Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

First Advisor

John S. Russin

Second Advisor

Edward C. McGawley


The replacement series approach was used to evaluate competition between Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr). In greenhouse tests, soil in pots containing 'Davis' soybean was not infested or infested with 1,000 vermiform nematodes in the following Mi:Rr ratios: 100:0, 75:25, 5:50, 25:75, and 0:100. After 86 days, relative nematode yields (RNYs) (number of each species in mixed culture divided by number in nonmixed culture) were calculated based on soil populations. Calculated values were plotted and the resulting line compared with a reference line representing equal inter- and intraspecific competition. RNYs for Mi were higher than predicted where Mi and Rr occurred together, suggesting increased reproduction in the presence of Rr. RNYs for Rr did not differ from predicted yields, indicating no effect of Mi on Rr. These relationships were not detected using analysis of variance and were independent of host colonization by Diaporthe phaseolorum var. caulivora. To determine if larger Mi soil populations resulted from increased reproduction or from migration, a grinding technique was developed to liberate vermiform and swollen nematodes from roots. Experiments on soybean and tomato evaluated the efficiency of method (stir, grind), carrier (water 0.5% NaOCl), and duration (1X, 2X) on extraction of nematodes and eggs. Grinding liberated more nematodes than stirring, but the reverse was true for egg recovery. Among grinding treatments, a duration of 10 sec in 0.5% NaOCl provided the most efficient nematode recovery. The effect of soybean genotype on competition between Mi and Rr was evaluated in greenhouse and microplot replacement series experiments on 'Davis' (susceptible to Mi) or 'Buckshot 66' (resistant to Mi) as described previously. After 91 days, the RNY of each species was calculated based on combined soil and root populations. On 'Davis', Mi greenhouse populations were larger in the presence of Rr. In microplots, small Mi and Rr populations likely resulted from severe galling and destruction of feeder roots. On 'Buckshot 66', Rr did not affect Mi greenhouse and microplot populations. With the single exception noted for 'Davis' in the microplot, Rr populations were not influenced by competition with Mi.