Marker Assisted Gamete Selection for Multiple Disease Resistance in Andean Bean Genotypes and Characterization of Colletotrichum lindemuthianum in Kenya
Resistant bean varieties can reduce yield losses especially in widespread low input production systems in eastern Africa and enhance production stability. Pathogenic variation for major diseases has received limited attention in eastern Africa. Marker technology has presented new opportunities to accelerate cultivar development with more precision. Gamete selection method is a recent, efficient and effective breeding method that facilitates simultaneous improvement of multiple traits in common bean. The objectives of this study were to (i) determine pathogenic variation of Colletotrichum lindemuthianum in Kenya, (ii) introgress genes for resistance to angular leaf spot, anthracnose, common bacterial blight and Pythium root rot into four susceptible large seeded bean varieties, and (iii) evaluate and select resistant plants and families from F1 and F1.2 populations under field conditions. Anthracnose diseased materials were collected from bean growing regions in Kenya. Donor and the recipient parents were phenotyped and genotyped to confirm presence or absence of resistance genes. Sixteen F1 populations were generated from crosses between four multiparent male gametes and four susceptible female varieties following the gamete selection breeding method. The F1 and F1-derived F2 (F1.2) families were evaluated for angular leaf spot, anthracnose, common bacterial blight and Pythium root rot resistance in the field at Kabete and Tigoni. Agronomic traits were also recorded. Twelve physiological races of Colletotrichum lindemuthianum were identified. Three markers (SAB-3, SH-13 and SU-91) were polymorphic. PYAA-19 the marker for root rot was not polymorphic. Of the 89 multi-parent plants screened with markers for angular leaf spot (SH-13), anthracnose (SAB-3) and common bacterial blight (SU-91), three plants were positive for three markers, 8 for two markers, while all others had one or no markers present. Among the four male gametes constituted, G10909/G2333//AND 1062 /VAX6 F1s showed intermediate resistance to angular leaf spot (4.8). MEX54/G2333//RWR719/VAX6 had intermediate resistance to anthracnose (5.2) and common bacterial blight (4.7). G10909/G2333//RWR719/VAX6 was resistant to root rot (2.1). Among the four commercial varieties introgressed, New Rosecoco F1s were intermediate resistant to the four diseases. All the F1s showed a resistance of 2.2 against Pythium root rot. All populations showed intermediate resistance to anthracnose (5.5), angular leaf spot (5.0) and common bacterial blight (4.9). Among the male gametes, progenies of G10909/G2333//RWR719/VAX6 were the best yielding with mean of 4095 kg ha-1. Among the female commercial varieties used in the final cross, F1 progenies of New Rosecoco were the best yielding with a mean of 4194.5 kg ha-1. F1.2 families of MEX54/G2333//RWR719/VAX6 gave the highest yields of 3202 kg ha-1. F1.2 families with Kenya Umoja as the female parent were the best yielding with a mean yield of 3320 kg ha-1. The population that produced lines with combined resistance to 3 diseases and high yield potential was MEX54/G2333//RWR719/VAX6///Kenya Umoja. The anthracnose pathogen Colletotrichum lindemuthianum population in Kenya is quite varied and there is need for continuous and extensive characterisation. Use of markers further improved precision and efficiency of gamete selection method. Families derived from crosses with New Rosecoco and Kenya Umoja seem to offer the best potential of developing new lines with multiple disease resistance, high grain yield and commercial grain type.