CHEMICAL INDUCTION OF SYSTEMIC AQUARID RESISTANCE AND EFFECT OF THEIR APPLICATION TIME ON RICE BLAST “MAGNAPORTHE GRISEA” INFECTION TO CULTIVARS SAKHA101 AND SAKHA104.

Abstract

Blast is the most destructive rice diseases in Egypt and could cause significant yield losses. The variable nature and race shifting of the pathogen often leads to resistance breakdown of high yielding varieties such as Sakha 101 and Sakha 104. Chemical control is not always effective and often has an undesirable impact on the environment and human health. Some antioxidants and organic compounds; Bion (BTH, benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester), at concentrations of 0.1, 0.3 and 1 mM; Salicylic acid 8 mM (SA), Benzoic acid 8 mM, Nicotinic acid 8mM, H2O2 30%, and Compost tea 100% were directly applied as foliar spray of 21-days old seedlings prior to challenge inoculation with Magnaporthe grisea to promote blast resistance in rice leaves. Under greenhouse condition, artificial inoculation was applied after four fixed periods (5, 10, 15 and 20 days after treatment (DAT)) from the application date of all antioxidants. All antioxidants and compost tea reduced the infection percentage compared with untreated check especially with the inoculation 5 DAT. Concerning infection % of rice blast, there are a remarkable significant differences among all antioxidants compared with control. All antioxidants were significantly reduced the infection percentage. Salicylic acid was the most effective antioxidant at concentration of 8 mM, it recorded 4.9, 9.7, 28 and 15.5 % with 5, 10, 15 and 20 DAT, respectively. Also, Bion (BTH) at both concentrations 0.3 and 1.0 mM exhibited a significant reduction in infection %. The rest of antioxidants exhibited significant increase in infection % especially under late induced periods from 10-20 DAT.The optimal period of induced resistance, was artificial inoculation 5 DAT which recorded the lowest infection percentage compared with the inoculation after 10 to 20 days. With both Salicylic acid and Bion, artificial inoculation 5 DAT to 15 days led to a significant reduction in disease infection percentage and severity. While the resistance was remarkably sharply decreased after 15 days from induced resistance treatment with all antioxidants. Optimal induced period of Benzoic acid, Nicotinic acid, H2O2, Compost tea and Cinnamic acid was continued from 5 to 10 days only. Treatment with salicylic acid at 8 mM recorded the lowest area under disease progress curve ( AUDPC), 409.48 compared by the control 1304.24, followed by Bion at 0.3 and 1.0. However, BTH and Salicylic acid had neither suppression nor fungicidal effect on linear growth, spore germination, sporulation and appressorium formation of Magnaporthe grisea in vitro. Concerning Peroxidase (PO) activity with both SA 4mM and BTH increased continuously in 0-25 min. intervals and markedly significant increase, although PO activities reach to be maximum at 25 min. in which was higher than that control and other treatments. SA had the highest activities in period intervals followed by BTH. Compost Tea and H2O2 showed no significant increase in PO activity with all time intervals while the other treatments showed PO activities only in 10-20 min. compared to control. Polyphenoloxidase (PPO) activity has gradually decreased during intervals 0 to3 min. Spraying by SA 4mM recorded the highest enzyme activity in all intervals and markedly significant increase in activity. For growth characters, all applications of antioxidants treatments led to a significant increase in leaf area, plant height, chlorophyll content, fresh and dry weight of rice leaves compared to control. In general, Sakha 101 rice cultivar exhibited the highest response to applications of all antioxidant compared with other cultivar Sakha 104 that have a weak response of growth characters to antioxidants application. Abbreviations: BTH, benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester; JA, jasmonic acid; SA, salicylic acid; SAR, systemic acquired resistance.