Abstract
Verticillium Wilt of Olive, a disease caused by the hemibiotrophic vascular fungus Verticillium dahliae Kleb. presents one of the most important constraints to olive production in the world, with an especially notable impact in Mediterranean agriculture. This study evaluates the use of RGB vegetation indexes in assessing the effects of this disease during the biotrophic phase of host-pathogen interaction, in which symptoms of wilt are not yet evident. While no differences were detected by measuring stomatal conductance and chlorophyll fluorescence, results obtained from RGB indexes showed significant differences between control and inoculated plants for indexes Saturation, a*, b*, green Area (GA), normalized green-red difference index (NGRDI) and triangular greenness index (TGI), presenting a reduction in plant growth as well as in green and yellow color components as an effect of inoculation. These results were contrasted across two scenarios of mineral fertilization in soil and soil amended with two different olive mill waste composts, presenting a clear interaction between the host-pathogen relationship and plant nutrition and suggesting the effect of V. dahliae infection during the biotrophic phase was not related to plant water status.
Highlights
Verticillium Wilt of Olive (VWO), a vascular disease caused by the pathogenic soil-borne fungus Verticillium dahliae Kleb, is one of the most severe threats to olive production today [1]
While no differences were detected by measuring stomatal conductance and chlorophyll fluorescence, results obtained from RGB indexes showed significant differences between control and inoculated plants for indexes Saturation, a*, b*, green Area (GA), normalized green-red difference index (NGRDI) and triangular greenness index (TGI), presenting a reduction in plant growth as well as in green and yellow color components as an effect of inoculation
Results obtained for pigment concentrations and RGB indexes (Table 4) showed significant correlations, and excepting those obtained for carotenoids, in all cases Pearson’s r-values pairing indexes measuring green with chlorophyll contents, or yellow with the Car/Chl ratio were positive, while an opposite pairing resulted in negative values
Summary
Verticillium Wilt of Olive (VWO), a vascular disease caused by the pathogenic soil-borne fungus Verticillium dahliae Kleb, is one of the most severe threats to olive production today [1]. Taxonomic classifications place this fungus in Division Ascomycota, Class Sordariomycetes, Subclass Hypocreomycetidae, Order incertae sedis, Family Plectosphaerellaceae [2]. MS are incorporated into soil from degrading host tissue, remaining viable for up to 14 years [4] establishing the non-parasitic phase of the biological cycle. The parasitic phase starts when favorable conditions stimulate MS germination, producing hyphae that penetrate young roots by a passive entry mechanism [5] and subsequently colonize the aerial part of the host via passive transport through the vascular system [6]
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