The objectives of this study are to identify optimal pH range for root function and minimize root turnover on HLB-affected rootstocks and how uneven pH levels in the root zone (e.g. irrigated vs. row middle portions of root system) affect the overall health of the tree. This is being done in a split root system in the greenhouse where pH of different parts of the root system can be controlled an maintained.
Trees for the first repetition of the experiment have been inoculated and regular pictures of roots in the rhizotrons are being taken and root tracings are being done on the controls and trees that have tested qPCR postive. A new individual side drip irrigation system has been developed to make irrigation and leachate collection less prone to error and more efficient. Currently about 20% of inoculated trees are qPCR positive for Las, so not quite enough are positive yet for statistical comparisons of treatments.
Because of the difficulty in developing a buffer system across the entire desired pH range that does not alter plant physiology, we have changed to using CREC well water and adjusting it’s pH with sulfuric acid. The well water provides good buffering capacity from pH 7.5 to 5.5 and this more accurately represents what occurs in grower groves.
We are currently testing methods to collect and quantify root leakage non-destructively in the rhizotron system that should provide additional information on root health with HLB and soil/irrigation water pH.