Effects of Initial Population Density of Meloidogyne graminicola and Plant Age of Infection on Thai Jasmine Rice and Nematode Multiplication

The effects were investigated of initial population densities (Pi; Pi levels = 0.01, 0.02, 0.1, 0.2, 1 or 10 infective second stage juveniles (J2)/g soil) of Meloidogyne graminicola and rice ages (10, 30, 60 and 90 days) of infection on the growth and yield of Thai Jasmine rice cv. Khao Dawk Mali 105 (KDML105) and the population dynamics of M. graminicola. Both factors influenced the growth and yield parameters of KDML105 as well as nematode development. There was a negative correlation between Pi levels and growth (plant height and chlorophyll content) and yield parameters. On the other hand, the plant ages of infection were positively correlated with these parameters. The number of tillers/plant and days to 50% flowering increased with increasing Pi. The range of maximal yield loss was at high Pi levels (>= 0.2 J2/g soil) in the 10-day plants of infection. However, at the lowest Pi level (0.01 J2/g soil), grain yield loss was up to 50% when inoculated in the 10-day and 30-day plants and a Pi value of at least 1.0 J2/g soil caused significant grain yield loss in all growth stages of infection. The Seinhorst model was used for grain yield loss prediction; increasing yield loss occurred at high Pi levels in the early growth stages. In addition, the Pi levels and growth stages were negatively correlated with nematode reproduction. The maximum reproductive factor of M. graminicola occurred at a Pi level of 0.02 J2/g soil when infected in the 30-day plant.