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# Marker Assisted Selection for Common Bean Diseases Improvements in Tanzania: Prospects and Future Needs

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

Submitted: May 2nd 2012Reviewed: August 29th 2012Published: May 22nd 2013

DOI: 10.5772/52823

## 1. Introduction

Common bean (Phaseolus vulgaris L.) is an important grain legume for direct human consumption [1]. It is an important source of dietary protein, calories, dietary fibres, and minerals especially iron and zinc in Africa and a primary staple in parts of the Great Lake Regions (GLR) [2, 3]. Beans consuming have medicinal benefits [4]. It is estimated that over 75% of rural households in Tanzania depend on it for daily dietary requirements [5]. Bean production also provides farm households with both income and food for nutrition [1]. Bean is a cash income earner crop where the dry seeds and fresh pods attract a higher market price [6].

Despite the importance of common bean in Tanzania and other developing countries, its production mostly relies on local cultivars [7- 9]. The local cultivars however, are commonly known to produce notoriously low yields as they are highly constrained by several biotic and abiotic factors, including diseases, insect pests, poor seed quality, drought, low soil fertility and poor crop management [1, 10-12]. Yield losses caused by bean diseases are very significant and devastating in the bean industry [11, 13-15]. The economic losses caused by diseases results from reduction of seed quality and yield [16]. Since most of landraces and improved cultivars grown in Tanzania are susceptible to the diseases, there is a need therefore to incorporate resistance against them in adapted cultivars. Currently, none of the commercial genotypes has multiple resistances to common bean diseases. However, using classical breeding, significant strides have been made in crop improvement through phenotypic selections for agronomical important traits. Considerable difficulties however, are often encountered during this process, due to genotype-environment interactions [17]. Furthermore, resistance to some diseases is complex as they are quantitatively inherited making it difficult to achieve rapid progress through classical breeding [13]. In addition, breeding is complicated by the pathogens variability and different genes conditioning resistances [1, 13]. The identification of plants carrying two or more resistance alleles of different genes using standard inoculation test is impractical because several races would be needed to screen for specific alleles [16]. Thus classical breeding is limited by the length of screening procedures and reliance on the environmental factors. Hence, deployment of the molecular markers linked to resistance genes could be an alternative, more reliable screening procedure to increase the efficiency of breeding for disease resistance using marker assisted selection (MAS) [13]. Molecular marker available include 23 RAPD and five SCAR markers linked to 15 different resistance genes in addition to QTL conditioning resistance to seven major pathogens of common bean [13, 66]. The use of DNA molecular markers will improve understanding of the genetic factors conditioning these traits and is expected to assist in the selection of superior genotypes [17, 18]. Molecular marker assisted selection can be used to simultaneously screen for resistance to diseases without affecting the growth of the plants [13, 19]. Selection for genetic markers linked with resistance genes and QTL can accelerate development of multiple resistant varieties and increase efficacy [14, 20, 21]. The use of disease resistant cultivars in combination with appropriate cultural practices is essential for the management of bean diseases [14, 22, 23]. This chapter discusses the importance of MAS and how it can be integrated into breeding programs for enhancing selection efficiency in developing disease resistant bean varieties in Tanzania.

## 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 produced 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 resistance sources among the available lines. The first line adapted in East Africa as being resistant to rust with good quality was Mexico 142 [11].

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 southern 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 population from multi-parent crosses among genetically diverse lines from Andean and Mesoamerican 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 Tanzania as shown in Table 1 [119]. However, none of those varieties have been developed through marker assisted selection technique.

