Differential accumulation of a 24-kd dehydrin protein in wheat seedlings correlates with drought stress tolerance at grain filling.

The Pacific Northwest (PNW), an important region for wheat production in the USA, is often subject to water deficits during sowing and grain filling. These deficits reduce the quality and yield of the crop. As a consequence, an important objective of breeding programs in the region is improving the genetic adaptation of wheat cultivars to drought stress. One response to dehydrative stresses is the accumulation of proteins called dehydrins, which are believed to protect membranes and macromolecules against denaturation. We characterized dehydrin accumulation in seedlings during drought stress and its correlation with stress tolerance during grain filling in seven wheat cultivars, 'Connie', 'Gene', 'TAM105', 'Rod', 'Hiller', 'Rhode', and 'Stephens'. A 24-kd dehydrin accumulated in seedlings under stress, but not in irrigated control plants. Connie, TAM105, and Gene started to accumulate dehydrins at the fourth day of stress, while the other cultivars showed dehydrins after twelve days of stress. This differential accumulation in seedlings was associated with stress tolerance at grain filling, characterized by a lower reduction in yield and in the rate of decrease in leaf water potential per day of stress. Connie, TAM105, Gene and Rod where the most tolerant cultivars. The results indicate that expression of this 24-kd dehydrin might serve as a rapid and non-destructive screening technique at the seedling stage. Even though the results are promising, selection experiments using a population segregating for stress tolerance are needed to test more conclusively whether this dehydrin can serve as a genetic marker for cultivars with tolerance to drought stress.

Association between dwarfing genes 'Rht1' and 'Rht 2' and resistance toSeptoria tritici Blotch in winter wheat (Triticum aestivum L. em Thell).

Differences in levels of resistance toSeptoria tritici blotch were observed in plants with a specific height-reducing gene. When the gene 'Rht 2' was present either as an isoline or in the progeny, a higher degree of resistance was found. The most susceptible plants were observed in populations carrying the 'Rht 1' gene. Associations, as determined by phenotypic correlations, were detected betweenSeptoria tritici blotch and tall stature, late heading, and maturity. Plants having short stature, early heading, early maturity, and acceptable levels of resistance were identified in the F2 population whenRht 2 was present. Results of this study indicated that wheat breeders must select the appropriate dwarfing source that may confer resistance and grow large F2 populations, in order to increase the probability of obtaining desired genotypes.

Tissue culture and plant regeneration from immature embryo explants of Barley, Hordeum vulgare.

Immature embryo explants taken 8 days after anthesis were used to establish callus cultures of spring barley. Two types of calli were observed. A soft, watery callus produced a limited number of shoots and a harder, more compact, yellowish callus gave rise to numerous green primordia and shoots. Gamborg's B5 basal medium supplemented with either 2,4-D (2,4-dichlorophenoxyacetic acid) or Cl3 POP (2,4,5-trichlorophenoxypropionic acid) was found to give good callus growth and shoot initiation. Media containing 2,4-D at 1.0 mg L(-1) or Cl3 POP at 5.0 mg L(-1) produced numerous cultures resulting in regeneration of plants. Plantlets developed roots on basal medium with Cl3 POP at 1.0 mg L(-1) or on auxin-free medium. Twenty genetically diverse genotypes were screened to determine if these techniques were suitable for a wide range of spring barley cultivars. Regeneration of plantlets was obtained for 19 of the 20 genotypes approximately 4 months after culture initiation. Lines differed in the ability to develop vigorously growing calli and in the ability of calli to develop large numbers of shoots and regenerated plantlets.