Introduction of foliar disease resistance into bean bruchid resistant genotypes and heritability studies at F2:3

Abstract

Common bacterial blight (CBB), Bean common mosaic virus (BCMV) and Bean common Mosaic Necrosis Virus (BCMNV) are the most common foliar diseases affecting common bean worldwide. CBB and BCMV/BCMNV are caused by Xanthomonas axonopodis pv. phaseoli and group of Potyviruses respectively, contributing to high yield and quality losses in Tanzania. Chemical control has not been effective or economical on both of these seed borne diseases. Elsewhere, breeding for resistant cultivars have been reported to be effective and a long-term control measure. The objective of this study was to incorporate foliar disease resistance to CBB, BCMV and BCMNV from KT020 into existing bruchid resistant genotype BR 59-63-10.  One way cross was performed under screen-house condition followed F₁ advancement to F₂ at which F_2:3 was screened using SCAR markers i.e SAP6 for QTL-CBB, SW13 for I gene-BCMV and ROC11 for bc-3 gene-BCMNV resistance. Among forty individuals screened, nine derivatives had resistance to all diseases; seventeen had two resistance genes to either of the disease while ten derivatives of APAx KT020 had one resistance gene to either of the diseases.   Results also showed positive correlation between phenotypic score and markers, while in phenotypic studies all individuals had resistance ranging from 1.40 to 3.29 on leaf lesions and 2.14 to 3.30 on pod severity for CBB based on 1-9 CIAT scale. High heritability of reduced infestation explained by 61.1% and 66.8% on leaf and pod symptoms respectively was obtained. Marker screening indicating a reliable procedure for selecting resistant individual using marker assisted selection (MAS).