Effects of isoflavones formononetin and biochanin A on powderly mildew infection on red clover leaves

Abstract

Certain plant isoflavones exert antimicrobial activity and inhibit disease development through different mechanisms. The aim of this study was to estimate the effects of externally applied isoflavones formononetin (F) and biochanin A (BA) on the development of mildew infection on red clover (Trifolium pratense L.) leaves. Red clover was sown and grown in a phytotron under controlled conditions for 2 months and then plant leaves were sprinkled with water containing mildew infection agent. Young contaminated leaves were cut and incorporated by 3 units into 0.5% agar medium Petri dish (5 groups in 4 replicates). Compounds for the treatments were injected by 10 µl aliquotes once in 3 days at a distance of 5-7 mm from a leave stem. The leaves were exposed to different combinations of isoflavones using different stock isoflavone solutions in DMSO: 1) 124 mM F; 2) 164 mM BA, 3) 112 mM F + 176 mM BA (F/BA=0.6); 4) 153 mM F + 128 mM BA (F/BA=1.2); 5) DMSO solution was used as a control. The amounts of applied isoflavones were close to those detected in red clover leaves before flowering (F/BA=1.2) and after flowering (F/BA=0.6). The development of powderly mildew infection was monitored for 13 days and the degree of infection was evaluated using 1-5 scale. Mildew agent in vitro did not settle on young seedling leaves and required high humidity, while it was spreading quite fast on leaves of seedlings at flowering stage. F treatment stimulated mildew infection spread on red clover leaves in vitro: after 13 days infection degree change was 28 % higher than in control. Treatment with BA had opposite effect – it strongly delayed infection development and no statistically significant change of mildew infection degree was estimated at the end of experiment. The inhibitory impact of BA on mildew spread was obvious also when combinations of isoflavones were applied [...]