Early stage effects of Verticillium wilt of olive (WVO) on nutrient use in young olive trees grown in soils amended with compost and mineral fertilisation

Abstract

Verticillium wilt, caused by the soil-borne pathogenic fungus Verticillium dahliae (Kleb), is one of the most severe diseases of olive trees in Mediterranean agriculture. At present, the use of organic amendments is considered an effective means to combat certain soil-borne plant diseases while in turn supplying plants with nutrients. The aim of this study was to determine the early stage effects of Verticillium wilt of olive (VWO) on macronutrient uptake and in planta mobility by analysing nutrients in young olive trees. Young olive trees were grown in unamended as well organically amended soils (employing two distinct olive mill waste composts, C1 and C2) in the presence or absence of mineral fertilisation. Half of the soils were inoculated with Verticillium dahliae (Vd) defoliating (D) pathotype, leaving the other half non-inoculated. At 22 and 100 days after inoculation, nutrient content (N, P, K, S, Ca, and Mg) was analysed in mature and young leaves. Olive mill compost enhanced N, P, K and S availability but did not prevent Verticillium infection in young olive trees. Pathogen inoculation affected nutrient content in mature and young leaves and reduced leaf nutrient input during the early stages of host colonization. Stronger effects were observed in pathogen inoculated plants grown in soil amended with C2, coinciding with high N and P and transiently low S availability. Leaf K input showed the highest sensitivity to V. dahliae inoculation. In high N conditions, deleterious effects caused by Vd on young olive trees may be overcome by promoting the growth of new shoots. We present evidence that Vd requires S during the initial stages of host colonization, in which plant-pathogen competition for this element is key, and that low levels of S in foliage during such early stages may enhance Verticillium wilt development.