INTERRELATIONSHIPS AMONG MACROPHOMINA-PHASEOLINA, CRICONEMELLA-XENOPLAX, AND TYLENCHORHYNCHUS-ANNULATUS ON GRAIN-SORGHUM

Microplot experiments were established in 1992, 1993, and 1994 to inve stigate the relationships among Macrophomina phaseolina, Criconemella xenoplax and Tylenchorhynchus annulatus on grain sorghum in Louisiana. A factorial treatment arrangement of two grain sorghum hybrids (De Ka lb DK 50 and Pioneer hybrid 8333), three levels of M. phaseolina (0, 1 0, and 100 colony-forming units (CFU)/g soil), and three nematode inoc ulum levels (0, Ix, and 2x) were used. Nematode inocula at Ix levels w ere 929, 1,139, and 1,445 C. xenoplax and T. annulatus/microplot in 19 92, 1993, and 1994, respectively. Plants were harvested after 90-105 d ays. In all 3 years, grain sorghum root and head dry weights were supp ressed as nematode inoculum level increased. These reductions were det ected both in the absence and in the presence of M. phaseolina at 10 C FU/g. Reproduction of both nematode species was suppressed by M. phase olina. Interactions between M. phaseolina and nematodes were antagonis tic with regard to plant dry; weights, yield, and nematode reproductio n, so that combined effects were less than the sum of the effect of ea ch pathogen alone.