Effects of Cold Temperatures on Pierce’s Disease
This year we repeated field inoculations of grapevines with the Pierce’s disease bacterium, Xylella fastidiosa , in two locations but used needle inoculations of cultured bacteria in addition to insect vector inoculations. We cultured from samples of inoculated canes to determine which canes became infected. In the winter we returned cane segments from infected canes to the greenhouse for rooting to determine how far the bacteria moved and their survival rate in canes by late winter. The previous year’s temperatures were unusually mild; this winter’s temperatures were below average, so there may be less survival of X. fastidiosa this year. Freezing treatments were completed, but their effects on therapy of Pierce’s disease will not be completed until early summer. It is apparent already from our culturing immediately after freezing treatments that disease recovery rates were lower this year than last year following similar treatments. It is also apparent that mortality of X. fastidiosa after freezing is not delayed. We detected bacteria immediately after freezing and anticipate that this year as last year, surviving bacteria will multiply in infected vines from undetectable levels to high levels within the next 2 months.