiative (KAFACI) project [28]. Recently, 13 accessions were also collected from Afari, Akumdan and Akuawu in the Ashanti region. The recent germplasm collected included accessions such as 'Atoa', 'Daagyine', 'Local 1', 'Power', Pectofake 1, Petomech, 'Akoma', Pectofake 2, Powerano, 'Bolga', 'Dwidwi' (cherry), 'Local 2' and Rano [29]. Most of the locally collected germplasm and introduced accessions have been evaluated for various agronomic and morphological traits as well as the establishment of genetic variation that exists within this germplasm. The Savanna Agricultural Research Institute evaluated three tomato varieties (ICRISIND, Petomech and Tropimech) for various agronomic traits. Variations were observed in plant height, days to flowering, number of fruits, fruit size and fruit weight [30]. Again in 2013, SARI evaluated the following accessions: S 22, Naywli, Bebi yereye, LBR 7, Keneya, LBR

Cultivars such as OK, MH series [38] and Wosowoso [39] were developed in the 1950s. Agble [40] also began breeding for processing quality traits, shelf life and heat tolerance lines by making crosses between local accessions with heat-tolerant and nonripening gene (norA) from exotic accessions. Nonetheless, due to lack of continuity, no variety was released despite the positive outlook [41].

The NRI focused on pure line selection of local landraces in the Brong Ahafo region of Ghana with the aim of releasing pure lines of good open-pollinated varieties. Six varieties consisting of three local and three introduced varieties were used in that study. These varieties were selected based on farmers and traders (fruit quality, good taste and longer shelf life) preferred traits. As part of this project, a tomato breeder seed production trial was then established at Wa in the Upper West region with the five selected varieties. The research was, however, not very successful because there was no long-term impact due to lack of sustainable seed distribution systems to ensure that the resource-poor farmers have access to the developed varieties [42].


From 2011 to 2013, pure line selection was used to advance a locally identified cultivar commonly called petofake. From the segregating population collected from farmers, 12 progenies (P002, P005, P011, P020, P026, P035, P057, P068, P074, P077, P082 and P085) were selected based on their fruit shape, size, color, surface and yield [43]. Trials are ongoing to release

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55

Dried seeds of SP 300/30.4.2.4, a variant line selected from second generation (M2) following the irradiation of *S. pimpinellifolium* at 300 Gy, were used for a study. Also, seeds (2000) of SP 300/30.4.2.4 were re-irradiated at 150 and 300 Gy and included in the study. From the study, it was found that the irradiation led to a reduction in plant height and a larger fruit size. Variation was also observed in color, plant height, architecture, number of days to flowering

Post 2000 has seen some breeding efforts made in screening tomato accessions against biotic stresses. However, most of these programmes focussed on the most devastating tomato dis-

TYLCD is a major tomato disease in Ghana and Africa as a whole and can lead to a massive yield loss and consequent impact on livelihood if the vector of the disease (whitefly) is not controlled and infection starts at an early stage of the plant growth [45]. The Tomato Yellow Leaf Curl Virus (TYLCV) causes the TYLCD. It was reported that the USAID West African Regional Programme identified research on Virus resistance (VR) as a priority, and Ghana was included in seven members' regional investigation of tomato virus complex [46]. The Agricultural Biotechnology Support Project II (ABSPII) aimed to improve agriculture production in the developing countries through Biotechnology, and that is why this project was initiated in 2005 to address tomato production in West Africa. This project was a partnership among researchers from AVRDC, Cornell University and University of California-Davis (UC Davis). The ABSII established the Regional Vegetable Germplasm Trailing Network that evaluated 100 putatively TYLCD-resistant tomato varieties that were adaptable to the growing conditions of West Africa which Ghana was a part from 2005 through 2008. In the 2005–2006 growing season, only 40 varieties were evaluated (**Table 2**). The resistant varieties used for the entire trial were mainly F1 hybrids since they were sourced from commercial seed companies and some breeding lines from breeding institutions. Based on the TYLCD scoring scale, at the end of the 2007–2008 multilocational trail, varieties such as Lety F1 scored below 1, Yosra scored 1, and Atak, Bybal and Gempride scored between 1.0 and 2.0 in Ghana (Navrongo and Technimanitia). The lower score was an indication of tolerance under the disease pressure. It was noted that the varieties suffered under farmers' field compared to research stations under comparable disease pressure. At the various trial locations, farmers preferred Lety F1, Yosra, Atak and Bybal. Due to the competitive nature of the tomato-breeding industry in developed world, some of the selected varieties were no longer in use in the countries where they were

and fruiting. This variation can be explored in future breeding programmes [44].

**3.4. Screening germplasm for tomato yellow leaf curl disease resistance**

these lines.

ease (TYLCD).

originally bred [47].

**3.3. Breeding for biotic stress**

**Table 1.** Tomato microsatellite markers used in DNA fingerprinting among five tomato accessions.

From 2011 to 2013, pure line selection was used to advance a locally identified cultivar commonly called petofake. From the segregating population collected from farmers, 12 progenies (P002, P005, P011, P020, P026, P035, P057, P068, P074, P077, P082 and P085) were selected based on their fruit shape, size, color, surface and yield [43]. Trials are ongoing to release these lines.

