PATHOGENICITY OF THE ROOT-KNOT NEMATODE, MELOIDOGYNE-INCOGNITA, TO CULTIVARS OF PHASEOLUS-VULGARIS AND VIGNA-UNGUICULATA

Screenhouse experiments were conducted in 2 000-3 000 cm(3) plastic ba gs to investigate the relationships between a range of population dens ities (0, 0.25, 0.5, 1, 2, 4, 8, 16, and 32 eggs and second stage juve niles/cm(3) soil) of Meloidogyne incognita race 2 and yield of the sus ceptible cultivars Tenerife, Montalban and Manuare of Phaseolus vulgar is and Metro of Vigna unguiculata. Results demonstrated that all culti vars were very susceptible to M. incognita. Seinhorst's curves fit the data well, and tolerance limits to M. incognita of 0.02 J2 + egg/cm(3 ) soil for the cvs Tenerife and Montalban and 0.03 J2 + egg/cm(3) soil for cvs Manuare and Metro were derived. Minimum yields at larger nema tode densities were 36.5, 43, 53 and 28%, respectively. Populations of M. incognita increased in soil infested with up to 8 J2 + eggs/cm(3) soil, but generally remained at same level at larger initial populatio n densities except for the cv Manuare on which a sharp decline was obs erved. Nematode reproduction rates were higher the lower the initial d ensities. Seinhorst's equation for population growth also fit data for initial and final nematode densities, assuming maximum reproduction r ates of 20, 16, 36, and 5, equilibrium densities of 25, 12, 28, and 9J 2 s eggs/cm(3) soil, and maximum potential nematode populations of 64, 64, 42, and 35 J2 + eggs/cm(3) soil for the cvs Tenerife, Montalban, Manuare and Metro, respectively.