Stress responses in three contrasting cowpea (Vigna unguiculata [L.] Walp.) cultivars with differential sensitivity to UV-B radiation.
Giridara K. Surabhi, Shardendu Kumar Singh, and K.R. Reddy. Mississippi State University, "117 Dorman Hall, Box 9555, Plant &", "117 Dorman Hall, Box 9555, Plant &", Mississippi State, MS 39762, United States of America
Current and projected increases in solar ultraviolet-B radiation may impact crop production. An experiment was conducted to study the influence of UV-B radiation on photosynthetic CO2 assimilation, photochemistry, pigments and UV-B screening potentials of three cowpea cultivars (CB-5, CB-27 and Mississippi Pinkeye; MPE). The cultivars were subjected to four levels of biologically effective UV-B radiation of 0 (control), 5, 10 and 15 kJm-2 d-1 in sunlit controlled environment chambers. Higher levels of UV-B radiation (15 kJ m-2 d-1) caused decrease in light saturated maximum photosynthesis (Pmax) in all the three cultivars, but the magnitude of decrease was 12% in MPE, 37% in CB-27 and 43% in CB-5. Less influence of UV-B on Pmax in tolerant cultivar was supported by a small decrease in Vcmax coupled with higher levels of Jmax and higher TPU capacity, compared to CB-5 and CB-27. The tolerance nature of MPE was further evidenced by less or no effect on ETR, qP, PSII efficiency and Fv’/Fm’ related to functional activities of photosynthesis compared to other two cultivars across the UV-B levels. Cutivar MPE maintained significantly higher levels of UV-B screening compounds, 44% more when averaged across UV-B levels, while it was 14% in CB-27 and 6% in CB-5, compared to control. In addition, pigments even though less responsive to UV-B, decreased less in MPE (9%) compared to other two cultivars (10 to 13%). In general, MPE showed more tolerance to UV-B radiation based on most of the parameters studied, compared to CB-5 and CB-27. This study demonstrates that cowpea cultivars respond differently to UV-B radiation based on photosynthetic and fluorescence parameters, which can be used as screening tools.