ISHS Acta Horticulturae 175: Symposium on Physiology of Productivity of Subtropical and Tropical Tree Fruits
THE USE OF LEAF XYLEM WATER POTENTIAL TO MEASURE THE IMPACT OF PHYTOPHTHORA ROOT ROT ACTIVITY IN AVOCADO (PERSEA AMERICANA MILL.) |
| Authors: | A.W. Whiley, K.G. Pegg, J.B. Saranah |
| Abstract:
A comparative index of Phytophthora cinnamomi activity in avocado roots was developed from a field study examining internal water deficit in healthy and diseased trees. Water deficit was monitored by recording diurnal cycles of leaf xylem water potential determined by the pressure chamber method while tree health was visually rated on a 0–10 scale. Daytime and nighttime values of xylem water potential were lower (more negative) in infected trees than in healthy trees. The lowest potentials were -1.425 mPa and -1.104 mPa respectively and these were measured at 1200 and 1400 hours. Trees with health ratings falling between the highest and lowest range similarly registered leaf xylem water potentials between -1.425 and -1.000 mPa. Xylem water potential at night recovered to -0.350 mPa for healthy trees and -0.470 mPa for diseased trees. A significant correlation was established between leaf xylem water potential and tree health ratings by regression analyses (R2 0.87). Leaf xylem water potential data used in the regression was collected under maximum environmental loading (1400 hrs) and when soil moisture was a non-limiting factor. Tree health was assessed three months later during winter when visual disease expression was well developed. The index will assist in the early detection of relative changes in tree health during the experimental assessment of treatments designed to control Phytophthora root rot in avocado trees. | |
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