Dried seeds of SP 300/30.4.2.4, a variant line selected from second generation (M2) following the irradiation of *S. pimpinellifolium* at 300 Gy, were used for a study. Also, seeds (2000) of SP 300/30.4.2.4 were re-irradiated at 150 and 300 Gy and included in the study. From the study, it was found that the irradiation led to a reduction in plant height and a larger fruit size. Variation was also observed in color, plant height, architecture, number of days to flowering and fruiting. This variation can be explored in future breeding programmes [44].

#### **3.3. Breeding for biotic stress**

**Marker no. Primer sequence (5′-3′) Number of bases**

ACAAATCAAAGGAACAATTTCAA (R) 23

CCACACAATAAAGACAGAAAAATG (R) 24

GTGTGTGTGTGTGTGTGTGTGT (R) 22

ACCGAGACTCCTGGCTCATA (R) 20

TCTCTTATAATTTTGTTGAGTCTCTGA (R) 27

TTTTTAAAATACCATTCCAGAAAAA (R) 25

CATTCGTGGCATGAGATCAA (R) 20

CTCGACAAGCTAATTTCTGGG (R) 21

CACCACGAAGGCTGTTGTTA (R) 20

GAGAGGTGCCACATCACCTT (R) 20

AGGTACAACTCACCTCCCCC (R) 20

TCATTTTCCAATGGTGTCAAA (R) 21

CCTTCCCCTTTTGTCTCTCC (R) 20

GCCGACTTCAAAAACTGCTC (R) 20

TTTCCAAAATGACCTAGCGG (R) 20

TGS0001F GCGACCCTCTATTGAACTTGAAGAC (F) 25

54 Recent Advances in Tomato Breeding and Production

TGS0002F GCAAACGTGTTCGAGTTCGTG (F) 21

TGS0003F ATGCATGCGTGTGTGTTGTA (F) 20

TGS0004F GCAATTTATTTTCATTTGTTATACCGGA (F) 28

TGS0005F GACAAAAATTTTCCACACGGC (F) 21

TGS0006F GTCGCATAAATATGGACAACGA (F) 22

TGS0007F GTGGATTCACTTACCGTTACAAGTT (F) 25

TGS0008F GCGGTGTGAAATACAACAAGACG (F) 23

TGS0009F GCGAAGCAAAAGAAAATTGGG (F) 21

TGS0010F TTGAAAAGCTGAAAAGTCAATCA (F) 23

TGS0012F GTCCCTACCCCACAAATTGAA (F) 21

TGS0013F GGTGGACATATGAGAAGACCTTG (F) 23

TGS0014F GTGAAGACGAAAAACAAGACGA (F) 22

TGS0020F TCTTTCAACTTCTCAACTTTGGC (F) 23

TGS0023F GTCCAAATTAAAAACTAACCGCA (F) 23

**Table 1.** Tomato microsatellite markers used in DNA fingerprinting among five tomato accessions.

NB: F: forward primer, R: **r**everse primer.

Post 2000 has seen some breeding efforts made in screening tomato accessions against biotic stresses. However, most of these programmes focussed on the most devastating tomato disease (TYLCD).

#### **3.4. Screening germplasm for tomato yellow leaf curl disease resistance**

TYLCD is a major tomato disease in Ghana and Africa as a whole and can lead to a massive yield loss and consequent impact on livelihood if the vector of the disease (whitefly) is not controlled and infection starts at an early stage of the plant growth [45]. The Tomato Yellow Leaf Curl Virus (TYLCV) causes the TYLCD. It was reported that the USAID West African Regional Programme identified research on Virus resistance (VR) as a priority, and Ghana was included in seven members' regional investigation of tomato virus complex [46]. The Agricultural Biotechnology Support Project II (ABSPII) aimed to improve agriculture production in the developing countries through Biotechnology, and that is why this project was initiated in 2005 to address tomato production in West Africa. This project was a partnership among researchers from AVRDC, Cornell University and University of California-Davis (UC Davis). The ABSII established the Regional Vegetable Germplasm Trailing Network that evaluated 100 putatively TYLCD-resistant tomato varieties that were adaptable to the growing conditions of West Africa which Ghana was a part from 2005 through 2008. In the 2005–2006 growing season, only 40 varieties were evaluated (**Table 2**). The resistant varieties used for the entire trial were mainly F1 hybrids since they were sourced from commercial seed companies and some breeding lines from breeding institutions. Based on the TYLCD scoring scale, at the end of the 2007–2008 multilocational trail, varieties such as Lety F1 scored below 1, Yosra scored 1, and Atak, Bybal and Gempride scored between 1.0 and 2.0 in Ghana (Navrongo and Technimanitia). The lower score was an indication of tolerance under the disease pressure. It was noted that the varieties suffered under farmers' field compared to research stations under comparable disease pressure. At the various trial locations, farmers preferred Lety F1, Yosra, Atak and Bybal. Due to the competitive nature of the tomato-breeding industry in developed world, some of the selected varieties were no longer in use in the countries where they were originally bred [47].


