Genetic variability is suspected among different isolates of Uncinula necator. Therefore, different isolates must be screened to ensure the validity of the research. Isolates of U. necator have been collected from Kern, Santa Barbara, Sacramento, and Napa Counties. Single spore colonies have been produced from each isolate. These isolates have been maintained on Carignane seedlings in a growth chamber maintained at 75 F. Isolates are now being transferred to additional seedlings to increase inoculum to conduct resistance studies on 23 varieties of Vitis selected for this project. The Vitis varieties were produced at ARS in Fresno, transported to Davis and are being maintained in greenhouses at high temperature to ensure that they are initially free of the pathogen when testing is done. Sulfur pots are also being utilized to ensure clean plants. The vines are being fertilized to induce production of a large amounts of new tissue to be used in testing their resistance to U. necator. Resistance is being assessed using an artificial inoculation method in the greenhouse and the leaf disk bioassay method and will be compared to total plant resistance in greehouse and field tests. For the artificial inoculation method, plants are sealed in four separate growth frames, one for each isolate, and are placed randomly throughout each frame. These plants were inoculated with a spore suspension, from one of the four U. necator isolates. Plants would then be individually rated to determine the degree of their resistance to the differing U. necator isolates. To this date, cuttings have been rooted from each of the 23 varieties in order to produce enough plants to conduct this portion of the experiment. In this process, cuttings were taken from the parent plant and soaked in de-ionized water. They were then dipped in rooting hormone and placed in a rooting sponge (Grow-Tech Inc.). Leaves on the cuttings were trimmed to reduce water loss due to transpiration. Cuttings were placed in a styrofoam tray and then set on heating mats under a misting system. In the leaf disk bioassay, a number of six day old leaves were collected from each Vitis variety. Leaf disks were cut from leaves using a one-centimeter cork borer. Three petri dishes containing eight leaf disks each were prepared for each variety. These petri dishes were placed in the vacuum-powered spore-settling tower and inoculated with one of the four U. necator isolates. The spore-settling tower was used to ensure uniform inoculation of leaf disks. Blank coverslips were placed in the tower with the leaf disks to determine the inoculum density which was determined after 24 hours by placing the cover slips on a hemocytometer and counting the number of spores per square centimeter. Leaf disks were rated ten days after inoculation using a dissecting microscope. The percentage of leaf disk coverage by powdery mildew was estimated to the nearest ten percent, providing an accurate means of selection for powdery mildew resistance.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1999-10-18 10:29:582017-10-18 10:30:41Development of Powdery Mildew Resistant Table and Wine Grape Cultivars and