Abstract
Damping-off disease of cucumber is one of the most destructive diseases of cucumber in worldwide. In this work, the potential of jasmonic acid (JA) for induce resistant against damping off disease was investigated. The effect of JA on activity of Polyphenol oxidase (PPO), Peroxidase (PO) and Catalase (CAT) enzymes and total phenol was assayed by spectrophotometric method. Expression level of three plant defense genes as Lipoxygenase, Cupi4 and Phenylalanine ammonia-lyase genes was analyzed using qRT-PCR method. Drop-plate method was used to assay inhibitory effect of JA on radial growth of fungi. Exogenic application of JA decreased disease severity in the infected plants but did not inhibit mycelia growth on solid medium compared to control. Our results showed that JA application substantially increased the activity of oxidative enzymes at different concentration. The highest enzyme activity was recorded after 48 hours post infection (hpi) at a concentration of 400 mg L-1 of JA. Gene expression analysis revealed that JA is differentially able to increase the mRNA transcripts of all tested genes at 48 hpi. The expression level of Cupi4 gene was higher than the other genes in treated plants. Induced systemic resistance by JA was mediated through an enhanced expression of ISR marker genes and increase of antioxidant enzymes activity. Based on these results, we suggest that exogenic application of JA could be considered as plant resistance inducer.
Highlights
Damping-off disease of cucumber caused by P. aphanidermatum is one of the most destructive diseases of cucumber under greenhouse condition (Chaube & Pundhir 2005)
The results of inhibitory growth test showed that radial growth of P. aphenidermatum on solid medium had not significantly affect from all concentrations of jasmonic acid (Table 2)
The effect of methyl jasmonate on mycelial growth of Aspergillus flavus showed that this compound did not affect mycelial growth or colony appearance (Goodrich-Tanrikulu et al 1995)
Summary
Damping-off disease of cucumber caused by P. aphanidermatum is one of the most destructive diseases of cucumber under greenhouse condition (Chaube & Pundhir 2005). Plant hormones play an important role in molecular signaling to enhance resistance mechanisms (Vallad & Goodman 2004). Different antioxidant enzymes such as polyphenol oxidase (PPO) and peroxidase (PO) are involved in phenol oxidation and are correlated with mechanisms of plant defense against microbial pathogens (Zhang & Klessig 2001; Maffei et al 2007). Volatile plant secondary metabolites could directly suppress growth and development of pathogens in attacked tissues. This suppression could be resulted from Lox-catalyzed reactions (Croft et al 1993). In this study the effect of JA on the radial growth of P. aphanidermatum, antioxidant enzymes activities, expression level of some defense related genes and disease severity in inoculated cucumber with P. aphanidermatum was investigated
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