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Title: NEW SOURCES OF RESISTANCE TO THE RENIFORM (ROTYLENCHULUS RENIFORMIS) AND ROOT-KNOT (MELOIDOGYNE INCOGNITA) NEMATODE IN UPLAND (GOSSYPIUM HIRSUTUM L.) AND SEA ISLAND (G. BARBADENSE L.) COTTON

Author
item Robinson, Arin
item Bridges, Alan
item Percival Jr, Albert

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2004
Publication Date: 11/1/2004
Citation: Robinson, A.F., Bridges, A.C., Percival, Jr., A.E. 2004. New sources of resistance to the reniform nematode (Rotylenchulus reniformis) in Upland (Gossypium hirsutum) and Sea Island (G. barbadense) cotton. Journal of Cotton Science. 8:191-197.

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. There are no commercial varieties of cotton with resistance to the reniform nematode and cotton seed companies need new sources of resistance that their plant breeders can use to develop resistant varieties for farmers. The purpose of this study was to examine 2,500 previously untested wild types of cotton from all over the world to find out if any of them are resistant to the nematode. We identified several sources of resistance that were better than any previously available. Most importantly, we found six moderately resistant Upland cottons. No reniform nematode resistance was previously known within Upland cotton and this is the kind of cotton that 98% of farmers grow. We also identified 22 resistant types of the related Sea Island cotton and five of these scored more resistant than any Sea Island cotton tested before. Cotton seed companies can utilize all of these materials to develop nematode-resistant commercial varieties that allow farmers to reduce nematicide use, increase production, and improve cotton quality.

Technical Abstract: The reniform nematode (Rotylenchulus reniformis) is an important problem in cotton production and all commercial cultivars support prolific reproduction by the nematode. The objective of this research was to identify within G. hirsutum and G. barbadense better sources of resistance to R. reniformis than are currently known and to ascertain whether any of the most resistant genotypes also exhibit resistance to the root-knot nematode of cotton (Meloidogyne incognita). A two-tiered approach was taken with tier one in a greenhouse and tier two in a growth chamber to evaluate 1,866 primitive accessions of G. hirsutum and 907 of G. barbadense from the U.S. Cotton Germplasm Collection. Tier one assays compared one plant per accession to six replicates of susceptible 'Deltapine 16' and six of moderately resistant G. barbadense 'TX-1348' to quickly eliminate highly susceptible genotypes. Tier two employed fully replicated experiments to rigorously test six replications of selected accessions against R. reniformis and six against M. incognita. In both tiers, plants were inoculated 2 weeks after planting seed in 500-cm3 pots and nematode populations were determined 7 weeks after inoculation by extracting nematodes from soil by Baermann funnel and expressing the final population density relative to root weight, and by scoring roots for nematode galling. Greenhouse results showed G. barbadense to be less susceptible than G. hirsutum overall; however, most accessions from both species supported prolific reproduction, and only 5% of G. hirsutum and 12% of G. barbadense plants had less reproduction than TX-1348. In growth chamber experiments, 32 (41%) of the 78 accessions tested suppressed nematode reproduction significantly (P = 0.05 or 0.01) compared with Deltapine 16. Accessions within each group that follows are in increasing order of resistance. G. hirsutum TX-2469, TX-1586, TX-748, TX-25, TX-1828, and TX-1860 and G. barbadense GB-127, GB-1083, GB-1141, GB-1143, TX-110, GB-1147, GB-207, GB-833, GB-210, GB-212, GB-126, GB-581, GB-1113, GB-1081, TX-502, GB-485, GB-536, and GB-262 had more than 10% but less than 34% of the R. reniformis observed for Deltapine 16 and were classified moderately resistant. TX-1828, TX-25, and TX-1860 were also root-knot nematode resistant (gall rating +/- 0.8 on a 0-5 scale; P = 0.01). TX-110 and TX-502 are G. barbadense phenotypes from the G. hirsutum 'TX' collection. G. barbadense GB-49, GB-13, GB-264, GB-171, and GB-713 had less than 11% of the R. reniformis observed for Deltapine 16 (P = 0.01 in all cases) and were classified resistant. G. barbadense GB-713 had the highest resistance to R. reniformis observed, with only 3% of the nematodes observed for Deltapine 16 in three experiments.