Maize weevil, Sitophilus zeamais Motschulsky, infests sorghum, Sorghum bicolor (L.) Moench, and other grains in the field, deposits eggs in stored kernels, and the larvae feed inside. Sorghum resistance to maize weevils has not been evaluated for more than 20 years. The goals of this research were to evaluate resistance to maize weevil and relate resistance to morphology of the seed coat of 20 sorghum genotypes.

Five weevils were put with 5 g of grain in each of 10 vials. Vials containing each sorghum genotype were sequentially set up and evaluated every 3 weeks for 105 days. Damage to each grain in 10 vials of one genotype was rated on a scale of 1-5, live and dead weevils were counted, and grain in each vial was weighed. Sureno and SC630-11E11 were most and least resistant. Grain of Sureno and SC630-11E11 weighed 0.8 and 46.8% less, respectively, at 105 days after infestation.

Grains of each sorghum genotype were split, exposed to osmium vapor, and coated with gold-palladium. The cross-section of seed coat was observed by using a JEOL JSM 6400 scanning electron microscope at 15 KeV, 12-mm working distance, and 500-2000x magnifications. Pieces of seed coat were dried, fixed, and embedded in epoxy resin and sectioned for observation by using a Zeiss Axiophot compound light microscope at 100-600x magnifications. Thickness of the seed coats of the different genotypes differed and was related to resistance. The thickness of the seed coat of resistant Sureno was twice that of susceptible SC630-11E11.