fastidiosa levels with ELISA and by symptomology, including leaf scorch and a cane maturation index.

arizonica population was also evaluated by quantifying X. fastidiosa populations in the resistant genotypes compared to the susceptible genotypes were greatest in the stem internodes. fastidiosa population levels, with highest levels in leaf blades, followed by petioles, and lowest levels in stem nodes and internodes. However, the resistant genotypes had lower X. fastidiosa populations in the tissues of susceptible genotypes did not differ among nodes, internodes, petioles, and leaf blades. fastidiosa populations between resistant and susceptible genotypes and also among different organs or tissues of resistant genotypes. Systemic infection studies under greenhouse conditions have shown differential distribution patterns of X. Once resistance genes are identified it may be possible to directly introduce resistance into elite wine grape cultivars by transgenic technologies. The introduction of PD resistance genes into wine grapes is complicated by the need for several generations of back-crossing to exclude unfavorable fruit characters associated with the resistant Vitis species. The goals of these breeding efforts are to develop durably resistant cultivars, map and identify DNA-based markers for resistance to aid in selection, and to identify resistance genes. Efforts to breed PD resistant grapes for California are underway. smalliana are highly resistant to PD, and breeding programs have utilized these resistant species to develop PD resistant grapes for the southeastern United States. For example, accessions of Vitis aestivalis, V. Resistance to PD exists in some grape species and cultivars have been bred from these species. In addition, as pesticide use becomes more restricted and as pesticide resistance develops, it is likely that the ultimate solution to PD will be host resistance. However, even low populations of the glassy-winged sharpshooter can have severe impact on vineyard health, thus limiting the effectiveness of predators to solve PD. Much of this research has focused on means of controlling the vector with insecticides and natural predators as a critical first step in integrated crop management. Over the past few years, federal, state governments, and the grape industry have funded PD research. The disease is caused by Xylella fastidiosa, a xylem-limited, gram negative bacterium that is hosted by a wide range of plant species in and around vineyards in the southern United States and Mexico. The threat from this disease has recently become more severe with the introduction and establishment of a more effective vector, the glassy-winged sharpshooter ( Homalodisca coagulate). Pierce's disease (PD) has been a chronic problem for California's grape industry since the 1880s. All the generated ESTs have been submitted to GenBank and are also available through our website for further functional studies.

This study constitutes the first attempt to characterize the Vitis differential transcriptome associated with host-pathogen interactions from different explants and genotypes. Among the three tissues, libraries from stem tissues showed significant differences in transcript quality suggesting their important role in grape- Xylella interaction. Comparative analysis found variations in EST expression pattern between infected and non-infected PD resistant and PD susceptible grape genotypes. Using Gene Ontology (GO) hierarchy, the non-redundant sequences were classified into the three principal categories: molecular function (30%), cellular components (9%) and biological processes (7%). A total of 5,794 sequences were obtained from these cDNA libraries from which 993 contigs and 949 singletons were derived. Twelve tissue specific subtractive suppression hybridization (SSH) cDNA libraries derived from a time course sampling scheme were constructed from stems, leaves and shoots of PD resistant and susceptible sibling genotypes ( V. However, the transcriptome level characterization of the host response to this pathogen is lacking. The current molecular breeding efforts have identified genetic basis of PD resistance in grapes. The gram-negative bacterium Xylella fastidiosa (Xf) is the causal agent of Pierce's disease (PD) in grape as well as diseases of many fruit and ornamental plants.

Xf and infection in plant