<em>In-vitro</em> studies on effect of fungicides against mycelial growth and sporangial germination of <em>Phytophthora infestans </em>(Mont) de Bary) causing late blight of potato

Abstract

Late blight of potato is most destructive disease. In the present study, a total of eleven fungicides, out of which eight systemic/translaminar funcides cymoxanil 50 WP, cymoxanil 8 + mancozeb 72 WP, cymoxanil 8 + mancozeb 64 WP, metalaxyl 8 + mancozeb 64 WP, metalaxyl 32 WP, fenamidone 10 + mancozeb 50 WP, difenoconazole 25 EC, dimethomorp 50 WP at concentrations of 10, 50, 100, 200 and 500 mg ml-1and three protectants viz. propineb 70 WP, mancozeb 70 WP and chlorothalonil 70 WP at concentrations of 100, 200, 500, 1000 and 2000 mg ml-1 were tested against the mycelia growth and sporangial germination ability on V8 agar medium by using poison food technique invitro. It was found that all the tested fungicides significantly inhibited the growth of mycelium compared to the control (untreated). Among the systemic fungicides dimethomorph exhibited the minimum overall mycelial growth of 38.86 mm followed by cymoxanil 8 + mancozeb 72 WP sustaining a radial growth of 43.00 mm compared to a radial mycelial growth 85.73 mm obtained in unamended check plates. An increasing trend in inhibition of mycelial growth was observed as the concentration of each fungicide was increased, such that each fungicide at 200-500 µg/ml exhibited more than 90 per cent inhibition of mycelia growth, compared to 10 µg/ml which yielded less than 10 per cent inhibition. Among protectant fungicides mancozeb exhibited highest inhibition percent with minimum mycelial growth of 46.77 mm followed by propineb yielding the mycelial growth of 50.13 mm as compared to 85.73 mm growth obtained in un amended check. The results also revealed that all the fungicides significantly reduced the sporulation and germination ability of the sporangia at all the test concentrations. Among systemic fungicides, dimethomorph proved most effective allowing sporangia germination to the extent of only 31.80 percent followed by metalaxyl + mancozeb 64 WP and cymoxanil+ mancozeb 72 WP with sporangia germination of 36.53-37.00 per cent as compared to 80.66 per cent germination observed in un-amended check (control) plates.Among the protectants.