NEW DEVELOPMENTS IN BIRD RESISTANT SORGHUMS

In recent years there has been a major shift of emphasis from lethal to nonlethal methods of controlling bird damage to agricultural crops. In addition to being unpopular, killing large number of birds has generally been ineffective because of rapid recovery of populations. Consequently, most of the methods that are now being investigated emphasize crop protection. Since sorghums are especially vulnerable to bird damage, considerable effort has been expended in the past 20 years to develop varieties that have morphological or chemical characteristics which are resistant to bird damage (Harris, 1969; Tipton et al., 1970; McMillian et al., 1972). Some bird resistance has been attained through genetic selection of certain morphological characteristics such as pendant heads, long awns, large glumes, and large seeds (Doggett, 1957) that physically make bird feeding difficult. However, in areas of high depredation, farmers have depended on high-tannin sorghums which more reliably resist bird damage because of their astringent taste properties. In areas of high rainfall farmers have also enjoyed the resistance of high-tannin sorghums to weathering (Harris and Burns, 1970; York, 1976) and preharvest sprouting in the panicle (Harris and Burns, 1970). Unfortunately, the same tannin characteristics that afford these beneficial properties are also responsible for the poor nutritional quality of many bird resistant (BR) sorghums. In a recent review, Price and Butler (1980) attributed deleterious nutritional properties of BR sorghums to several possible tannin-related effects. In general, the suspected tannin-protein binding effects in the digestive tract can be expressed as follows: undigestible complexes with dietary protein, deactivation of digestive enzymes, and tanning of some areas within the digestive tract. In addition, the low palatability of high-tannin sorghums can depress feed intake and lower the weight gain. At least one investigator (Morton, 1970; Morton, 1978) has proposed that there is a link between geographical zones where a high incidence of esophageal cancer occurs and the usage of tannin-containing plants within these zones. The result is that these negative qualities in high-tannin sorghum grains cause them to have less value in the market place; and farmers that produce them are at a disadvantage. In recent years the detente between proponents of crop protection and nutritional quality has resulted in an impasse to any common solution. In fact, varieties which both resist bird predation and have good nutritional quality have been recognized for at least a decade (Harris, 1969). Apparently, the barrier to progress has been in the understading of tannin biochemistry. The role of the Denver Wildlife Research Center has been to fuse the two camps by providing information on that most important factor. The objective of the present paper is to inform professionals involved in bird damage control of the new biochemical, agronomic, and nutritional developments in bird resistant sorghums