ANALYSIS OF THE SPATIAL PATTERNS OF PIERCE'S DISEASE INCIDENCE IN THE LOWER SAN JOAQUIN VALLEY

Authors: Tubajika, Kayimbi; Civerolo, Edwin; WENDEL, L. - USDA-APHIS, TX; CIOMPERLIK, C. - USDA-APHIS, TX; BARTELS, D. - USDA-APHIS, TX; LUVISI, D. - UCCE-BAKERSFIELD; HASHIM, J. - UCCE-BAKERSFIELD

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2004
Publication Date: 10/1/2004
Citation: Tubajika, K.M., Civerolo, E.L., Wendel, L.E., Ciomperlik, C.A., Bartels, D.W., Luvisi, D.A., Hashim, J.M. 2004. Analysis of the spatial patterns of Pierce's Disease incidence in the lower San Joaquin Valley. Phytopathology. 94(10):1136-1144.

Interpretive Summary: The incidence of Pierce's disease, caused by Xylella fastidiosa, was monitored in commercial vineyards. Disease incidence doubled in most vineyards during the 2002 production season compared to that in 2001. The within-row and across-row orientation generally were the predominant directions of increased disease incidence, consistent with vine-to-vine spread of the pathogen. This implied that either the invading population of the insect vector was not infective or the later movements within citrus after arriving were most important in spreading infections that resulted in disease symptoms. The predominant vector species observed within commercial vineyards was the glassy-winged sharpshooter. Presumably, the distribution of PD in the field reflected the feeding pattern of infectious vectors carrying the pathogen. Based on these results, effective PD management is likely to be based on practices that reduce significant insect vector populations, removal of infected vines as soon as identified, and use of resistant cultivars. This paper presents novel results about the within field patterns of PD where GWSS is likely vector of X. fastidiosa. These observations provide valuable information about the need to develop accurate and reliable diagnostics, detect infected vines early, rogue infected vines, manage the vector and reduce sources of inoculum.

Technical Abstract: The incidence of Pierce's disease caused by Xylella fastidiosa, was monitored in 11 naturally- infested commercial vineyards to examine the spatial patterns of the disease, elucidate possible influences of surrounding environments, and presence of a X. fastidiosa vector, Homalodisca coagulata (Say), (glassy-winged sharpshooter). Disease incidence ranged from <1% in field 1 in 2001 to 71% in field two in 2002. Disease incidence doubled in most vineyards during the 2002 production season. The lack of evidence for a gradient or presence of at most a weak gradient relative to GWSS sources (like citrus) was observed. Spatial patterns of symptomatic vines in 2001 and 2002, as determined by ordinary runs analysis, showed strong evidence for within and across-row aggregation of infected vines. Two-dimensional distance class analyses revealed a higher frequency of infected pairs of vines and a greater degree of clustering of diseased vines as disease incidence increased. In most fields, they were no disease gradients observed relative to GWSS source (e.g. citrus). Within fields, however, disease incidence displayed strong spatial dependence and a high degree of anisotropy, indicating strongly aggregated patterns of disease with distinct directional orientation. The within-row (0o) and across-row (90o) orientation generally were the predominant directions of increased disease incidence, consistent with vine-to-vine spread of X. fastidiosa. The predominant vector species observed within commercial vineyards was H. coagulata. Presumably, the distribution of PD in the field should reflect the feeding pattern of infectious vectors carrying the bacteria. Based on these results, effective PD management is likely to be based on practices that reduce significant insect vector populations, remove infected vines as soon as identified, and use of resistant cultivars.