Caracterização do nematoide das galhas (Meloidogyne spp.) em cultivo de arroz irrigado nos Estados do Rio Grande do Sul e de Santa Catarina e hospedabilidade de plantas daninhas e forrageiras a Meloidogyne graminicola.

Abstract

The southern Brazil is the largest area cutivated with irrigated rice in the country. However, the production can be limited by various phytopathogenic agents, including the root-knot nematodes (Meloidogyne spp.). Thus, the aim of this research was to perform a root-knot nematode survey in irrigated rice fields in the states of Rio Grande do Sul (RS) and Santa Catarina (SC) as well as to check the host suitability of forage species and the main weeds found most often in the offseason and during the rice cultivation regarding the root-knot nematode Meloidogyne graminicola. The obtained populations were characterized biochemically by the isoenzymes esterase (Est) and malate dehydrogenase (Mdh) and morphologically by the configuration of the perineal region of the females. Subsequently, it was evaluated in greenhouse the reaction of 18 species of autumn/winter and spring/summer weeds that occurr in rice fields to M. graminicola. Fifty-five Meloidogyne spp. populations were detected in 48% of the collected samples, identifying five esterastic (Est) phenotypes and two Mdh phenotypes. In the samples from RS, were detected 16 populations of M. graminicola with the phenotype Est VS1 (Rm: 0.70), eight populations of Meloidogyne sp.2 Est Ar2 (Rm: 0.81, 0.91) and two populations of Meloidogyne sp.3 Est VS1a2 (Rm: 0.61, 0.70), which corresponded to 80, 40 and 10% of the analyzed samples, respectively. In state of SC were detected 15 populations of M. graminicola Est VS1 phenotype (Rm: 0.70), two populations of M. javanica Est J3 (Rm: 1.00, 1.20 and 1.35), 10 populations of Meloidogyne sp.1 Est Ar1 (Rm: 1.02), two populations of Meloidogyne sp.2 Est Ar2 (Rm: 0,81, 0.91) and one population of Meloidogyne sp.3 Est VS1a2 (Rm: 0.61, 0.70), corresponding to 93.75, 12.5, 62.5, 12.5 and 6.25% of the analyzed samples, respectively. When using the Mdh enzyme, all nematode populations showed monomorphic bands, being those from M. graminicola, Meloidogyne sp.1, and Meloidogyne sp.2 and Meloidogyne sp.3, by the phenotype N1a (Rm: 1.4) and M. javanica with the phenotype N1 (Rm: 1.0). The perineal patterns of the females of M. javanica Est Mdh J3N1 and M. graminicola Est Mdh VS1N1a were similar to the description of the species of that type. However, the analysis of the perineal configurations of the atypical populations Meloidogyne sp.1, Meloidogyne sp.2 and Meloidogyne sp.3 did not allow the identification at the specific level. Studying the reaction of the weeds to M. 10 graminicola, it was observed that Avena strigosa and Lolium multiflorum that occurr in autumn/winter as well as Alternanthera philoxeroides, Oryza sativa-ARV, Echinochloa crusgalli, Cyperus difformis, Cyperus esculentus, Cyperus iria and Fimbristylis miliacea that occurr in spring/summer behaved as good hosts of the root-knot nematode; Cyperus esculentus behaved as resistant in waterlogged soil condition and Aeschynomene denticulata and Leersia hexandra were immune to M. graminicola independently of the irrigation regime.