Pathogenic variability of Puccinia melanocephala and Ustilago scitaminea in the State of São Paulo / Variabilidade patogênica de Puccinia melanocephala e Ustilago scitaminea no estado de São Paulo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Rust and smut are among the most important diseases of sugarcane, being considered in every breeding program both in parent selection as well as in evaluating progeny behavior. When the crop is distributed to large extensions, it becomes very important to know the amplitude of the pathogenic variation in the population of the causal agent. Considering the importance of obtaining varieties with effective and long lasting resistance, the objective of the present study was to verify the occurrence, in the state of São Paulo, of pathogenic variability in Puccinia melanocephala and Ustilago scitaminea. Twelve populations of each pathogen were collected from three sugarcane producing regions: Piracicaba, Jaú and Ribeirão Preto. For the rust experiments three varieties of known behavior to the disease were used, SP70-1143, SP91-1397 and R570, susceptible, intermediate, and resistant, respectively. Twenty day-old plants were inoculated with 104 viable spores/mL suspensions of each population, and incubated at 20 ºC with 12 h photoperiod. Fourteen days later, symptoms were evaluated in the leaf +1, quantifying severity as the percentage of the leaf area affected and incidence as the number of pustules/cm2. For smut, three varieties with know response to the disease were used, SP84-2066, susceptible, Co421, intermediate and SP71-8210, resistant. Buds of each variety were inoculated with 1,7 x 106 viable spores/mL of each population. After growth in the greenhouse the plants were transplanted to the field in a random block trial with 4 repetitions. Disease was monitored every fourteen days during the plant cane cycle, determining the incidence according to the accumulated percentage of diseased stools per plot, also obtaining the area below the disease progression curve. For rust, it was observed that the populations showed different levels of aggressiveness. Two populations from Jaú, named J3 and J4, behaved as the most aggressive in the three varieties. Moreover, populations from Jaú showed different virulence among studied populations. The populations of U. scitaminea showed distinct aggressiveness levels, however it was not observed changes in the virulence among tested populations. According to the evaluated parameters, one population from Piracicaba and two from Jaú behaved as the most aggressive ones. Thus, it was showed that a considerable pathogenic variability exists among Brazilian populations of both pathogens. The sugarcane breeding programs that perform artificial inoculations with rust and smut spores at some stage in the program must take into consideration the variability in the aggressiveness of the pathogens determined in this study.

ASSUNTO(S)

smut patogenicidade ferrugem (doença de planta) pathogenicity sugarcane cana-de-açúcar rust carvão (doença de planta)

ACESSO AO ARTIGO

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