**2. Evaluation and deployment of rice varieties**

#### **2.1 Introduction of rice varieties to Uganda**

Irrigated and rain-fed lowland rice varieties were introduced into Uganda in two phases namely, first from 1921 to 1970 and second during 1971–2020. In the first phase, a total of eight irrigated and rain-fed lowland rice varieties, specifically Jaggery, Cakala, Matama, Kawemba, Kigaire, Seena, SUPA LOCAL and Bungala were introduced and grown (**Table 1**). On the basis of aroma, all the eight rice cultivars except Bungala were aromatic types.

In the second phase covering the period from 1971 to 2020, six released varieties and up to 70 unreleased but informally released rice varieties were commonly being grown by the farming communities. The 70 informally released varieties are classified into two different groups according to their generations. The first are called the K-series of rice introduced from China under technical assistance program, while the second are introductions from major breeding centers detailed in **Table 1**. Both groups are modern varieties with high-yielding capacity and tolerance for various biotic and abiotic field stress conditions. The K-series is an acronym of Kibimba lines, named so probably due to the series being grown then in the Kibimba government rice irrigation scheme. Fortunately, most of the K- series had a desirable combination of intermediate amylose content and intermediate gelatinization temperature and a notable variety is IR64, which has been widely accepted as a high-quality rice. Later, however, there were several devastating stresses that undermined the importance of these varieties for which reasons more introductions from other centres were requested and received. The major breeding centers that provided rice germplasm to Uganda include Africa Ricer Center (AfricaRice), International Rice Research Institute (IRRI), International Centre for Tropical Agriculture (CIAT), Colombia, Tanzania Agricultural Research Organization (TARO), Nigeria, Crop Research Institute (CRI) Ghana, Yunnan Agricultural University, Kunming, China and Chinese Academy of Agricultural Sciences (CAAS), China. Overall, the germplasm received include the following specie of *Oryza sativa*, generations involving crosses between *O. sativa* and *O. glaberrima*, *Oryza barthi* x *O. sativa* crosses, and *O. sativa* x *O. longistaminata* crosses.

#### **2.2 Screening introduction, genetic studies and hybridization**

#### *2.2.1 Rice diseases*

Rice yellow mottle virus (RYMV) disease is apparently the most serious disease of rice under irrigated and rain-fed lowland conditions in Uganda. In order to identify lines with resistance to RYMV disease, 934 rice lines were screened in the years 2015, 2016, 17 and 2018. These list excluded IR 64, K 34, K 38, K 85 and KOMBOKA (susceptible control), Gigante from AfricaRice (resistant check), Namche 2, NERICA 4 (MET P71), NERICA 8 (MET P72) and WITA 9 (local resistant check) that were included in each set [20, 21]. Each line was sown in the field at high plant population of 10 grams in a land area measuring 20 cm x 20 cm in size. Mechanical inoculations were carried out on seedlings (10 plants test line) at 3 weeks post germination as described by Thouvenel and Fauquet [22]. Symptom appearance was monitored on daily basis to assess the stage of disease initiation and thereafter, disease severity was scored using a scale of 1 (no symptoms) to 9 (severe symptoms) [23, 24] at 45 days post-inoculation (DPI). Of the 934 lines evaluated, a total of 54 either highly resistant or just resistant were identified (**Table 2**). Majority of the RYMV resistant lines were crosses with Tongil


#### *Irrigated and Rain-Fed Lowland Rice Breeding in Uganda: A Review DOI: http://dx.doi.org/10.5772/intechopen.97157*


*Cereal Grains - Volume 2*


#### *Irrigated and Rain-Fed Lowland Rice Breeding in Uganda: A Review DOI: http://dx.doi.org/10.5772/intechopen.97157*



*Rice varieties grown in Uganda.*


#### *Irrigated and Rain-Fed Lowland Rice Breeding in Uganda: A Review DOI: http://dx.doi.org/10.5772/intechopen.97157*


**Table 2.**

*Rice genotypes resistant to RYMV.*

#### *Irrigated and Rain-Fed Lowland Rice Breeding in Uganda: A Review DOI: http://dx.doi.org/10.5772/intechopen.97157*

rice types in their background developed under Korea-Africa Food and Agriculture Cooperation Initiative (KAFACI) rice collaborative research.

