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Cucumber and other Cucurbitaceae plants have a high transpiration rate and sensitivity to water deficit stress. Ascorbic acid (AsA) and gamma aminobutyric acid (GABA) participate in a variety of plant processes and increase plant resistance to different stresses. The current study was aimed to assess the efficacy of the foliar application of AsA (100, 200 and 300 mg l−1) and GABA (20 and 40 mM) on growth, physiological parameters and water use efficiency related properties of cucumber plants under deficit irrigation (DI) strategy (0, 25 and 50%). Results showed that the highest values of measured morphological properties were recorded in plants treated with GABA at 40 mM and AsA at 100 mg l−1. The highest water use efficiency was observed in plants sprayed with GABA at 40 mM. Also, foliar spraying of GABA at 40 mM was the best treatment to improve the free proline content of leaves and the activity of antioxidant enzymes under drought stress conditions. Findings of this study showed that foliar application of AsA and GABA can be a useful and inexpensive treatment to improve morphological, physiological and water use efficiency related properties of cucumber plant under water deficit stress.

Some of the most cultivated commercial cultivars of asparagus are susceptible to abiotic stresses. Different species of asparagus plant are distributed in different regions of Iran which could be useful genetic resources for applying in asparagus breeding programs. The purposes of the current study were to evaluate morphological variation of A. azerbaijanensis accessions and drought tolerance assessment of Iranian asparagus in order to introduce superior accessions. Two different accessions of A. azerbaijanensis species were collected. A number of 30 plants were selected and 22 morphological traits were then evaluated. A factorial experiment based on completely randomized design was performed in order to drought tolerance assessment of 9 Iranian asparagus accessions. The average of spear length and diameter in Ahar and Makou plants were 48.94 cm and 4.70 mm, respectively. Based on results, plants of Ahar accession produced short and thick spears but on the other hand, Makou accession plants produced longer and thinner spears. Score 8 (80% similarity rate) was averagely chosen by panel members in terms of similarity rate of A. azerbaijanensis accessions spears taste to that of Mary Washington commercial cultivar. The highest percentage of seed germination was recorded in Baladeh and Gazanak accessions (71.66 and 70.83%, respectively). Baladeh accession showed the highest carotenoid content under drought stress conditions (0.43 mg g Fw− 1). Suitable size and delicious taste of spear in A. azerbaijanensis species has made it a suitable candidate for commercial cultivation and also improving spear characteristics by using selection method. Baladeh and Gazanak accessions could be introduced as superior accessions with high drought tolerance rate. High resistance rate of these accessions can be related to their ploidy level and distribution areas characteristics.

Bacillus firmus I-1582 is approved in Europe for the management of Meloidogyne on vegetable crops. However, little information about its modes of action and temperature requirements is available, despite the effect of these parameters in its efficacy. The cardinal temperatures for bacterial growth and biofilm formation were determined. The bacteria was transformed with GFP to study its effect on nematode eggs and root colonization of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) by laser-scanning confocal microscopy. Induction of plant resistance was determined in split-root experiments and the dynamic regulation of genes related to jasmonic acid (JA) and salicylic acid (SA) by RT-qPCR at three different times after nematode inoculation. The bacteria was able to grow and form biofilms between 15 and 45 C; it degraded eggshells and colonized eggs; it colonized tomato roots more extensively than cucumber roots; it induced systemic resistance in tomato, but not in cucumber; SA and JA related genes were primed at different times after nematode inoculation in tomato, but only the SA-related gene was up-regulated at 7 days after nematode inoculation in cucumber. In conclusion, B. firmus I-1582 is active at a wide range of temperatures; its optimal growth temperature is 35 C; it is able to degrade Meloidogyne eggs, and to colonize plant roots, inducing systemic resistance in a plant dependent species manner. Thanks are given to the Spanish Ministry of Economy and Competitiveness (MINECO) for funding the AGL2013-49040- C2-1-R project, to the Ministry of Science and Innovation from the Spanish Government for funding the AGL2017-89785-R, and to the European Regional Development Fund (FEDER). MC,JA, and PL-A acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” program for Centers of Excellence in R&D (SEV-2015-0522), from Fundació Privada Cellex, Fundación Mig-Puig and from Generalitat de Catalunya through the CERCA program and Laser lab Europe through the research and innovation programme under grant agreement No. 654148

