The importance of harvest index and vegetative growth rate as selection ceriteria, and also the contribution of these traits to grain yield of wheat (Triticum aestivum L.) were studied by using diallel crosses involving 8 genotypes. Parents and Fl crosses were evaluated in completly randomized design with 4 replications in the greenhouse .Data were analyicd according to the methods of Hallauer and Miranda, and also model 1 of Griffing’s method 4 for diallel crosses. Significant differcncess occurred between parental lines and between crosses for all traits studied. The GCA mean squares for all the characteristics were more than SCA varianccs.Thcrefore, it seems that the contribution of additive effect to the expression of these traits is more important than the non-additive genetic effects. The significant mean square of parental lines vs crosses revealed that it is possible to select desirable lines with high harvest index or vegetative growth rate among the progenies of segregating generations. Arvand, Rashid, and Moghan had possitive GCA effects for harvest index. Therefore, they have ahigh potential to transfer photosynthetic products to grain. These cultivars can be used in the breeding programmes to improve harvest index. The crosses of Arvand with Rashid and Moghan showed high and positive SCA effects for harvest index. The highest values of harves index was found for’ the crosses of these cultivars, especially the crosses of Arvand. The GCA effects of Isfahan and Arvand for vegetative growth rate was high and possitive . The highest growth rates were found for crosses of these cultivars. The crosses of Isfahan with Rashid and Moghan showed the highest values and positive SCA effects for growth rate. These results revealed the potential of these cultivars and crosses for improving growth rate through the breeding programmes. According to the perediction equations for yield, if the harvest index be fixed at 50% , with the increase of growth rate from 0.45 to 0.55 gr/day, it is expected to achieve a yield increase of 0.90 g/ plant. Likewise, if the growth rate be fixed at 0.5 g/day, an increase of harvest index from 45% to 55% will result in 3.65 g/ plant increase in yicld.These results, revealed the potential, of growth rate and harvest index, and the more relative importonce of harvest index as indirect creterion of selection for grain yield.
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