Submitted to: Society of Nematologists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 20, 1999
Publication Date: N/A
Interpretive Summary: Nematodes are microscopic worms that live in the soil. There are more than 10,000 different kinds and many can be devastating to crops because of the damage they cause while feeding on roots. In some crops, nematode resistant crop varieties have been developed; these varieties are not damaged by nematodes and somehow prevent nematodes from feeding. The purpose of this study was to get a better understanding of nematode resistance in cotton by examining data from 20 experiments that compared the ability of the two most important nematode pests of cotton to reproduce on more than 300 varieties and wild strains (or accessions) of cotton from all over the world. Several conclusions were drawn. Significant levels of resistance to the southern root-knot nematode are currently present in only three commercial varieties. No varieties are resistant to the reniform nematode. Wild strains of cotton vary widely in nematode resistance. New resistant commercial varieties can probably be developed from wild cottons. The most efficient way to measure resistance to the root-knot nematode in cotton is by a technique called gall indexing. The most efficient way to measure resistance to the reniform nematode in cotton is by a technique called Baermann funnel extraction of soil.
Technical Abstract: Rotylenchulus reniformis and Meloidogyne incognita race 3 are the most damaging nematodes of Upland cotton (Gossypium hirsutum). Only a few genotypes of G. hirsutum are highly resistant to M. incognita and none are highly resistant to R. reniformis. We conducted a series of studies in which reproduction by R. reniformis and M. incognita were directly compared dunder standardized growth chamber conditions on 6-12 replicate pairs of more than 300 cultivars, breeding lines, and primitive accessions of Upland cotton. We measured plant height, foliar and root weights, root length, main stem nodes, fruiting, gall index for M. incognita, number of vermiform stages of R. reniformis extractable by Baermann funnel, and eggs per plant for both nematodes. Gall index was highly correlated with extractable eggs of M. incognita and was the less variable and cheaper indicator of resistance. Vermiform stages of R. reniformis and galling induced by M. incognita were weakly correlated; complete suppression of galling was associated with a 40% average decrease in R. reniformis egg production per plant. Reproduction by M. incognita commonly differed 100-fold whilst reproduction by R. reniformis seldom differed more than 5-fold among cotton genotypes. The results suggest that cultivars with strong resistance to M. incognita and moderate resistance to R. reniformis can be developed from known genotypes of G. hirsutum.