Isolates of Uncinula necator have been collected from Sacramento, Napa, Santa Barbara and Kern counties and were being maintained on Carignane seedlings in individual grow tubes housed in a 75F chamber. Seedling development was found to be hampered by this unnatural environment and poor infection rate resulted, requiring a change in system. The isolate inoculum source seedlings are now kept in separate growth chambers, where they receive adequate light and air for proper growth. Sufficient inoculum is being built up in these chambers for mass inoculation of the test seedlings. Each isolate will be tested at 3 different temperatures and 3 different humidities twice. 30 Carignane seedlings will be inoculated by means of a spore settling tower and transferred by sealed boxes to growth chambers set at either 15, 25 or 33 C. Slip covers were inoculated along with the seedlings to determine the density of the inoculation. One growth chamber has been obtained for each isolate and equipped with 30 humidity subchambers comprised of an airtight plastic contained filled with a salt solution. 10 subchambers will maintain 23%RH, 10 will maintain 60%RH and 10 will maintain 95%RH. Through experimentation with different compounds, Lithium chloride, Manganese chloride and sterile water, were found to best establish the determined humidities (respectively). In February, separate inoculations of 3 isolates were performed on 30 4-leaf seedlings each and the youngest leaf from each inoculated plant was placed in the humidity subchamber to incubate. After 10 days of incubation, the mildew on the leaves was too thick because of an excess of spore inoculum, making individual colony measurement impossible. Furthermore, the weather stripping that seals around the petioles had become saturated from multiple mixings of the solutions and was causing some phytotoxicity on the tissues that were touching it. It was determined through trials that a pure silicon sealant would work better at sealing off the container without imbibing any of the salt solution. Some follow up trials were done with the new sealant and 6-leaf seedlings whose youngest leaves have a thicker epidermis to resist phytotoxicity. The seedlings showed none of the earlier problems. 3 more inoculations were performed on various days in the second week of March. Inoculum concentration was reduced from 6 fully infected leaves to 1 fully infected leaf. The first chamber inoculated is ready to be measured and shows numerous distinct colonies on each leaf. No phytotoxicity is present in any of the chambers with the new silicon sealant and the larger seedlings. Several lesions from each leaf will be measured at 10 day intervals for rate of growth in mm/time and some will be destructively sampled for spore concentration/lesion. Slides of spores produced in each subchamber will be incubated at their respective humidities and the percentage of germination will be counted. The fourth chamber is in the process of being fitted with the silicon sealant and will be filled with the fourth isolate inoculation this week.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1999-10-18 10:20:292017-10-18 10:21:04Factors that Influence Disease Onset from Overwintering Powdery Mildew