Triggering Systemic Resistance in Tomato Plants using Salicylic Acid and Gibberellic Acid against Tomato Mosaic Disease under Greenhouse

Abstract

Tomato mosaic disease (ToMD), caused by Tomato mosaic virus (ToMV, Genus: Tobamovirus, Family: Virgaviridae) is economically important disease of the tomato. Under favorable environmental conditions sever yield losses have been reported due to ToMD. Therefore, present study was conducted for its management through enhancing systemic resistance using Salicylic acid (SA) and Gibberellic acid (GA) in tomato crop. The phytotoxic effect of either chemical was evaluated prior to treatments, 500, 750, and 1000 µg/ml of SA and 250, 500, and 750 µg/ml of GA were used for further experiments. Tomato plants were treated with various concentrations of SA and GA. Four days following treatment, sap obtained from symptomatic tomato plants was inoculated on healthy plants. Incidence and severity of disease were observed weekly. In the first week of observation, SA at 750 and 1000 µg/ml kept plants disease-free. At second week of observation, SA at 1000 µg/ml remained effective. At third week of observation, 500 and 750 µg/ml SA led to 100% incidence, while 1000 µg/ml had significantly lower 33.333% incidence. GA at 500 and 750 µg/ml suppressed symptoms in the first week of observation. In second and third week of observation, 500 µg/ml GA had 100% incidence, but plants treated with 750 µg/ml had 33.333% incidence.250 µg/ml GA showed no suppression at all weeks of observations same as inoculated control. Inoculated control plants had maximum severity score of 2.6667. Lower SA (500 µg/ml) concentration had severity scores 1.0, 1.3333, 2.3333 during the observation on 1^st, 2^nd and 3^rd week after foliar application, respectively. Middle SA (750 µg/ml) concentration had severity scores 0.0, 0.3333, 1.6667 during the observation on 1^st, 2^nd and 3^rd week after foliar application, respectively. Similarly, during 1^st and 2^nd week after foliar application of SA @ 1000 µg/ml the severity score 0.0 and during 3^rd week severity score was 0.333. Likewise severity score of 1.0, 1.3333, and 2.6667 was recorded in GA at lower concentration (250 µg/ml). During 1^st, 2^nd and 3^rd week after foliar application of GA @ 500 µg/ml the severity score was 0.0, 1.0 and 2.0, respectively. Severity score of 0.0 during 1^st and 2^nd week of observation and 0.3333 score at 3^rd week of observation was recorded with the application of 750 µg/ml of GA in tomato plants. It is concluded based on results, that SA @ 1000 µg/ml and GA @ 750µg/ml were effective to reduce the incidence of ToMD. Lower doses of either SA or GA were not effective to reduce the severity of ToMD, whereas in middle dose the severity was slight reduced. Higher dose of both chemical suppressed the development of the disease in treated tomato plants. Therefore, it is suggested that with the application of SA and GA @ 750 and 1000 µg/ml, respectively can enhance resistance level of tomato plants against ToMD.