Coffea canephora genotypes adopt distinct strategies to cope with drought and rehydration. We hypothesized that the greater drought tolerance of genotype ‘3V’ compared to ‘A1’, previously reflected in physiological and anatomical leaf traits after two water-stress (WS) cycles, could also be observed in P–V curve responses, root and branch anatomy, leaf midrib elongation (CVL), and root distribution. The ‘3V’ and ‘A1’ plants were grown under well-watered (WW) conditions and two cycles of water stress (WS). The ‘3V’ was more sensitive to WS, with reduced branch xylem vessel density (BXVD), while ‘A1’ demonstrated increased BXVD. Root xylem vessel area (RXVA) decreased to a greater extent in ‘3V’ than in ‘A1’, and both genotypes showed increased bulk elastic modulus. Regardless of water conditions, ‘A1’ maintained a higher relative leaf water content at the turgor loss point (RWC_TLP). Morphological acclimation did not occur in the second WS cycle. The ‘3V’ plants developed greater root mass in deeper soil layers than ‘A1’ under the WS condition. These findings suggest that ‘A1’ follows a conservative drought-avoidance strategy with lower physio-morphological plasticity, while ‘3V’ exhibits greater drought tolerance. Such responses highlighted coordinated physiological, morphological, and anatomical adaptations of the above- and below-ground organs for resource acquisition and conservation under WS.

Understanding the dynamics of physiological changes involved in the acclimation responses of plants after their exposure to repeated cycles of water stress is crucial to selecting resilient genotypes for regions with recurrent drought episodes. Under such background, we tried to respond to questions as: (1) Are there differences in the stomatal-related and non-stomatal responses during water stress cycles in different clones of Coffea canephora Pierre ex A. Froehner? (2) Do these C. canephora clones show a different response in each of the two sequential water stress events? (3) Is one previous drought stress event sufficient to induce a kind of “memory” in C. canephora? Seven-month-old plants of two clones (’3V’ and ‘A1’, previously characterized as deeper and lesser deep root growth, respectively) were maintained well-watered (WW) or fully withholding the irrigation, inducing soil water stress (WS) until the soil matric water potential (Ψ_msoil) reached ≅ −0.5 MPa (−500 kPa) at a soil depth of 500 mm. Two sequential drought events (drought-1 and drought-2) attained this Ψ_msoil after 19 days and were followed by soil rewatering until a complete recovery of leaf net CO₂ assimilation rate (A_net) during the recovery-1 and recovery-2 events. The leaf gas exchange, chlorophyll a fluorescence, and leaf reflectance parameters were measured in six-day frequency, while the leaf anatomy was examined only at the end of the second drought cycle. In both drought events, the WS plants showed reduction in stomatal conductance and leaf transpiration. The reduction in internal CO₂ diffusion was observed in the second drought cycle, expressed by increased thickness of spongy parenchyma in both clones. Those stomatal and anatomical traits impacted decreasing the A_net in both drought events. The ‘3V’ was less influenced by water stress than the ‘A1’ genotype in A_net, effective quantum yield in PSII photochemistry, photochemical quenching, linear electron transport rate, and photochemical reflectance index during the drought-1, but during the drought-2 event such an advantage disappeared. Such physiological genotype differences were supported by the medium xylem vessel area diminished only in ‘3V’ under WS. In both drought cycles, the recovery of all observed stomatal and non-stomatal responses was usually complete after 12 days of rewatering. The absence of photochemical impacts, namely in the maximum quantum yield of primary photochemical reactions, photosynthetic performance index, and density of reaction centers capable of Q_A reduction during the drought-2 event, might result from an acclimation response of the clones to WS. In the second drought cycle, the plants showed some improved responses to stress, suggesting “memory” effects as drought acclimation at a recurrent drought.

Boron (B) deficiency is commonly found in tropical crops, among which sorghum stands out for its limited yield under B shortage. However, as a micronutrient, the range between its adequate and toxic levels is narrow, thus fertilization should be cautiously applied. Our goal was to evaluate the physiological and physical quality, as well as early performance, of grain sorghum seedlings under different B doses applied via seeds. Treatments consisted of six doses of boric acid (0.0, 2.5, 5.0, 7.5, 10.0, and 12.5 g Kg-1 seeds) plus a control (uncoated seeds). Boron doses were applied to seeds by coating, in which dolomitic limestone and glue were used for pellet formation. Coated seeds were assessed for physical, physiological, and nutritional characteristics in the laboratory, and early seedling performance was evaluated in a greenhouse. Seed tests were carried out in a fully randomized design, while seedling evaluations were carried out in a randomized block design. Boron application to seeds had no significant effect on seed physical characteristics, despite increases in coated seed sizes. Boron doses had a negative effect on the length and dry mass accumulation of both plant shoot and root. Seed-applied B accumulated mainly in roots and significantly interfered with Ca and Mg accumulations in sorghum seeds, shoots, and roots.

