TESTING TRANSGENIC GRAPEVINES FOR RESISTANCE TO PIERCE’S DISEASE

About 80 ‘Chardonnay ’ lines transformed with the magainin-type antimicrobial peptide (AMP) genes, mag-2 and MSI99, and with a PGL class gene, were produced and about 40 were chosen for detailed analysis. Magainins are small peptides that inhibit growth of numerous bacteria and fungi. Some of these AMP-transgenic lines have improved resistance to tumorigenic strains of crown gall (Agrobacterium vitis). Other researchers have claimed that similar AMPs induce grapevine resistance to Pierce’s disease (PD). The goal of our project was to characterize gene insertion, expression, and disease resistance in ‘Chardonnay ’ grapevines harboring mag-2, MSI99, and a PGL class gene. These lines were shown to harbor between 1 and 5 copies of the foreign gene. RT-PCR testing showed that the genes are transcribed into RNA but efforts to directly detect peptide production in leaf tissues have been hampered by technical difficulties. We were able to show that some lines do produce the peptide, and that several have improved resistance to crown gall disease. The Walker Lab (UC Davis) has tested the same set of vines for resistance to PD. Symptom development was delayed in a few lines, which also showed improved lignification and re-growth following symptom development. Using an ELISA test to quantify the presence of the causal bacterium, 15 lines were classified as ‘susceptible ’ while one line was classified as ‘intermediate ’ in terms of resistance. Plants have been grafted to determine whether resistance (and/or transgene products) can be transmitted from a transformed rootstock to a non transformed scion cultivar. These tests are now underway