The development of cotton cultivars with higher levels of resistance to pests will depend on detailed knowledge of resistance mechanisms, gene action and inheritance of specific traits. The multi-adversity resistance (MAR) program has developed five MAR hybrid pools which have produced cotton cultivars having a progressive improvement in resistance to plant pathogens and insects, yield and fiber quality. Many secondary products have been isolated from the cotton plant and several have been reported to confer resistance to various cotton insects. Researchers have documented that condensed tannin and gossypol protect cotton from insects. This research was conducted to determine differences in tannin and gossypol concentrations between MAR and non - MAR cultivars and among germplasm from four MAR hybrid Pool S. The role these allelochemicals have as a mechanism for resistance in the MAR cottons was examined.

Two sets of cultivars were planted in the field in a randomized complete block with five replications. The 1984 experiment consisted of 12 cultivars and the 1985 - 1987 tests had seven cultivars. Six cultivars were common in all tests. The non-MAR cultivars were Lankart 57 and Lockett 4789A. Leaf and flower petal discs (28 mm²) were collected from 10 plants chosen at random from each plot. Condensed tannin and gossypol concentrations were determined by a modification of the techniques by Swain and Hillis, and Storherr and Holley, respectively. Glands were counted under the microscope.

Significant differences in gossypol concentration were obtained among cultivars in 1986 and 1987; concentrations ranged from 2.16 to 2.61 mg/g fresh weight. Numbers of glands per petal disc were significantly different among cultivars and ranged from 116 to 261. Differences in gossypol/gland were significant only in 1984, ranging from on 95 to .0208 mg. Lankart 57 and Tamcot CD3H had the highest gossypol content. There was no relationship between gossypol concentration or number of glands and resistance to insects in the MAR cottons.

Differences in tannin concentrations among cultivars were significant for all years, ranging from 0.218% to 0.386% fresh weight. Lankart 57 and Lockett 4799A had the lowest tannin concentrations. Tannin concentrations in the MAR germplasm and Tamcot cultivars increased linearly with progressive increases in levels of resistance to insects and plant pathogens from the MAR-1 to the MAR-4 hybrid pools. Results indicated that the MAR genetic improvement system may be indirectly selecting for increased levels of condensed tannins.