Métodos de evaluación y reacción de cultivares para resistencia al a？ublo de la vaina del arroz causado por Rhizoctonia solani AG-1 IA

the rice (oryza sativa l.), in venezuela, is affected by sheath blight caused by rhizoctonia solani (teleomorph = thanatephorus cucumeris). no complete resistance has been found in the world. in consequence, breeding programs should evaluate many cultivars for selecting those with the best quantitative level of resistance. the objectives were to compare methods of evaluation and cultivars reaction for resistance to the sheath blight caused by r. solani ag-1 ia. the evaluation methods were microchamber and mycelium ball in greenhouse conditions, kinetin test in laboratory and colonized rice infestation under field conditions. the cultivars were 23 genotypes of rice, including control varieties. three haplotypes of r. solani, previously characterized, were used for the inoculations. the experimental designs were randomized complete block with three replications. the effectiveness of the trials was determined based on the discrimination of controls with well-known reaction and the best correlation of the laboratory and greenhouse methods with the field results. the method of microchamber using the isolate a5b4 (64) had the best correlation with field results (r = 0.50 on average), followed by the method of ball mycelium (r = 0.49, on average). the control cultivars 'tetep' (resistant) and 'lemont' (susceptible) were consistent across the experiments. the principal component analysis identified the genotypes ct15150-m-11-4-3-2-m (derived from a cross with o. glaberrima), 'sd20a' and 'd-sativa' with the best levels of resistance. these results indicate the existence of reliable methods to evaluate this disease and adapted cultivars with resistance to rice sheath blight.