Sclerotinia sclerotiorum, causal agent of white mould, is the most destructive and widely distributed soilborne pathogen of common bean during the autumn–winter season in Brazil. Nevertheless, little is known about the genetic structure of the pathogen population. Microsatellite (SSR) markers and mycelial compatibility groups (MCGs) were used to characterize 118 isolates collected from 20 bean fields located in the most important growing regions of Minas Gerais State (MG). Additionally, the genetic variability among 10 isolates obtained from a single sclerotium was investigated in 10 different sclerotia. Seventy SSR haplotypes and 14 MCGs were identified among the 118 isolates. The genetic differences within bean growing areas accounted for most of the genetic variation (72%). Despite the relatively high genotypic diversity, the SSR loci were at linkage disequilibrium. Moreover, 70% of the isolates were assigned to only two MCGs, and haplotypes of a given MCG were closely related. The discriminant analysis of principal components revealed five groups. There was strong genetic differentiation between isolates collected in one municipality in southern MG when compared to other regions. Common bean resistance to white mould should be assessed with representative isolates of the five genetic groups and, if possible, of the different MCGs detected in the present study. One to five haplotypes were detected among the 10 isolates obtained from a single sclerotium. Therefore, in order to ensure genetic identity of an isolate, hyphal tip or monoascosporic isolates should be used.

RESUMO -O manejo inadequado das plantas daninhas é uma das principais causas da baixa produtividade da cultura da mandioca no Brasil. Objetivou-se com este trabalho identificar as espécies de plantas daninhas infestantes da cultura da mandioca e o grau de interferência que estas exercem sobre o cultivo, em função do período de convivência com a cultura. Dois experimentos foram realizados em áreas adjacentes, no município de Viçosa-MG, utilizando-se o cultivar Cacauzinha, do grupo das mandiocas mansas. O delineamento experimental adotado foi em blocos casualizados, com sete tratamentos e quatro repetições. Os tratamentos do primeiro experimento foram compostos por períodos iniciais de convivência da cultura com as plantas daninhas: 25, 50, 75, 100 e 125 dias após o plantio (DAP); no segundo experimento, as plantas de mandioca, inicialmente, permaneceram livres das plantas daninhas pelos mesmos períodos. Em ambos os experimentos adotou-se o espaçamento de 1,0 x 0,5 m, sendo a área útil da parcela constituída pelas duas linhas centrais, deixando-se 1,0 m em cada extremidade como bordaduras frontais, totalizando 8,0 m 2 . As plantas daninhas foram avaliadas aos 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325 e 350 DAP. As características produtividade de raízes, peso da parte aérea, índice de colheita, teor de amido e matéria seca das raízes foram avaliadas aos 12 meses após o plantio. As espécies de plantas daninhas que predominaram na área experimental foram: Bidens pilosa, Raphanus raphanistrum, Cyperus rotundus e Commelina benghalensis, com a primeira delas predominando em quase todas as épocas de coletas. Os períodos de convivência com as plantas daninhas não interferiram nos índices de colheita, teor de amido e matéria seca das raízes. Todavia, considerando a produtividade de raízes, o final do período anterior à interferência foi próximo dos 25 dias, e o período crítico de prevenção da interferência situou-se entre 25 e 75 DAP. Cultivos realizados após 75 DAP não afetaram as características da cultura da mandioca avaliadas.Palavras-chave: capinas, competição, período de convivência.ABSTRACT -Inadequate handling of weeds is one of the main causes of cassava low yield in Brazil. The objective of this work was to identify the weed species interfering in cassava crop and the degree of this interference, in function of then coexistence period. Two experiments were carried out in adjacent areas in Viçosa-MG, Brazil, using the "cacauzinha" cultivar of the cassava group. A randomized block design was adopted, with seven treatments and four replications. The treatments in the first experiment were composed by the initial crop periods and weed coexistence 25, 50, 75, 100 and 125 days after planting (DAP). In the second experiment, the cassava plants initially remained weed-free for the same periods. For both experiments, 1.0 x 0.5 m spacing was adopted, being the useful portion area constituted by the two central lines, with 1.0 m being

Autogamous plant breeders obtain numerous populations annually, and in the progeny selection process, the merit of the population is not considered. Thus, it would be important to have a progeny selection index that includes not only the effects of progenies in the different generations but also the effects of populations in all the generations and the data from parents and the F1 and F2 generations simultaneously. The main objective of this paper was to develop a selection method that encompasses the entire structure of an autogamous plant breeding program including all the data as of the parents, the F1 and F2 generations, and also both the progeny and population effects in the F3 to F6 generations. To do so, a selection index (called selection index with parents, populations, progenies, and generations [SIPPPG]), which includes all these effects, was proposed. Estimators were also derived for computation of the contribution (through indirect heritabilities and selective accuracies) of each source of information for predicting the additive genetic value of the lines to be obtained at the end of the selection process. The new approach was assessed through numerical evaluation and a total index was also obtained using field data derived from a breeding program with the common bean crop. This new index yields gains in selection efficiency ranging from 5 to 28% depending on the relative magnitude of the genetic variation among populations.

