Effect of Diurnal Changes in Soil Temperatures on Resistance to Metoidogyne incognita in Tomato.

Thermoper iodism is known to influence the growth of tomato, Lycopersicon esculenturn (10), but its effect on reproduct ion of the root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, infecting tomato has not been reported. T o m a t o genotypes carrying the Mi gene for resistance to root-knot nematodes lose their resistance when exposed to constant high temperature (4,5,6,8). T h e objective of this research was to investigate the effects of h igh/ low (day/ night) temperature on the resistance of Lycopersicon esculenturn Mill. and L. peruvianurn var. dentatum Dun. genotypes to M. incognita. T h e degree of nematode reproduct ion on the host plant, i.e., host efficiency (3,9), was the parameter used for determining host resistance. Two greenhouse experiments were conducted. In the first experiment, selected plant introductions of L. peruvianum var. dentaturn were used: PI 306811, PI 1291492(sib)-5-4, PI 129149-3-1-2, and PI 129149-32-1 (R2). In the second experiment, L. esculenturn selections and commercial cultivars were tested: Floradade, Nematex-22, Floradade × Nematex-22, Patriot-17, Piersol, P! 266376, PI 129149-2(sib)-5.4, and PI 129149-2(sib)-5-I 6 ×43. T e n 12-day-old tomato seedlings of each cultivar or selection were individually transplanted into plastic pots (12 cm d × 16.5 cm deep) containing previously autoclaved sandy soil. T h e pots were placed in a controlled temperature tank and maintained at a constant soil temperature (32.5 C) for the durat ion of the experiment. T e n 12-day-