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Tropentag, September 14 - 16, 2022, Prague

"Can agroecological farming feed the world? Farmers' and academia's views."

UV-B radiation-induced photosynthetic depression in cowpea (Vigna unguiculata (L.) Walp) nullified through inoculation of Bradyrhizobium strain

Tewodros Ayalew1, Tarekegn Yoseph2

1Hawassa University, Plant Sciences, Ethiopia
2Hawassa University, Plant Sciences


During the era of climate change, an increase in ultraviolet-B (UV-B) (280-315 nm) radiation affects the growth and physiology of crop plants. Cowpea may already be experiencing the effects of the increasing doses of UV-B radiation since the crop mostly grows in the tropical and sub-tropical regions, where maximum solar UV-B radiation reaches the earth’s surface. Knowledge of the varietal response and extent of the UV-B effect under inoculation is important in identifying a suitable variety and agronomic management to current and future changes in UV-B radiation. A pot experiment was conducted to evaluate the sensitivity of inoculated cowpea varieties to UV-B radiation. Two cowpea varieties and Bradyrhizobium strain CP-24 tested in the preceding pot and field experiment were combined with two biologically effective UV-B radiation levels (ambient and 0.4 W m−2 supplement). The UV-B radiation of 0.4 W m−2 was supplemented from nine days after emergence up to fifty-five days of the crop growth stage. Significant varietal differences were observed for UV-B responsiveness of twelve plant attributes measured. The magnitude of the sensitivity to UV-B radiation also varied among cowpea varieties. Plants grown under elevated UV-B radiation had much shorter and lower shoot dry weight than those grown under ambient UV-B radiation. The physiological gas exchange parameters exhibited a significantly negative response to elevated UV-B radiation with 58, 65, 31, and 8% lower performance for stomatal conductance (gs), net photosynthesis (Pn), stomatal number, and maximal photosystem II efficiency (Fv/Fm), respectively. Furthermore, comparing the inoculated plants under elevated UV-B radiation with those inoculated under ambient UV-B radiation, a reduction of 42, 42, and 79%, for leaf area, leaf area index, and net photosynthesis was observed, respectively, indicating the negative effect of UV-B radiation on inoculant performance. It was also observed that inoculating Bradyrhizobium strain CP-24 has the potential to nullify UV-B radiation-induced photosynthetic depression. The negative effect of UV-B radiation demonstrated over many of the measured parameters emphasises the need for selecting or developing varieties and bio-fertilisers that can withstand the potential effect of the current and projected UV-B radiation.

Keywords: Chlorophyll fluorescence, gas exchange, inoculants, leaf growth, photosynthesis rate, stomata

Contact Address: Tewodros Ayalew, Hawassa University, Plant Sciences, 05, 100 Hawassa, Ethiopia, e-mail: teddy1360@yahoo.com

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