Submitted to: Journal of Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/1/2009
Publication Date: 12/10/2009
Citation: Livingston, S., Chen, J., Civerolo, E.L. 2009. Seasonal Behavior of Xylella fastidiosa Causing Almond Leaf Scorch Disease Under Field Conditions and Improved Detection of the Bacteria by Means of Array-PCR. Journal of Phytopathology. 158:40-45. Interpretive Summary: Almond leaf scorch diseases (ALSD) caused by Xylella fastidiosa has re-emerged as a threat to the almond industry in California. Knowledge of X. fastidiosa behavior in the plant host under field conditions is important for disease control. In this two-year research project, we found that the first occurrence of ALSD symptoms in the field varied from year to year (June in 2006 and July in 2007). In both years, PCR detected X. fastidiosa one month before onset of symptoms. PCR was slightly more sensitive than cultivation method for early bacterial detection. Correlation between cultivation and PCR detection was over 90%. An array-PCR protocol was developed to improve detection accuracy.
Technical Abstract: Almond leaf scorch disease (ALSD) caused by Xylella fastidiosa is potentially a serious threat to the almond industry in San Joaquin Valley of California. Knowledge of X. fastidiosa behavior in the plant host under field conditions is important for disease control and this issue is being addressed in this project. Occurrence of ALSD is strongly influenced by environmental factors. In 2006, the earliest leaf scorching symptoms were observed in June, whereas in 2007, the earliest occurrence of leaf scorching symptoms was in July, a delay of one month. In both years, PCR detected X. fastidiosa one month before symptom expression. PCR was slightly more sensitive than cultivation method for early bacterial detection. However, uneven bacterial distribution and random sampling errors may have contributed to differences among the assays. Correlation between cultivation and PCR detection was greater than 90%. During the processing of a large number of samples, we noticed occasional failures in PCR amplifications of some samples, interfering with interpretation of results. We developed an array-PCR protocol using primers from seven housekeeping genes to correct the deficiency.