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Ecology and Epidemiology

Effects of Cultivar, Soil Temperature, and Population Levels of Meloidogyne incognita on Root Necrosis and Fusarium Wilt of Tomatoes. G. S. Abawi, Departments of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; K. R. Barker, Departments of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 74:433-438. Accepted for publication 1 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-433.

Seedlings of tomato cultivars Bonny Best, Rutgers, Manapal, Floradel, Florida MH-1, and Nematex were inoculated with 0, 1, 5, 25, or 50 103 eggs of Meloidogyne incognita (MI) per 15-cm-diameter pot. After 3 wk, 30 106 washed conidia of Fusarium oxysporum f. sp. lycopersici (FOL) race 1 were added per pot to half the number of plants at each nematode population level. Plants were incubated on greenhouse benches at 16± 5 or 30± 5 C, and in soil temperature tanks at 25, 30, or 35 C. Nematex was the only cultivar with known resistance to M1. Manapal, Floradel, Florida MH-1, and Nematex were resistant to race 1 of FOL because they possess the I-1 or I-2 genes for resistance. Bonny Best and Rutgers were susceptible and field tolerant to FOL race 1, respectively. Factorial analysis of data showed no interaction between MI and FOL race 1 on plants resistant or susceptible to MI and/or FOL race 1. Reaction of tomato cultivars possessing the I-1 or I-2 genes for resistance to FOL race 1 was not altered by previous inoculation with MI. In addition, Nematex became susceptible to MI at 35 C, but remained resistant to FOL race 1 in the presence of both organisms. High levels of MI enhanced infection by Fusarium spp. or FOL race 1 and the rate of wilt development in the susceptible cultivars Bonny Best and Rutgers, although the final level of wilting was not different. However, numbers of MI were correlated with root necrosis (r = 0.83**) and wilting symptoms (r = 0.95**) regardless of the presence of FOL race 1. MI-infected plants showed greatest wilt and necrosis symptoms at 30 C. Similar results were obtained in a field microplot (50 50-cm) test with tomato cultivars Manapal and Florida MH-1 that were simultaneously inoculated with FOL race 1 and MI (105 eggs per plot). In this test, numbers of MI were correlated with wilt indices (r = 0.87**), root gall indices (r = 0.92**), and fruit yield (r = 0.98**). Wilt indices also were correlated to yield (r = - 0.92**) but were not related to the presence of FOL race 1. The apparent increases in wilting and root necrosis symptoms observed were additive and may involve saprophytic soilborne organisms.