Electron transport chains (ETC) are drastically inactivated in chloroplasts of in vitro shootlets due to presence of carbon source in the growth media. This inactivation consequently creates limitations for in vitro studies on the role of chloroplasts in biotic and abiotic stresses. This research was carried out to evaluate reactivation of electron flow in chloroplasts ETC by elimination of carbon source and subsequent comparison of the effects of ETC inhibitors in the presence and absence of carbon source (i.e., sucrose) on the in vitro shootlets of apple rootstock, MM-111. All the tested ETC inhibitors, including uracil; glutaraldehyde, methyl viologen (MV) and DCMU triggered necrosis appearance on the in vitro apple shootlets exclusively on the carbon source-free media. Moreover, exposure of the in vitro shootlets to the various concentrations of ETC inhibitors demonstrated different severity of ETC inhibition by these inhibitors and their concentration-dependent effects on chloroplasts ETC. Uracil, the inhibitor of photosystem II, triggered the weakest shootlets necrosis, while DCMU exhibited no necrogenic effects at 50 mg/L and lower concentrations. MV, contrary to glutaraldehyde, did not have necrogenesis effects at 1 mg/L, but both of them caused sharp necrosis trigger on the shootlets as soon as 48–96 h after exposure to their effective concentrations. Evaluation of the shootlets H+-ATPase activity revealed that proton extrusion and pH decline in the growth media were mainly associated with the sucrose uptake by the shootlets, while no considerable pH decline observed in the presence of carbon source in the media. Finally, chloroplasts ETC activity of the shootlets was confirmed by higher percentage of O2 and less CO2 quantity in the atmospheres of the jars containing sucrose-free media, as well as by higher initial fluorescence (Fo) and maximum fluorescence (Fm) quenching parameters in the shootlets, in comparison with the sucrose-enriched condition.

Meloidogyne spp. are the most damaging plant parasitic nematodes for horticultural crops worldwide. Pochonia chlamydosporia is a fungal egg parasite of root-knot and cyst nematodes able to colonize the roots of several plant species and shown to induce plant defense mechanisms in fungal-plant interaction studies, and local resistance in fungal-nematode-plant interactions. This work demonstrates the differential ability of two out of five P. chlamydosporia isolates, M10.43.31 21 and M10.55.6, to induce systemic resistance against M. incognita in tomato but not in cucumber in split-root experiments. The M10.43.231isolate reduced infection (32%-43%), reproduction (44%-59%), and female fecundity (14.7%-27.6%), whilst the isolate M10.55.6 only reduced consistently nematode reproduction (35%-47.5%) in the two experiments carried out. The isolate M10.43.231 induced the expression of the salicylic acid pathway (PR-1 gene) in tomato roots 7 days after being inoculated with the fungal isolate and just after nematode inoculation, and at 7 and 42 days after nematode inoculation too. The jasmonate signaling pathway (Lox D gene) was also up-regulated at 7 days after nematode inoculation. Thus, some isolates of P. chlamydosporia can induce systemic resistance against root-knot nematodes but this is plant species dependent.

Attempts were made to identify eight pathogenesis related (PR) genes (i.e., PR-1a, PR3-ch1, PR3-Ch2, PR3-Ch3, PR3-Ch4, PR3-Ch5, PR-5 and PR-8) from 27 genotypes of apple, quince and pear, which are induced in response to inoculation with the pathogen Erwinia amylovora, the causal agent of fire blight. Totally, 32 PR genes of different families were obtained, excepting PR3-Ch2 (amplified only in apple) and PR3-Ch4 (amplified only in apple and pear), the others were successfully amplified in all the genotypes of apple, quince and pear. Evolutionary, the genes of each family exhibited significant homology with each other, as the corresponded phylogenetic neighbor-joining-based dendrograms were taken into consideration. Meanwhile, according to the expression assay, it was deduced that the pathogen activity can significantly affect the expression levels of some selected PR genes of PR3-Ch2, PR3-Ch4, PR3-Ch5 and particularly Cat I in both resistant (MM-111) and semi-susceptible (MM-106) apple rootstocks. Lastly, it was concluded that the pathogen E. amylovora is able to stimulate ROS response, particularly using generation of hydrogen peroxide (H2O2) in both aforementioned apple rootstock.

