Genetic diversity of Meloidogyne spp. from rice and identification of multiresistant sources in Oryza spp. accessions

Recently a Meloidogyne species complex was detected parasitizing and causing damage to irrigated rice in southern Brazil, highlighting the need to study the genetic diversity of these species and their pathogenicity to Oryza spp. in order to select genotypes of rice with multiple resistance. This study compared the genetic diversity of Brazilian Meloidogyne spp. isolates from irrigated rice and evaluated the reaction of four wild accessions of Oryza species (O. glumaepatula, O. longistaminata, O. grandiglumis, and O. alta) and two cultivated species, O. glaberrima and O. sativa (control) to M. ottersoni, M. oryzae, and two variants of M. graminicola (Est G2 and Est G3). Genetic variability was assessed using RAPD and AFLP markers. M. graminicola and M. ottersoni showed high intraspecific variability: 83.76% and 41.14%, respectively. Cluster analysis showed a clear separation among rice root-knot nematodes (RKNs) into subclades according to their esterase phenotypes with 100% bootstrap. For rice resistance screening, plants were inoculated with 5,000 eggs, and the nematode reproduction factor evaluated 90-120 days postinoculation. O. glumaepatula, an American wild species, was highly resistant or resistant to all rice RKNs tested and is a valuable source of multiple resistance. Overall, the other rice species also showed different levels of resistance. Conversely, O. longistaminata exhibited low levels of resistance. M. graminicola Est G3 was the most aggressive isolate. Sources of resistance against RKN in wild Oryza genotypes, especially in an AA genome like O. glumaepatula, may be of great interest for future breeding programmes in cultivated rice.