Efeito do tamanho do sistema radicular do algodoeiro na tolerância a Rotylenchulus reniformis e Meloidogyne incognita raça 3

Abstract

Tolerance to plant-parasitic nematodes is characterized by the ability of plants suffer parasitism with minim yield loss. As yet, there is insufficient understanding of the mechanisms which govern this important characteristic. Cotton genotypes may differ according to the size of the root system which exerts significant influence on the development of plants under both abiotic and biotic stress conditions. The hypothesis proposed in this research is that the size of the cotton root system influences the crop tolerance of both Rotylenchulus reniformis and Meloidogyne incognita race 3. The objectives of this study were to determine: 1) whether cotton genotypes differ in the percentage yield loss caused by R. reniformis and M. incognita, and 2) whether the size of the root system of these genotypes or the host reaction to R. reniformis and M. incognita affect the percentage yield loss caused by the nematode. Two groups of cotton genotypes (each consisting of 12 entries) were selected as representatives of the area under production in Brazil to determine, in comparison with previous studies, variations in the level of tolerance to nematodes. One of the groups was assigned to the study of R. reniformis and the other to the analysis of M. incognita. Nematode reproduction and root system length were measured under greenhouse conditions and these variables were related to the percentage yield loss in naturally infested fields. There was significant variation in the tolerance level of cotton genotypes to both R. reniformis and M. incognita. Genotypes differed considerably in terms of total length of the root system. The relationship between the size of the cotton root system and nematode tolerance differs according to the species of nematode. Greater root system size increases the tolerance to R. reniformis and the parasitic load (nematodes per root unit) was related to cotton tolerance to R. reniformis. In the case of M. incognita the size of the root system does not have a direct influence on cotton tolerance. Tolerance to M. incognita was influenced primarily by the resistance level of each genotype as measured by the total number of nematode supported by the plant and the gall index.