Short-distance dispersal of splashed bacteria of Xanthomonas citri subsp. citri from canker-infected grapefruit tree canopies in turbulent wind

Abstract

Citrus canker (Xanthomonas citri subsp. citri (Xcc)) can cause yield loss and trade restrictions. The pathogen is dispersed in rain splash and spread is promoted by wind. The goal of this study was to gain some insight into the properties of short-distance splash dispersal of Xcc from ~1·5m-tall cankered grapefruit canopies in turbulent wind, common during rainstorms in Florida. Turbulent wind up to 19·9m s -1 was tested in five experiments. Bacteria flux density (BFD, bacteria cm -2 min -1) was quantified at heights of 30, 70, 110, 130 and 180cm above ground, and at four horizontal points (17, 51, 85 and 119cm) at each height across the direction of the wind 1m downwind. BFD varied among experiments, but the lowest BFDs were consistently detected at the greatest sample height. Despite differences between experiments, the relationship between log BFD and sample height was consistently described by a linear function (P=0·06-<0·0001, R 2= 0·75->0·99). The BFD collected at the horizontal points across the wind path was variable. BFDs collected were sometimes significantly different, but no relationship was discernible. Stronger, turbulent wind resulted in greater BFD, with a linear function describing the relationship between log BFD and wind speed (P=0·2-0·02, R 2= 0·94-0·96). Multiple regression analysis demonstrated predictability of the proportion of total bacteria collected (F=141, P<0·0001, d.f.=3, R 2= 0·53). © 2012 The Authors. Plant Pathology © 2012 BSPP.