 SN Name of varieties Year of release Institutions involved Yield (t/ha) Reaction to diseases 1 Canadian wonder 1977 ARI Selian 1.1-2.4 Moderately resistant to halo blight and bean common mosaic virus 2 Kabanima 1980 ARI Uyole 1.5-1.8 Resistant to anthracnose and rust 3 Uyole 84 1984 ARI Uyole 1.5-2.0 (non staked) 2.5-4.0 (staked) Resistant to anthracnose and halo blight 4 Uyole 90 1990 ARI Uyole 1.5-2.0 It is tolerant to halo blight and angular leaf spot 5 Uyole 94 1994 ARI Uyole 1.0-1.8 Resistant to ascochyta and rust, tolerant to Bean Common Mosaic Virus and Angular Leaf Spot 6 Uyole 96 1996 ARI Uyole 1.0-1.8 Tolerant to rust, ascochyta and Bean Common Mosaic Virus 7 Uyole 98 1998 ARI Uyole 1.2-2.0 Resistant to anthracnose, angular leaf spot and rust. Tolerant to halo blight and ascochyta 8 Ilomba 1990 ARI Uyole 1.5-2.5 Resistant to anthracnose, halo blight and rust, Tolerant to ascochyta 9 Lyamungu 85 1985 ARI Selian 1.2-1.5 Resistant to anthracnose, angular leaf spot, Bean Common Mosaic Virus and intermediate to common bacteria blight. 10 Lyamungu 90 1990 ARI Selian 1.2-1.6 Resistant to leaf rust and anthracnose 11 Selian 94 1994 ARI Selian 2.5-3.5 Moderately susceptible to anthracnose and angular leaf spot 12 Jesca 1997 ARI Selian 2.0-3.4 Resistant to anthracnose, Bean Common Mosaic Virus and halo blight, moderately resistant to bean rust, angular leaf spot, common bacterial blight 13 Selian 97 1997 ARI Selian 2.0-2.8 Resistant to anthracnose, Bean Common Mosaic Virus and halo blight, moderately resistant to bean rust, angular leaf spot, common bacterial blight 14 Rojo 1997 SUA 2.2 Resistant to Bean Common Mosaic Virus, moderately resistant to common bacterial blight and nematodes. 15 Wanja 2002 ARI Uyole 1.5 Drought tolerant. 16 Bilfa 2004 ARI Uyole 1.5-2.5 Tolerant to Halo blight, Drought resistant Resistant to Anthracnose and bean rust 17 Uyole 04 2004 ARI Uyole 2.0 – 2.5 Resistant to Bean rust, Anthracnose and Tolerant to Halo blight and drought 18 Pesa 2006 SUA 0.9-1.5 Moderate resistant and Angular Leaf Spot. Resistant to Bean Common Mosaic Virus 19 Mshindi 2006 SUA 0.9-1.5 Moderate resistant to Angular Leaf Spot and Resistant to Bean Common Mosaic Virus 20 Selian 05 2005 ARI Selian 1.0-1.6 Resistant to Bean rust, Anthracnose, Mosaic Virus, and Halo blight 21 Selian 06 2007 ARI Selian 2.5-3.0 Resistant to Bean rust, Anthracnose, Mosaic Virus, and Halo blight 22 Cheupe 2007 ARI Selian 2.5-3.0 Resistant to Bean rust, Anthracnose, Mosaic Virus, and Halo blight 23 Njano Uyole 2008 ARI Uyole 2.5 – 3.0 Resistant to Anthracnose

### Table 1.

Common bean varieties released in Tanzania since 1970s and their characteristics

Source: MAFSC, 2008 [119]

## 14. Conclusion

Plant breeders have traditionally and routinely used various recurrent selection methods to cumulate favourable alleles for yield and other polygenic traits. This selection will provide 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 successful 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 improvements 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 consumables. 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 benefits 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 programme 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 improvement 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.

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George Muhamba Tryphone, Luseko Amos Chilagane, Deogracious Protas, Paul Mbogo Kusolwa and Susan Nchimbi-Msolla (May 22nd 2013). Marker Assisted Selection for Common Bean Diseases Improvements in Tanzania: Prospects and Future Needs, Plant Breeding from Laboratories to Fields, Sven Bode Andersen, IntechOpen, DOI: 10.5772/52823. Available from:

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