PATERNAL AND MATERNAL EFFECTS ON GRAIN WEIGHT AND PROTEIN PERCENTAGE IN CROSSES BETWEEN HEXAPLOID AND TETRAPLOID HIGH-PROTEIN AND LOW-PROTEIN WHEAT GENOTYPES

The inheritance of grain protein percentage and of grain weight were studied by crossing common and durum wheat cultivars with hexaploid and tetraploid breeding lines that excel in grain protein percentage. All high protein lines were descendants of the tetraploid wild emmer Triticum turgidum var. dicoccoides. One hexaploid cultivar was also crossed with a high-protein var. dicoccoides genotype. All crosses were made between low- and high-protein genotypes and were carried out reciprocally for any combination of genotypes; some of them between genotypes of the same ploidy level and some between hexaploid and tetraploid lines. Weight and protein percentage were determined in selfed and crossed grains that developed on the same spike. Mean weight and protein percentage were also determined in F2 grains of all crosses of the same ploidy level, either tetraploid or hexaploid. At any ploidy level, F1 grains resembled the selfed grains of the mother plant both in grain weight and in grain protein percentage, indicating a major maternal effect on both traits. F2 grains had similar grain weight to the heavy-grained parent, and their protein percentage was close to the midparents value. However, a slight indication of cytoplasmic inheritance of grain protein percentage was found in the comparison between most pairs of F2 reciprocals. The interspecific crosses (hexaploid with tetraploid combinations) yielded shrivelled seeds with highly reduced weight but relatively unchanged protein percentage. Weight reduction in the shrivelled hybrid grains (compared with the selfed ones) was more severe when the mother plant was hexaploid rather than tetraploid. The significance of the different tissues in determining grain weight and protein percentage is discussed.