Physiological and biochemical effect of biostimulants on Abelmoschus esculentus (L.) and Cleome gynandra (L.)
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Date
2021
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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.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.