Abstract
This study was conducted to compare the effects of foliar spray and rhizosphere irrigation with purple phototrophic bacteria (PPB) on growth and stevioside (ST) yield of Stevia. rebaudiana. The S. rebaudiana plants were treated by foliar spray, rhizosphere irrigation, and spray plus irrigation with PPB for 10 days, respectively. All treatments enhanced growth of S. rebaudiana, and the foliar method was more efficient than irrigation. Spraying combined with irrigation increased the ST yield plant -1 by 69.2% as compared to the control. The soil dehydrogenase activity, S. rebaudiana shoot biomass, chlorophyll content in new leaves, and soluble sugar in old leaves were affected significantly by S+I treatment, too. The PPB probably works in the rhizosphere by activating the metabolic activity of soil bacteria, and on leaves by excreting phytohormones or enhancing the activity of phyllosphere microorganisms.
Highlights
Stevia rebaudiana Bertoni is a herb native to certain regions of South America
Regulatory authorities worldwide have permitted the use of the steviol glycosides extracted from S. rebaudiana leaves as a dietary supplement
It has been reported that increasing chlorophyll content could directly affect steviol glycosides yield [7], and there is a significant positive correlation between total sugar content and ST content [8]
Summary
Stevia rebaudiana Bertoni is a herb native to certain regions of South America. It produces several valuable and sweet steviol glycosides in its leaves [1]. Stevioside (ST), one of the steviol glycosides, is 300 times sweeter than cane sugar and non-calorific, and has specific immunomodulatory activities [2], [3], leading to its use as a sweetener by diabetic and phenylketonuria patients and obese persons. It has been reported that increasing chlorophyll content could directly affect steviol glycosides yield [7], and there is a significant positive correlation between total sugar content and ST content [8]. Contents of chlorophyll and total sugar are correlated to photosynthesis. Enhancing photosynthesis may be a way to help increase ST production
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