ABSTRACT
Orange rust (Puccinia kuehnii) has impaired sugarcane yield in Brazil. Resistant varieties is the best method to control this disease. Nevertheless, the success of this measure is directly related to the correct evaluation of the material reaction and pathogen diversity. Disease scores and percentage of injured area are the most employed parameters to study resistance in sugarcane. The diversity of the pathogen is examined by a set of differential varieties, which is not established yet for this pathosystem. Therefore, the present study aimed to test different parameters to evaluate the reaction of commercial sugarcane varieties to P. kuehnii. Three isolates of the pathogen were employed in a single inoculation into five sugarcane varieties and their reaction was evaluated after 21, 28, 35 and 42 days, using a disease score scale. The quantity and viability of uredniospores were also assessed through two different trials, 42 days after inoculation; first trial: urediniospores from RB855156 obtained from lesions with distinct classifications: score 2 (resistant) and score 3 (susceptible); second trial: urediniospores originated from lesions with the same disease classification but from different varieties: RB855156 (susceptible) and RB975201 (resistant). Data of the present study showed that the reaction of RB855156 varied according to date of evaluation since it was resistant in the first and susceptible in the last evaluation. Moreover, the viability of urediniospores was the parameter that could best distinguish between susceptible and resistant genotypes, showing to be superior to the other parameters that have been employed, such as size, sporulating pustules and quantity of urediniospores.
Keywords
orange rust; resistance; urediniospores; Saccharum
