| Título: | Identification of races os soybean rust and its problems. |
| Autores: |
KATO, M. YORINORI, J. T. |
| Fecha: |
2014-10-17 2014-10-17 2006 2007-01-23 |
| Publicador: | Repositório Acesso Livre à Informação Científica da Embrapa (ALICE) |
| Fuente: |
 |
| Tipo: | Resumo em anais de congresso (ALICE) |
| Tema: |
Soja Doença de planta Fungo Ferrugem Doença fúngica |
| Descripción: |
Asian soybean rust caused by Phakoprsora pachyrhizi is one of the most important diseases for soybean cultivation. The disease causes yield loss as high as 80%. Until now, fungicide applications were most reliable control measure. However, farmers often lose timing of application due to frequent raining. Soybean cultivation with irrigation sometimes requires more than four times of fungicide applications. From economical and ecological points of view, cultivation of resistant cultivars to soybean rust is desirable. To obtain the knowledge of the diversity of pathogenic races of soybean rust in Brazil, we tried to identify races. Rusted soybean leaf samples were collected from five states of Brazil, Mato Grosso, Mato Grosso do SuI Goias, Parana and Rio Grande do SuI in Brazil in 2002, 2005 and 2006. Urediniospores on samples were trapped with small pieces of filter paper and inoculated onto healthy susceptible soybean leaflets in a plastic box. The plastic box was kept in an air-conditioned chamber with illumination. Before urediniospores appeared from uredinia, a small section including one lesion was cut and transferred to a microtube with wet paper. Fresh uredospores were spread to healthy soybean leaflets, thus single lesion isolates were established. Some isolates were used for race identification without this process, i.e. bulk isolates. Urediniospores were multiplied enough to race identification by repeated inoculations in plastic boxes. Thirteen isolates were used for race identification. Fourteen differential cultivars of soybean were used for race identification: Wayne, PI200492, PI230970, PI23097l, Ankur, PI459024, PI459025, TN #4, TK 5, Shiranui, BRS 134, BRS 154, BRS 231 and BRSMS Bacuri. Five seeds were sown in a potted soil and cultured in a growth chamber at 24 °C and 12 ill-light and 12 ill-dark for about three weeks. One to three plants were inoculated depending on germination rates. Urediniospore suspensions were inoculated to lower surface of leaflets of the first trifoliate leave. The inoculated plants were covered with plastic bags to maintain humidity for 20-22 hr at 24 °C in the dark, and then cultivated for further 13 days at 24 °C and under the photoperiod of 12 hr-light and 12 hr-dark. Soybean reaction was rated based on color of lesions: tan lesions (TAN) as susceptible; reddish brown lesions (RB) as resistant. During the progress of assessment, it was found that color of lesions varied continuously from extreme tan to dark reddish brown and that it was difficult to divide clealy lesions into TAN and RB reactions. To make a detailed assessment, a range of lesion colors was subdivided into six categories (T1, T2, Rl, R2, R3 and R4). Tentatively, T1 and T2 were rated as susceptible, and R1 to R4 as resistant. When lesions ranging from T1 or T2 to R1, R2 or R3 on a differential cultivar, the reaction was rated as intermediate. There were more than one pathogenic races in Brazil. Differentials of PI230970 having Rpp2 resistance gene and PI459025 having Rpp4 showed resistant reactions to all the isolates tested. During the maintenance of isolates on detached leaves in plastic cases, we encountered two problems, mycoparasitic fiungi and mycofagous mites. They made it difficult to multiply urediniospores. 2006 |
| Idioma: | en |