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Ecology and Epidemiology

Effects of Meloidogyne incognita and Fusarium oxysporum f. sp. vasinfectum on Plant Mortality and Yield of Cotton. J. L. Starr, Department Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843; M. J. Jeger(2), R. D. Martyn(3), and K. Schilling(4). (2)Overseas Development Natural Resources Institute, London, UK WC1X 8LU; (3)Department Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843; (4)Jacob Hartz Seed, Inc., Stuttgart, AK 72160. Phytopathology 79:640-646. Accepted for publication 21 December 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-640.

The effects of population densities of Meloidogyne incognita and Fusarium oxysporum f. sp. vasinfectum on growth, mortality, and yield of cotton were examined in a factorial experiment in field microplots. Both Fusarium and Meloidogyne had significant main effects on cotton mortality. At initial populations of Fusarium of 2.34.2 103 colony-forming units per gram of soil and initial populations of Meloidogyne of 1050 eggs and juveniles per 100 cm3, a significant Fusarium nematode interaction was observed. No interaction was observed at lower nematode populations or at higher populations of Fusarium. Populations of Meloidogyne had significant effects on cotton growth measured qualitatively as a growth index; the growth index was increased by low initial nematode populations and reduced by high initial nematode populations. Fusarium had no effect on the growth index but did tend to negate the effects of Meloidogyne. A repeated-measures analysis was used to identify significant effects of time on the growth indices and plant mortality. The time nematode interactions were significant for both of these parameters. Only Meloidogyne had significant effects on seed cotton yields; the treatments with Fusarium and the fungus nematode interactions were not significant. When yield responses to nematode populations at different levels of Fusarium were analyzed by the Seinhorst model, Fusarium consistently reduced the minimum yield parameter. The lack of significant effects of Fusarium on yield were believed to be due to constraints of the microplot system.

Additional keywords: Fusarium wilt, population dynamics, root-knot, stunting.