**12. Cost effectiveness of MAS to conventional screening method**

As conventional breeding systems attempt to combine more and more target traits, there are tends to lose overall of breeding gains and an increase in the number of breeding cycles re‐ quired to generate a finished product. In contrast, MAS offers the potential to assemble tar‐ get traits in single genotypes more precisely, with less unintentional losses and in fewer selection cycles [20]. By means of MAS, breeding programmes have reported twice the rate of genetic gain over phenotypic selection for multiple traits such as yield, biotic and abiotic stress resistance and quality attributes [29, 32].

It has been described that the time, precision, number of traits and efficiency for traits with low heritability has increased with MAS. The cost-effectiveness of MAS depends on four parameters which are: the relative cost of phenotypic versus marker screening; the time saved by MAS; the time and temporal distribution of benefits associated with accel‐ erated release of improved germplasm; the availability in the breeding program of operat‐ ing budgets [20]. For example, in [16] estimated the cost for using SCAR and RAPD markers to analyse 100 bean samples (lines) would be \$4.24 and 4.59 per data point, re‐ spectively after the markers were developed. This included the costs of labour to plant seeds, watering the plants daily for eight days, extract genomic DNA and conduct PCR and electrophoresis as well as the costs for chemicals and greenhouse space, but not the initial costs of developing the markers. Conversely, conventional greenhouse screening was estimated to cost approximately \$6.99 per data point. This included the costs of la‐ bour to prepare inoculums, inoculate the plants, take care of plants for 32 days (fertilizer application, daily plant watering, insect control, growth room cleaning) and rate disease symptoms as well as the cost of greenhouse rental.

#### **13. Historical background of common bean improvement in Tanzania**

Bean production in Tanzania is affected by many problems that range from diseases to poor soil fertility as well as drought as the production is heavily rain-fed [11]. Some of the major bean production areas have acid soils with pH *<*5.5 which limit crop productivity [1].

Effort has been put on developing varieties that are resistant to biotic and abiotic stresses. This came in when breeding programs that set up across the country. Since the initiation of the breeding programme in Tanzania in 1959 [11], the white haricot beans was pro‐ duced for the canning industry though it is susceptible to bean rust disease and has a poor seed quality. The objectives were to i) determine the reasons for poor bean yields among smallholders in the Southern Highlands and ii) to select high-yielding cultivars. It was established that diseases were the major yield-limiting factor and disease resistance became the main thrust of the programme. Therefore, its first step was to identify resist‐ ance sources among the available lines. The first line adapted in East Africa as being re‐ sistant to rust with good quality was Mexico 142 [11].

**11. Other case studies of MAS**

134 Plant Breeding from Laboratories to Fields

are being obtained using MAS.

stress resistance and quality attributes [29, 32].

symptoms as well as the cost of greenhouse rental.

MAS has been proposed as the most practical and realistic approach to provide efficient long term control of bean anthracnose, ashly stem, bean common mosaic virus, common mosaic necrosis virus, bean golden mosaic virus [69], bean rust [115] and common bacterial blight [16, 64]. It has been or is being used to assist the simultaneous transfer of resistance genes for rust, anthracnose and angular leaf spot into Brazilian commercial cultivars [29]. Several lines resistant to rust [115, 116]; bean golden mosaic virus [69] and anthracnose [117]

As conventional breeding systems attempt to combine more and more target traits, there are tends to lose overall of breeding gains and an increase in the number of breeding cycles re‐ quired to generate a finished product. In contrast, MAS offers the potential to assemble tar‐ get traits in single genotypes more precisely, with less unintentional losses and in fewer selection cycles [20]. By means of MAS, breeding programmes have reported twice the rate of genetic gain over phenotypic selection for multiple traits such as yield, biotic and abiotic

It has been described that the time, precision, number of traits and efficiency for traits with low heritability has increased with MAS. The cost-effectiveness of MAS depends on four parameters which are: the relative cost of phenotypic versus marker screening; the time saved by MAS; the time and temporal distribution of benefits associated with accel‐ erated release of improved germplasm; the availability in the breeding program of operat‐ ing budgets [20]. For example, in [16] estimated the cost for using SCAR and RAPD markers to analyse 100 bean samples (lines) would be \$4.24 and 4.59 per data point, re‐ spectively after the markers were developed. This included the costs of labour to plant seeds, watering the plants daily for eight days, extract genomic DNA and conduct PCR and electrophoresis as well as the costs for chemicals and greenhouse space, but not the initial costs of developing the markers. Conversely, conventional greenhouse screening was estimated to cost approximately \$6.99 per data point. This included the costs of la‐ bour to prepare inoculums, inoculate the plants, take care of plants for 32 days (fertilizer application, daily plant watering, insect control, growth room cleaning) and rate disease

**13. Historical background of common bean improvement in Tanzania**

bean production areas have acid soils with pH *<*5.5 which limit crop productivity [1].

Bean production in Tanzania is affected by many problems that range from diseases to poor soil fertility as well as drought as the production is heavily rain-fed [11]. Some of the major

**12. Cost effectiveness of MAS to conventional screening method**

Since 1984, CIAT has introduced a number of varieties with different attributes into its breeding programmes for the mid- and high altitude areas of central, eastern and south‐ ern Africa. Twenty three bean varieties have been released in Tanzania since 1970 and several of these have been CIAT lines or were selections made in Tanzania from CIAT crosses [11, 118, 119].

