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Title: ROTYLENCHULUS RENIFORMIS BELOW PLOW DEPTH SUPPRESSES COTTON YIELD AND ROOT GROWTH

Author
item Robinson, Arin
item COOK, C - SYNGENTA SEEDS INC
item WESTPHAL, A - PURDUE UNIVERSITY
item Bradford, Joe

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2005
Publication Date: 12/2/2005
Citation: Robinson, A.F., Cook, C.G., Westphal, A., Bradford, J.M. 2005. Rotylenchulus reniformis below plow depth suppresses cotton yield and root growth. Journal of Nematology. 37(3):285-291.

Interpretive Summary: There are many kinds of microscopic worms called nematodes that feed on the roots of cotton and other crops, debilitating the plants and markedly decreasing yields. The direct losses to U.S. cotton farmers caused by nematodes each year are estimated by the National Cotton Council to exceed $300,000,000. The reniform nematode is one of the most important nematodes on cotton in the U.S. All varieties of cotton available to farmers are susceptible to this nematode but there are wild species of cotton that have been found to be resistant when they are grown in greenhouse pots containing the nematode. Thus it may be possible to make genetic crosses between resistant wild species and agronomic cotton to develop resistant varieties for farmers. Developing varieties possessing an altogether new trait like reniform nematode resistance, however, is a long, expensive process requiring at least 10 years and so it is very important before starting to be absolutely certain that the reductions in nematode numbers in the soil that these plants cause in pots in greenhouse experiments, also happens in cotton fields. In this study, various known resistant wild species of cotton were planted in selected cotton fields in Texas, Louisiana, Mississippi and Alabama. Plant root growth and nematode populations in soil were monitored to a depth of 4 feet. The study concluded that the nematode population suppression that occurs in the soil in cotton fields is not as fast as in pots due to more favorable conditions for survival in the field. Also, the degree of suppression depends on soil depth and the type of soil present. Overall, however, the results indicated that new varieties developed with resistance from these wild sources should do a good job of controlling reniform nematodes in most fields, if those resistant varieties are planted for a couple of years in a row.

Technical Abstract: Resistance to Rotylenchulus reniformis is absent in Upland cotton (Gossypium hirsutum) and could be introduced from G. barbadense, G. arboretum, or G. herbaceum, but resistant accessions identified in pots need field confirmation. In 2001, six accessions suppressed nematode populations 70 to 98% in microplots (P<0.01) but not in the field relative to susceptible cotton. A growth chamber experiment ruled out nematode genetic variability and implicated soil-specific factors. In 2002, tests in four states measured late-season root and R. reniformis density 0 to 122 cm deep under eight resistant accessions. Root length density varied with site but not accession. Population suppression relative to the control varied with site and was less than in pots. At three sites, zero, four, and six accessions had populations below the treatment threshold in the plow zone. The most resistant were G. arboretum A2-87 and G. barbadense GB-713. Subtracting nematodes under fallow from nematode data elevated apparent resistance, indicating survival masked resistance. Results predict cultivars developed from resistant Gossypium species will not suppress R. reniformis populations as well as in pots the first year.