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Low UV-C dose exposition elicits disease resistance against bacterial leaf spot caused by Xanthomonas hortorum pv.vitians in lettuce

Olbert Nicolas , Marie Thérèse Charles , Vicky Toussaint , Sylvie Jenni , Jawad Aarrouf, Carole Beaulieu Low UV-C dose exposition elicits disease resistance against bacterial leaf spot caused by Xanthomonas hortorum pv.vitians in lettuce. Joint Annual Conference for the Canadian Society of Agronomy and the Canadian Society for Horticultural Science, La Plaza, Montreal, QC, Canada, 24-26 July, 2016. (Oral presentation)

Abstract

Postharvest application of short wave ultraviolet (UV-C) is claimed to increase disease resistance of fresh fruits and vegetables during storage. However, little is known about the potential of UV-C hormesis on growing plants. Low dose of UV-C was applied to lettuce cultivars with different level of susceptibility to bacterial leaf spot and the effect of this treatment on symptoms development was analyzed. Two susceptible lettuce cultivars (‘Chief’ and ‘Paris Island Cos’) and one resistant cultivar (‘Little Gem’) were treated every other day over a period of 8 days with a radiation dose of 0.4 kJ.m-2 for 60 s. Forty-eight hours following the UV-C treatment, control and treated plants were inoculated with a bacterial suspension of Xanthomonas hortorum pv. vitians strain B07-007. Severity of the bacterial leaf spot was evaluated 14 days after inoculation. For the two susceptible cultivars, the severity index was significantly lower in UV-C treated plants than it was for the control plants. Disease severity indices of ‘Chief’ were 2.47 and 4.97 (P = 0.0004) for UV-C treated and control plants, respectively, while indices for ‘Paris Island Cos’ were 2.45 and 4.47 (P = 0.0081), respectively. However, the UV-C treatment did not cause significant change in disease severity (P = 0. 2891) for the resistant cultivar ‘Little Gem’. Work is in progress to assess the possible involvement of phytoalexin production in the enhanced resistance of lettuce to X. hortorum pv. vitians following UV-C exposition.

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