SEPARATION OF THE EFFECTS OF DROUGHT AND INFECTION BY PHYTOPHTHORA CINNAMOMI ON ‘HASS’ AVOCADO

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⁺.

International Symposium on the Culture of Subtropical and Tropical Fruits and Crops

June M. Nevin, Irving L. Eaks, Carol J. Lovatt, Howard D. Ohr

https://doi.org/10.17660/ActaHortic.1990.275.91