In 2018, another set of 112 germplasm was screened for rice yellow mottle virus disease (RYMVD) resistance. The germplasm comprised of *O. barthi* interspecific lines generated from crosses between *Oryza sativa* L. and *O. barthi.* These breeding lines were selected for their high yield potential, resistance to diseases and other desirable culinary qualities. Seventeen promising genotypes were identified, among which six comprising of [ARS126–3-B-1-2 (11), ARC36–2-P-2 (2), ARC39–145-P-2 (5), Gigante, IRL 2 (GP 54) and IRL 4 (69 GP 54)] were highly resistant to RYMV disease. List of the 11 resistant lines for RYM derived from *O. barthi* crosses are shown in **Table 2**.

In 2019, a total of 307 lines including the 247 KAFACI lines were introduced into East African Regional Rice Research and Training centre at NaCRRI, Namulonge-Uganda and each of the introduced seed samples were divided into three parts. The first part was planted using a single row plots in the screen house at NaCRRI. Each row had 10 cm spacing with 15 hills and the rows were. Spaced 15 cm apart. A prepared RYMV inoculate was used to inoculate 5 plants in each row following procedure described by [22]. Symptom appearance was monitored on daily basis to assess the stage of disease initiation. Also, symptom expression post inoculation (DPI), severity on weekly intervals from 21 DPI, through 28 DPI, 35 DPI and 42 DPI were collected. We also took record of plant height for inoculated and noninoculated plants and the percentage reduction for each of the lines were calculated The results revealed that 3 lines ofIR64/rymv1-2, IR64/rymv1-3 and IR64/RYMV3 showed severity score of 1 on score 1-9; 14 lines showed severity score of 3. These 7 lines are; SR34574-HB3565-284, ARS1958-1, SR34574-HB3565-285, SR34574- HB3565-290, HR32068F1-4-20-1-6-3-2, HR32068F1-4-20-1-6-4-2 and HR32068F1-4-20-1-6-4-3, which were also found to exhibit resistance to all other diseases assessed, namely rice blast, BB, sheath rot and narrow leaf brown spot. A total of 39 lines showed severity score of 5 while up to 57 lines showed reduction in plant height by at most 30%. Further analysis based on a rating scale for Susceptible (7-9), Medium resistance (4-6) and Resistance (0-3) indicated line, namely, HB4057, rymv1-2, rymv1-3, RYMV3, Hannam, NamChe-2 and Ungwang as the resistant donors.

In respect to bacterial leaf blight (BLB) disease, a total of 18 isogenic lines developed for BLB disease were screened in three hotspot areas of Namulonge-Wakiso, Olweny-Lira and Kibimba- Bugiri districts in Uganda. The results revealed IRBB21 (Xa 21) as the most resistant line in all the three locations followed by IRBB8 [27], implying that lines with these genes could be used to pyramid for multiple stress resistance in our breeding programme.

In another study, 32 lines were screened for resistance to BLB and six other lines, namely, CT 12, WITA 132 x NERICA 14, NERICA 10, NERICA 4 and NERICA 1 were reported resistant to BLB [27]. These four lines could be donor parents in breeding for BB resistance as currently, several rice lines have shown resistance to leaf bacterial blight (**Table 3**).

Rice blast disease has been mentioned in several articles as a major constraint in rice production in Uganda [2, 3, 5, 6]. Accordingly, 450 lines were progressively screened in 2014, 2015, 2016, 2017, 2018 and 2020 for sources of resistance to the rice blast disease. In 2014, a total of 50 lines introduced from South Korea though the KAFACI were screened alongside a resistant (IR-64) and a susceptible (NERICA 1) checks. These were the breeding population from a cross of an African cultivated rice, *Oryza glaberrima* of Niger Delta origin and Milyang 23, a Tongil-type Korean rice variety and a total of 29 lines were resistant to rice blast [26] (**Table 4**).


*Key: HR = high resistance; NaCRRI = National Crops Resources research Institute, Namulonge - Uganda. Source; Lussewa et al. [27].*

#### **Table 3.**

*Lines resistant to bacterial leaf blight disease.*

Another set of 46 rice genotypes introduced from South Korea though the KAFACI were screened for resistance to rice blast under screen house condition and in the field at NaCRRI Uganda in the year 2015 [28]. The screening exercise involved infecting and selecting the infected rice plants and by observing the symptoms on the leaves based on the rice blast identification guide. Data on leaf blast severity, lesion size, area under disease progress curve (AUDPC) for leaf blast severity and lesion size, panicle blast and yield were collected on five randomly selected plants in the field and on three plants in the screenhouse from each plot according to the standard evaluation system of rice [24]. Results revealed that genotypes SR33859-HB3324-133, SR33859-HB3324-93 and SR33701-HB3330-78 were highly resistance to rice blast and had good performance for yield [28] (**Table 4**).

