Identification and characterization of Sorghum bicolor (L.) moench lines with resistance to preharvest grain deterioration

Abstract

Deterioration of sorghum grain prior to harvest results primarily from attack by microorganisms, initiation of germination processes, insect damage and/or combinations of these factors. Other terms used to refer to preharvest grain deterioration include grain weathering, grain mold and sprout damage. The causal agents of deterioration produce physical, physiological and chemical changes in the grain which ultimately lead to loss of viability. Periods of high humidity or alternate wetting and drying during pre- and post-physiological maturity condition the grain for possible sprouting and/or invasion by microorganisms. In addition, the environment influences the populations and types of organisms present. The final expression of grain deterioration results from an interaction between grain and/or plant characteristics and the environment. Deteriorated grain usually has a dark, discolored external appearance; a dark, discolored germ; and a chalky endosperm. The external and internal changes in deteriorated grain are characterized by a loss of dry matter and decreased test weight, bulk density, kernel weight, density and hardness of the grain. The grain of several non-brown sorghum lines (SC0279- 14E, SC0566-14, SC0748-5, SC0630-11E and BTx398) was identified as resistant to preharvest microbial deterioration. SC0630-11E was identified as the only non-brown line with resistance to preharvest sprouting. Grain of more resistant nonbrown lines has an intermediate to corneous endosperm, loses moisture rapidly after maturation, has differences in the cellular structure and cellular organization in the hylar and stylar areas, has more complete coverage by surface wax and possesses clasping glumes. These characteristics affect water uptake and movement in the grain. Water uptake and movement in the grain may influence microbial entry and colonization as well as germination of the grain. Bioassays of water extracted constituents of grain implicate chemical constituents which inhibit microbial growth and influence germination and early embryo growth and development.