Soil inoculum density of Verticillium dahliae and Verticillium wilt of olive in Lebanon

Abstract

In the Mediterranean basin, Verticillium Wilt of Olive (VWO) is diffused throughout its range of cultivation, causing severe yield losses and tree mortality. The disease was reported in almost all the Mediterranean and Middle East countries, and in Lebanon it is of increasing significance also on many valuable crops. The disease has already been reported on potato, peach and almond in the Bekaa valley; however, to date no information is available about the incidence of VWO and the inoculum density of Verticillium dahliae microsclerotia in soil of the main agricultural areas of Lebanon. Results from the present investigations demonstrate a high V. dahliae frequency in soils (75.3%), coupled with a mean soil inoculum density of 17.0 MS g−1, clearly indicating a great impact on the production of susceptible hosts in Lebanon, mainly in Bekaa region. Molecular method to assess the microsclerotia inoculum density in soil allowed the detection of a higher frequency of infested soils, as compared with the traditional plating, thus confirming its higher sensitivity. The overall Verticillium wilt prevalence in the inspected olive orchards was 46.2%, and the frequency of V. dahliae‐infected trees was 25.7%. The widespread presence of V. dahliae in all olive growing areas of Lebanon enforces the adoption of measures aimed at reducing the soil inoculum density before any new olive plantation, and the use of strong phytosanitary regulations to improve the certification schemes of propagating material.

Long-Distance Spread of Verticillium dahliae Through Rivers and Irrigation Systems

“…The selected rivers were surrounded by agricultural fields planted with V. dahliae-susceptible crops, and distributed in the main Lebanese agricultural regions: the Bekaa Valley, North Lebanon, and South Lebanon. In order to define the sampling areas and the number of samples from each river, the locations of infested potato and olive fields, identified in previous studies (Baroudy et al 2016;Habib et al 2017), were plotted on a map in which the main rivers are shown (Fig. 1).…”

“…Molecular protocols. For each replicate of the processed dried residues of sediments from rivers and canals and from samples of soil and organic filters residues, two aliquots (0.5 g) were subjected to the extraction of total nucleic acids (TNA) by the cetyltrimethylammonium bromide (CTAB) method (Cullen et al 2001), slightly modified as described by Habib et al (2017). Briefly, extraction was made in 1,000 ml of extraction buffer (0.12 M Na 2 HPO 4 , 1.5 M NaCl, and 2% CTAB) with 50 mg of acid-washed glass beads (425 to 600 mm; Sigma-Aldrich, St. Louis) and two 5-mm steel balls, and the suspension was thoroughly agitated using the mixer mill Retsch MM301 (Retsch GmbH, Haan, Germany).…”

“…TNA was used as template in two separate protocols: (i) a conventional nested-PCR protocol developed as a quick screening method for the detection of the pathogen (Nigro et al 2002;Schena et al 2004a) and (ii) the qnPCR protocol, founded on the previous one reported by Schena et al (2004b) and recently optimized on soil samples, as detailed by Habib et al (2017).…”

“…In Lebanon, thousands of hectares of Verticillium-susceptible hosts are irrigated by means of regional pumping stations and canals or by direct use of river water. Recent nationwide surveys have highlighted the widespread occurrence of the pathogen and its potential impact on the agricultural sector (Baroudy et al 2016;Habib et al 2017). In fact, a high frequency (75.3%) of V. dahliae was reported in soils of the main Lebanese agricultural areas, coupled with a mean soil inoculum density (ID) of V. dahliae of 17.0 MS/g (Habib et al 2017).…”

“…Recent nationwide surveys have highlighted the widespread occurrence of the pathogen and its potential impact on the agricultural sector (Baroudy et al 2016;Habib et al 2017). In fact, a high frequency (75.3%) of V. dahliae was reported in soils of the main Lebanese agricultural areas, coupled with a mean soil inoculum density (ID) of V. dahliae of 17.0 MS/g (Habib et al 2017). The pathogen was also detected in 46.2% of olive orchards, infecting 25.7% of the total sampled trees (Habib et al 2017), and in 77.5% of potato fields, with a frequency of 61.2% infected plants ( Baroudy et al 2016).…”