Resistência de cultivares de Urochloa à Bipolaris sp

Abstract

Diseases in pastures have intensified in recent years, mainly in the Central-West and Northern regions of Brazil. The objective of this study was to evaluate resistance of cultivars of Urochloa brizantha, Urochloa ruziziensis, and their hybrids, to Bipolaris sp., by inoculation in 90 mm sections of detached leaves. The inoculum consisted of 5 mm three-day-old culture disks placed in the central portion of the leaf section. Each leaf section was previously punctured in four points with a needle. The experiment was conducted in a completely randomized design with five replications. Eleven cultivars were evaluated: BRS Ipyporã, Camello, Cayana, Cayman, Cobra, Marandú, Mavuno, Mulato II, Ruziziensis, Sabiá and 780J. The necrotic leaf area was evaluated in the eleven cultivars, and the area under the lesion progress curve (AUDPC) was calculated. Necrotic lesions were observed on the third day after inoculation (dai), right after the removal of the culture disks, in all genotypes evaluated. At 9 dai, last evaluation, cvs. Cayana, Cobra, Marandú, and 780J had a smaller necrotic leaf area and lower AUDPC values than cvs. BRS Ipyporã, Camello, Mavuno, Mulato II, Ruziziensis and Sabiá.