SURVEY ON RICE BLAST AND MORPHOLOGICAL VARIATION AND IN VITRO MANAGEMENT OF MAGNAPORTHE ORYZAE

Abstract

A survey on rice blast caused by Magnaporthe oryzae was done in three northern districts of Bangladesh namely Gaibandha (Gobindogonj and Mohimagonj), Dinajpur (Birampur) and Bogura (Dupchanchia). The highest incidence (84.26%) of blast was recorded from Gobindogonj with a severity score of 7. The highest severity score 9.00 (65%) of blast was recorded in Mohimagonj where blast incidence was only 29.12%. Magnaporthe oryzae was isolated on five different media namely Water Agar (WA), Potato Dextrose Agar (PDA), Potato Sucrose Agar (PSA), Rice flour Yeast Agar (RfYA) and Oat Meal Agar (OMA). The highest mycelia growth was recorded in Oat Meal Agar (20mm) and the lowest in Water Agar (10mm) at 7 DAI. Colony characters like growth rate, color, surface structure and shape of 28 isolates were differed from location to location. Twelve fungicides namely Folicur EW 250, Amistar Top, Nativo 75WP, Tropper 75WP, Blastin 75WDG, Azonil 56SC, Seltima 100SC, Autostin 50WDG, Filia 525SE, Differ 300EC, Dithane M-45 and Knowin 50WP were evaluated against mycelia growth of Magnaporthe oryzae in vitro. Folicur EW 250, Seltima 100SC, Filia 525SE and Differ 300EC showed 100% inhibition of growth at 7 DAI, 10 DAI and 14 DAI. Eight botanicals namely Kalijira (Nigella sativa), Turmeric (Curcuma longa), Ginger (Zingiber officinalis), Garlic (Allium sativum), Onion (Allium cepa), Neem (Azadirachta indica), Allamanda (Allamanda cathartica), Aloevera (Aloe vera) extracted by either water or ethanol were tested against Magnaporthe oryzae in vitro. Maximum growth inhibition of tested pathogen was achieved with water extract of turmeric 1:1 (w/v) with 86.57% growth inhibition and ethanol extracts of neem with 92.62% (1:1 w/v) mycelial growth inhibition at 14 DAI, respectively. In another experiment five different designs of dual culture technique between Magnaporthe oryzae and Trichoderma harzianum THR 4 was conducted to find out the best in vitro evaluation technique of T. harzianum THR 4 against M. oryzae. The dual culture technique where four discs of T. harzianum THR 4 was set on the periphery of the petridish surrounding one disc of M. oryzae on the center of the petridish gave most satisfactory result in both case of mean mycelium growth and interactions with Magnaporthe oryzae. Comparing chemical fungicides, botanicals and Trichoderma harzianum THR 4, highest reduction of mycelia growth was recorded in chemical fungicides (Folicur EW 250, Seltima 100SC, Filia 525SE, Differ 300EC) followed by ethanol extract of neem, water extract of turmeric, and Trichoderma harzianum THR 4.