Morphogenetic variability, cultural characteristics, aggressiveness, and transmission of Bipolaris oryzae isolates in Rio Grande do sul: Variabilidade morfogenética, características culturais, agressividade e transmissão de Bipolaris oryzae isolados no Rio Grande do Sul

Abstract

Brown spot disease, caused by Bipolaris oryzae, is one of the most important rice diseases. This pathogen causes reductions in rice crop yield and quality, and its variability has been a problem for the management of brown spot disease due to its morphological and cultural similarity with other species that cause leaf spots and grain blight. The aim of this study was to determine the variability of B. oryzae isolates using different approaches and report information on patterns in aggressiveness and transmission of this pathogen from rice seed to seedlings. Fifteen isolates from different geographic rice crop regions of Rio Grande do Sul were used. The isolates were analyzed for genetic diversity, morphological and cultural characteristics, aggressiveness, and transmission ability from rice seeds to seedlings. Isolates fell into five morphological groups, based on cultural characteristics. Range values of the spore dimensions, color and mycelial growth showed high variation among the isolates. The most aggressive and transmissible isolates were those that form black colonies and had suppressed growth. The results show that isolates from Rio Grande do Sul are morphologically and genetically diverse and distributed throughout the state. This is the first study in which isolates representing the main rice growing areas in Rio Grande do Sul were taken into consideration for the study of variability, aggressiveness, and transmission