Quantifying Verticillium dahliae in the soil profile using two methods in USA and Australian cotton soil



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Quantifying inoculum levels of Verticillium dahliae in field soil is essential for understanding potential disease pressure of Verticillium wilt in cotton and making informed management decisions. A number of semi-selective medium and several techniques for pathogen isolation have been developed for determining the inoculum levels of V. dahliae present in soil. Soil sampling methods, timing of sampling, media, and isolation techniques all influence the estimated inoculum levels in soil. The objective of this study was to determine the ideal combination of soil plating technique, media, sampling depth, and time of sampling for the detection and quantification of V. dahliae in field soils. Two soil plating techniques (dilution, or wet, plating and hand-spreading, or dry, plating) on four semi-selective media (Sorenson’s NP-10, PDA, and acidified versions of each) were compared to quantify naturally occurring soil inoculum in germinated microsclerotia propagules per gram of soil. Soil from three depths was compared to examine the vertical distribution of the fungus in order to determine the ideal sampling depth. Sampling was conducted pre-planting and post-harvest to determine the ideal sampling time. The results suggest sampling soil prior to planting from 2-12 cm depth and using the dry-plating method on Sorenson’s NP-10 media.



Cotton, Disease, Verticillium wilt, Verticillium dahliae