ASSESSING GENOTYPIC SOFTNESS IN SINGLE WHEAT KERNELS USING STARCH GRANULE-ASSOCIATED FRIABILIN AS A BIOCHEMICAL MARKER

The end-use quality of wheat (Triticum aestivum L.) is determined in l arge part by the texture of the grain (soft or hard). Endosperm textur e is currently determined by several empirical methods. These methods are limited because they use bulk grain lots, as opposed to individual kernels; assess phenotypic, as opposed to genotypic hardness; require a quantity of grain greater than that generally available in the earl y generations of wheat breeding programs, and are destructive. Recent approaches that use single kernels address the problems associated wit h bulk grain lots, but suffer the other limitations of providing only the phenotype and being destructive. An objective method for determini ng the texture genotype of single kernels of wheat was developed using starch granule-associated friabilin, a family of closely related 15 k Da proteins, as a biochemical marker. The occurrence of friabilin on w ater-washed wheat starch granules is apparently unaffected by the envi ronment and is perfectly correlated (no exceptions) with grain softnes s. The technique presented here can detect friabilin on as little as 0 .2 mg of starch and provides a 250-fold improvement in friabilin detec tion compared to previous methods. The method is capable of correctly assessing the genotype of F-1 heterozygotes from hard x soft and soft x hard crosses. Further, the method uses only a portion of the endospe rm from the kernel and therefore accommodates embryo propagation and h igh molecular weight glutenin subunit characterization. This single ke rnel method also facilitates the genetic characterization of mixed, bu lk grain lots.