Reação de genótipos de cana-de-açúcar à ferrugem alaranjada nos ciclos de cana-planta e de cana-soca

Abstract

Sugarcane orange rust is a disease caused by the fungus Puccinia kuehnii, which can cause drops of more than 40% in crop productivity. In the literature, there are few studies on the disease in different crop cycles; therefore, the objective of the present work was to evaluate the reaction of sugarcane varieties to orange rust in the cane-plant and ratoon cane cycles. Two field experiments were carried out in Araras, SP, under natural infection conditions. In the borders and between the blocks of the two experiments, the variety SP89-1115, susceptible to orange rust, was planted, which acted as a multiplier and donor of inoculum of P. kuehnii. Disease severity assessments were performed on the +3 leaf, on average every 15 days from the appearance of the first pustules. The variables analyzed were the area under the relative disease progress curve (AACPDR), calculated from the disease severity data, and the maximum severity score during the cycle. There was a significant difference between the varieties in both experiments. It was possible to observe, from plant cane to ratoon cane, an increase in AACPDR in the more susceptible genotypes in both experiments, which did not happen in the resistant and intermediate varieties. For maximum score, the few differences from one cycle to another were not enough to change the classification of the variety's reaction to the disease, except in the case of RB855453 in the second experiment, which in cane-plant was grouped between the most resistant varieties and among the intermediate reaction in ratoon cane. Given the results obtained, it is recommended that experiments to evaluate the response of sugarcane genotypes to orange rust be carried out for at least two cycles (plant and ratoon cane), and that the variable be used. AACPDR for comparison between genotypes.