In 2008, three distinct isolates of the TYLCD virus were identified in Ghana from infected tomato plant samples collected from the Ashanti region in Ghana. The three strains of virus identified are the Tomato Yellow Leaf Curl Ghana Virus, Tomato Yellow Leaf Curl Kumasi

F1 3019 Galina Nadira

Susceptible check

*Ty-1*

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57

Fifteen tomato accessions (collected from AVRDC-Taiwan and CSIR-Crops Research Institute, Ghana) that have been reported to be resistant to TYLCD as well as susceptible checks were screened against the TYLCD in a greenhouse at the Kwame Nkrumah University of Science and Technology (KNUST) in Kumasi (**Table 3**). These 15 accessions were later on evaluated in the field at Afari (hot spot) in the Ashanti region. The whiteflies used for the greenhouse inoculation were collected from infested tomato plants at Akumadan, Agogo and Afari. The incidence and severity of TYLCV were scored 30, 45 and 60 days after transplanting using the severity scale 0–4 developed by Lapidot and Friedmann in 2002. At 60 days after transplanting in the greenhouse, accessions A2 (FLA456-4), G14 (WSP2F7 (3) PT.3) and G15 (WSP27F7 (3) PT.3) expressed moderate symptoms in terms of incidence of the TYLCD while accessions A8 (99S-C-39-20), A9 (H24), G13 (WS273.3LARGE) and G12 (WSP2F1PT.3) also showed mild symptom of the disease. A1 (TY52), A3 (FLA478-6-3-0), A6 (TLB111) and A7 (LA 1969) expressed slight severity to the TYLCD. Accessions G11 (PIMPILIFOLIUM) and A1 (FLA505) had the lowest incidence rate compared to accessions A10 (CLN2026D), G13 (WS273.3LARGE) and A4 (FLA653-3-1-0) that had the highest incidence of TYLCV infection in the field. At 60 days

after transplanting only accession, A1 (FLA505) showed no TYLCD symptoms [49].

Again, 30 accessions (including the 15 accessions that were screened in the greenhouse and the field in 2010) were screened against the local strains of virus in Afari in the Ashanti region (**Table 4**). Some of these accessions were reported to be resistant in other countries. Only two accessions (Local Rano and Petomech-Ghana/France) out of the 30 accessions expressed mild symptoms whilst accessions WSP2F1pt.3 and Tomato Red Cloud expressed moderate symptoms after 60 days of transplanting. In order to confirm the resistance or susceptibility

Virus and the Tomato Yellow Leaf Curl Mali Virus [48].

**Table 2.** Forty varieties evaluated in 2005–2006 TYLCD resistance trails.

**Seed source Variety name Resistance source**

Nirouz TH 99806 Yassamen TH 99802

PS 43316

Takii TY 75 *Ty-2*

Nadira Roma VF

Seminis GemPride

Seminis—India Sasya 0202 F1 Syngenta Cheyenne E448

Tropicasem F1 3019 Galina


**Table 2.** Forty varieties evaluated in 2005–2006 TYLCD resistance trails.

**Seed source Variety name Resistance source**

Ty-2 Ty-2 Ty-2 Ty-2 Ty-2 Ty-2 Ty-2 Ty-2

*Ty-1 Ty-1*

*S. chilense* LA 1969, *S. habrochaites* H24

*Ty-2*, *S. habrochaites* H24 *S. chilense* LA 1969 and LA2779

*S. pimpinellifolium S. chilense* LA 1969

CLN 2460E Ty-2 CLN 2468A Ty-2 CLN 2498E Ty-2 CLN 2545A Ty-2 CLN 2545B Ty-2 PT 4722A Ty-2 TLCV 15 Ty-2

O4 240 O4 495 O4 498 O4 501

Lety F1 Realeza Thoriya

Lety F1 Realeza Thoriya

Chenoa Ponchita Yosra

FTC 6236 FTC 7088 FTC 7127 FTC 7351 FTC 7483 HMX 4810

Hebrew University Favi 9 Ih902

Industry DR 10403

Industry DR 10403

AVRDC CLN 2123A Ty-2

56 Recent Advances in Tomato Breeding and Production

Cirad Guadeloupe O4 108

De Ruiter Seeds Bybal

Enza Zaden Bybal

Enza Zaden Atak

Harris Moran FTC 6231

Hazera HA 3060

In 2008, three distinct isolates of the TYLCD virus were identified in Ghana from infected tomato plant samples collected from the Ashanti region in Ghana. The three strains of virus identified are the Tomato Yellow Leaf Curl Ghana Virus, Tomato Yellow Leaf Curl Kumasi Virus and the Tomato Yellow Leaf Curl Mali Virus [48].

