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Abiotic stress represents a main constraint for agriculture, affecting plant growth and productivity. Drought and soil salinity, especially, are major causes of reduction of crop yields and food production worldwide. It is not unexpected, therefore, that the study of plant responses to abiotic stress and stress tolerance mechanisms is one of the most active research fields in plant biology. This Special Issue compiles 22 research papers and 4 reviews covering different aspects of these responses and mechanisms, addressing environmental stress factors such as drought, salinity, flooding, heat and cold stress, deficiency or toxicity of compounds in the soil (e.g., macro and micronutrients), and combination of different stresses. The approaches used are also diverse, including, among others, the analysis of agronomic traits based on morphological characteristics, physiological and biochemical studies, and transcriptomics or transgenics. Despite its complexity, we believe that this Special Issue provides a useful overview of the topic, including basic information on the mechanisms of abiotic stress tolerance as well as practical aspects such as the alleviation of the deleterious effects of stress by different means, or the use of local landraces as a source of genetic material adapted to combined stresses. This knowledge should help to develop the agriculture of the (near) future, sustainable and better adapted to the conditions ahead, in a scenario of global warming and environmental pollution.

Wall rocket is a leafy vegetable with pungent flavor related to the presence of isothiocyanates (ITCs). Despite interest in it as a crop of high organoleptic quality, the variability of the volatile profile in the species remains unknown. Twenty-four populations grown under a greenhouse were evaluated. A considerable diversity for the total levels of volatiles was found, providing information of the aroma intensity among accessions. ITCs represented the main fraction. Allyl ITC was the main compound, and levels showed up to 6-fold difference among populations. The esters fraction was mainly represented by cis-3-hexenyl isovalerate and cis-3-hexenyl butyrate, with 20-fold differences among populations. Additionally, the content in sinigrin was evaluated as main GSL in wall rocket. Differences reached up to 13-fold. These results suggest that some populations can be used to develop highly pungent varieties, whereas some others can be selected for mild-pungent varieties, as it is the case of DER045 with low levels of ITCs and high in esters. The presence of several ITCs in the profile also suggested the presence of other novel GSLs. Overall, the work increases the knowledge in the variability of wall rocket for the volatile profile and sinigrin accumulation, a starting point for future breeding programs.

Agriculture will face many challenges regarding food security and sustainability. Improving phosphorus use efficiency is of paramount importance to face the needs of a growing population while decreasing the toll on the environment. Pepper (Capsicum spp.) is widely cultivated around the world; hence, any breakthrough in this field would have a major impact in agricultural systems. Herein, the response to phosphorus low-input conditions is reported for 25 pepper accessions regarding phosphorus use efficiency, biomass and root traits. Results suggest a differential response from different plant organs to phosphorus starvation. Roots presented the lowest phosphorus levels, possibly due to mobilizations towards above-ground organs. Accessions showed a wide range of variability regarding efficiency parameters, offering the possibility of selecting materials for different inputs. Accessions bol_144 and fra_DLL showed an interesting phosphorus efficiency ratio under low-input conditions, whereas mex_scm and sp_piq showed high phosphorus uptake efficiency and mex_pas and sp_bola the highest values for phosphorus use efficiency. Phosphorus low-input conditions favored root instead of aerial growth, enabling increases of root total length, proportion of root length dedicated to fine roots and root specific length while decreasing roots’ average diameter. Positive correlation was found between fine roots and phosphorus efficiency parameters, reinforcing the importance of this adaptation to biomass yield under low-input conditions. This work provides relevant first insights into pepper’s response to phosphorus low-input conditions.

