Heat induced susceptibility of mlo-barley to powdery mildew (Blumeria graminis hordei)
2001
Schwarzbach, E.
Primary leaf segments of two Mlo barley lines, the extremely susceptible SM4142 and the medium susceptible Diamant, and of two mlo-barley lines, the less resistant Apex and the more resistant HLN70-8, were inoculated with the mildew isolates PV-4 and HL-3, differing in their level of partial mlo-virulence. The leaf segments, laid out in Petri-dishes on an agar medium, were exposed for 30, 60 and 120 min to 36 deg C prior to uniform inoculation with conidia of the mildew isolates in a settling tower. After 5-6 days of incubation at 17-18 deg C the colonies were counted and compared with counts on simultaneously inoculated segments without heat treatment. The heat treatments resulted in increased susceptibility of all tested varieties to both mildew cultures. The effect was largest with the most resistant variety and the less mlo-virulent mildew culture. The largest observed increase was by one order of magnitude. In contrast, cooling the leaf segments to 1 deg C prior to inoculation for 30, 60 or 120 min did not have a significant effect with the culture PV-4 and only a slight effect with HL-3. The heat induced susceptibility was temporary and declined within 13 hours to approx. 130 % , relative to not heat-treated leaf segments. Since the heat induction operates at temperatures occurring in nature, it may contribute to occasionally observed outbreaks of mildew in fields of mlo-varieties. Heat induced susceptibility also can be utilised for collecting partially mlo-virulent pathotypes from agricultural environments.
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