Fifteen tomato accessions (collected from AVRDC-Taiwan and CSIR-Crops Research Institute, Ghana) that have been reported to be resistant to TYLCD as well as susceptible checks were screened against the TYLCD in a greenhouse at the Kwame Nkrumah University of Science and Technology (KNUST) in Kumasi (**Table 3**). These 15 accessions were later on evaluated in the field at Afari (hot spot) in the Ashanti region. The whiteflies used for the greenhouse inoculation were collected from infested tomato plants at Akumadan, Agogo and Afari. The incidence and severity of TYLCV were scored 30, 45 and 60 days after transplanting using the severity scale 0–4 developed by Lapidot and Friedmann in 2002. At 60 days after transplanting in the greenhouse, accessions A2 (FLA456-4), G14 (WSP2F7 (3) PT.3) and G15 (WSP27F7 (3) PT.3) expressed moderate symptoms in terms of incidence of the TYLCD while accessions A8 (99S-C-39-20), A9 (H24), G13 (WS273.3LARGE) and G12 (WSP2F1PT.3) also showed mild symptom of the disease. A1 (TY52), A3 (FLA478-6-3-0), A6 (TLB111) and A7 (LA 1969) expressed slight severity to the TYLCD. Accessions G11 (PIMPILIFOLIUM) and A1 (FLA505) had the lowest incidence rate compared to accessions A10 (CLN2026D), G13 (WS273.3LARGE) and A4 (FLA653-3-1-0) that had the highest incidence of TYLCV infection in the field. At 60 days after transplanting only accession, A1 (FLA505) showed no TYLCD symptoms [49].

Again, 30 accessions (including the 15 accessions that were screened in the greenhouse and the field in 2010) were screened against the local strains of virus in Afari in the Ashanti region (**Table 4**). Some of these accessions were reported to be resistant in other countries. Only two accessions (Local Rano and Petomech-Ghana/France) out of the 30 accessions expressed mild symptoms whilst accessions WSP2F1pt.3 and Tomato Red Cloud expressed moderate symptoms after 60 days of transplanting. In order to confirm the resistance or susceptibility


**Table 3.** Tomato accessions used for the TYLCD screening in both the greenhouse and the field.

observed in the field, six viral detection primers were used to screen all the 30 tomato accessions (**Table 5**). From the results obtained in that study, none of the primers amplified viral DNA in Tomato Red Cloud. For WSP2F1pt.3, only one of the six primers (PAL/PAR) amplified the viral DNA. Only MF/MR primer amplified the viral DNA in Local Roma. For Petomech (Ghana/France), two primers (GHF/GHR and KR/KF) amplified the viral DNA. None of the 30 accessions was considered resistant since none of them showed no symptom in the field as well as no TYLCV DNA amplification [50].

Again, between 2010 and 2011, seven tomato varieties (**Table 6**) were grown in the fields against the TYLCD in the University of Ghana and the Volta region of Ghana. The symptom expression of the varieties against the TYLCV was confirmed in the laboratory using the set of primers in **Table 5** in addition to Beta 01/02. The study also identified Ty-3 gene in tomato that confer resistance to TYLCV using the primers in **Table 7**. From the field screening, it was found that Burkina (obtained from farmers in the Volta region) had the highest TYLCD incidence, followed by Petomech and the susceptible check. However, Petomech expressed higher severity than Burkina. Both severity and incidence were lower in the hybrids in exception of F1 Thorgal that showed no symptom. AC1048/AV494 detected the most viral DNA in the samples collected. The primer set T0302-F/T0302-R did not amplify the Ty-2 gene in any of the varieties evaluated. However, Primer P6-25-F/P6-25-R amplified a band size of approximately 400 bp in F1 Jaquar, F1 Nadira and *S. pimpinellifolium* [51].

Between 2011 and 2012, a group of researchers also evaluated the susceptibility of 10 accessions to TYLCD under field conditions. The accessions include *S. pimpinellifolium*, Wosowoso, Cherry red, Roma, Hyb−1 (Wosowoso × *S. pimpinellifolium*), Hyb-2 (Roma × *S. pimpinellifolium*), Hyb-3

**Entries Code Resistance source Origin**

TLB 111 A6 H24 AVRDC

H24 A9 *L. hirsutum* f.sp. *glabratum* G. Kallo, India CLN2026D A10 Susceptible check AVRDC *Pimpinellifolium* G11 Unknown CSIR-CRI WSP2F1pt.3 G12 Unknown CSIR-CRI WS273.3 Large G13 Unknown CSIR-CRI WSP2F7 (3) pt.3 G14 Unknown CSIR-CRI 2641A B16 Unknown AVRDC Tomato Money Maker B17 Unknown USA

Tomato Roma-Jam Vf B18 Unknown Burkina Faso

Petomech (Ghana/Burkina) B28 Unknown Burkina Faso Petomech (Ghana) B29 Unknown Ghana Tomato Ventura F B30 Unknown USA

**Table 4.** A list of tomato accessions screened against the tomato yellow leaf curl disease in Afari.

Parona B19 Unknown Local Local Roma B20 Unknown Local Rando B21 Unknown Local Tomato Slumac B22 Unknown Holland Tomato Tima B23 Unknown France Tomato Red Cloud B24 Unknown Holland Tomato Rio Grande B25 Unknown Holland Petomech (Ghana/France) B26 Unknown France Tomato Roma VF B27 Unknown USA