Coffea canephora cultivation areas in Brazil are frequently exposed to successive cycles of water deficit, triggering plant stress responses. In addition to water deficit, increased air temperature can act as a second stress factor. The recurrence of these stress factors may induce plant tolerance mechanisms, potentially mitigating future stress responses even of a different stress nature. We hypothesized that repeated cycles of water deficit can trigger tolerance mechanisms that make C. canephora leaves more resilient to supra-optimal temperatures. To test this hypothesis, young C. canephora plants were grown under non-limited water conditions for seven months (Ψ_mSoil > −20 kPa), after which they were subjected to two consecutive cycles of water deficit (Ψ_mSoil < −300 kPa), followed by rehydration. Two clones were used, ‘A1’ and ‘3V’, previously classified as drought sensitive and tolerant, respectively, considering the dynamics of physiological and architectural responses. After the second cycle, leaf discs were collected from completely expanded leaves formed during the two stress cycles and exposed to heat treatments (35 °C, 40 °C, 45 °C, 50 °C, and 55 °C) for 15 min in a water bath. Chlorophyll a fluorescence emission was then monitored, and the results were analyzed using OJIP transient kinetics and the JIP_Test. High temperatures induced negative changes in both OJIP kinetics and JIP_Test-derived parameters. A significant increase in F₀ and a reduction in F_M were observed mainly at 50 °C and 55 °C, due to changes in the stages of the OJIP curve. These changes impacted the “energy connectivity” and consequently the electron transport along the electron transfer chain (ETC), increasing energy dissipation, as confirmed by the JIP_Test variables. Despite the high temperature impacts, previous water deficit induced heat tolerance in clone ‘A1’, while it increased sensitivity in clone ‘3V’. This study suggests that selecting drought-resistant varieties should consider their subsequent response to short high-temperature stress to avoid cross-sensitivity caused by selecting for a single environmental factor.

UV radiation drives adaptation and acclimation via biochemical and physiological mechanisms. UV is a relevant environmental signal that modulates plant physiology, while excessive UV acts as a stress factor. To test the ability of Coffea canephora to acclimate to UV levels, young coffee plants were cultivated for six months in a mini greenhouse under either near ambient (UVam) or reduced (UVre) UV conditions. Afterwards, analyses of the changes in metabolic reprogramming and in UV-response proteins from leaf proteome profile were performed, including antioxidant enzymes (e.g., ascorbate peroxidase, APX;, Cu,Zn-superoxide dismutase, Cu,Zn-SOD; glutathione reductase, GR; catalase, CAT), and proteins involved in repair, folding, and detoxification. UVam exposure induced the highest CAT and GR activities, but lower APX activity, suggesting a shift in ROS detoxification strategies, while Cu,Zn-SOD activity remained unchanged. The 817 proteins identified by proteomic analysis were categorized into: (1) accumulation patterns of the isoforms of the analyzed antioxidant enzymes, and (2) proteins involved in critical responses. Specific antioxidant isoforms reinforced the suggested mitigation of oxidative damage at UVam exposure, even though several isoforms remained unchanged. Comparative analysis identified 61 accumulated proteins, of which 31 were up-accumulated and 30 were down-accumulated between UVam/UVre comparison. These findings indicated that UVre conditions favored cellular homeostasis and energy conservation, whereas UVam induced proteomic shifts that support UV acclimation responses. Overall, the study revealed how C. canephora fine-tunes its antioxidant and proteostatic systems in response to UV variation, offering new insights into the molecular basis of acclimation in tropical crops.

The investigation of genotype behavior under varying conditions is conducted to maximize selection gains in coffee breeding programs, aiming to identify genotypes that sustain good performance across different environments and years. The objective of this study was to estimate the magnitudes of the effects of genotype and year on seed and seedling traits of Coffea canephora . 43 C. canephora genotypes were evaluated for the physical and physiological traits of seeds and seedlings during two crop years (2019 and 2020). Both individual and joint analyses were performed to obtain estimates of genetic parameters and the effects of genotype, year, and genotype × year interaction. Individual analyses identified significant differences ( p ≤ 0.01) among genotypes for all traits in both evaluated years. The year effect was significant for all variables except germination, whereas the interaction significantly impacted all traits. The proportion of simple interactions exceeded that of complex ones for germination speed index (GSI), area, roundness, circumference, and thousand seed weight (TSW). The complex interaction was predominant over simple ones for germination and shoot (SL) and root lengths, reaching 97.79% of the total interaction. Genotypes Bicudo, Penirão e Pirata showed good performed for TSW and SL, with little variation in the averages between the years. Bamburral exhibited average performance and least variation between years. The significant effect of year was attributed to the genotype effect rather than climatic differences. Therefore, the selection of superior C. canephora materials for seed traits should consider the average performance of the genotypes across different years.