Assessment of the effect of surface drip irrigation on Verticillium dahliae propagules differing in persistence in soil and on verticillium wilt of olive

Abstract

For efficient integrated management of verticillium wilt in olive (VWO), it is important to establish whether irrigation treatments (with Verticillium dahliae‐free water) that mitigate the disease in V. dahliae‐infested soil, also reduce the levels of more and less persistent propagules of the pathogen in the soil. Effects of irrigation on VWO and V. dahliae propagules were evaluated under natural environmental conditions. Potted plants were irrigated (pathogen‐free water) to two ranges of soil water content (RWC; high and low) at three surface drip‐irrigation frequencies (daily, weekly, and daily during some periods and otherwise weekly). VWO and total inoculum density (ID), density of less persistent micropropagules (MpD) and more persistent sclerotia in wet soil (SwD), and sclerotia density for air‐dried soil (SdD) were monitored. A logistic model (multiple sigmoid) of disease incidence revealed the lowest parameter values in treatments irrigated daily. Daily frequency of irrigation showed significantly lower disease incidence (39.2%) and disease intensity index (43.9%) and MpD (88.0%) values as areas compared with other frequencies, regardless of the RWC. High RWC significantly reduced (70.8–84.9%) ID, SwD and SdD as areas, but significantly increased (18.0%) the incidence of infected plants (IIP), regardless of the irrigation frequency. The disease incidence was not correlated with temperature. Daily irrigation to low RWC mitigated the VWO and the IIP, kept soil to the lowest MpD and resulted in the lowest SdD level at the end of the trial. Results suggested that less persistent propagules could have played a part in the disease development.

Morphophysiological response of young olive trees to verticillium wilt under different surface drip irrigation regimes

“…The authors of that study (Gaudreault et al ., ) postulated that high soil water pressures may hasten potato early dying by slowing root growth and/or indirectly increasing the rate of microsclerotial germination. Previous findings in olive plants (Santos‐Rufo et al ., ) indicated that AUIPC ID , AUIPC SwD and AUIPC SdD were lower at HR than at LR, and that AUIPC MpD , which is partly related to the rate of microsclerotial germination, was not affected by RWC. Thus, because HR increases IIP but reduces relative below‐ground biomass and R wr , together with relative above‐ground biomass and AUGPC, it is suggested, in line with Gaudreault et al .…”

“…Stomatal conductance ( g s ) was not significantly affected by irrigation treatments or soil infestation before maximum values of the derivative function of the DI progress curves (d y /d t ) for all irrigation treatments were reached each year (23, 388 and 752 dpt), according to Santos‐Rufo et al . () (Table ). However, significant ( P < 0.05) average reductions in g s were observed (33.3%, 47.7% and 17.2%) in +V plants at approximately maximum time values of the d y /d t for all irrigation treatments for the three years under study (49, 433 and 794 dpt, respectively) (Table ).…”

“…This research provides novel information about the effect of differential irrigation treatments on verticillium wilt in terms of growth and physiological responses in olive. The effects of the irrigation on morphological (shoot length and AUGPC), biomass (relative above‐ and below‐ground biomass and R wr ) and physiological (S Ψ and g s ) parameters found here could dispose olive trees, as established in a previous, related study (Santos‐Rufo et al ., ), to fewer infections in LR treatments and lower disease at DF in +V plants. Overall, V. dahliae inoculation reduced several morphological, biomass and physiological parameters.…”

“…(), that there is more potential for fungus–root contacts in HR than LR treatments. Moreover, cutting the frequency of irrigation (to 2.05 ± 0.05 days/irrigation event or at DF) decreased DI but increased aerial vegetative growth (relative above‐ground biomass, shoot length and AUGPC) in olive (Santos‐Rufo et al ., ; Tables & ). It is proposed that less vascular colonization due to the decrease in the amount of fungus per unit of aerial tissue length could reduce or prevent the disease in daily‐irrigated plants.…”

“…A thorough description of the trial can be found in Santos‐Rufo et al . (), and so only the key details are given here.…”