FLA 505 A1 LA 1969 (*L. chilense*) J. Scott, Univ. Florida FLA 456–4 A2 Tyking, LA2779 (*L. chilense*) J. Scott, Univ. Florida FLA 478–6–3-0 A3 LA1938, Tyking, Fiona J. Scott, Univ. Florida FLA 653–3–1-0 A4 LA2779 (*L. chilense*), Tyking J. Scott, Univ. Florida FLA 496–11–6-1-0 A5 LA1932 (*L. chilense*), Tyking J. Scott, Univ. Florida

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TY52 A7 LA 1969 (*L. chilense*) D. Zamir, Hebrew Univ. 99S-C-39-20-11-24-17-0 A8 Unknown Namdhari Seeds, India


**Table 4.** A list of tomato accessions screened against the tomato yellow leaf curl disease in Afari.

observed in the field, six viral detection primers were used to screen all the 30 tomato accessions (**Table 5**). From the results obtained in that study, none of the primers amplified viral DNA in Tomato Red Cloud. For WSP2F1pt.3, only one of the six primers (PAL/PAR) amplified the viral DNA. Only MF/MR primer amplified the viral DNA in Local Roma. For Petomech (Ghana/France), two primers (GHF/GHR and KR/KF) amplified the viral DNA. None of the 30 accessions was considered resistant since none of them showed no symptom in the field as

Again, between 2010 and 2011, seven tomato varieties (**Table 6**) were grown in the fields against the TYLCD in the University of Ghana and the Volta region of Ghana. The symptom expression of the varieties against the TYLCV was confirmed in the laboratory using the set of primers in **Table 5** in addition to Beta 01/02. The study also identified Ty-3 gene in tomato that confer resistance to TYLCV using the primers in **Table 7**. From the field screening, it was found that Burkina (obtained from farmers in the Volta region) had the highest TYLCD incidence, followed by Petomech and the susceptible check. However, Petomech expressed higher severity than Burkina. Both severity and incidence were lower in the hybrids in exception of F1 Thorgal that showed no symptom. AC1048/AV494 detected the most viral DNA in the samples collected. The primer set T0302-F/T0302-R did not amplify the Ty-2 gene in any of the varieties evaluated. However, Primer P6-25-F/P6-25-R amplified a band size of approxi-

well as no TYLCV DNA amplification [50].

mately 400 bp in F1 Jaquar, F1 Nadira and *S. pimpinellifolium* [51].

**Accessions Resistance source Origin**

58 Recent Advances in Tomato Breeding and Production

H24 (A9) *L. hirsutum* f.sp. *glabratum* G. Kalloo, India

**Table 3.** Tomato accessions used for the TYLCD screening in both the greenhouse and the field.

TLB111 (A6) H24 AVRDC CLN2026D (A10) Susceptible check AVRDC WSP2F1PT.3 (G12) Unknown CSIR-CRI WS273.3LARGE (G13) Unknown CSIR-CRI WSP2F7 (3) PT.3 (G14) Unknown CSIR-CRI PIMPILIFOLIUM (G11) Unknown CSIR-CRI WSP27F7 (3) PT.3 (G15) Susceptible Check CSIR-CRI

TY52 (A7) LA 1969 D. Zamir, Hebrew University 'FLA456–4 (A2) Tyking, LA2779 (*L. chilense*) J. Scott, University of Florida FLA505 (A1) LA1969, Tyking, Fiona J. Scott, University of Florida FLA496–11–6-1-0 (A5) LA1932 J. Scott, University of Florida FLA478–6–3-0 (A3) LA1938 (*L. chilense*), Tyking J. Scott, University of Florida FLA653–3–1-0 (A4) LA2779 (*L. chilense*), Tyking J. Scott, University of Florida 99S-C-39-20 (A8) Unknown Namdhari Seeds, India

> Between 2011 and 2012, a group of researchers also evaluated the susceptibility of 10 accessions to TYLCD under field conditions. The accessions include *S. pimpinellifolium*, Wosowoso, Cherry red, Roma, Hyb−1 (Wosowoso × *S. pimpinellifolium*), Hyb-2 (Roma × *S. pimpinellifolium*), Hyb-3


the viral DNA among the accessions. This work also deployed both triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) and PCR method (using the primers in **Table 5**) for the TYLCV detection in order to recommend a better way of detecting TYLCV in infected samples. A TAS-ELISA kit with a known TYLCV-infected *Nicotiana benthamiana*positive control was used for the study. The study confirmed the superior sensitivity of the PCR technique as a TYLCV detection method compared to the TAS-ELISA technique. There were no observable TYLCV symptoms on the BC-3 (C-Red × (C-red × *S. pimpinellifolium*)) in the field and both methods did not detect viral DNA in the leaf samples. BC- 1 (Wosowoso × (Wosowoso × *S. pimpinellifolium*)) behaved similarly like BC-3 in the field but there was amplification of viral DNA by the AV494/AC1048 primer set. In addition, two PCR primers detected viral DNA in the *S. pimpinellifolium* even though there was no TYLCV symptom observed in

Ji and Scott (2006)

61

Ji et al. (2007)

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**Primer Primer sequence Reference**

