PHYSIOLOGICAL AND PRODUCTIVITY ATTRIBUTES OF AMAZONIAN ROBUSTAS (Coffea canephora) CULTIVATED IN RONDÔNIA, BRAZIL

Abstract

The coffee (Coffea canephora) cultivation is one of the main economic activities in the state of Rondônia, in Brazilian Amazon, however, there is a lack of studies about physiology and ecophysiology aspects of the cultivated genotypes. The objective of the research in this thesis was to study physiological parameters of coffee trees cultivated in Rondônia and their implications for management and production. Two different works were carried out. In one of them, we explored how variations in morphoanatomical and physiological leaf traits can explain differences in yield and vulnerability to embolism in eleven Coffea canephora genotypes cultivated in Rondônia state. It was observed that higher efficiency in water transport (Kleaf) was strongly related to an increase in A, revealing a diffusive limitation to photosynthesis associated with hydraulic restrictions. All genotypes showed a narrow or negative hydraulic safety margin (HSM), suggesting a high leaf vulnerability to drought-induced mortality (DIM) under non-irrigated conditions, especially on the most productive genotypes. Modeling exercises revealed that variations in DIM across genotypes were associated with differences in leaf and canopy water leaks, as a reflex of their contrasting growth strategies. In the other study the seasonal variation of parameters associated with photosynthesis was studied. The study was carried out under field conditions, in the municipality of Rolim de Moura. Variables of gas exchange, chlorophyll a fluorescence and pigment index of three genotypes (clones 03, 08 and 25), cultivated in three cropping systems (fertigated, irrigated and dryland farming), were evaluate at four times throughout the production cycle (peak drought, onset of rain, rainy season, onset of drought). It was observed that there is a reduction in the net photosynthetic rate (A) in the dry period, associated with a drop in stomatal conductance (gs). Use of irrigation reduces the effect of the dry period, but it is not enough to maintain the levels of A, observed in the other seasons. In this case, the air vapor pressure deficit (DPVar) is associated with lower gs. Higher values of anthocyanin were observed in coffee leaves during the dry season. The yields obtained could not be explained by the variables obtained at the leaf level. Overall, our results provide a new perspective on the challenges of sustaining coffee production in the Amazon region under a drier and warmer climate. Amazonian Robustas reduce A with the increase in VPD, this decrease is associated with a decrease in gs. The use of localized irrigation, widely adopted in the region, mitigates, but does not prevent, the negative effect of the elevation of VPD on A. The most productive materials present higher gleaf-res, significantly reducing the time to hydraulic failure (THF) of the leaves. The selection of genotypes with greater drought tolerance is essential to anticipate the deleterious impact of water restriction predicted for the region.