Author
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Davis, Richard |
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MAY, O - UNIVERSITY OF GEORGIA |
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Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/17/2003 Publication Date: 12/1/2003 Citation: Davis, R.F., May, O.L. 2003. Relationships between tolerance and resistance to Meloidogyne incognita in cotton. Journal of Nematology. 35(4):411-416. Interpretive Summary: The southern root-knot nematode, Meloidogyne incognita, is the most damaging pathogen of cotton in the United States. Plants with nematode resistance reduce the amount of nematode reproduction that occurs, and plants with tolerance suffer less damage when parasitized by nematodes. Nematode resistance and tolerance in plants are not always linked and can occur independently of each other. Both resistance and tolerance to M. incognita in cotton could be valuable management tools. Our objectives in this study were to evaluate advanced cotton breeding lines to document levels of resistance and tolerance to M. incognita and to determine if there is a relationship between resistance and tolerance. Reproduction of M. incognita was evaluated on 17 breeding lines in two greenhouse trials; a susceptible variety and a highly resistant germplasm were included for comparison. Eight breeding lines were resistant and had significantly less nematode reproduction than the susceptible variety, with reductions ranging from 45 to 57%. Reproduction on the resistant germplasm was reduced 90%. The eight resistant lines had similar levels of M. incognita reproduction, and none of them were as resistant as the highly resistant germplasm. Yield was determined in 2001 and 2002 in fumigated and non-fumigated plots in a field infested with M. incognita. The amount of yield suppression caused by nematode infection differed among genotypes. Six genotypes in 2001 and nine in 2002 were tolerant to M. incognita and had no difference in yield between the fumigated and non fumigated plots, however, only three genotypes had no significant yield suppression in either year. Two of the consistently tolerant breeding lines also were resistant to M. incognita. Regression analysis showed that yield suppression decreased as nematode resistance increased, which indicates that tolerance in these breeding lines was largely a result of resistance. Technical Abstract: The southern root-knot nematode, Meloidogyne incognita, is the most damaging pathogen of cotton in the United States, and both resistance and tolerance to M. incognita could be valuable management tools. Our objectives were to evaluate advanced cotton breeding lines to document levels of resistance and tolerance to M. incognita and to determine if there is a relationship between resistance and tolerance. Reproduction of M. incognita was evaluated on 17 breeding lines, a susceptible control, and a resistant control in two greenhouse trials. Seedlings were inoculated with 8,000 M. incognita eggs per pot two weeks after planting, and eggs were extracted ca. 56 days after inoculation. Eight breeding lines had less (P<0.05) nematode reproduction than the susceptible control, with reductions ranging from 45 to 57%. Reproduction on the resistant control was reduced 90%. The eight resistant genotypes had similar levels of M. incognita reproduction, and none of them were as resistant as M-120. Yield was determined in 2001 and 2002 in fumigated and non-fumigated plots in a strip-plot design. The amount of yield suppression caused by nematode infection differed among genotypes (a genotype X fumigation interaction; P<0.05). Six genotypes in 2001 and nine in 2002 were tolerant to M. incognita and had no difference in yield between the fumigated and non fumigated plots (P>0.10), however, only three genotypes had no significant yield suppression in either year. Two of the consistently tolerant breeding lines also were resistant to M. incognita. Regression analysis found that yield suppression decreased in a linear manner as nematode resistance increased. |