Review on Tomato (*Solanum lycopersicum*, L.) Improvement Programmes in Ghana

T0302-F/T0302-R F: TGGCTCATCCTGAAGCTGATAGCGC

P6–25-F/P6–25-R F: GGT AGT GGA AAT GAT GCTGCTC

**Table 7.** Primer pairs and sequences for TYLCV gene detection.

R: AGTGTACATCCTTGCCATTGACT

R: GCT CTG CCT ATT GTC CCA TAT ATA ACC

Recently, there was a phenotypic evaluation of 36 local tomato genotypes (**Table 8**) for the source of resistance against TYLCD in two locations (University of Cape Coast and Asuansi) in Ghana. The results showed that five accessions (K005-Petomec, K100-Local 3, K213-AVTO 9804, K116-Ashanti 2 and K042-Tomatose) out of the 36 genotypes were selected for mild severity, two genotypes showed severe symptoms (K027-Local, K202- AVTO 0102) and one genotype (LV-Fadzebegye) showed moderate severity. In order to confirm the infection or otherwise of the eight tomato accessions selected for mild and severe symptom expression, two of the viral detection primers (AV494/AC1048 and PTYv787/ PTYc1121) were used for the detection of the virus in infected plant samples (**Table 5**). The primer pair AV494/AC1048 amplified the viral DNA in all the eight genotypes (K100, K027, K116, K005, K202, LV, K213 and K042) in the University of Cape Coast and six out of the eight genotypes in Asuansi (K100, K027, K116, K005, K202 and K042) (**Table 8**). The primer pair PTYv787/PTYc1121 on the other hand amplified viral DNA in all the samples from

**3.5. Molecular screening of tomato germplasm for root knot nematodes resistance**

This study involved the use of primer Mi23/F//Mi23/R to detect the presence or absence of *Mi* genes in twenty eight (28) tomato cultivars (**Table 9**). The primer amplified the homozygous resistant genotypes (*Mi/Mi*) in cultivars VFNT, FLA 505-BL 1172, 2641A, "Adwoa Deede" and Terminator FI while the heterozygous resistant genotypes (*Mi/mi*) were amplified in cultivars

the field.

both locations [53].

Tima and 2644A [54].

**Table 5.** A list of primers used in TYLCV DNA detection.

(Cherry red × *S. pimpinellifolium*), BC-1 (Wosowoso × (Wosowoso × *S. pimpinellifolium*)), BC-2 (Roma × (Roma × *S. pimpinellifolium*)) and BC-3 (C-Red x (C-red × *S. pimpinellifolium*)). The observed TYLCD symptoms on *S. pimpinellifolium* were no visible symptom to slight yellowing of margins of apical leaflets.

The observed symptoms on the hybrids together with the backcrosses were slight yellowing of margins of apical leaflets and moderate yellowing and slight curling of leaflet tips. The results from the phenotypic screening were verified with a molecular marker detection of


**Table 6.** Tomato germplasm used for field screening against TYLCD in Volta region and University of Ghana.


**Table 7.** Primer pairs and sequences for TYLCV gene detection.

(Cherry red × *S. pimpinellifolium*), BC-1 (Wosowoso × (Wosowoso × *S. pimpinellifolium*)), BC-2 (Roma × (Roma × *S. pimpinellifolium*)) and BC-3 (C-Red x (C-red × *S. pimpinellifolium*)). The observed TYLCD symptoms on *S. pimpinellifolium* were no visible symptom to slight yellow-

**Marker name Primer sequence Source**

Rojas et al. (1993)

Wyatt and Brown (1996)

Zhou et al. (2008)

Osei et al. [48]

Osei et al. [48]

Osei et al. [48]

R: 5'AATACTGCAGGGCTTCTRTACATRGG

R: GGATTAGAGGCATGTGTACATG

R: 5-ATGTAACAGAAACTCATG-3

R: ACCCCATTACCCCAATACCA

R: ACCAATGGCTCCCCAAAGCGT

R: ACGGATGGCCGCTTTGGGT ATTCG

PARc1496/PAL1v1978 F:5'GCATCTGCAGGCCCACATYGTCTTYCCNGT

AV494/AC1048 F: GCCCATGTATAGAAAGCCAAG

60 Recent Advances in Tomato Breeding and Production

PTYv787/PTYc1121 F: 5-GTTCGATAATGAGCCCAG-3

MF/MR F:TGGCCGCGCCCTTCCTTTTGT

GHF/GHR F: GCCCGAAAGCTTCGTTGTT TTCCCGCT

KF/KR F: GGACCCGGCGCACTATTTAT GTTGGC

The observed symptoms on the hybrids together with the backcrosses were slight yellowing of margins of apical leaflets and moderate yellowing and slight curling of leaflet tips. The results from the phenotypic screening were verified with a molecular marker detection of

F1 Jaguar TYLCV Technisem (AgriSeed Company Ltd.) F1 Nadira TYLCV Technisem (AgriSeed Company Ltd.) F1 Thorgal TYLCV Technisem (AgriSeed Company Ltd.)