In a related study aimed at understanding transmission of genes for resistance to rice blast, it was found that both additive and non-additive effects contributed to transmission of resistance genes for rice blast disease to the progenies. The inheritance of rice blast resistance has been indicated to be mainly controlled by additive gene effects, besides a small influence of a non-additive effects [28].

In an effort to combat brown spot disease caused by *Biplaris oryzae* pathogen, a total of 100 lines were screened for resistance to rice brown spot in 2017 and 2018 at Namulonge. The results showed that 18 lines were rated as highly resistant, 52 resistant, 27 moderately resistant and three lines including the checks were susceptible [29]. The list of the highly resistant lines recommended for further breeding work is presented in **Table 5**.

Further studies where F2 progenies from the crosses involving parents with distinct phenotypic classes of brown spot revealed information of segregation ratios for the different crosses. In particular, crosses TXD 306 NERICA 4, NERICA 1 NERICA 4, NERICA 4 NERICA 1 and E 22 PAK conformed to the 3:1 ratio, suggesting the presence of at least one gene showing dominance [30].

Another study conducted to identify lines resistant to bacterial leaf streak (BLS) identified three lines of NERICA 1, NERICA 6 and IURON 2015-1 as highly resistant to the pathogen causing bacterial leaf streak [31].

#### *2.2.2 Insect pests*

A study was also conducted to identify rice lines resistant to African rice gall midge (AfRGM) and 20 rice genotypes with diverse breeding background were evaluated for the resistance to AfRGM under controlled conditions in a screen house and under the field conditions at NaCRRI, Namulonge - Uganda [32]. Infestation was done in accordance with the method use by Ogah [33] where 3 females and 2


#### *Irrigated and Rain-Fed Lowland Rice Breeding in Uganda: A Review DOI: http://dx.doi.org/10.5772/intechopen.97157*

#### **Table 4.**

*Lines resistant to rice blast.*

male of AfRGM were released in each cage. A total of 180 females and 120 males of gall midge was used. Genotypes MET P-7 and NERICA 6, NERICA 4 and NERICA 1 consistently exhibited high tolerance to AfRGM. The most desirable (high negative)


#### **Table 5.**

*List of rice lines resistant to brown spot.*

SCA effects were observed in the crosses from NERICA 6 X E 22, NERICA 1 X K 85, NERICA 1 X KOMBOKA and NERICA 4 X KOMBOKA. Low (desirable) GCA values were witnessed in the case of genotypes of NERICA 6, NERICA 1, NERICA 4 and MET P-7, indicating the importance of the parents in contributing resistance towards AfRGM in rice.

In another study to identify sources of resistance to stalk-eyed fly pest (*D. longicornis*) in rice plants, four out of eight lines namely, NERICA 4, TXD 306, K 85 and NM7-22-11-B-P-1-1, showed high resistance to stalk eyed fly upon screening on-station at Namulonge in 2015 [34]. These four-high resistant (HR) lines were crossed with moderately susceptible lines NERICA 1, NERICA 6, Namche 2 and PAKISTAN in a North Carolina II mating design to determine their combing abilities for the insect pest resistance. The results showed that NERICA 4 and K 85 were good general combiners for resistance to the pest. The crosses Pakistan TXD 306 and NERICA 1 NM7-22-11-B-P-1-1 were identified as promising lines for advancement. Further analysis revealed that the stalk-eyed fly in rice seems to be controlled both by additive and non-additive genes, thus selection at early

generations (F1 and F2) would not be effective. Therefore, selection can be appropriately delayed to a later generations, between F4 and F6. Advancement of selected breeding lines (Pakistan TXD 306 and NERICA 1 NM7-22-11-B-P-1-1) is, therefore, recommended for further evaluation for resistance to the stalk-eyed fly in later generations [34]. The parental lines NERICA 4 and K 85 are recommended as good general combiners and could be used as the donor parents in the breeding programme for the pest.
