Sr isotope ratio in vegetable crops and apple trees depends on that of the soil environment while is unaffected by the genotype

The 87Sr/86Sr ratio is an effective geographical tracer for horticultural products. In plants this ratio reflects closely the characteristics of the growing area. However, information about the variability of this parameter when measured in different plant species or cultivars is still scarce. In this work, we have tested the hypothesis that, when plants are growing in the same environment, their 87Sr/86Sr ratio is independent from the plant species or cultivar. For this, four to six vegetable species were collected from two fields in different locations in South Tyrol (Italy), together with the corresponding soils. Additionally, within a single apple orchard located in the same area, apple leaves were collected from trees of five cultivars. The 87Sr/86Sr ratio was measured applying an established and validated method. In general, vegetable species growing in the same field had similar 87Sr/86Sr ratios and showed a lower variability compared to their corresponding soils, while a significant difference was found comparing the 87Sr/86Sr ratios of the two vegetable fields. Apple leaves sampled from different tree cultivars also did not show a significant difference in their 87Sr/86Sr ratio. We concluded that the 87Sr/86Sr ratio in vegetables and apple trees was affected by the soil, but not significantly by the type of species or cultivar. Therefore, within limited areas, the results of the 87Sr/86Sr ratio analysis based on samples of a certain species/cultivar can be extended to other similar plants growing in the same site.

Identification of Genes Associated with Nitrogen Stress Responses in Apple Leaves

Nitrogen (N) is an essential macronutrient that regulates diverse physiological processes for plant survival and development. In apple orchards, inappropriate N conditions can cause imbalanced growth and subsequent physiological disorders in trees. In order to investigate the molecular basis underlying the physiological signals for N stress responses, we examined the metabolic signals responsive to contrasting N stress conditions (deficient/excessive) in apple leaves using transcriptome approaches. The clustering of differentially expressed genes (DEGs) showed the expression dynamics of genes associated with each N stress group. Functional analyses of gene ontology and pathway enrichments revealed the potential candidates of metabolic signals responsible for N-deficient/excessive stress responses. The functional interactions of DEGs in each cluster were further explored by protein–protein interaction network analysis. Our results provided a comprehensive insight into molecular signals responsive to N stress conditions, and will be useful in future research to enhance the nutrition tolerance of tree crops.

Genome-wide association study (GWAS) of leaf wax components of apple

The wax layer of apple leaves plays an important role in improving stress resistance, but relatively little is known about the mechanisms of wax synthesis and transport in apple leaves. In this study, 17 wax components, including alcohols, alkanes, fatty acids and terpenes, were analyzed by gas chromatography-tandem mass spectrometry (GC-MS) from the leaves of 123 apple germplasms. Whole-genome sequencing of these apple accessions yielded 5.9 million high-quality single nucleotide polymorphisms (SNPs). We performed a genome-wide association study (GWAS) on 17 wax components and identified several genes related to wax synthesis and transport, including MdSHN1 (SHINE1), MdLTP4 (LIPID TRANSFER PROTEIN4), MdWSD1 (WAX ESTER SYNTHASE/ACYL-COA DIAC-YLGLYCEROL ACYLTRANSFERASE1), MdRDR1 (RNA-DEPENDENT RNA POLYMERASE1), MdACBP6 (ACYL-COA-BINDING PROTEIN6), MdNLE (NOTCHLESS) and MdABCG21 (ATP-BINDING CASSETTE G21). Moreover, we identified some prominent SNPs that may affect gene expression and protein function. These results provide insights into mechanisms of wax synthesis and transport in apple leaves and broaden the genetic resources and basis for facilitating resistance breeding.

Nitrogen Content Estimation of Apple Leaves Using Hyperspectral Analysis

Leaf nitrogen content (LNC) is an important factor reflecting the growth quality of plants. We estimated the nitrogen content of apple leaves using hyperspectral wavelength analysis using the differential spectrum, differential spectrum transformation, and vegetation spectrum index with different derivative gaps. We then used the characteristic wavelengths extracted via the correlation coefficient method as the input vectors to the gradient boosting decision tree (GBDT) model for analysis and performed cross-validation to optimize the inversion model parameters. We analyzed the results with different input variables and loss functions and compared the GBDT model with other mainstream algorithm models. The results show that the R2 value of the optimized GBDT inversion model is higher than that obtained using the random forest (RF) and support vector regression (SVR) models. Thus, the GBDT model is accurate, and the characteristic wavelength analysis is helpful for the tasks of real-time monitoring and detection of apple tree health.

