Systemic Induction of Resistance in Phaseolus vulgaris L. to Tobacco Necrosis Virus (TNV) by Uromyces phaseoli (Pers.) Wint.

Abstract

AbstractPreinoculation of primary half leaves or whole primary leaves of bean plants (Phaseolus vulgaris, cv. Pinto) with Uromyces phaseoli induced resistance against tobacco necrosis virus (TNV) in the opposite half leaves and in the trifoliate leaves, respectively. For expression of systemically induced resistance an interval of at least 4 days between primary and challenge inoculation was required. The most pronounced effectiveness was found after an induction period of 6 days.Preinfectional treatment with intercellular washing fluids extracted from rust infected bean leaves (IWF‐R) also reduced disease incidence of TNV. Extracts taken 6 days after rust inoculation induced the most pronounced effect on resistance. For induction of resistance an interval of at least three days between application of IWF‐R and TNV‐inoculation was necessary. IWFs from healthy leaves (IWF‐H) did not induce resistance to TNV. The disease reductions of systemic protection by IWF‐R in the untreated primary half leaves and in the trifoliate leaves averaging 50%. The IWF‐R could be diluted to 1/4 of its original concentration without appreciable loss of the resistance‐inducing capacity.Besides the resistance inducing effects, the IWF‐R and in addition IWF‐H showed virus inactivating activity; this effect was restricted to the treated leaf area. When IWFs were applied at short time intervals either (0–8 h) before or (0–4 h) after TNV inoculation, the number of local lesions was markedly reduced. Increasing the pre‐ or postinfectional time intervals (0.5–2 dai or 6–8 hpi) diminished the activity significantly. The effectiveness of IWF‐R increased at prolonged preinfectional time intervals (e.g. 3 and 4 dai) while extracts of healthy plants were ineffective. The biphasic pattern of activity indicates that IWF‐R contains ingredients reducing virus infectivity and inducing resistance to TNV.When the transcription inhibitor actinomycin D and the translation inhibitor cycloheximide were applied simultaneously with IWF‐R 3 dai the resistance inducing effect of IWF‐R was prevented. In preliminary ultrafiltration experiments, the molecular size of the inducing ingredients of IWF‐R could be limited to 10–20 kd and those of the virus inactivating compounds to 1–5 kd.