Competition between Tylenchorhynchus annulatus and Mesocriconema xenoplax on grain sorghum as influenced by Macrophomina phaseolina

Greenhouse experiments were conducted to examine competition between Tylenc horhynchus annulatus and Mesocriconema xenoplax on grain sorghum roots that were colonized by the fungus Macrophomina phaseolina or free from fungus c olonization. An incomplete factorial treatment design consisted of two leve ls of M. phaseolina (0 or 10 colony-forming units/g soil) and 12 T, annulat us:M xenoplax ratios: 1,000:0; 750:0; 500:0; 250:0; 0:0; 0:250; 0:500; 0:75 0; 0:1,000; 750:250; 500:500; and 250:750. Plants were harvested after 105 days. Despite similar feeding habits, competition between these ectoparasit ic nematode species was limited. Tylenchorhynchus annulatus was more suscep tible to antagonism by M.. xenoplax than the reverse, but susceptibility de pended on initial inoculum ratio. Root colonization by M. phaseolina reduce d competitive effects of T. annulatus on M, xenoplax bur not the reverse. B oth nematode species reduced shoot dry weight but only T. annulatus reduced root dry weight. Both plant weight parameters were reduced by M. phaseolin a.