Abstract :
Blast is the most destructive rice diseases in Egypt and could causesignificant yield losses. The variable nature and race shifting of the pathogen oftenleads to resistance breakdown of high yielding varieties such as Sakha 101 andSakha 104. Chemical control is not always effective and often has an undesirableimpact on the environment and human health. Some antioxidants and organiccompounds; 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 foliarspray of 21-days old seedlings prior to challenge inoculation with Magnaporthe griseato promote blast resistance in rice leaves. Under greenhouse condition, artificialinoculation 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 teareduced the infection percentage compared with untreated check especially with theinoculation 5 DAT. Concerning infection % of rice blast, there are a remarkablesignificant differences among all antioxidants compared with control. All antioxidantswere significantly reduced the infection percentage. Salicylic acid was the mosteffective antioxidant at concentration of 8 mM, it recorded 4.9, 9.7, 28 and 15.5 % with5, 10, 15 and 20 DAT, respectively. Also, Bion (BTH) at both concentrations 0.3 and1.0 mM exhibited a significant reduction in infection %. The rest of antioxidantsexhibited significant increase in infection % especially under late induced periods from10-20 DAT. The optimal period of induced resistance, was artificial inoculation 5 DATwhich recorded the lowest infection percentage compared with the inoculation after 10to 20 days. With both Salicylic acid and Bion, artificial inoculation 5 DAT to 15 daysled to a significant reduction in disease infection percentage and severity. While theresistance was remarkably sharply decreased after 15 days from induced resistancetreatment 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 diseaseprogress curve ( AUDPC), 409.48 compared by the control 1304.24, followed by Bionat 0.3 and 1.0. However, BTH and Salicylic acid had neither suppression norfungicidal effect on linear growth, spore germination, sporulation and appressoriumformation of Magnaporthe grisea in vitro. Concerning Peroxidase (PO) activity withboth SA 4mM and BTH increased continuously in 0-25 min. intervals and markedlysignificant increase, although PO activities reach to be maximum at 25 min. in whichwas higher than that control and other treatments. SA had the highest activities inperiod intervals followed by BTH. Compost Tea and H2O2 showed no significantincrease in PO activity with all time intervals while the other treatments showed PO activities only in 10-20 min. compared to control. Polyphenoloxidase (PPO) activityhas gradually decreased during intervals 0 to3 min. Spraying by SA 4mM recordedthe highest enzyme activity in all intervals and markedly significant increase in activity.For growth characters, all applications of antioxidants treatments led to a significantincrease in leaf area, plant height, chlorophyll content, fresh and dry weight of riceleaves compared to control. In general, Sakha 101 rice cultivar exhibited the highestresponse to applications of all antioxidant compared with other cultivar Sakha 104 thathave a weak response of growth characters to antioxidants application.
Keywords :
Rice blast , Magnaporthe grisea , induce resistance , salicylic acid , BTH , systemic acquired resistance
