To determine the effects of low temperature on populations of the bacterial plant pathogen, Xylella fastidiosa, in American sycamore hosts, field and laboratory experiments were conducted to examine population dynamics in both naturally and mechanically infected host plants. Bacterial presence, population density estimates, and bacterial distribution in host tissue were analyzed in relation to the extraction method used, environmental air and soil temperature and rainfall, low temperature treatment, host resistance, and reciprocal transmissibility of three strains of X. fastidiosa from sycamore, oak, and grape. Results indicate that increasing hours below -5C were best associated with reductions in bacterial populations in field trees at two sites. No relationship was detected between bacterial populations and either low temperature treatment at 5C or putative host resistance. Host reciprocity tests suggest significant differences in density and distribution of the three bacterial strains within their reciprocal hosts.
