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Variation, Heritability, and Relationship to Yield of Physiological Characters in Peas¹

Seven quantitative physiological characters [photosynthetic CO₂ exchange rate (CER), specific leaf weight, N₂(C₂H₂) fixation, root respiration, respiratory cost of N₂(C₂H₂,) fixation, growth duration, and relative growth rate] were examined in 25 pea( Pisum sativum L.) genotypes. To assess the possible use of these traits as criteria for selection in plant breeding, studies were carried out in three field environments, and four yield characters (total plant dry weight, seed dry weight, harvest index, and seed N) were determined.

Despite the significant environmental effects on all characters except seed N, overall genotype means differed significantly for all but the cost of N₂ fixation and relative growth rate. These last two characters were affected by large genotype x environment interactions which may have obscured the significant within-environment genotypic differences. Genetic coefficients of variation for the physiological characters varied from 2 to 13% and estimates of broad sense heritability were high except for cost of N₂(C₂H₂) fixation and relative growth rate. Significant correlations were found between yield characters and physiological characters [total weight and growth duration; total weight and cost of N₂(C₂H₂) fixation (negative); seed N and N₂ fixation (negative); harvest index and specific leaf weight; harvest index and CER]; and among physiological characters (N₂ fixation and root respiration; CER and relative growth rate).

for areas with short growing seasons, rapid growth for a limited period with more assimilate being placed into seeds (high harvest index) may be desirable. The combination of such characters of such characters might produce maximum potential yield in the short time available. Because CER appears to be correlated with these traits and is highly heritable, selection on the basis of this non-destructive character might be profitable in breeding such conditions.

Key Words: CO₂ exchange rates • Pisum sativum L. • N₂ fixation • Relative growth rate • Yield characters • Phenotypic correlation

² Research associate and associate research officer.

Received for publication May 4, 1981.