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It is recognized by many that plant bugs, Lygus lineolaris (Palisot de Beauvois), can reduce the yield of cotton. A basic problem in breeding for increased plant bug resistance is the lack of an efficient method of detecting genetic resistance. To detect resistance breeders need to know how many plant bugs per unit area of cotton row are needed to cause detectable damage. Without the use of cages in the greenhouse or field, adult plant bugs cannot be used for genotypic evaluation as they migrate freely from plant to plant. However, nymphs are not nearly so mobile. Nymphs can be reared in the laboratory and then exact numbers of nearly the same age can be transferred to plants in the greenhouse or field. Using this strategy nymphs were placed on field plots in 1981 and 1982. The genotypes used in 1981 were 'Stoneville 213', 'Stoneville 825', Stoneville 817F, 'Gumbo', Stoneville 213 Sm(1), 'Coker 310', Coker 310ne, and La 560 FN. The first four mentioned genotypes were also used in 1982. In 1981, plot size was one row, 40" X 18' with 3 replications. In 1982, plot size was one row, 40" X 3' with 10 replications. In both years, three densities of 4-5 day old nymphs were established on plants at the onset of squaring. The densities were 0, 1, and 3 nymphs per row foot. First harvest yields are probably more indicative of plant sensitivity than are total yields. First harvest lint yields in 1981 averaged 647, 552, and 407 lbs/acre for the respective nymph densities. In 1982, the average first harvest lint yields were 320, 327, and 258 lbs/acre, respectively. Average total lint yields for both years was 741, 689, and 607 lbs/acre for the 0, 1, and 3 nymphs/row foot, respectively. The genotype X nymph density interaction was significant at the 5 and 20% probability levels in 1981 and 1982, respectively. Gumbo an okra leaf cotton, had greater yield reductions due to nymphs than the other genotypes. No consistent trend for greater or lower sensitivity was detected for the other genotypes. In general, a nymph density of 1/row foot was not consistent in reducing lint yields. From these and other studies on this subject it appears that a minimum of 3 nymphs/row foot are needed for accurate genetic evaluations. |
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©National Cotton Council, Memphis TN |
Document last modified Sunday, Dec 6 1998
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