Quantification of Xylella fastidiosa in pecan (Carya Illionoinensis) plant tissues
Pecan Bacterial Leaf Scorch (PBLS) caused by xylem-limited bacterium, Xylella fastidiosa, is a chronic, debilitating disease in species of Carya. PBLS has been recently identified in California, Arizona, New Mexico, and Texas. As new reports of incidence emerge, it is critical to uncover the epidemiology of this pathogen to combat PBLS. The first aim of this study was to determine the distribution of the bacterium within a seedling. A quantitative PCR platform was developed using a novel Xylella-specific TaqMan probe. The bacterial concentration of roots, shoots, and leaves in infected ‘Elliott’ pecan seedlings were determined. X. fastidiosa was detected in the DNA isolated from roots and shoots, and roots were found to contain the highest titer levels. Our second aim was to determine the relationship between pecan nut quality and concentration of X. fastidiosa. We collected 150 nuts from a known PBLS-infected ‘Cape Fear’ tree and measured nut density on individual nuts. Nut volume was calculated by measurement of buoyancy and used to determine nut density (mass/vol). Three categories were established to represent nut densities: high (.72 g/cc), medium (.62 g/cc) and low (.52 g/cc). DNA will be isolated from the cotyledons of each nut, and the concentration of X. fastidiosa will be determined. Pearson’s correlation of coefficient will be used to determine the relationship between X. fastidiosa concentration and nut density. Information on the correlation between nut quality and presence of Xylella will be useful when determining seed selection strategies for distribution and cultivation of pecan rootstocks.