Incidência de ustilago operta em sementes comerciais de braquiaria

Abstract

Ustilago operta, causal agent of smut, represents a serious risk to the seed production of brachyaria grass. The objective of this work was to evaluate the incidence of smut in commercial seeds of Brachiaria spp. seeds of cultivars of B. brizantha, B. decumbens, B. humidicola, and B. ruziziensis, destined for the internal market, produced in BA, GO, MG, MS, MT and SP, Brazil, during 2004–2005 and 2005–2006. The occurrence of smut in lots of high purity, destined for the external market, was also analyzed. After a longitudinal cut, 400 seeds/lot/harvest, divided in 4 repetitions of 100, were examined under a stereomicroscope for the presence of a black pulverulent mass, composed of fungal structures. The frequency of U. operta in lots produced in 2004–2005 and 2005–2005 was 32% and 28%, respectively. In the 2004–2005 harvest, the highest incidences of smut in Marandu seeds were observed in lots produced in Barreiras, BA (7.3%) and Paraíso, MS (2.3%). In the next harvest, the highest number of smut-contaminated seeds was detected in lots of Marandu seeds produced in Rio Verde, GO. Smut signals were detected in Xaraés seeds produced in regions of MG and MS (incidence £ 1%), in both harvests. In one lot of Basilisk (origin: Paraíso, MS, 2004–2005) there was observed an incidence of smut in seeds (1%). This constitutes the first report of the U. operta – B. decumbens interaction. The smut was not visualized in Humidicola and Ruziziensis seeds. The occurrence of U. operta in lots of high-purity Marandu seeds was confirmed.