Tirhut College of Agriculture
Gene action for knob number in corn --Mandal, SS, Akhtar, SA The combining ability analysis revealed that significant differences existed for general (gca) and specific (sca) combining ability for number of knobs. The fixed effect model (Model 1 and Method 1 of Griffing 1956a) in the present study does not provide estimates of variance components and thus it was not possible to know precisely the relative importance of additive and dominance components in the control of knob number. However, the relative importance of gca and sca in determining progeny performance can be obtained by calculating general predictability ratio (GPR), on the basis of gca and sca variance components of mean squares. The value of GPR for knob number was 0.13 (Table 1). The estimates of this ratio indicated that progeny performance was based on both gca and sca for genetic variability. Moll et al. (1972) suggested additive and dominance, and dominance and dominance gene action for knob number in maize.

Table 1. Analysis of variance for combining ability
Character gca (df=3) sca (df=6) reciprocal (df=6) error (df=30) GPR
Knob number 1.48** 2.315** 1.74** 0.01 0.13

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