Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr) interactions on sweet potato were studied in the greenhouse and in naturally and artificially infested field plots for 3 years. In a naturally infested field, negative correlations were found between early Mi and subsequent Rr, and early Rr and subsequent Mi counts. In field plots with a high natural population of Rr (2700/250 cm('3) soil 8 April), artificial infestation with high levels of Mi (4000/250 cm('3) in upper 30 cm) in both fumigated and nonfumigated treatments inhibited Rr, while the final Mi population was not affected. In various greenhouse tests, using inoculum levels of 500-10,000 Mi eggs and/or Rr eggs or larvae + young adults per 15 cm pot, and times from 45 to 95 days, Rr was inhibited by Mi, while Mi was not affected by Rr. In field plots fumigated with methyl bromide and then infested with low levels of Rr, Mi, and Rr + Mi (100/250 cm('3)), final populations of Mi were inhibited by Rr but Rr was not affected by Mi. In greenhouse tests, fibrous root weights of plants inoculated with Rr + Mi frequently were higher than those inoculated with Mi alone, indicating an early suppression of Mi and/or root stimulation by Rr. Rr + Mi failed to affect each other when inoculated simultaneously onto root systems developed in separate pots from different nodes of the same plant. After shoot excision, Rr increased in the soil but Mi decreased. Results from field studies indicate that a competitive interaction exists with each species capable of inhibiting the other. In natural infestations, Rr predominance may be favored by a much higher survival rate between crops. Effects of the nematodes on yield were not significant either alone or mixed. Both nematodes increased cracking of the sweet potatoes, but mixed populations did not differ in incidence of cracking from either Rr or Mi alone.