Effect of Jojoba Seed Extract and Riboflavin in Preventing the Transmission of Iris Yellow Spot Virus (IYSV): Tospovirus by Thrips tabaci L. to Onion Plants in Egypt

Background and Objective: Iris Yellow Spot Virus (IYSV) genus Tospovirus, family Bunyaviridae is one of the most important viruses affecting onion crops worldwide. In Egypt, IYSV was recorded for the first time from onion since, 2004. Thrips tabaci L. is the mainly vector of this virus. The present study was conducted to test the effect of jojoba seeds extract and riboflavin on decrease the transmission rate of IYSV by Thrips. Materials and Methods: The virus has been isolated from naturally infected onion plants grown in the experimental farm, Faculty of Agriculture, Cairo University, Giza. It was identified by mechanically and T. tabaci transmissibility, symptomatology, serology and transmission electron microscopy. Two pots experiments were conducted in 2013-2014 seasons to study the effect of spraying with jojoba seeds extract at 100, 500 and 1000 g mLG 1 and riboflavin at 0.5, 1.0 and 2.5 mM to inhibit infection with IYSV in onion plants (cv. Giza 20) exposed to Thrips. Data were subjected to analysis of variance and the means were compared using the Least Significant Difference (LSD) test at the 0.05 levels. Results: All treatments with jojoba seeds extract caused virus inhibition through reduction in the transmission rates of IYSV by T. tabaci and riboflavin through induced resistance against virus infection when plants were sprayed before the virus transmission. The highest concentration of jojoba seed extract (1000 g mLG 1 ) and riboflavin at (1 mM) were the best treatments which resulted in the highest reduction of viral infection (58 and 36%), respectively. The different treatments resulted in significant increase in photosynthetic pigments, pungency compounds and activity of peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) and glutathione content compared with infected plants. Moreover, all treatments recorded decrements in activity of superoxide dismutase (SOD) compared with the untreated ones. Conclusion: It is suggested that reduction in the incidence and severity of IYSV infection in onion plant may be achieved by treatments with jojoba seeds extract and riboflavin when onion plants were sprayed before IYSV Thrips transmission.