Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

Document Type



Xylella fastidiosa colonizes the xylem of a wide range of plants and causes symptoms in many of them. It was of interest to determine how widespread X. fastidiosa was and what its potential impact might be in rabbiteye blueberry. X. fastidiosa was detected from two of 17 Louisiana orchards from which samples were collected. A yield study was conducted at one of these orchards, and mean yields of X. fastidiosa-positive plants were 55% and 62% less than those of X. fastidiosa-negative plants in 2013 and 2014, respectively. Average berry weight was also lower in X. fastidiosa-positive plants. However, plants that were X. fastidiosa-negative in 2013 remained so until 2015, suggesting that the bacterium does not spread rapidly in established orchards. Regular testing of plants that had tested positive for X. fastidiosa revealed that root sap was more reliable than stem sap for detection by real-time PCR. Detection by ELISA using leaf petiole/midrib tissue or, in the winter, shoot terminals, was not as consistent as detection in root sap by real-time PCR. However, it was comparable or better in some months and was consistently as good as or better than detection in stem sap by real-time PCR, except in April, when detection by ELISA in petiole/midrib tissue cannot be relied upon. Genotypes of X. fastidiosa identified from rabbiteye blueberry in Louisiana include combinations of alleles that are believed to have resulted from recombination between X. fastidiosa subspecies multiplex and fastidiosa. One genotype (ST 42) found at two Louisiana orchards was previously identified from southern highbush blueberry in Georgia. Inoculation of seven rabbiteye cultivars and one southern highbush cultivar with an X. fastidiosa isolate from rabbiteye blueberry did not result in detected infection within nine months. X. fastidiosa warrants awareness as a possible cause of yield loss and plant decline in rabbiteye blueberry. Rabbiteye blueberry likely harbors a genotype of X. fastidiosa that is pathogenic to southern highbush blueberry, so growers should take care to use clean planting material if introducing rabbiteye plants into an orchard that contains susceptible southern highbush cultivars.



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Committee Chair

Clark, Christopher A.