*Article* **Drought Tolerance Assessment of Okra (***Abelmoschus esculentus* **[L.] Moench) Accessions Based on Leaf Gas Exchange and Chlorophyll Fluorescence**

**Sonto Silindile Mkhabela 1,2,\*, Hussein Shimelis 1,3, Abe Shegro Gerrano <sup>2</sup> and Jacob Mashilo 1,3**


**Abstract:** Physiological and complementary phenotypic traits are essential in the selection of droughtadapted crop genotypes. Understanding the physiological response of diverse okra genotypes under drought stress conditions is critical to the selection of drought-tolerant accessions for production or breeding. The objective of this study was to assess the levels of drought tolerance in preliminarily selected okra accessions based on leaf gas exchange and chlorophyll fluorescence to determine best-performing genotypes for drought-tolerance breeding. Twenty-six genetically diverse okra accessions were screened under non-stressed (NS) and drought-stressed (DS) conditions under a controlled glasshouse environment using a 13 × 2 alpha lattice design in three replicates, in two growing seasons. Data were subjected to statistical analyses using various procedures. A significant genotype × water condition interaction effect was recorded for transpiration rate (T), net CO2 assimilation (A), intrinsic water use efficiency (WUE*i*), instantaneous water use efficiency (WUE*ins*), minimum fluorescence (*Fo*- ), maximum fluorescence (*Fm*- ), maximum quantum efficiency of photosystem II photochemistry (*Fv*- */Fm*- ), the effective quantum efficiency of *PSII* photochemistry (*φPSII)*, photochemical quenching (*qP*), nonphotochemical quenching (*qN*) and relative measure of electron transport to oxygen molecules (ETR/A). The results suggested variable drought tolerance of the studied okra accessions for selection. Seven principal components (PCs) contributing to 82% of the total variation for assessed physiological traits were identified under DS conditions. Leaf gas exchange parameters, T, A and WUE*i*, and chlorophyll fluorescence parameters such as the *φPSII*, *Fv*- */Fm*- , *qP*, *qN*, ETR and ETR/A had high loading scores and correlated with WUE*i*, the *φPSII*, *qP* and ETR under DS conditions. The study found that optimal gas exchange and photoprotection enhance drought adaptation in the assessed okra genotypes and tested water regimes. Using the physiological variables, the study identified drought-tolerant accessions, namely LS05, LS06, LS07 and LS08 based on high A, T, *Fm*- , *Fv*- */Fm* and ETR, and LS10, LS11, LS18 and LS23 based on high *AES*, *Ci*, *Ci/Ca*, *WUEi*, *WUEins*, *φPSII* and AES. The selected genotypes are high-yielding (≥5 g/plant) under drought stress conditions and will complement phenotypic data and guide breeding for water-limited agro-ecologies.

**Keywords:** abiotic stress; chlorophyll fluorescence; drought tolerance; leaf gas exchange; physiological traits
