Impact of Sclerospora graminicola infection on physiological mechanisms and hormonal regulation of floral reversion in pearl millet [Pennisetum glaucum (L.) R. Br

Abstract

The present study was undertaken to assess the impact of Sclerospora graminicola infection on the physiological and developmental changes in pearl millet. Disease progression of biotrophic pathogen Sclerospora graminicola causing downy mildew was determined to alter the anatomical, biochemical and photosynthetic characteristics of the flag leaf. The defense mechanism was initiated by the host plant in response to S. graminicola infection. The plugging of stomatal pores and vascular bundles with an increase in trichome density was observed post infection. The infection caused an increase in internal CO2 concentration, decrease in net photosynthetic rate, stomatal conductance and transpiration rate of the flag leaf. The disease infection reduced the total soluble sugar content of the host plant, whereas increased the starch and the total phenolic content. The increase in starch content in the downy mildew infected leaves might have imparted feedback inhibition leading to reduced photosynthetic activity. The leaf malondialdehyde (MDA) content and enzymatic antioxidants viz. peroxidase, polyphenol oxidase and indole-3-acetic acid (IAA) oxidase increased post infection. Hence, this imbalance in flag leaf metabolic activity affected the developing panicle and induced developmental alterations which redirected floral development and fate of the meristem. An increase in tiller number was possibly due to the release of apical dominance caused by fungal infection which regulated the endogenous auxin content to a three fold increase. Floral reversion due to the pathogen infection suggests that there was transport of auxin from the developing axillary buds that might have led to malformed ear proliferation. The information on carbon assimilation and hormone imbalance causing floral reversion in pearl millet by downy mildew pathogen can aid in management practices aimed at reducing the disease impact on the crop.