Source: http://www.secheresse.info/spip.php?article84343
Timestamp: 2019-04-20 00:58:32+00:00

Document:
Verticillium wilt of olive (VWO), caused by the vascular-colonizing, soilborne fungus Verticillium dahliae Kleb., is the most serious disease affecting this crop, in terms of the potential phytopathological and economic consequences. The current context of an ever-expanding area dedicated to irrigated olive groves, together with the knowledge that irrigation affects VWO and the possible presence of V. dahliae in irrigation water in Andalusia, makes it important to not only determine which irrigation strategy (with non-infested water) may help mitigate VWO, but also to know the phytosanitary status of irrigation water in terms of V. dahliae infestation, so that it can be disinfected if it is contaminated. Separating the effects of water on the development of VWO from the effects of repeated inoculum supply through irrigation water would help to better understand why irrigation has an effect on VWO, and thus to be able to integrate both management measures when circumstances require it. The first objective of this study was to evaluate the effect of irrigation on V. dahliae in soil and on VWO since, to ensure efficient integrated management of VWO, it is important to establish whether irrigation treatments (with V. dahliaefree water) that mitigate the disease, also reduce the levels of more and less persistent propagules of the pathogen in the soil. To that end, a trial was carried out with the Picual olive cultivar and a highly virulent V. dahliae defoliating isolate. The susceptible combination was placed under natural environmental conditions, where plants were grown in large pots and were irrigated to two ranges of soil water content (RWC ; high and low) at three surface drip-irrigation frequencies. In the infested soil, regardless of temperature and RWC, daily irrigation events led to greater reductions in disease incidence (39.2%) and disease intensity index (43.9%) than in plants under other irrigation frequencies, as well as to greater reductions in micropropagules (MpD), or less persistent fungus propagules, in the soil (88.0%). On the other hand, high RWC caused lower levels of sclerotia, or more persistent structures, in the soil (70.8-84.9%), but a higher percentage of infected plants (18.0%) than low RWC, regardless of the frequency of irrigation. Daily irrigation to low RWC helped halt the development of VWO and reduced the incidence of infection, keeping the soil at the lowest levels of MpD and resulting in the least amount of sclerotia in the soil after two and a half years. Under the conditions described above (the same irrigation treatments), the next objective was to compare the morphological and physiological responses in olive plants grown on V. dahliae-infested and non-infested soil, subjected to drip irrigation treatments that cause differential reactions in terms of VWO. The aim was to determine which of these responses help explain the effects of irrigation on the disease. In general, the comparative responses were affected by RWC, irrigation frequency and V. dahliae, as simple factors. The fungus showed reduced morphological and physiological parameters. High RWC irrigation resulted in a lower root weight ratio than with low RWC, meaning that high RWC could favour root infections and vascular colonization. In addition, daily irrigation could prevent the increase in symptoms characteristic of other irrigation frequencies, as a result of the greater growth increases in length and biomass of the aerial part of the plants associated with this irrigation frequency, together with highest water potential values, improved by lower stomatal conductance reduction. The last objective was to evaluate the efficacy of chemical water disinfestation in reducing V. dahliae conidia. Three disinfestants were tested for their efficacy against previous (suppressive efficacy) and subsequent (preventive efficacy) conidia infestations, as a function of the concentration of the disinfestant and the differential virulence of V. dahliae isolates to olive trees.

References: V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V.