Browsing by Author "Ronald J. Thomas"

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    Effects of Concomitant Development on Reproduction of Meloidogyne incognita and Rotylenchulus reniformis on Sweet Potato
    (1983-04) Ronald J. Thomas; Christopher A. Clark
    The influence of various factors on reproduction of concomitant Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr) on sweet potato were studied in the green- house. Reproduction of Rr was reduced by Mi at all inoculum levels and experiment durations used, while Mi reproduction was not inhibited. Both species failed to affect each other when inoculated simultaneously onto root systems developed in separate pots from different nodes of the same plant. Reproduction of each species was not significantly greater when inoculation of the second species was delayed 1-2 weeks compared to simultaneous inoculation. After shoot excision, Rr increased in the soil but Mi decreased. Fibrous root weights of plants inoculated with Rr + Mi in some tests were higher than those inoculated with Mi alone, indicating an early suppression of Mi and/or root stimulation by Rr. Drought stress delayed Rr egg hatching and movement of larvae into the soil, but had little effect on Mi reproduction. Key words: Ipomoea batatas, root-knot nematode, reniform nematode.
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    Population Dynamics of Meloidogyne incognita and RotylenchulusTenchulus reniformis Alone and in Combination, and Their Effects on Sweet Potato
    (1983-04) Ronald J. Thomas; Christopher A. Clark
    Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr) interactions on sweet potato were studied in naturally and artificially infested field plots for 3 years. In a naturally infested field, early season counts of Mi or Rr were positively correlated with later counts of the same nematode, but negative correlations were found between early Mi and subsequent Rr, and early Rr and subsequent Mi counts. In field plots fumigated with methyl bromide and then infested with low levels of Rr, Mi, and Rr + Mi, final population densities of Mi juveniles were reduced by Rr, but Rr was not affected by Mi. In field plots with a high natural population density of Rr, artificial infestation with high levels of Mi in both fumigated and nonfumigated treatments inhibited Rr, while the final Mi juvenile population density was not affected. Results indicate that a competitive interaction exists with each species capable of inhibiting the other and becoming the dominant population. The nematodes had no apparent effect on yield at the inoculum densities used, either alone or mixed. Both nematodes increased cracking of sweet potatoes, but mixed populations did not differ in incidence of cracking from either Rr or Mi alone. Key words: Ipomoea batatas, root-knot nematode, reniform nematode, interactions.