ABSTRACT. The use of genetically resistant cultivars is the best method to reduce losses caused by white mold (Sclerotinia sclerotiorum (Lib.) de Bary). As the best known resistance sources are not adapted, the genetic control of white mold in the common bean must be understood to guide breeding more efficiently. The objective of the present study was to identify the genetic control of the resistance of common bean to white mold by an indirect method using oxalic acid. For this, the descendents of the VC3 cross (susceptible) x G122 (resistant) were used. The trait was assessed by a descriptive key of scores after treatment with oxalic acid. The assessments were made on individual plants (P 1 , P 2 , F 1 , F 2 populations and within F 2:3 families) in a complete randomized design and on family means where the randomized block design was used with two replications. The oxalic acid method was efficient in detecting genetic differences. The additive effects dominated and genetic control was characterized by partial dominance (d/a = 0.47). At least one resistance gene is involved, although the trait is greatly influenced by the environment. The broad sense heritability at the family mean level (0.47) was greater than that obtained at the individual plant level (0.33), indicating that selection should be more efficient based on progeny mean assessments.

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Natural selection acts to select better adapted individuals or alleles in segregating population and help plant breeding. The objective of this work was to verify the effect of natural selection on microsatellite alleles as indicators of better adaptation and identification of quantitative trait loci (QTLs) for grain yield. This study evaluated 107 progenies from the F8 and 107 from the F24 generation derived from crossing Carioca MG and ESAL 686 lines, carried out by the bulk method, and evaluated in three different seasons: winter 2001; rainy 2001 and dry 2002. It was utilized 22 polymorphic markers and the natural selection acted in all of them. The frequency of the alleles of the parent Carioca MG, the most adapted, was increased in all of the 22 loci in F8 and 19 loci in F24. Selection affected each locus with different intensities in different generations. All of the selected alleles can be important for breeding program. QTLs were identified in generation F8 and F24 at varied magnitudes. The best marker PVttc002 explained 11.76% of variation in grain yield. However, an elevated interaction between QTLs and the environments was observed, showing the great difficulty in assisted selection.

-This study aimed to determine the minimum number of plants per plot to assess the field resistance in common bean to white mold. Thirteen cultivars were inoculated with six isolates of Sclerotinia sclerotiorum and evaluated in a randomized block design with three replications and plots consisting of 1-m rows with 15 plants. Plants were inoculated by the straw test as proposed by Petzoldt and Dickson (1996)

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