Physiological and biochemical effect of biostimulants on Abelmoschus esculentus (L.) and Cleome gynandra (L.)

Abstract

Abelmoschus esculentus (L.) and Cleome gynandra (L.) are neglected plants, often collected from the wild, with dual benefits of nutritional and medicinal values, especially in rural communities. Biostimulants are well-known for their stimulatory effect on plant physiological processes, from germination to full maturity. In the current study, the effect of biostimulant application was investigated on the germination, growth, yield and biochemical quality of selected A. esculentus and C. gynandra genotypes, as a tool for improving their physiological and biochemical aspects. The study involved two biostimulants [Kelpak® (1:100, 1:40 and 1:20, dilutions)] and plant growth promoting rhizobacteria = PGPR (1:5, 1:10 and 1:15, dilutions)] as well as their interaction effect on the different genotypes of A. esculentus (Okra PB1, PB2, PB3, PB4 and PB5) and C. gynandra (TOT10212, TOT8420, Cleome 3, CleomeMaseno and Cleome Arusha). The parameters evaluated were seed germination, vegetative growth, yield, biochemical (ꞵ-carotene, vitamin C, total phenolic, flavonoids and condensed tannins) and mineral elements content (Ca, Fe, K, Mg, Na and Zn). Germination of A. esculentus and C. gynandra was influenced by different genotypes and biostimulants. Okra PB2 and Okra PB4 had significantly enhanced Final Germination Percentage (FGP), Germination index (GI) and Germination Rate Index (GRI). Similarly, genotype TOT10212 had significantly increased FGP, GI and GRI while Cleome 3 had least FGP, GI, GRI and Coefficient of Velocity of Germination (CVG). The effect of Kelpak® treatments on FGP, GI, Mean Germination Time (MGT) and GRI was significantly comparable to that of control. The effect of PGPR treatments on FGP, GI and GRI significantly increased with increasing PGPR dilutions. In A. esculentus, the interaction of Kelpak® (1:100) and genotype OkraPB1 significantly improved germination parameters (FGP, GI and GRI) while no stimulatory effect was observed on the interaction of biostimulants and Okra PB2, PB3, PB4 and PB5. In C. gynandra, the biostimulants especially PGPR (1:5, 1:10 and 1:15), inhibited germination parameters (FGP, GI and GRI) of genotype TOT10212. A. esculentus genotypes showed different growth parameters. For instance, Okra PB5 had significantly higher plant height while Okra PB4 had least plant height. Biostimulants further influenced the vegetative growth and yield of A. esculentus and C. gynandra genotypes. Plant height, chlorophyll content and stem diameter of A. esculentus genotypes was significantly enhanced by PGPR (1:5, 1:10 and 1:15) application. The yield (number of pods, total fresh weight and total dry weight) of A. esculentus was enhanced by PGPR (1:5, 1:10 and 1:15) application. Plant growth promoting rhizobacteria (1:5, and 1:10) enhanced the chlorophyll content, stem diameter and yield (total fresh and total dry weight of leaves) of C. gynandra genotypes. No inhibitory effect was observed on the growth and yield of A. esculentus and C. gynandra genotypes following biostimulant treatments. Interaction of biostimulants with A. esculentus and C. gynandra genotypes had no significant effect on growth and yield parameters. The biochemical and mineral elements content of A. esculentus and C. gynandra genotypes was influenced by genotype and biostimulant (both Kelpak® and PGPR dilutions) application. In C. gynandra, biostimulants enhanced the ꞵ-carotene, total flavonoid and total phenolic content. Okra PB4 had significantly enhanced vitamin C and total phenolic content while Okra PB5 had significantly higher total flavonoid content. Genotype TOT10212 had significantly increased Ca, Fe, Mg and Na content. However, the content of condensed tannins together with Fe and Mg of C. gynandra genotypes was inhibited by biostimulants application. Application of PGPR-1:5, Kelpak®-1:40 and Kelpak®-1:20 significantly enhanced total phenolic, total flavonoid and condensed tannins of A. esculentus genotypes. Furthermore, biostimulants had varying effects on the mineral element content. A significant increase was observed on Fe content when A. esculentus genotypes were treated PGPR (1:10). Application of Kelpak® (1:100 and 1:40) caused a significant decrease on the Ca content of A. esculentus genotypes. The interaction effect of biostimulants application and genotypes significantly inhibited the mineral elements of C. gynandra genotypes while significantly enhancing the vitamin C and condensed tannins of Okra PB3. The current study demonstrated the differential effect of biostimulants application (Kelpak® and PGPR) on A. esculentus and C. gynandra genotypes. The application of biostimulants can therefore, be used to enhance germination, growth, yield, biochemical content and mineral elements, depending on the crop genotype, and hence assist in combatting food insecurity in food insecure communities.