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Effect of Puccinia kuehnii on two sugarcane cultivars with intermediate resistance to orange rust.

Fernanda Aline Cavalcante Leite: Federal University of São Carlos

<div>The first report of the first outbreak of orange rust (<em>Puccinia kuehnii</em>) in Brazil was in 2010. The main strategy of control was the elimination of susceptible cultivars, as done in Australia. Nevertheless, RB92579, and RB865156 show intermediate resistance and are ranked third and fourth to establish new sugarcane fields in 2015, demonstrating that intermediate canes will persist in the Brazilian sugarcane industry. Therefore, the present study aimed to examine the effect of <em>P. kuehnii</em> on two intermediate cultivars towards orange rust. Plants derived from single eye bud were transplanted to plastic pots three months after planting and divided in inoculated and uninoculated treatments. Two-way design was considered, with six repetitions and single potted plant as experimental unit. Inoculation of <em>P. kuehnii</em> was carried out biweekly with concentration of 10<sup>5</sup><sup>-1</sup> and volume of 13-30 ml, according to plant growth. Uninoculated plants were protected with fungicide to ensure disease-free control plants. After six months, wet and dry weight were measured. Results indicated that the effect of inoculation was significant, i.e., wet and dry weight were significantly reduced when plants were submitted to the disease, and no interaction between disease and cultivars was verified. This indicated that chemical protection is necessary for these two intermediate cultivars under high disease pressure and when favorable conditions for orange rust are prevalent.</div>