Soil Temperature Determines the Reaction of Olive Cultivars to Verticillium dahliae Pathotypes

Abstract

BackgroundDevelopment of Verticillium wilt in olive, caused by the soil-borne fungus Verticillium dahliae, can be influenced by biotic and environmental factors. In this study we modeled i) the combined effects of biotic factors (i.e., pathotype virulence and cultivar susceptibility) and abiotic factors (i.e., soil temperature) on disease development and ii) the relationship between disease severity and several remote sensing parameters and plant stress indicators.MethodologyPlants of Arbequina and Picual olive cultivars inoculated with isolates of defoliating and non-defoliating V. dahliae pathotypes were grown in soil tanks with a range of soil temperatures from 16 to 32°C. Disease progression was correlated with plant stress parameters (i.e., leaf temperature, steady-state chlorophyll fluorescence, photochemical reflectance index, chlorophyll content, and ethylene production) and plant growth-related parameters (i.e., canopy length and dry weight).FindingsDisease development in plants infected with the defoliating pathotype was faster and more severe in Picual. Models estimated that infection with the defoliating pathotype was promoted by soil temperatures in a range of 16 to 24°C in cv. Picual and of 20 to 24°C in cv. Arbequina. In the non-defoliating pathotype, soil temperatures ranging from 16 to 20°C were estimated to be most favorable for infection. The relationship between stress-related parameters and disease severity determined by multinomial logistic regression and classification trees was able to detect the effects of V. dahliae infection and colonization on water flow that eventually cause water stress.ConclusionsChlorophyll content, steady-state chlorophyll fluorescence, and leaf temperature were the best indicators for Verticillium wilt detection at early stages of disease development, while ethylene production and photochemical reflectance index were indicators for disease detection at advanced stages. These results provide a better understanding of the differential geographic distribution of V. dahliae pathotypes and to assess the potential effect of climate change on Verticillium wilt development.

Early Detection and Quantification of Verticillium Wilt in Olive Using Hyperspectral and Thermal Imagery over Large Areas

“…Chen et al [70,71] confirmed that the spectral characteristics of cotton infected plants changed gradually with the increase in the visible region with disease severity, while a reduction occurred in the near-infrared region. Moreover, results obtained in this study at canopy level confirmed those obtained at leaf level under controlled conditions by Calderón et al [13], who identified SPAD readings (chlorophyll content) and chlorophyll fluorescence as early VW indicators. In addition, these results were also in agreement with the study carried out by Calderón et al [12] at canopy level in two olive commercial orchards, proving the potential for early detection of V. dahliae infection in olive crops using hyperspectral imagery acquired with an unmanned aerial vehicle.…”

“…Normalized canopy temperature (Tc-Ta), chlorophyll fluorescence and blue ratios B/BG/BR were found to be the best indicators of early stage infection by VW while the Photochemical Reflectance Index (PRI), structural, chlorophyll and carotenoid indices detected only moderate to severe V. dahliae infection. These results obtained at the canopy level using airborne imagery were confirmed by those obtained by Calderón et al [13] at leaf level under controlled conditions. SPAD readings (as an indicator of leaf chlorophyll content), leaf chlorophyll fluorescence and normalized leaf temperature were demonstrated to be early VW indicators while the ethylene production and PRI detected only advanced stages of VW development.…”

“…Moreover, the reduction in photosynthesis caused by V. dahliae infection leads to an increase of the dissipation of energy by fluorescence. Considering these changes, several studies showed the feasibility of VW detection of olive trees at leaf and local scale even before characteristic disease symptoms were visible using normalized temperature, chlorophyll content, chlorophyll fluorescence and blue B/BG/BR indices [12,13]. However, to our knowledge no studies have explored the robustness of these methods using narrow-band indices and thermal imagery for the early detection of VW in larger olive growing areas (i.e., thousands of hectares) characterized by large differences in crop age, tree-crown size, olive cultivars, crop managements and classes of disease severity.…”

“…Nilsson [69] reported that oilseed rape plants infected with V. dahliae showed leaf temperatures 5-8 °C higher than non-infected plants. In addition, normalized leaf and canopy temperature were identified as early indicators of V. dahliae infection in olive trees [12,13], showing up to 2 °C higher in VW infected trees. Hyperspectral reflectance differences were also demonstrated to identify VW in cotton and olive crops.…”

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

“…Calderón et al . () showed that soil temperatures in the range of 16–24 °C promoted infection by the defoliating pathotype in Picual plants grown in soil tanks placed inside a walk‐in growth chamber for 3 months. In late spring in the present trial, when maximum values of d y/ d t were registered, optimal soil temperatures, as indicated by Calderón et al .…”