UC Riverside

The challenge to produce more food under sustainable agricultural practices is to develop more efficient systems in the use of natural resources, avoiding agrochemical contamination, and prediction of yield under a changing environment. This dissertation has focused on providing information of the physiological and floral gene expression behavior of avocado trees under different environmental conditions building upon three different chapters: (1) the identification of water-use efficient avocado varieties using leaf carbon isotopic composition (δ 13C), (2) the analysis of the physiological behavior of salinity-tolerant avocado rootstocks, and (3) the analysis of the effects of temperature, soil moisture, and light intensity on the temporal pattern of floral gene expression and floral intensity in avocado.

In the first chapter, we found carbon isotope composition measurements to be useful for identifying water-use efficient plants. In the second chapter, the relationship between the physiological performance, health and productivity of avocado exposed to a salinity treatment is described. Low photosynthetic rate and canopy damage describe the effect of salinity on avocado yield. In the third chapter, we successfully identified the gene expression profile of putative floral genes when avocado flowering is promoted by low temperature. The results from the floral gene expression analysis in avocado suggest that the significantly greater bud expression levels of LFY and AP1/FUL promoted by low temperature were sufficient to confer bud determination, since transferring the trees from low to warm temperatures did not prevent flowering. Overall, the first two chapters successfully allowed the identification of trees or cultivars that are saline tolerant or water-use efficient while the gene expression analysis showed how the expression of putative floral genes are coordinated with bud determination, suggesting a role during the reproductive development in P. americana.