Molybdenum (Mo) reserve in large seeds can complement Mo uptake by plants from soil, but the content of Mo in common bean (Phaseolus vulgaris L.) seed for this purpose is unknown. We hypothesized that 3.639 ± 0.751 μg Mo seed -1 would be suffi cient to complement Mo uptake by irrigated common bean plants from a Mo-poor soil. Th ree fi eld experiments were performed in a clayey Ultisol naturally infested by native strains of Rhizobium in Zona da Mata, Minas Gerais, Brazil. Treatments were arranged as 4 × 2 factorial combination of Mo contents in seeds [small (0.007 ± 0.007 or 0.248 ± 0.057 μg Mo seed -1 ) or large (3.639 ± 0.751 or 6.961 ± 1.844 μg Mo seed -1 )] and Mo spraying treatments (90 g ha -1 or unsprayed) with six replications. Phosphorus, N (25 kg ha -1 ), and K were applied together in the furrow during planting time. No topdressing N was applied. Final plant population and seed yield were evaluated in two experiments. Molybdenum contents in the seeds did not aff ect plant population. On average, unsprayed plants from seeds with small Mo contents yielded 1785 kg ha -1 , while those from seeds with large Mo content yielded 2109 kg ha -1 . Foliar application of Mo increased plant N status, plant growth, and yield in plants originated from seeds with small Mo content, but not in plants grown from seeds with large Mo content. We conclude that 3.639 ± 0.751 μg Mo seed -1 suffi ciently complement the Mo uptake by common bean plants from soil.

The objective of this study was to understand the infection process of Fusarium oxysporum f. sp. phaseoli (Fop) in bean cultivars classified as resistant (Manteigão Fosco 11), intermediate (VP8) and susceptible (Meia Noite). Plants of the three cultivars were inoculated at 10 days after emergence with a suspension of 1×10 6 conidia of Fop per mL. At 43 days after the inoculation, stem segments were observed with a scanner electronic microscope. The cultivars Manteigão Fosco 11 and VP8 presented an occluding material in the xylem vessels, which may have restricted tissue colonization by Fop. The resistance of bean cultivars to Fop seemed also to be explained by structural differences in the xylem tissue. Key words: Phaseolus vulgaris, Fusarium wilt, host defense.The fungus Fusarium oxysporum Schlecht. f. sp. phaseoli Kendrick & Snyder (Fop) is the causal agent of the Fusarium wilt on common beans (Phaseolus vulgaris L.) and is present in all the regions that produce beans in the world (Alves-Santos et al., 2002;Abawi & Pastor-Corrales, 1990;Schwartz & McMillan, 1989;Buruchara & Camacho, 2000). The inadequate rotation of cultures, especially in areas irrigated with central pivot, the lack of preventive measures of control of the pathogen dissemination and the increase of soil compaction made the Fusarium wilt one of the most important bean diseases in Brazil (Paula Júnior et al., 2006).The dark, thick-walled chlamydospores are the longterm survival structures in soil (Abawi & Pastor-Corrales, 1990). Management practices alone may not be enough to keep the disease in low levels of intensity. Thus, the most efficient and viable alternative for the control of this disease is the use of resistant cultivars (Abawi, 1989;Abawi & Pastor-Corrales, 1990;Paula Júnior et al., 2006).The pathogen is capable of penetrating intact root tissue, although penetration of older parts of root and hypocotyl tissue also occurs, usually through wounds or natural openings (Abawi, 1989;Dongo & Müller, 1969;Duque & Müller, 1969). After penetration, hyphae of Fop move inter-and intracellularly and invade the xylem vessels (Mace et al., 1981). The fungus is confined to xylem vessels until the later stages of disease development, although limited invasion of the adjacent tissues may occur; growth of hyphae and transportation of microconidia in the xylem vessels are observed in susceptible cultivars (Abawi, 1989). On the other hand, in resistant plants the colonization between adjacent xylem vessels is restricted, probably as a result of chemical and structural alterations (Mace et al., 1981), including vascular occlusion by the formation of gel plugs, tyloses, deposition of additional wall layers and infusion of these structures with phenols and other metabolites (Mace et al., 1981).Although there are some reports about the differences in the histopathology of stem tissues from resistant and susceptible bean cultivars infected by Fop, detailed studies that approach the infectious process in plant tissues are scarce, especially compari...