The use of biological control agents could be a non-chemical alternative for management of Meloidogyne spp. [root-knot nematodes (RKN)], the most damaging plant-parasitic nematodes for horticultural crops worldwide. Pochonia chlamydosporia is a fungal parasite of RKN eggs that can colonize endophytically roots of several cultivated plant species, but in field applications the fungus shows a low persistence and efficiency in RKN management. The combined use of P. chlamydosporia with an enhancer could help its ability to develop in soil and colonize roots, thereby increasing its efficiency against nematodes. Previous work has shown that chitosan enhances P. chlamydosporia sporulation and production of extracellular enzymes, as well as nematode egg parasitism in laboratory bioassays. This work shows that chitosan at low concentrations (up to 0.1 mg ml-1) do not affect the viability and germination of P. chlamydosporia chlamydospores and improves mycelial growth respect to treatments without chitosan. Tomato plants irrigated with chitosan (same dose limit) increased root weight and length after 30 days. Chitosan irrigation increased dry shoot and fresh root weight of tomato plants inoculated with Meloidogyne javanica, root length when they were inoculated with P. chlamydosporia, and dry shoot weight of plants inoculated with both P. chlamydosporia and M. javanica. Chitosan irrigation significantly enhanced root colonization by P. chlamydosporia, but neither nematode infection per plant nor fungal egg parasitism was affected. Tomato plants cultivated in a mid-suppressive (29.3 ± 4.7% RKN egg infection) non-sterilized clay loam soil and irrigated with chitosan had enhanced shoot growth, reduced RKN multiplication, and disease severity. Chitosan irrigation in a highly suppressive (73.7 ± 2.6% RKN egg infection) sterilized-sandy loam soil reduced RKN multiplication in tomato. However, chitosan did not affect disease severity or plant growth irrespective of soil sterilization. Chitosan, at an adequate dose, can be a potential tool for sustainable management of RKN. This research was funded by two grants from the Spanish Ministry of Economy and Competitiveness (AGL 2013-49040-C2-1-R and AGL2015-66833-R,) and by a Ph.D. fellowship from the University of Alicante to NE (UAFPU2011). Part of this work was filed for a patent (P201431399) by LL-L, FL-M, and NE as inventors.

Fire blight is an important disease of pome fruits, especially pears and quinces. Substitution of susceptible with tolerant cultivars is an economically and technically effective control method. Identifying tree traits associated with disease tolerance, may be helpful to screening and breeding programs, as well as genetic studies of resistance. Disease tolerance was evaluated in the national pear collection of SPII in two main categories of 8 and 20 indigenous commercial cultivars. The disease severity was evaluated using the USDA index in two successive epidemic years. 83 vegetative and reproductive traits were considered based on International Union for the Protection of New Varieties of Plants (UPOV) descriptor in all pears. Cultivars ‘Dar Gazi’ and ‘Tashkandi’ demonstrated the highest resistance level among tested cultivars. Among evaluated traits, 15 out of 83 were correlated with disease resistance. Among tree traits that were correlated to the disease resistance, 7 traits were from flowers, the main entrance of pathogen into the host. Low branching, fruit ripening variation, shape of leaf apex and number of buds in the clusters demonstrated the strongest correlation with disease tolerance; followed by other traits such as sepal color of immature fruits, fruit juiciness, size of flower and leaf, and pedicle length. The significant correlated traits could be useful as morphological or physiological markers in breeding programs.

Research has demonstrated that the interaction between HrpN and the mitochondrial electron transport chain (ETC) causes the generation of the reactive oxygen species (ROS) and an oxidative burst in host cells. To date, the interaction between bacterial infection and host chloroplasts has not been studied. This research was carried out to study the role of chloroplast ETC in this interaction in two host species, apple (Malus x domestica Borkh.) and pear (Pyrus communis L.). Accordingly, apple rootstocks, 'MM-111' (tolerant) and 'MM-106' (susceptible) and pear cultivars, 'Harrow Sweet' (tolerant) and 'Spadona' (susceptible) were micropropagated. Uracil was used as chloroplast ETC inhibitor at the presence and absence of sucrose to compare effects of ETC inhibition both in low and high photosynthesis activity of in vitro shootlets. E. amylovora Ea273 was used for basal inoculation of shootlets and the disease progression was studied by establishing necrosis indices. The in vitro system was initially optimized on 'MM-111' apple. Shoots were exposed to uracil prior to inoculation, in the absence of sucrose to separated herbicide effects of uracil from bacterial necrosis in ETC activated chloroplasts. Uracil on activated ETC chloroplasts and in the presence of E. amylovora, delayed necrosis appearance, the visible symptoms of oxidative burst in shootlets of both hosts. Uracil presence significantly reduced ROS generation during pathogen-host interaction, and ROS generation corresponded with the appearance of necrosis in all cultivars.

Erwinia amylovora is a necrogenic bacterium, causing the fire blight disease on many rosaceous plants. Triggering oxidative burst by E. amylovora is a key response by which host plants try to restrain pathogen spread. Electron transport chain (ETC) of chloroplasts is known as an inducible source of reactive oxygen species generation in various stresses. This research was performed to assess the role of this ETC in E. amylovora–host interaction using several inhibitors of this chain in susceptible and resistant apple and pear genotypes. All ETC inhibitors delayed appearance of disease necrosis, but the effects of methyl viologen, glutaraldehyde, and DCMU were more significant. In the absence of inhibitors, resistant genotypes showed an earlier and severe H2O2 generation and early suppression of redox dependent, psbA gene. The effects of inhibitors were corresponding to the redox potential of ETC inhibitory sites. In addition, delayed necrosis appearance was associated with the decreased disease severity and delayed H2O2 generation. These results provide evidences for the involvement of this ETC in host oxidative burst and suggest that chloroplast ETC has significant role in E. amylovora–host interaction.