Abstract
AbstractSurvival, 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.
Highlights
Verticillium wilt (VW) of olive, caused by Verticillium dahliae, is one of the most destructive fungal diseases affecting olive worldwide and the primary phytopathological problem for olive cultivation in Andalusia, mainly due to the prevalence of the defoliating pathotype of the fungus and of the extremely susceptible olive cultivar, ‘Picual’ (Jiménez-Díaz et al, 2012; López-Escudero & Mercado-Blanco, 2011; Montes-Osuna & Mercado-Blanco, 2020)
We demonstrated the potential capabilities of machine learning techniques for studying the influence of irrigation on VW in most of the points of the disease cycle of V. dahliae in olive
The effect of differential irrigation treatments—based on the resistance level of olive cultivars to VW—was assessed by their influence on the pathogen and on the plant simultaneously
Summary
Verticillium wilt (VW) of olive, caused by Verticillium dahliae, is one of the most destructive fungal diseases affecting olive worldwide and the primary phytopathological problem for olive cultivation in Andalusia, mainly due to the prevalence of the defoliating pathotype of the fungus and of the extremely susceptible olive cultivar, ‘Picual’ (Jiménez-Díaz et al, 2012; López-Escudero & Mercado-Blanco, 2011; Montes-Osuna & Mercado-Blanco, 2020). These results contrast with those of Pérez-Rodríguez, Alcántara, et al (2015) obtained in microplots with naturally infested soil when four irrigation frequencies (determined by a volumetric method) were studies for three olive cultivars with differing levels of disease resistance These authors indicated that DI, mortality, and area under the disease progress curve increased more in ‘Picual’ plants subjected to a daily irrigation schedule (unknown days per irrigation event, with the possibility of not being purely daily) than to either weekly or biweekly schedules, or in plants subjected to a water deficit. Irrigation treatments that led to greater V. dahliae infections and visible symptoms reported by Santos-Rufo et al (2017), reduced water-use efficiency (WUE) of biomass production by the same proportion under the same conditions (Santos-Rufo et al, 2018) This could explain how these treatments increase the incidence of the disease, only ‘Picual’, which is the most susceptible olive cultivar to VW (López-Escudero et al, 2004; Rodríguez Jurado, 1993) was evaluated in these conditions. These research objectives were based on the hypothesis that a holistic approach, accounting for the temporary effects of water and cultivar susceptibility on the disease cycle of V. dahliae, would help to explain why some irrigation schedules exalt the virulence of VW more than others
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