Alleviation of verticillium wilt in pepper ( Capsicum annuum L.) by using the organic amendment COA H of natural origin

Abstract

Pepper seedlings cv. “Piquillo” were grown for 3 months in unamended medium with organic growing medium COA H (containing salicylic acid (SA), soluble ammonium salts and sea weed extract from Ascophyllum nodosum) inoculated or not inoculated with Verticillium dahliae Kleb. and in amended growing medium with COA H inoculated or not inoculated with V. dahliae. Seedling growth parameters, leaf content of relative water and chlorophyll, leaf gas exchange and resistance as well as total phenolics in stems were determined on days 0, 7, 21, 28 and 33 after inoculation with V. dahliae. SA in stems was measured on days 0, 21 and 33 and leaf nutrient content was analysed on day 33. Results indicate that the organic amendment COA H delayed senescence in Verticillium-inoculated seedlings. In fact, inoculated seedlings that received COA H always exhibited similar leaf resistance to water vapour as well as leaf content of chlorophyll, relative water and nutrients to their relative healthy controls. By contrast, the content of chlorophyll a and relative water in leaves from unamended seedlings significantly decreased on days 21 and 28, respectively, reaching values 30 and 20% lower than those found in the unamended healthy controls. Likewise, the content of chlorophyll b, potassium (K) and magnesium (Mg) in leaves from unamended seedlings inoculated with V. dahliae had declined 35, 40 and 50%, respectively, of the control values by day 33 after pathogen inoculation. On the other hand, while Verticillium-inoculated seedlings grown in amended medium with COA H maintained control photosynthetic rates for 21 days after inoculation, CO 2 exchange rates decreased from day 21 in unamended ones and the leaf resistance in these seedlings enhanced 50% 1 week after inoculation. In addition, Verticillium-inoculated seedlings supplied with COA H delayed the appearance of disease symptoms and their disease index on day 33 was about 40% lower than that measured in unamended pepper. The early accumulation of phenolics (from day 7 after inoculation) in pepper grown in amended medium with COA H could be involved in the greater disease resistance and/or tolerance exhibited by these seedlings.