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Carbon Isotope Discrimination and Gas Exchange of Cowpea Accessions and Hybrids
Author(s) -
Ismail Abdelbagi M.,
Hall Anthony E.
Publication year - 1993
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1993.0011183x003300040032x
Subject(s) - biology , morning , vigna , hybrid , irrigation , stomatal conductance , cultivar , agronomy , genotype , water use efficiency , horticulture , heritability , zoology , botany , photosynthesis , gene , genetics , biochemistry
Carbon isotope composition may be useful for selection in plant breeding. Theory predicts a negative association between 13 C discrimination (Δ) and the ratio of CO 2 assimilation (A) to leaf diffusive conductance (g) in C 3 plants. In cowpea [ Vigna unguiculata (L.) Walp.] previous studies showed that the association between Δ and gas exchange efficiency (A/g) agreed with theory for drought‐induced effects, but not for genotypic effects when gas exchange was measured in the afternoon. Field studies were conducted for 2 yr to evaluate the association between Δ and A/g measured during different time periods within the day. Four cowpea genotypes were grown either on weekly irrigation or stored soil moisture in 1 yr, and under weekly irrigation, together with two hybrids between low and high Δ parents, in the second year. Cultivars CB46 and Prima had higher leaf Δ than genotypes UCR 237A and TVx 309‐1G with different irrigation treatments, sampling dates and years. The hybrids had values of Δ and gas exchange close to their midparent means. A negative correlation was observed between Δ and A/g for both drought‐induced and genotypic effects. Genotypic mean values of Δ were more strongly correlated with A/g when measured early in the morning than in the afternoon. Both A and leaf conductance to water vapor (g h ) were significantly higher early in the morning and then decreased progressively towards the end of the day. Early morning measurements were most effective in detecting genotypic differences in A/g, and they were associated with genotypic differences in Δ, as expected, based on theory, but with some unexplained variation. Low Δ was associated with high photosynthetic rate for TVx 309‐1G, but low stomatal conductance for UCR 237A.