ISHS Acta Horticulturae 275: International Symposium on the Culture of Subtropical and Tropical Fruits and Crops
SEPARATION OF THE EFFECTS OF DROUGHT AND INFECTION BY PHYTOPHTHORA CINNAMOMI ON ‘HASS’ AVOCADO |
| Authors: | June M. Nevin, Irving L. Eaks, Carol J. Lovatt, Howard D. Ohr |
| Abstract:
Water-deficit stress resulted in a statistically significant increase in the NH3-NH4+ content of leaves of ‘Hass’ avocado scions on Mexican seedling or clonal ‘Duke 7’ rootstocks, 6 months from budding, when xylem pressure potentials were less than -1.8 MPa. Three months after inoculation, recovery of Phytophthora from well-watered Mexican seedling and clonal ‘Duke 7’ rootstocks was 60 and 40%, respectively. Xylem pressure potentials and leaf NH3-NH4+ concentrations of these trees were the same as those of the well-watered, uninoculated (control) trees. Water-deficit stress reduced the recovery of P. cinnamomi 20 and 50% for Mexican seedling and clonal ‘Duke 7’ rootstocks, respectively. For these trees, root infection by P. cinnamomi did not increase the severity of water-deficit stress nor the accumulation of NH3-NH4+ in the scions. The results provide evidence that root infection by P. cinnamomi does not cause increased NH3-NH4+ production by a direct action of the pathogen on the metabolism of the roots prior to pathogen-induced water-deficit stress. In detached leaves of the ‘Hass’ avocado, NH3-NH4+ accumulation stimulated ethylene biosynthesis. Evidence is presented suggesting that leaf damage, in part, results from an interaction of ethylene with NH3-NH4+. | |
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