The pattern of change in the endogenous levels of several plant hormones and hydroxycinnamic acids in addition to growth and photosynthetic performance was investigated in banana plants (Musa acuminatacv. “Grand Nain”) subjected to various cycles of drought. Water stress was imposed by withholding irrigation for six periods with subsequent rehydration. Data showed an increase in abscisic acid (ABA) and indole-3-acetic acid (IAA) levels, a transient increase in salicylic acid (SA) concentration, and no changes in jasmonic acid (JA) after each period of drought. Moreover, the levels of ferulic (FA) and cinnamic acids (CA) were increased, and plant growth and leaf gas exchange parameters were decreased by drought conditions. Overall, data suggest an involvement of hormones and hydroxycinnamic acids in plant avoidance of tissue dehydration. The increase in IAA concentration might alleviate the senescence of survival leaves and maintained cell elongation, and the accumulation of FA and CA could play a key role as a mechanism of photoprotection through leaf folding, contributing to the effect of ABA on inducing stomatal closure. Data also suggest that the role of SA similarly to JA might be limited to a transient and rapid increase at the onset of the first period of stress.

Salinity is a serious threat for global agriculture, especially in arid and semi-arid regions where its incidence leads to considerable damages in the crop growth and production. Carica papaya L. is currently one of the most cultivated fruit crops in the tropical and subtropical areas, and generally, papaya cultivars exhibit a moderate sensitivity to salinity, although such responses may depend on the genotypes. In the present study, papaya seedlings were subjected to salt stress (100 mM NaCl) for 41 d and to exogenous gibberellic acid (GA₃; 0.1 mM) and proline (10 mM) pretreatments to evaluate plant physiological variables linked to stress responses. Analysis of the data (P < 0.05) showed a general decrease of plant growth parameters induced by solely salt stress compared to control, such as stem height (47%) and thickness (33%) and plant fresh and dry mass (84% and 83%, respectively), as well as a reduction in the stomatal opening (93%), chlorophylls (40%) and carotenoids (71%) concentration. By contrast, a significant increase was found in foliar and radicular proline levels under stress (87% and 47%). Exogenous foliar GA₃ or proline respectively induced a better performance of plants under salt stress by increasing stomatal conductance (444% or 350%), stem height (142% or 144%) and plant biomass (49% or 41%) regarding solely stressed plants, and leading to pigments concentrations close to those from control plants. The results suggest that exogenous gibberellic acid and proline as growth regulator and osmo-regulator solute, respectively could increase papaya seedlings adaption against salt stress.

The current genotypes of Carica papaya L. cultivated worldwide are considered relatively tolerant or sensitive to drought conditions, depending specifically on the cultivar features and the severity of water shortage. In this work an experimental field was established by subjecting “Intenzza” and “Siluet” to the following water regimes: Control (“CT”), plants irrigated at field capacity (100%); Moderate Deficit Irrigation (“MDI”, watered at 66%); and Severe Deficit Irrigation (“SDI”, watered at 50%). The results indicated that water deficit decreases leaf number leading to a decline of total leaf area, being “Intenzza” equally affected by “SDI” and “MDI”, whereas in “Siluet” the major decrease was induced by “SDI”. Regarding fruit development, in “Intenzza”, “MDI” and “SDI” did not affect fruit number except two dates (120 and 202 DAT), decreased fruit fresh weight (FW), and increased total soluble solutes (TSS) levels, while in “Siluet” only “SDI” reduced fruit FW and watering systems did not change TSS, suggesting a better performance of this cultivar under “MDI”. In addition, drought did not impair fruit mineral concentrations excepting in few dates, and in such cases stressed fruits accumulated a slight minor or even major concentration of some nutrients than control, maintaining consequently suitable organoleptic quality.

Generally, water deficit induces a negative impact on vegetative growth and physiological and biochemical processes in Carica papaya L. However, the effects of drought magnitude and duration may be dependent on the ability of the genotype to activate mechanisms of defense against the imposed stress. Thus, the purpose of this research was to investigate the effectiveness of adding salicylic acid (SA) to the root system via irrigation against water stress. To assess the morphological and physiological responses of papaya to drought stress, seedlings were exposed to a regulated deficit irrigation system combined with the addition of SA to their irrigation water for 44 days. Results showed that water shortage inhibited papaya growth through the reduction in functional leaf number (27%), fresh (13%) and dry weights (17%), and stem width (9%). Moreover, water scarcity significantly decreased stomatal conductance (48%) and chlorophyll content (21%) and increased proline production (31%). Nevertheless, the exogenous application of SA relieved the effects of water stress on these characteristics, yielding similar values to those from control plants. Therefore, these findings prove the effectiveness of SA applied via irrigation in alleviating papaya damage under water deficit by preserving growth, stomatal conductance, photosynthetic pigments, and proline levels.

The current lack of natural water resources, mainly due to the absence of sufficient precipitation and the deterioration of irrigation water (IW) quality, urgently requires a search for alternative resources, especially in arid and semiarid areas. Desalination of sea water is well established in numerous regions where water is scarce. To investigate the effects of the combination of regular fresh water and desalinated sea water (DSW) on mineral nutrient changes in crops, an experimental system based on Musa acuminata AAA plants was performed in Frontera (El Hierro, Canary Islands). Data showed that banana crops irrigated with a mixture of fresh water and DSW exhibited an adequate nutritional status and did not suffer any injuries of salt ions (Na⁺ and Cl⁻) or B toxicity. Moreover, plants may tolerate higher concentrations of these elements and a major supply of the other essential micronutrients. The obtained results suggest that irrigating crops with a combination of fresh water and DSW is a good strategy to respond to the high water requirements, at least under the tested experimental conditions. This strategy could be very helpful in arid regions, as well as in other areas where precipitation is seasonal and scarce, like the Mediterranean or the Canaries.