Classical breeding methods were also used by CIAT in East Africa to develop a popula‐ tion from multi-parent crosses among genetically diverse lines from Andean and Mesoa‐ merican gene pools. Several new lines were selected with combined resistance to ALS, root rot, low soil N, low soil P and low soil pH. These lines are being evaluated in seven countries in the region including Tanzania [121]. The plant breeders in the national and regional breeding programmes have been able to release a number of varieties in Tanza‐ nia as shown in Table 1 [119]. However, none of those varieties have been developed through marker assisted selection technique.




**Table 1.** Common bean varieties released in Tanzania since 1970s and their characteristics

#### **14. Conclusion**

**SN**

**Name of varieties**

136 Plant Breeding from Laboratories to Fields

**Year of release**

7 Uyole 98 1998 ARI Uyole 1.2-2.0

9 Lyamungu 85 1985 ARI Selian 1.2-1.5

12 Jesca 1997 ARI Selian 2.0-3.4

13 Selian 97 1997 ARI Selian 2.0-2.8

14 Rojo 1997 SUA 2.2

17 Uyole 04 2004 ARI Uyole 2.0 – 2.5

20 Selian 05 2005 ARI Selian 1.0-1.6

21 Selian 06 2007 ARI Selian 2.5-3.0

15 Wanja 2002 ARI Uyole 1.5 Drought tolerant.

<sup>16</sup> Bilfa <sup>2004</sup> ARI Uyole 1.5-2.5 Tolerant to Halo blight, Drought resistant

<sup>18</sup> Pesa <sup>2006</sup> SUA 0.9-1.5 Moderate resistant and Angular Leaf Spot.

<sup>19</sup> Mshindi <sup>2006</sup> SUA 0.9-1.5 Moderate resistant to Angular Leaf Spot and

**Institutions**

**involved Yield (t/ha) Reaction to diseases**

<sup>8</sup> Ilomba <sup>1990</sup> ARI Uyole 1.5-2.5 Resistant to anthracnose, halo blight and

10 Lyamungu 90 1990 ARI Selian 1.2-1.6 Resistant to leaf rust and anthracnose

<sup>11</sup> Selian 94 <sup>1994</sup> ARI Selian 2.5-3.5 Moderately susceptible to anthracnose and

*ascochyta*

rust, Tolerant to *ascochyta*

angular leaf spot

common bacterial blight

common bacterial blight

blight and nematodes.

Virus, and Halo blight

Virus, and Halo blight

Bean Common Mosaic Virus and intermediate to common bacteria blight.

Resistant to anthracnose, angular leaf spot and rust. Tolerant to halo blight and

Resistant to anthracnose, angular leaf spot,

Resistant to anthracnose, Bean Common Mosaic Virus and halo blight, moderately resistant to bean rust, angular leaf spot,

Resistant to anthracnose, Bean Common Mosaic Virus and halo blight, moderately resistant to bean rust, angular leaf spot,

Resistant to Bean Common Mosaic Virus, moderately resistant to common bacterial

Resistant to Anthracnose and bean rust

Resistant to Bean rust, Anthracnose and Tolerant to Halo blight and drought

Resistant to Bean Common Mosaic Virus

Resistant to Bean Common Mosaic Virus

Resistant to Bean rust, Anthracnose, Mosaic

Resistant to Bean rust, Anthracnose, Mosaic

Plant breeders have traditionally and routinely used various recurrent selection methods to cumulate favourable alleles for yield and other polygenic traits. This selection will pro‐ vide the population or breeding lines with diverse genetic recombination. The selection methods using classical breeding should be compared with that of MAS. To make it suc‐ cessful to the breeder, gains made from MAS must be more cost effective as compared to gains through classical breeding. It is anticipated that the applications and technology im‐ provements will result in a reduction in the cost of markers, which will subsequently lead to a greater adoption of using molecular markers in plant breeding. The obstacles in using MAS are equipment, infrastructure, skilled man power and supplies or consuma‐ bles. The available projects in Tanzania which involves the use MAS are time based and focuses on few bean pathogen. The available projects are facing several problems such as timely purchase and acquisition of consumables for molecular biology laboratories is frustrating even when funds are available. The main reasons include the reduced number of commercial flights between the supplier countries and Tanzania, the lack of proper cold chains in the supply chain and inappropriate policies hampering imports. The bene‐ fits of using MAS need to be critically compared to those achieved or expected from any existing classical breeding programmes. This is because; although classical breeding pro‐ gramme have their limitations, they have also shown over time that they can be highly successful. The use of molecular tools should not be a substitute for classical breeding methods but these two approaches should complement one another so as to archieve the benefits of both in crop breeding programmes. Development of comprehensive crop im‐ provement programmes that will deploy the available sources of resistance to diseases and make proper use of MAS in selection is very important and this can in a proper way leap the benefits associated with these new tools and technologies as MAS in breeding for disease resistance. That can be true if government, donors and private sectors can join efforts to invest on facilities which can be shared for cost effective and efficiency delivery of services using MAS in breeding for disease resistance.

## **Author details**

George Muhamba Tryphone, Luseko Amos Chilagane, Deogracious Protas, Paul Mbogo Kusolwa and Susan Nchimbi-Msolla

Department of Crop Science and Production, Faculty of Agriculture, Sokoine University of Agriculture, Chuo Kikuu, Morogoro, Tanzania
