Results and Discussion

As for kernels per spike, in low nitrogen level in F₁., (Fig. 1a) indicated the full dominance type of gene action, as the regression line passes the Wr/axis through the origin. As the line deviates significantly from a unit slope it signifies some kind of gene interaction. The position of array points on the line suggested that LU75 carried most of the dominant genes while Ch70 being away from the origin had most of the recessinve alleles. For F₂, (Fig. 1b) shows additive gene action with partial dominance. The b value (0.5519 + or - 0.3213) reveals interallelic gene interaction. C273 lying nearest to the origin possessed most dominant gencs, while reverse was true for Mexipak 65.

As for higher nitrogen dose, in F₁ (Fig. 1c) and for F₂ (Fig. 1d), the regression line cuts the Wr/axis above the origin, indicating additive gene action with partial dominance. Mexipak 65, being nearest to the origin possessed maximum dominant genes while Chenab 70 farthest away from the origin had most of the recessive alleles, and in F₂, LU75 possessed most dominant genes while Mexipak 65 was shown to have most recessive alleles. KRONSTAD & FOOTE (1964), BROWN et al. (1966), GYAWALI et al. (1968), made observation about the relative importance of additive effects for kernels per spike and other wheat characters.

As for 100-kernel weight in F₁, under low nitrogen, additive type of gene action coupled with partial dominance was evident from Fig. 2a, Array point position on regression line suggested that Chenab 70 possessed most dominant genes while reverse was true of Mexipak 65 which had most of the recessive alleles. For F₂ (Fig.2b) overdominance type of gene action with epistatic gene interaction was indicated. C273 carried most dominant genes while LU75 had maximum recessive alleles.

As it is seen from Fig. 2c and 2d, under high nitrogen, the regression line cuts the Wr/axis below the origin revealing overdominance with interallelic interaction in F₁ and F₂. Array point position showed that C273 and Mexipak 65 possessed, most dominant genes respectively and LU75 had preponderance of the recessive alleles. Similar results have been presented by JHONSON & AKSEL (1964), HSU & WALTON (1970), and WALTON (1971a) they found major part of the variability for yield and 100-kernel weight due to overdominance and some degree of additive genetic effects.

A reference to (Fig. 3a and 3b) for F₁ and F₂ under low nitrogen shows overdominance with interallelic interaction and complete dominance type of gene action respectively. The position of array points on the regression line showed that Mexipak 65 was nearest to the origin and thus contained most of the dominant gencs while most recessive alleles were present in Chenab 70.

Figures 3c and 3d revealed that the regression line intercepted the Wr/axis below the origin, indicating overdominance. Mexipak 65 possessed most dominant genes while Chenab70 had most recessive alleles.

A perusal of foregoing findings would indicate the presence of overdominance in F₁ and complete dominance in F₂ suggesting that non-additive gene effects played a significant role in the expression of grain yield. Identical results have been reported by several workers including for example, WHITEHOUSE et al. (1958) who attributed a large part of the total genetic variability for yield and its components to overdominance with significant environmental influence.