**Table 6.** Tomato germplasm used for field screening against TYLCD in Volta region and University of Ghana.

**Varieties Resistance Source**

Petomech Unknown University of Ghana Burkina Unknown Farmer variety *Solanum pimpinellifolim* Reported resistance to TYLCV Farmers CLN2026D Susceptible check AVRDC

ing of margins of apical leaflets.

NB: F: Forward primer, R: Reverse primer.

**Table 5.** A list of primers used in TYLCV DNA detection.

the viral DNA among the accessions. This work also deployed both triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) and PCR method (using the primers in **Table 5**) for the TYLCV detection in order to recommend a better way of detecting TYLCV in infected samples. A TAS-ELISA kit with a known TYLCV-infected *Nicotiana benthamiana*positive control was used for the study. The study confirmed the superior sensitivity of the PCR technique as a TYLCV detection method compared to the TAS-ELISA technique. There were no observable TYLCV symptoms on the BC-3 (C-Red × (C-red × *S. pimpinellifolium*)) in the field and both methods did not detect viral DNA in the leaf samples. BC- 1 (Wosowoso × (Wosowoso × *S. pimpinellifolium*)) behaved similarly like BC-3 in the field but there was amplification of viral DNA by the AV494/AC1048 primer set. In addition, two PCR primers detected viral DNA in the *S. pimpinellifolium* even though there was no TYLCV symptom observed in the field.

Recently, there was a phenotypic evaluation of 36 local tomato genotypes (**Table 8**) for the source of resistance against TYLCD in two locations (University of Cape Coast and Asuansi) in Ghana. The results showed that five accessions (K005-Petomec, K100-Local 3, K213-AVTO 9804, K116-Ashanti 2 and K042-Tomatose) out of the 36 genotypes were selected for mild severity, two genotypes showed severe symptoms (K027-Local, K202- AVTO 0102) and one genotype (LV-Fadzebegye) showed moderate severity. In order to confirm the infection or otherwise of the eight tomato accessions selected for mild and severe symptom expression, two of the viral detection primers (AV494/AC1048 and PTYv787/ PTYc1121) were used for the detection of the virus in infected plant samples (**Table 5**). The primer pair AV494/AC1048 amplified the viral DNA in all the eight genotypes (K100, K027, K116, K005, K202, LV, K213 and K042) in the University of Cape Coast and six out of the eight genotypes in Asuansi (K100, K027, K116, K005, K202 and K042) (**Table 8**). The primer pair PTYv787/PTYc1121 on the other hand amplified viral DNA in all the samples from both locations [53].

#### **3.5. Molecular screening of tomato germplasm for root knot nematodes resistance**

This study involved the use of primer Mi23/F//Mi23/R to detect the presence or absence of *Mi* genes in twenty eight (28) tomato cultivars (**Table 9**). The primer amplified the homozygous resistant genotypes (*Mi/Mi*) in cultivars VFNT, FLA 505-BL 1172, 2641A, "Adwoa Deede" and Terminator FI while the heterozygous resistant genotypes (*Mi/mi*) were amplified in cultivars Tima and 2644A [54].


**3.6. Screening for abiotic stress**

**Table 9.** Tomato cultivars evaluated for nematode resistance.

**Cultivar Source/origin** FLA 505-BL1172 AVRDC, Taiwan 2641A AVRDC, Taiwan Wosowoso Commercial, Ghana FLA 496–11–6-0 AVRDC, Taiwan Adwoa Deede Commercial, Ghana TLB111 AVRDC, Taiwan Terminator F1 Green seeds, India 3008A AVRDC, Taiwan Roma-JAM VF Commercial, USA Burkina Petomech Commercial, France Roma VF Commercial, B. Faso Ventura F Commercial, France Slumac Commercial, Holland Red Commercial, Holland Rando Commercial, Ghana Akoma Commercial, Ghana

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Ghana Petomech Petomech Commercial, France

Floradade Commercial, USA FLA 478–6–3-0 AVRDC, Taiwan Money maker Comm. South Africa Tima Commercial, France Rio grande Commercial, Holland Parona Commercial, Ghana Biemso Commercial, Ghana Power Commercial, Ghana 2644A AVRDC, Taiwan

Another important tomato-breeding objective is breeding for abiotic stress; nonetheless, there is limited published work on screening of tomato against abiotic stresses in Ghana. It was reported that 19 tomato cultivars (**Table 10**) were screened for adaptation to high temperature,

VFNT (Resist. check) TGRC, V. Williamson VFNT (Resist. check) TGRC, V. Williamson UC82 (Suscept. check) TGRC, V. Williamson UC82 (Suscept. check) TGRC, V. Williamson

**Table 8.** Code, name and sources of 36 tomato genotypes screened against TYLCD.


**Table 9.** Tomato cultivars evaluated for nematode resistance.

#### **3.6. Screening for abiotic stress**

**Codes Genotype names Source**

62 Recent Advances in Tomato Breeding and Production

K116 Ashanti 2 Ghana (Ashanti region) K045 Tomatose Ghana (Volta region) K042 Tomatose Ghana (Volta region) K100 Local 3 Ghana (Upper East) K074 Local 6 Ghana (Northern region) K144 BK-Dotvert Yako Burkina Faso (Burkina Faso) K124 Local 1 Ghana (Ashanti region) K005 Petomec Ghana (Eastern region) K214 AVTO 9001 Taiwan(AVRDC) K138 BK-Koly zy Burkina Faso K146 BK-Kong-L6 Burkina Faso K194 Magmet Korea K087 5(K) Ghana (SARI) K084 1R Ghana (SARI) K188 Madiso Korea

