Caracterização biológica e fisiológica de populações de Sclerotinia sclerotiorum e avaliação da resistência genética em cultivares de soja

• Autor(a) principal: GARCIA, Riccely ávila
• Data de Publicação: 2012
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tde/449
• topic: mofo-branco; variabilidade; agressividade; sensibilidade à fungicidas e temperatura; métodos de inoculação; resistência; white mold; variability, aggressiveness, sensibility to fungicides and temperatures, inoculation methods, resistance.; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA

The soybean (Glycine max L. Merril) is the main cultivated species on the country, having an average productivity of 3,106 kg.ha-1 in an area of 24.2 million hectares, giving to Brazil the second place in world production. Among the factors that limit the yield, the profitability and the successful production of this legume, diseases are a highlight. Among them, the white mold, caused by Sclerotinia sclerotiorum (Lib.) of Bary, is gaining importance in the soybean fields on the Brazilian Cerrado . The control of this disease is being considered difficult due to the absence of resistant cultivars, fungus survival in soil during long periods, range of hosts, large number of ascospores produced by apothecium and their fast dissemination on relatively long distances from the source and survival in seeds on mycelial dormant form or sclerotia, contaminating the batches. This work had the aim to study the genetic variability of S. sclerotiorum populations; evaluate the aggressiveness of isolates in soybean culture; evaluate the sensitivity of isolates to fungicides, temperatures and light regime; select an inoculation method of S. sclerotiorum in soybean plants, efficient and practical and; characterize soybean cultivars for reaction to S. sclerotiorum. The experiments were conducted on the Escola de Agronomia e Engenharia de Alimentos da Universidade Federal de Goiás . The collection of isolates was obtained by collecting sclerotia in soybean plants in eight municipalities of the Brazilian Central Region, Silvânia GO, Anápolis GO, São Miguel do Passa Quatro GO, Água Fria GO, Montividiu GO, Chapadão do Sul MS, Uberlândia MG and Patrocínio MG. The tests of mycelial compatibility were performed in MPM (Modified Patterson s Medium) and in PDA (Potato Dextrose Agar) medium, having the mycelial reactions of compatibility and incompatibility evaluated seven days after incubation. Analyzes of mycelial compatibility were performed in each sampled municipality, with a number of 25 isolates, as well as among groups of mycelial compatibility of each municipality, totaling 31 isolates. To evaluation of aggressiveness, 21 isolates representing each group of mycelial compatibility, found in each studied locality, were inoculated by the tip method on the petiole in the cultivars M-SOY 7908 RR and BRSGO 7760 RR. The evaluations of lesion length on stem were made three and seven days after inoculation. The same 21 isolates used on aggressiveness experiments were evaluated for sensibility to fungicides fluopyram, boscalid, thiophanate methyl, carbedanzim, dimoxystrobin + boscalid, procymidone and fluazinam. Those isolates were also evaluated for sensibility on temperatures 10oC, 15oC, 20oC, 25oC and 30oC, in light regime conditions of 12 hours and continuous darkness. For selection of a inoculation method both efficient and practical, four inoculation methods were used in soybean cultivars M-SOY 7908 RR and BRS 7760 RR using only one isolate. The characterization of soybean cultivars regarding reaction to S. sclerotiorum was made by means of an aggressive isolate, selected on aggressiveness experiments, and by the tip method. In this experiment forty cultivars were evaluated in totally randomized design with 3 repetitions. In intrapopulation analysis, was verified that the genetic variability in S. sclerotiorum was low, while in interpopulation analysis, eight compatibility groups were found, one of the groups more aggressive than the other ones. There was significant difference among isolates for the aggressiveness in the two cultivars, being the M-SOY 7908 RR cultivar the most susceptible. The isolates were highly sensible to fungicides boscalid, carbendazim, dimoxystrobin + boscalid, procymidone, fluopyram and fluazinam, only the isolate SSUB 18 was moderately sensible to the fungicide fluopyram. Most of isolates had insensibility to the fungicide thiophanate methyl. The best temperature for mycelial growth of isolates was 25oC, regardless the light regime. The tip method of inoculation in petiole was efficient and practical for characterization of soybean cultivars for their reaction to S. sclerotiorum. There is varietal difference among soybean cultivars for resistance to white mold, being cultivars BRSGO 8460RR, BRSGO Ipameri and P98Y11 the most resistant ones, on the present study conditions.