Influence of date of sowing wheat on the population growth of the plant parasitic nematodes, Meloidogyne triticoryzae and Tylenchorhynchus mashhoodi and saprozoic nematodes and relationships with temperature

Population of the cereal root-knot nematode, Meloidogyne triticoryzae, the stunt nematode, Tylenchorhynchus mashhoodi and the saprozoic nematodes (mainly rhabditids and dorylaims) was monitored in wheat crop sown on 4 different dates viz., mid-November, late November, mid-December and late December. The rate of population growth of both M. triticoryzae and T. mashhoodi was highest in the mid-November sown crop which was significantly higher than late-November and mid-December sown wheat crops. The lowest population growth rate was observed in the late-December sown crop. The saprozoic nematodes were less affected by date of sowing except that slightly greater increase in population occurred in the late-November and mid-December sown wheat crop. The soil population densities of all the nematodes, studied, were highest at the mid-season followed by decline at harvest, probably because of drying of soil at the time of sampling and retention of the M. triticoryzae eggs inside the root. Bioassay of soil samples, however, revealed high population densities of root-knot nematodes in the soil, probably in the form of eggs while few juveniles could be extracted from the same soil samples. Application of a computer program developed to compute the mean daily specific growth rates (DSGR) of the different nematodes, confirmed the above conclusion and helped to pinpoint, quantify and simulate the period and rate of population growth in the crop. The study shows that the late sown wheat crops would allow significantly lesser growth of the root-knot and stunt nematodes which may help in the management of these nematodes using cultivars otherwise suitable for sowing at the relevant time.