Unravelling the relationships among Verticillium wilt, irrigation, and susceptible and tolerant olive cultivars

Survival, germination, olive colonization, and water-use efficiency (WUE) impairments by Verticillium dahliae could be influenced by cultivar susceptibility or irrigation, and this could modify the irrigation-pathogen-disease relationship. In this study, the combined effects of irrigation and cultivar susceptibility on Verticillium wilt (VW) development were modelled by the temporary assessment of V. dahliae propagules (total inoculum density, density of micropropagules, and sclerotia in wet and air-dried soil; ID, MpD, SwD, and SdD, respectively), root (RCI) and shoot (SCI) colonization indexes, and WUE. The relationship of disease severity to the measured parameters was then explored. Under controlled conditions, plants of cultivars 'Picual' and 'Frantoio' were irrigated to a high and low rate by varying drip-irrigation frequencies: daily, twice weekly, and a combination of daily for 11 days and then twice weekly. Disease severity and colonization parameters were higher in 'Picual', while WUE was higher in 'Frantoio'. However, high rate and twice weekly and combination treatments significantly increased disease incidence and reduced time-to-symptoms-onset only in 'Picual', while high rate reduced WUE and increased relative ID, MpD, and SwD in both cultivars. Irrigation did not affect SCI, but a higher RCI was found at high rate during the development of symptoms in 'Picual'. By using classification trees to examine parameters-disease severity relationships, it was possible to determine the degree to which VW was affected by irrigation and/or cultivar susceptibility. MpD was the best indicator for VW detection at any time, WUE was best before symptoms developed, and RCI, total ID, and SdD after symptoms developed.

Automated summary

The study investigated the combined effects of irrigation and cultivar susceptibility on the development of Verticillium wilt, finding that 'Picual' cultivar had higher disease severity and colonization parameters, while 'Frantoio' had higher WUE. High-rate irrigation increased disease incidence and reduced time-to-symptoms-onset only in 'Picual'.