THE EFFECT OF GENETIC-IMPROVEMENT AND HYBRIDIZATION ON GRAIN AND BIOMASS YIELD OF BREAD WHEAT

Bread wheat cultivars that were genetically improved by traditional me thods or by hybridization show higher grain yields than older cultivar s. The increase in grain yield associated with the use of semldwarf ge notypes is generally explained by an increase in harvest index since t he biological yield was not affected. It is not known; however, whethe r this is also true for wheat hybrids with higher yield perfomance. Th e objective of this work is: (I) to compare biomass production, grain yield and harvest Index of traditional and semidwarf varieties, and of wheat hybrids and their parents; (II) to compare the morphogenesis an d survival of florets and spikelets for the same materials. The growth and the development of old; new and hybrid cultivars were followed fr om emergence to physiological maturity. The experiment was conducted a t INTA Balcarce Experimental Station during the 1987 growing season. T he treatments were eight wheat genotypes, four with Gai/Rht genes, 2 h ybrids (with Gai/Rht parents) and two traditional cultivars with gai/r ht genes. The experiment was a randomized complete block design with 4 replications. Genotypes with Gai/Rht genes showed higher yields and m ore grains/m(2) than the traditional genotypes. This increase In yield was linked to an improvement in harvest Index. The hybrids also showe d higher yields and more grains than their parents but these character istics were explained by a greater biomass yield. The larger number of graine/m(2) in improved materials was due to a greater survival of re productive structures within the ear rather than to improved reproduct ive morphogenesis.