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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.

International audience; The high diversity of tropical forests complicates predictions of how canopy trees and lianas will respond to drought. Detail ed physiological measurements are necessary to improve predictions, yet these measurements are tedious and time-consuming, so relatively little data is available. The DROUGHT Project, initiated in 2016, aims to elucidate how hydraulic traits related to drought vulnerability are coordinated among canopy species across the Neotropics by increasing the scope of data available. Method: So far, we have performed detailed measures of hydraulic conductivity, xylem vulnerability curves, sapwood pressure-volume curves, and wood density on emergent branches of 35 common liana and tree species from French Guiana and Panama. Our measurements were stratified across a broad range of wood density. Objectives included determining the range of hydraulic traits, evaluating coordination among hydraulic traits to identify strategies, and providing trait values for inclusion in predictive models. Result: Wood density was correlated with sapwood pressure-volume traits, including capacitance, sapwood water content and turgor loss point. Xylem hydraulic conductivity was related to xylem vulnerability to embolism at some sites, but not others, indicating variation in the xylem safety versus efficiency trade-off. Relationships between wood density and xylem vulnerability to embolism varied among sites. In general, wood density showed greater correlation with sapwood pressure-volume traits than with xylem vulnerability to embolism. Conclusion: Detailed physiological traits offer a way forward for predicting tropical liana and tree responses to drought. An understanding of the trade-offs and coordinated functions that separate tropical canopy species along an axis of drought vulnerability may be an important component for parameterizing Earth system models.

The high diversity of tropical forests complicates predictions of how canopy trees and lianas will respond to drought. Detail ed physiological measurements are necessary to improve predictions, yet these measurements are tedious and time-consuming, so relatively little data is available. The DROUGHT Project, initiated in 2016, aims to elucidate how hydraulic traits related to drought vulnerability are coordinated among canopy species across the Neotropics by increasing the scope of data available. Method: So far, we have performed detailed measures of hydraulic conductivity, xylem vulnerability curves, sapwood pressure-volume curves, and wood density on emergent branches of 35 common liana and tree species from French Guiana and Panama. Our measurements were stratified across a broad range of wood density. Objectives included determining the range of hydraulic traits, evaluating coordination among hydraulic traits to identify strategies, and providing trait values for inclusion in predictive models. Result: Wood density was correlated with sapwood pressure-volume traits, including capacitance, sapwood water content and turgor loss point. Xylem hydraulic conductivity was related to xylem vulnerability to embolism at some sites, but not others, indicating variation in the xylem safety versus efficiency trade-off. Relationships between wood density and xylem vulnerability to embolism varied among sites. In general, wood density showed greater correlation with sapwood pressure-volume traits than with xylem vulnerability to embolism. Conclusion: Detailed physiological traits offer a way forward for predicting tropical liana and tree responses to drought. An understanding of the trade-offs and coordinated functions that separate tropical canopy species along an axis of drought vulnerability may be an important component for parameterizing Earth system models.

Annona muricata (guanábana) es una planta cultivada por la calidad nutritiva y organoléptica de su fruto. No obstante el carácter recalcitrante de las yemas vegetativas de esta especie ha dificultado la micropropagación de material seleccionado por su alta productividad. Esta investigación tuvo como objetivo evaluar medios de cultivo combinados con la técnica de microinjertación seriada para promover el desarrollo vegetal in vitro de A. muricata. En medios de cultivo específicos para cada material vegetal, se sembraron semillas y estacas para la formación de microinjertos; luego se aplicaron tres tratamientos de microinjertación (M1, M2, M3) y un control, donde el número indica las veces en las que una estaca es injertada en un portainjerto. M1 es una microinjertación monofásica o estacas microinjertadas en un portainjerto. M2 son estacas microinjertadas dos veces, es decir, permanecen en dos portainjertos diferentes con un lapso de un mes entre cada traspaso. M3 son estacas microinjertadas tres veces, es decir, permanecen en tres portainjertos diferentes con un lapso de un mes entre cada traspaso. Las estacas fueron separadas del portainjerto y sembradas en medio de cultivo para evaluar su revigorización; se realizaron pruebas de Anova y Freedman para los datos paramétricos y no paramétricos, respectivamente. Los resultados indicaron que la microinjertación monofásica es suficiente para estimular el desarrollo in vitro de material adulto de A. muricata; sin embargo, en los tratamientos no se logró el desarrollo de un sistema radicular adecuado. Annona muricata is grown due to the nutritional and organoleptic quality of the fruit. The recalcitrance of the vegetative buds of this species has hindered the micropropagation of selected material according to its high productivity. This research aimed to evaluate culture medium combined with the technique of serial micrografting to promote in vitro plant growth of Annona muricata. In specific culture media for each plant material, seeds and cuttings were planted for the formation of micrografts. Three micrografting treatments were applied (M1, M2, M3) and a control, where the number indicates the times when a shoot is micrografted onto a rootstock. M1 is a monophasic micrografting or cuttings micrografted in one rootstock. M2 are micrografted cuttings for two times, that is, these remain on two different rootstocks with a lapse of one month between each transfer. M3 are micrografted cuttings three times, that is, these remain in three different rootstocks with a lapse of one month between each transfer. The shoots were separated from the rootstock and planted in culture medium to assess their reinvigoration, ANOVA and Freedman tests were performed for parametric and nonparametric data respectively. The results indicated that the monophasic micrografting is sufficient to stimulate the in vitro development of adult material of Annona muricata; however, none of the treatments was able to develop a root system in the shoots.