Molecular and Conventional Breeding Strategies for Improving Biotic Stress Resistance in Common Bean

Abstract

Common bean (Phaseolus vulgaris L.) is one of the most important grain legumes for direct human consumption worldwide. However, several diseases limit its production and deteriorate quality of bean. Hence, breeding for disease resistance is of global importance in common bean which is addressed with emphasis on conventional and molecular breeding strategies. Disease resistance does not directly increase yield, but in the absence of adequate levels of resistance to diseases like viruses (bean common mosaic virus (BCMV), bean golden mosaic virus (BGMV)), similarly, fungal diseases like anthracnose (ANT), angular leaf spot (ALS), powdery mildew (PWM) and rust and bacterial diseases like common bacterial blight (CBB), halo blight and other major diseases, bean yields will fall below optimum. Adequate levels of disease resistance to a number of pathogens are needed to help stabilize dry bean yield. Therefore, breeders need to recognize the disease constraints within their production zones and restrict resistance breeding to these specific pathogens. Given this constraint, breeders attempt to choose parents that are genetically diverse based on measures such as the coefficient of parentage (CP) and could be have higher disease resistance level. On the other hand, conventional plant breeding relies on the discovery, phenotypic selection and introgression of disease-resistant gene to develop superior cultivars. This process usually takes 7–10 years and significant economic resources. However, the application of marker-assisted selection (MAS), for the detection of genes or genomic regions underlying a trait of interest, can increase the genetic gain over phenotypic selection in breeding programs by reducing time and costs. Till date, more than 30 individual genes for disease resistance and a similar number of genes for QTL underlying major traits with significant impact to common bean cultivation in the tropics have been successfully linked with markers. The current status of MAS in breeding for resistance to angular leaf spot, anthracnose, bean common mosaic and bean common mosaic necrosis viruses, common bacterial blight, halo blight and rust is discussed in this chapter. In addition to that, examples are given of gene tagging for major disease that are important for bean breeding for tropical environments and aspects considered that contribute to successful application of MAS. Subsequently, the use of markers for disease resistance traits in marker-assisted backcrossing and introgression across Andean and Mesoamerican gene pools is suggested.