| Abstract | Genotypic variability for carbon dioxide exchange rate per unit leaf area (CER) in field-grown peas (Pisum sativum L.) is positively correlated with chlorophyll content and ribulose-1,5-bisphosphate carboxylase (RUBPC-ase) activity, and negatively correlated with stomatal resistance. To examine the genetic control of these latter three characters, six pea genotypes selected for high or low expression of CER were crossed in all possible combinations to produce a complete diallel. The F2 generation of the crosses and the parental types were evaluated in the field in 1983. Means ranged from 30.8 to 46.0 μg cm⁻² for chlorophyll content, from 12.4 to 22.5 nmol s⁻¹ cm⁻² for RUBPC-ase activity, and from 0.44 to 1.25 s cm⁻¹ for stomatal resistance. General Combining Ability (GCA) was significant for all characters and Specific Combining Ability (SCA) was also significant for chlorophyll content and RUBPC-ase activity. In no instance were reciprocal effects significant. The ratio of sum of squares for GCA to total entry sum of squares indicated that GCA was the predominant genetic component in all characters. Significant SCA effects were only associated with crosses involving certain genotypes (PI244089 and PI244197). The high proportion of additive gene action should allow selection for improvement of these characters, using as parents those genotypes with high positive (or negative in the case of stomatal resistance) GCA effects. |
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