Seed durability is a current issue of cotton ginners, who have noted smaller and weaker seed, lower seed grades, and increased seed coat fragments within ginned cotton fiber. To better understand the differences in the seed hull properties of Upland (Gossypium hirsutum L.) and Pima (G. barbadense L) seed, compression testing was conducted to determine the seed hull fracture resistance of both species. Plants were grown in Five Points, CA, U.S., for two years. After roller ginning, seed were conditioned to standard environmental conditions and were compressed until rupture on a material strength tester. Seed of the Pima cultivars generally required greater maximum compressive force and energy to rupture than did the seed of the Upland cultivars. However, when the seed were compressed in a vertical orientation, a few individual Upland cultivars did have compression properties within the range of values observed for the Pima cultivars. Hence, it is possible to find Upland seed with compression properties comparable to or slightly greater than those of some Pima seed. Differences in the data for the two years showed that growing environment affects seed hull strength properties. The results should help clarify some conflicting literature regarding the relative strength attributes of Gossypium species seed.
