Identification of five root-knot nematode (Meloidogyne sp.) lines and comparison of their effects on the growth and yield of selected rice cultivars grown under different water regimes and soil types.

Results of isozyme characterization and the total protein patterns indicated homogeneity among the five RKN lines studied which were similar with the isozyme phenotypes of M. graminicola. Under field conditions, varying levels of susceptibility based on the number of j square at harvest were observed among cultivars tested depending on water regime. IR72, PSBRc 18, and PSBRc 20 were considered less susceptible to RKN in rainfed and flooded conditions, IR36 was less susceptible under flooded conditions while intermediate under rainfed water regime. IR20 was less susceptible under flooded rainfed conditions. IR29 and IR74 were the most susceptible in both water regimes. In terms of yield, IR72, IR20, and PSBRc20 had the highest yield under both water regimes while IR74 had high yield under flooded conditions only. PSBRc 18 had low yield under rainfed conditions and, together with IR29, in flooded conditions. RKN was able to reproduce and develop in all soil types and water regimes. All cultivars were tolerant under flooded conditions regardless of soil type. However, the panicle number, total flagleaf area, and root length of IR20 and IR29 were affected by RKN infection under flooded conditions in sandy soil. More j square RKN and severe root damage were observed under rainfed than under flooded conditions for all cultivars. However, IR72 and IR74 were tolerant in all water regimes and soil types. IR20 and IR29 were nontolerant under rainfed conditions in both soil type. Tolerance for RKN in IR36 was influenced by soil and water regime. Nematode effect was expressed only in clay soil, which was favorable to the growth of IR36. IR29 was not tolerant of the RKN lines tested. PSBRc 20 was tolerant of O-LB and I-NE only. The effect of the five RKN lines on the growth and yield of IR29 and PSBRc 20 varied under rainfed conditions. I-LB was the most aggressive in both cultivars. The rest of the lines were moderately aggressive based on yhield and growth parameters used in IR29 and PSBRc 20. I-NE was found to have consistently the lowest aggresiveness. The nematode effect was compensated by good crop stand under flooded conditions.