Abstract
Angular Leaf Spot (ALS) caused by the fungus Pseudocercospora griseola and Bean common mosaic and necrosis virus (BCMV/BCMNV) are important diseases of common bean in Tanzania that can cause severe yield reduction when uncontrolled. This study was conducted to incorporate resistant genes for ALS and BCMV/BCMNV diseases into adapted, market class and farmers and consumers preferred bean genotype using Marker assisted selection. The parents Mexico 54 and UBR(25)95 donor of Phg-2 and I/bc-3 genes for ALS and BCMV/BCMNV, respectively were used the recipient being Kablanketi. In selection, SCAR markers SNO2, ROC11 and SW13 linked to Phg-2, bc-3 and I gene, respectively were used. A parallel backcrossing (modified double cross) procedure was used. The F1, F2 and backcrosses from single crosses were characterized. The Chi square values for ALS were 0.081 (P<0.776) and 0.017 (P<0.896) and for BCMNV were 1.609 (P<0.205) and 1.2 (P<0.273) for molecular and phenotypic screening, respectively. The resistance to ALS and BCMNV was found to be monogenic and the genes involved are dominant and recessive, respectively. The heritability of ALS was found to be high (0.772) implying that selection for ALS can be done early in segregating populations. High correlation values, r = 0.741 and 0.624 for ALS and BCMNV, were obtained between phenotypic and molecular data, indicating high reliability for markers. In selection, it was possible to select lines with multiple disease resistances. This work signified the use of MAS for multiple gene screening. Key words: Common bean, Pseudocercospora griseola, marker assisted selection, genotype, inheritance.
Highlights
Common beans (Phaseolus vulgaris L.) belong to the family fabaceae
The genotypes used in this study included two non recurrent genotypes that are resistant to angular leaf spot (Mexico 54) and to Bean common mosaic virus disease (BCMV)/bean common mosaic necrosis virus (BCMNV) [UBR (95) 25] and one adapted recurrent variety (Kablanketi) which is susceptible to both diseases and to which resistance is to be incorporated
Segregation ratios were 3:1 for the F2 populations in both the phenotypic evaluation and genotypic evaluation, 1:1 for the BC1-1F1 and 1:0 for the BC1-2F1. These results show that the observed ratios and the calculated ratios are not significantly different at the 0.05 level of significance; where P < 0.896 for F2 and P < 0.655 for the backcross in phenotypic screening and P < 0.776 for F2 in molecular marker screening. These ratios and the results are in agreement with the previous work on Angular leaf spot (ALS) using Mexico 54 as the donor parent that suggested that the gene for ALS follows the single gene inheritance pattern (Namayanja et al, 2006; Chataika et al, 2010; Sartorato et al, 2000)
Summary
Common beans (Phaseolus vulgaris L.) belong to the family fabaceae. It is an annual, predominantly self pollinated legume grown in all continents under extremely variable environmental conditions (Melotto et al, 2005). Predominantly self pollinated legume grown in all continents under extremely variable environmental conditions (Melotto et al, 2005) It is the most commonly and widely cultivated crop in the tropics and sub tropical regions and is one of the most. In Tanzania, common bean is the main grain legume crop It is often intercropped with maize and the main areas of production are the mid to high altitude areas of the country. Tanzania is among the top ten largest producers of dry beans and the largest producer in sub-Saharan Africa (FAOSTAT, 2010)
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