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A Chemo Attractant in Onion Root Exudates Recognized by Ditylenchus dipsaci in Laboratory Bioassay

A quantitative bioassay that translates preferences of axenically cultured and field population of Ditylenchus dipsaci, observed in vitro, into relative attractiveness of sterile root exudates preparations and their components is described. Onion (Allium cepa cv. White Lisbon) root exudates (ORE) are consistently and significantly much more attractive than the buffer control in all these assays. Exudates from oat cv. Lodi, mustard cv. Albatross and tomato cv. Rehovot 13 are significantly more attractive than the buffer but less attractive than ORE; Arabidopsis sp. cv. Landsberg erecta, oil seed rape cv. Cetes and wheat cv. Bet Hashita are as attractive as the buffer, but canary grass and clover exudates are less attractive than the buffer and, therefore, are classified as repellent. No significant differences in relative attractiveness were detected among exudates from other two cultivars of onion (Texas Grano 502 and Granex Hybrid) and one cultivar of leek (Large American Flag), but exudates from one onion (cv. Evergreen Long White Bunching) and one leek (cv. Broad London) were less attractive than ORE. Relative attractiveness is linear in relation to dilution exponent and therefore log-linear in relation to ORE concentration. Host (onion) penetration study reveals that penetration preferences by D. dipsaci follow the same pattern as those predicted by relative attractiveness coefficients estimated in the bio-assays. Preliminary characterization of the chemo attractant from ORE, using the behavioral bioassay, demonstrated that it was stable to heat and to proteolytic enzymes, nonvolatile and water soluble with a molecular mass <700 kDa.