K027 Local Ghana (Volta region)

K088 Local1 Ghana (Upper East) K205A AVTO 1006 Taiwan (AVRDC) K197 REX Ghana (Eastern region) P077 Local 9 Ghana (Northern region)

K213 AVTO 9804 Taiwan (AVRDC K083 6(A) Ghana (SARI)

K050 Asante tomato Ghana (Western region) K011 Ntose Ghana (Eastern region) K106 Local 2 Ghana (Upper East) P085 21(B) Ghana (SARI)

K200 2001 heat tolerant Ghana (Eastern region)

K006 Power Rano Ghana (Eastern region) K202 AVTO 0102 Taiwan (AVRDC) P009 Mmoboboye Ghana (Eastern region) K206 AVTO 1008 Taiwan (AVRDC) L.V Fadzebegye Ghana (Central region)

**Table 8.** Code, name and sources of 36 tomato genotypes screened against TYLCD.

K191 Dyune Korea K186 Superdotaerang Korea K190 Orange carl Korea

K098 Local 1 Ghana

Another important tomato-breeding objective is breeding for abiotic stress; nonetheless, there is limited published work on screening of tomato against abiotic stresses in Ghana. It was reported that 19 tomato cultivars (**Table 10**) were screened for adaptation to high temperature,


irradiation, resistance to other biotic and abiotic stresses as well as sensory and nutritional value. Due to the pressing nature of these short-term breeding objectives, students of the West Africa Centre for Crop Improvements (WACCI), University of Ghana, are currently breeding for TYLCDresistant varieties and prolonged tomato shelf life. Other students of the same institution are also

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Tomato is indispensable in all Ghanaian recipes and contributes significantly to the economy of Ghana. Ghana has the potential to meet the country's tomato demand; however, low yield, unavailability of quality tomato varieties, pests and diseases have hindered this potential. This review presented tomato production trends in Ghana, past tomato-breeding programmes that have been carried out as well as some potential tomato-breeding objectives. Ghana will achieve self-sufficiency in tomato production if the government, Universities, Research Centres and National Research Institute (NRI) will invest more resources into tomato breeding to achieve both the short- and long-term-breeding objectives. This review will serve as a

I would like to thank Mr. Richard Agyare of the Savannah Agriculture Research Institute (SARI), Mr. Emmanuel K. Quartey and Mrs. Rosemary Adjei-Kusi, of the Biotechnology and Nuclear Agriculture Research Institute (BNARI), for sharing information on tomato-breeding

Leander D. Melomey1,2\*, Agyemang Danquah1,2, Samuel K. Offei1,3, Kwadwo Ofori1,2,

1 West Africa Centre for Crop Improvement, College of Basic and Applied Science,

2 Department of Crop Science, College of Basic and Applied Science, University of Ghana,

3 Biotechnology Centre, College of Basic and Applied Science, University of Ghana, Legon,

working on breeding for processing quality and Bacteria Wilt-resistant tomato varieties.

**4. Conclusion**

**Acknowledgements**

**Author details**

Legon, Ghana

Ghana

activities in their various institutions.

Eric Danquah1,3 and Michael Osei1,4

University of Ghana, Legon, Ghana

\*Address all correspondence to: lmelomey@wacci.edu.gh

4 CSIR-Crops Research Institute, Kumasi, Ghana

reference for improving tomato in the country.

**Table 10.** Tomato cultivars used for the heat stress.

and it was found that Nkansah, King 5, 181 (CLN 2318 F) and DV 2962 cultivars were better adapted to heat stress [55].

The outcome of these various screening programmes can be utilized in a hybridization programme by crossing genotypes expressing mild symptoms to the TYLCV and nematodes as well as genotypes that are tolerant to heat with locally adapted accessions that are susceptible to these stresses to develop resilient varieties.

#### **3.7. Potential tomato breeding objectives**

Tomato varieties currently grown in Ghana are generally acidic, watery, poor in color, poor shelf life and susceptible to TYLCV as well as intolerant to heat. Future tomato-breeding programmes should focus in the short-term on introgression of Tomato Yellow Leaf Curl Disease Resistant genes into locally adapted varieties and improving the shelf life of these locally adapted tomato varieties. These will address the major constraints facing the tomato industry in Ghana. Longterm tomato-breeding objectives should encompass the improvement of fruit color, increasing brix, improving rainy season varieties with good fruit-quality traits, increasing variability through irradiation, resistance to other biotic and abiotic stresses as well as sensory and nutritional value. Due to the pressing nature of these short-term breeding objectives, students of the West Africa Centre for Crop Improvements (WACCI), University of Ghana, are currently breeding for TYLCDresistant varieties and prolonged tomato shelf life. Other students of the same institution are also working on breeding for processing quality and Bacteria Wilt-resistant tomato varieties.