Eggplant (Solanum melongena) has been described as moderately sensitive to salinity. We characterised the responses to salt stress of eggplant and S. insanum, its putative wild ancestor. Young plants of two accessions of both species were watered for 25 days with an irrigation solution containing NaCl at concentrations of 0 (control), 50, 100, 200, and 300 mM. Plant growth, photosynthetic activity, concentrations of photosynthetic pigments, K+, Na+, and Cl− ions, proline, total soluble sugars, malondialdehyde, total phenolics, and total flavonoids, as well as superoxide dismutase, catalase, and glutathione reductase specific activities, were quantified. Salt stress-induced reduction of growth was greater in S. melongena than in S. insanum. The photosynthetic activity decreased in both species, except for substomatal CO2 concentration (Ci) in S. insanum, although the photosynthetic pigments were not degraded in the presence of NaCl. The levels of Na+ and Cl− increased in roots and leaves with increasing NaCl doses, but leaf K+ concentrations were maintained, indicating a relative stress tolerance in the two accessions, which also did not seem to suffer a remarkable degree of salt-induced oxidative stress. Our results suggest that the higher salt tolerance of S. insanum mostly lies in its ability to accumulate higher concentrations of proline and, to a lesser extent, Na+ and Cl−. The results obtained indicate that S. insanum is a good candidate for improving salt tolerance in eggplant through breeding and introgression programmes.

Capsicum peppers (Capsicum spp.), especially C. annuum L., are one of the most important vegetables and spices in the world and their fruits are used in a range of food dishes, to provide aroma and flavor. Pungency has been largely studied, while studies on the volatile fraction are more recent and less diverse. A considerable varietal diversity among peppers has been reported in terms of the aroma quality and the qualitative and quantitative variation in the volatile fraction, particularly in fully ripe fruits, which encompass most diverse food applications and aroma profiles. Thus, a study was designed to study the inheritance of the volatile fractions in peppers and to determine if they can be improved by breeding strategies. The volatile fraction of 175 samples of ripe fruits from a diverse collection of peppers, encompassing a range of varietal types and aroma qualities, were isolated by headspace-solid-phase microextraction (HS-SPME) and analyzed by gas chromatography–mass spectrometry (GC–MS). A diverse profile of volatiles including terpenoids, esters, alkanes, and several aldehydes and alcohols, was found among the evaluated accessions. Our findings indicated that, in most cases, hybridization provided higher amounts of total volatiles and a more complex composition, particularly in the pericarp. In addition, the volatile fraction can be inherited from the parents to the offspring, as most individual volatiles in hybrids, especially major volatiles, were present in at least one of the parents, following intermediate (levels between parents) or transgressive (levels higher than the best parent) inheritance. De novo compounds (present in the hybrid, absent in the parents) were found in many samples. Comparatively, placental tissues had higher total and individual volatile levels compared with the pericarp in most parent accessions and hybrids, which must be considered by breeders if this part of the fruit is included in food formulations. By combining parent lines with complementary volatile fractions, hybridization offers a feasible method to improve the volatile composition of ripe fruits in Capsicum peppers.

Wall rocket is a wild vegetable with interest to become a crop. However, the information regarding morphological variability in the species is scarce, despite the interest it has received for breeding programs. In addition, evaluating the phytochemical composition can also be useful for developing materials of a high quality. In this study, forty-four populations were evaluated for selected morphoagronomic traits and contents in ascorbic acid (AA), total phenolics (TP), and nitrates (NO3−). Wall rocket plants had, on average, an intermediate growth habit and a good response to transplant. Moderate variability, mainly for size-related traits, was found, with low to moderate heritability estimates (H2 < 0.35). A Principal Component Analysis revealed that some materials may be selected for differenced traits. On the other hand, wall rocket materials had, on average, high contents in AA (53 mg 100 g−1) and TP (116 mg CAE 100 g−1) but also accumulated high levels of NO3− (891 mg 100 g−1). Significant positive correlations were found for AA and TP, which could be exploited for increasing the antioxidant activity and properties of the final product. We provide new information on the variation of wall rocket for traits of morphological and phytochemical interest, which together with other traits, such as the profile of glucosinolates, can be useful for the selection of materials in future breeding programs.