PS 36-181 - Contrasting leaf water conservation strategies in adult avocado (Persea americana) scion varieties in a common garden

Background/Question/Methods

In water-limited regions, plants are experiencing more frequent and severe droughts from climate change. Subsequent changes in water availability will have a particularly strong effect on the physiological function and survivorship in long-lived crops with important habitat value. Plants have the unique ability to adjust their leaves to water restriction; key traits include turgor loss point (i.e., wilting point), cuticular conductance, and water potential. Scientific advances have allowed for the molecular breeding of species like avocado (Persea americana), which can help develop and characterize new scion and rootstock varieties. Genetic approaches can be used to greatly improve breeding efforts; however, little is known about physiological consequences relating to plant water-use and conservation strategies. Our research seeks to contrast different leaf hydraulic strategies in P. americana varieties and how they may have changed via domestication to protect their hydraulic apparatus from failure. We measured the water potential, cuticular conductance, and turgor loss point on leaves collected from Fuerte, Hass, and GEM scions of P. americana, all grafted to a common rootstock and grown in a common garden at the South Coast Research and Extension Center in Irvine, California.

Results/Conclusions

Scions differed in their leaf hydraulic responses under ambient water conditions, suggesting that Fuerte, Hass, and GEM may have evolved a diversity of ways to adjust leaf water relations to protect their hydraulic apparatus from failure. Fuerte had a more negative midday leaf water potential (Ψ_midday) of -1.58 MPa than turgor loss point (π_TLP) of -1.17 MPa, suggesting leaves adjust other hydraulic features to avoid drought-induced embolism. GEM had the opposite trend, where Ψ_midday was -1.38 MPa and π_TLP was more negative at -1.59 MPa, which may be advantageous to prevent excessive wilting. When contrasting π_TLP across varieties, we found that π_TLP was significantly less negative in Fuerte than Hass and GEM. Preliminary research indicates no significant differences in cuticular conductance across adult leaves; however, previous literature found variation in cuticular conductance on young newly expanding leaves as a major pathway for water loss in proportion to stomata conductance. Further analysis of leaf functional traits such as venation, hydraulic conductance, and stomatal conductance may help better understand how water conservation strategies across P. americana varieties are integrated and related to long-term yield. Understanding such novel phenotypic variation associated with domestication will aid science in predicting agricultural response to future drought.