Growth and Photosynthetic Responses of Cowpea Genotypes under Waterlogging at the Reproductive Stage

Omolayo J Olorunwa; Bikash Adhikari; Skyler Brazel; Ainong Shi; Sorina C Popescu; George V Popescu; T Casey Barickman

doi:10.3390/plants11172315

Growth and Photosynthetic Responses of Cowpea Genotypes under Waterlogging at the Reproductive Stage

Plants (Basel). 2022 Sep 4;11(17):2315. doi: 10.3390/plants11172315.

Authors

Omolayo J Olorunwa¹, Bikash Adhikari¹, Skyler Brazel¹, Ainong Shi², Sorina C Popescu³, George V Popescu⁴, T Casey Barickman¹

Affiliations

¹ North Mississippi Research and Extension Center, Department of Plant and Soil Sciences, Mississippi State University, Verona, MS 38879, USA.
² Department of Horticulture, PTSC 316, University of Arkansas, Fayetteville, AR 72701, USA.
³ Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University, Mississippi State, MS 39762, USA.
⁴ Institute for Genomics, Biocomputing, and Biotechnology, Mississippi State University, Mississippi State, MS 39762, USA.

Abstract

Waterlogging is an important environmental stress limiting the productivity of crops worldwide. Cowpea (Vigna unguiculata L.) is particularly sensitive to waterlogging stress during the reproductive stage, with a consequent decline in pod formation and yield. However, little is known about the critical processes underlying cowpea's responses to waterlogging during the reproductive stage. Thus, we investigated the key parameters influencing carbon fixation, including stomatal conductance (g_s), intercellular CO₂ concentration, chlorophyll content, and chlorophyll fluorescence, of two cowpea genotypes with contrasting waterlogging tolerance. These closely related genotypes have starkly contrasting responses to waterlogging during and after 7 days of waterlogging stress (DOW). In the intolerant genotype ('EpicSelect.4'), waterlogging resulted in a gradual loss of pigment and decreased photosynthetic capacity as a consequent decline in shoot biomass. On the other hand, the waterlogging-tolerant genotype ('UCR 369') maintained CO₂ assimilation rate (A), stomatal conductance (g_s), biomass, and chlorophyll content until 5 DOW. Moreover, there was a highly specific downregulation of the mesophyll conductance (g_m), maximum rate of Rubisco (V_cmax), and photosynthetic electron transport rate (J_max) as non-stomatal limiting factors decreasing A in EpicSelect.4. Exposure of EpicSelect.4 to 2 DOW resulted in the loss of PSII photochemistry by downregulating the PSII quantum yield (F_v/F_m), photochemical efficiency (Φ_PSII), and photochemical quenching (qP). In contrast, we found no substantial change in the photosynthesis and chlorophyll fluorescence of UCR 369 in the first 5 DOW. Instead, UCR 369 maintained biomass accumulation, chlorophyll content, and Rubisco activity, enabling the genotype to maintain nutrient absorption and photosynthesis during the early period of waterlogging. However, compared to the control, both cowpea genotypes could not fully recover their photosynthetic capacity after 7 DOW, with a more significant decline in EpicSelect.4. Overall, our findings suggest that the tolerant UCR 369 genotype maintains higher photosynthesis under waterlogging stress attributable to higher photochemical efficiency, Rubisco activity, and less stomatal restriction. After recovery, the incomplete recovery of A can be attributed to the reduced g_s caused by severe waterlogging damage in both genotypes. Thus, promoting the rapid recovery of stomata from waterlogging stress may be crucial for the complete restoration of carbon fixation in cowpeas during the reproductive stage.

Keywords: Vigna unguiculata; biomass; hypoxia; leaf gas exchange; photochemistry; recovery; stomatal conductance; waterlogging tolerance.

Grants and funding

MIS 149210/National Institute of Food and Agriculture