Abstract
A backcross breeding program between commercial common bean cultivars (VC3 and M20) and sources of resistance (Ex-Rico 23 and G122) was conducted with a view toward selecting carioca (beige with brown stripes) progenies resistant to white mold. Forty-eight progenies (27 F2:6 BC1 and 21 F1:5 BC2) were evaluated for yield, growth habit, grain type and pathogen response by two methodologies for assessment (straw test and oxalic acid). The methods were effective in discriminating the progenies, showing differing results, for they may assess different resistance mechanisms. Thus, they should be used together. Simultaneous selection for yield, growth habit, grain type and white mold resistance proved to be viable. The most appropriate strategy was to use lower intensities of selection and prioritize traits such as resistance and grain type, which are essential for commercial acceptance. Two progenies proved their superiority for the breeding program for they combine the traits of resistance and favorable grain type.
Highlights
Common bean (Phaseolus vulgaris L.) is one of the staple foods of the Brazilian diet
White mold (Sclerotinia sclerotiorum (Lib.) de Bary) is a pathogen that affects the crop, especially in crop areas irrigated with a center pivot in successive crop seasons, and it may lead to annual losses in excess of 50% (Oliveira 2005, Soule et al 2011)
White mold is controlled by physiological resistance mechanisms and by escape mechanisms, such as a bushy growth habit of the plant, resulting in a more aerated microenvironment
Summary
Common bean (Phaseolus vulgaris L.) is one of the staple foods of the Brazilian diet. The two types of mechanisms are not sufficient for control of the disease (Kim et al 2000, Kolkman and Kelly 2002, Huang et al 2003, Soule et al 2011). These mechanisms are found mainly in unadapted sources of resistance and may be incorporated in commercial cultivars by means of backcrosses. Given the complexity of resistance to white mold, the study was performed for the purpose of assessing, by different methodologies, the reaction of the progenies derived from backcrosses of sources of resistance, and selecting progenies for resistance, growth habit, yield and grain type
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