Variation in water use efficiency and leaf carbon isotope ratio in navy bean (Phaseolus vulgaris L.) with growth stages

Full text: One pot culture experiment was carried out to determine if leaf carbon isotope ratio and water use efficiency (WUE) in four genotypes of navy bean (BAT 477, DOR364, BAT881 and G21212) change with growth stages (initial flowering, peak flowering and fruit growth). One set of pots were irrigated regularly to 85% field capacity (well watered) and other set was maintained at 35% field capacity (water stressed). Plants were monitored for water-use and leaf 13C (13C/12C expressed with a differential notation as 13C ). The leaf 13C values decreased from initial flowering to fruit growth stage in both well watered and water stressed treatments. This result suggests that carbon might have been relocated as the plants advanced in growth. The differences between initial flowering and fruit growth stage, and between peak flowering and fruit growth were significant (p<0.05) for both leaf 13C and WUE, and there were no significant genotype x growth stage interactions. There was a positive correlation between WUE and above ground dry matter (AGDM) across genotypes, and a good relationship (r=0.74*) between WUE and specific leaf area (cm2/g) was found at initial flowering. These results support the hypothesis that a higher WUE for the four genotypes of navy bean was achieved by higher photosynthetic capacity. Significant differences in leaf 13C were also noted between the well watered and water stressed plants. Well watered plants maintained a correlation between leaf 13C and WUE (r=0.92* 0.67* and 0.51* at initial flowering, peak flowering and fruit growth stage, respectively), but no such correlation was found for water stressed plants. Based on these results we conclude that (i) WUE of navy bean genotypes can best be assessed by determining leaf 13C of well watered plants at initial flowering stage and (ii) leaf 13C was not a promising indicator of adaptation to water deficit in navy beans