O presente trabalho teve como objetivo determinar o número mínimo de plantas por plota para avaliar a resistência do feijoeiro ao mofo branco em campo. Treze cultivares foram inoculadas com seis isolados de Sclerotinia sclerotiorum. O delineamento utilizado foi o de blocos casualizados com três repetições, com plota constituída de quinze plantas por metro linear. A inoculação foi realizada utilizando o método do straw test. Oito dias após a inoculação foi realizada a avaliação utilizando uma escala diagramática de 1 (plantas assintomáticas) a 9 (morte da planta). Foram utilizados os métodos: curvatura máxima, modelo segmentado linear, modelo segmentado quadrático e o modelo CV relativo, para determinar o número mínimo de plantas por plota. Houve diferença significativa entre as cultivares, entre os isolados e entre a interação cultivares x isolado. Observou-se que oito plantas por plota é um número adequado para avaliar a reação de feijoeiro ao mofo branco.

ABSTRACT 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), to evaluate partial resistance in a greenhouse. Eight days after inoculation the disease severity was evaluated on a 1-9 diagrammatic scale, where 1 = asymptomatic plants to 9 = plant death. To determine the minimum number of plants per plot, the following methods were used: maximum curvature, segmented linear model, quadratic segmented model and the relative CV model. There were significant differences among cultivars and isolates and no significant cultivar - isolate interaction. It was observed that eight plants per plot is an adequate number to assess the reaction of common bean to white mold.

O objetivo foi estudar a natureza e a magnitude dos efeitos genéticos da resistência ao mofo branco. Para se obter as estimativas de parâmetros genéticos, foram utilizados os genitores resistente (G122) e suscetível (M20), as gerações F1, F2 e progênies F2:3. Foi utilizado o delineamento de blocos casualizados com duas repetições. Cada progênie foi submetida, duas vezes (repetição), à inoculação do micélio (Straw test) após, aproximadamente, 28 e 38 dias da semeadura. Seis a oito dias após a inoculação, foi realizada a avaliação em nível de planta individual e em nível de média de progênies por meio de uma escala diagramática de 1 a 9. O modelo aditivo-dominante adotado foi eficiente e no controle da resistência houve predomínio de efeito aditivo. As estimativas da herdabilidade no sentido amplo obtidas indicam que a seleção é mais eficiente com base na média de progênies e inoculações sucessivas.

The objective of the research was to investigate the nature and magnitude of the genetic factors involved in the resistance of the common bean to white mold. The lines G122 (resistant) and M20 (susceptible) were crossed to yield F1 and F2 generations and F2:3 progenies. The experiment was set up using the random block design with two replications, each of which was evaluated twice with fungal inoculations being performed on 28 and 38 day-old plants using the straw test method. Six to eight days after inoculation evaluations were conducted on individual plants and at the level of means of progenies using a diagrammatic scale ranging from 1 to 9. The additive-dominance model adopted was efficient, and the genetic control of resistance was predominantly due additive effects. Estimates of broad-sense heritability indicated that selection would be more efficient when based on the means of progenies and when successive inoculations are employed.

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.

Molecular markers may accelerate selection through the identification of plants with higher proportion of recurrent parent genome, as well as identifying those plants bearing target alleles like quantitative traits loci (QTLs) for white mold resistance. The objectives of this work were: 1) to employ microsatellite markers (SSR) in order to accelerate the recovery of recurrent parent genome 2) to validate sequence characterized amplified region (SCAR) Phs associated with a QTL that confers resistance to white mold, as previously identified in bean populations. Lines G122 and M20 were crossed, which generated 267 F1 plants from backcross (BC) BC1 and 113 plants from backcross BC2.SSR polymorphic markers were adopted. The relationship between BC plants and the recurrent parent was estimated based on the recurrent genome proportion (PR) in each BC plant, and the Sorensen-Dice genetic similarity (sg ir). To determine how much the phenotypic variation is explained by SCAR Phs, 56 F1:2BC1 progenies were evaluated on the field following a random block design with two replications through the straw test method. SSR markers are efficient in identifying individuals with a greater proportion of the recurrent genome. SCAR Phs was not efficient for the indirect selection of common beans for white mold resistance.

Com objetivo de verificar se há associação entre a resistência ao nematóide e ao Fusarium oxysporum (Fop), dezoito linhagens de feijão, sendo oito resistentes e oito suscetíveis ao Fop mais duas testemunhas foram avaliadas com relação à reação ao nematóide Meloidogyne incognita. Essa avaliação foi realizada em casa de vegetação no delineamento de blocos casualizados com cinco repetições. A parcela foi constituída por um vaso com duas plantas de feijão, e uma de tomate suscetível ao nematóide. Aos 15 dias após a semeadura, foi realizada a infestação, na região da rizosfera, com 5000 ovos de Meloidogyne incognita, raça 3. Foi avaliado o número de massas de ovos, aproximadamente 45 dias após a inoculação. Somente as linhagens ESAL 522, ESAL 519 e 'Aporé' foram resistentes ao nematóide. Apenas a 'Aporé' foi resistente aos dois patógenos. A correlação entre as notas de severidade do Fop e o número médio de massa de ovos obtida foi praticamente nula (r = 0,0252; <0,9293).

To verify a possible relationship between resistance to nematodes and to Fusarium oxysporum (Fop) in common bean, 18 lines (eight resistant and eight susceptible to Fop plus two controls) were evaluated for resistance to the nematode Meloidogyne incognita. This evaluation was conducted in a greenhouse in a randomized block design with five replications. The plot consisted of one pot with two bean plants and a nematode-susceptible tomato plant. Two weeks after sowing, plants were infested in the rhizosphere with 5000 eggs of Meloidogyne incognita, race 3. The number of egg masses was assessed, about 45 days after inoculation. Only lines ESAL 522, ESAL 519 and 'Aporé' were resistant to the nematode. Only 'Aporé' was resistant to both pathogens. The correlation between grades of Fop severity and mean egg mass was practically zero (r = 0.0252, P < 0.9293).