Nep1-like Proteins from Valsa mali Differentially Regulate Pathogen Virulence and Response to Abiotic Stresses

Necrosis and ethylene-inducing peptide 1(Nep1)-like protein (NLP) is well known for its cytotoxicity and immunogenicity on dicotyledonous, and it has attracted large attention due to its gene expansion and functional diversification in numerous phytopathogens. Here, two NLP family proteins, VmNLP1 and VmNLP2, were identified in the pathogenic fungus Valsa mali. We showed that VmNLP2 but not VmNLP1 induced cell death when transiently expressed in Nicotiana benthamiana. VmNLP2 was also shown to induce cell death in apple leaves via the treatment of the Escherichia coli-produced recombinant protein. VmNLP1 and VmNLP2 transcripts were drastically induced at the early stage of V. mali infection, whereas only VmNLP2 was shown to be essential for pathogen virulence. We also found that VmNLP1 and VmNLP2 are required for maintaining the integrity of cell membranes, and they differentially contribute to V. mali tolerance to salt- and osmo-stresses. Notably, multiple sequence alignment revealed that the second histidine (H) among the conserved heptapeptide (GHRHDWE) of VmNLP2 is mutated to tyrosine (Y). When this tyrosine (Y) was substituted by histidine (H), the variant displayed enhanced cytotoxicity in N. benthamiana, as well as enhanced virulence on apple leaves, suggesting that the virulence role of VmNLP2 probably correlates to its cytotoxicity activity. We further showed that the peptide among VmNLP2, called nlp25 (VmNLP2), triggered strong immune response in Arabidopsis thaliana. This work demonstrates that NLPs from V. mali involve multiple biological roles, and shed new light on how intricately complex the functions of NLP might be.

ASSESSMENT OF INTRODUCED APPLE VARIETIES BY SCAB AFFECTION (VENTURIA INAEQUALIS (COOKE) G. WINTER)

The article presents data on the identifying of apple varieties resistant to scab for their further use in breeding. The research was carried out on the basis of the Orenburg branch of the Federal Horticultural Research Center for Breeding, Agrotechnology and Nursery from 2010 to 2020 in the orchard established in 2004. The objects of research were introduced apple varieties and local hybrids. Scab (the causative agent is the marsupial mushroom Venturia inaequalis (Cooke) G. Winter) causes great damage to the apple tree. This disease affects the fruits and leaves, while dramatically reducing the apple productivity and marketability. According to the results of the studies, the greatest development of scab was observed in 2011, 2013 and 2016. In dry years (2010, 2012, 2014, 2015, 2017-2020 years) scab lesions were not observed. We have identified apple introduced varieties, which over the years of observation had a weak scab lesion and few spots on the apple leaves. In the control variant, in summer varieties in 2011, the scab on the leaves of the Serebryanoe kopytse variety was 0.9 points, all other studied varieties had a lower parameter. In autumn varieties, the varieties Sverdlovchanin and Gornist had the lowest parameter — 0.3-0.4 points, respectively, with a control parameter of 0.8 points (Prizemlennoye variety); in winter varieties, all the studied samples were lower than the control variant — 0.9 points. Weather conditions 2013 and 2016 also showed apple varieties less susceptible to scab in the conditions of the Orenburg region. As a result, we identified apple varieties that are weakly affected by scab: summer varieties — Letneye polosatoye, Mechtatel’nitsa, Solntsedar, Chudnoye; autumn varieties — resident of Sverdlovsk, Hornist; winter — Anis Sverdlovsky, Krasa Sverdlovsk, Persian. The obtained data can be used in breeding to create new apple varieties resistant to scab in the conditions of the Orenburg region.

Effects of Interval Flooding Stress on Physiological Characteristics of Apple Leaves

As a result of the continuous global warming in recent years, the average annual number of rain days in China has been on the decline, while the number of rainstorm days has gradually increased. These conditions make it extremely easy to form a waterlogging environment, which has an adverse impact on plant growth and development. In many apple-producing areas in China, apples are subject to severe flooding during planting. In this study, two-year-old apple rootstock M9T337 was used to explore the effects of interval water stress on the morphological and physiological parameters of apple leaves. The purpose was to determine the plant’s adaptability to waterlogged environments and provide theoretical reference for management and maintenance after waterlogging. The results showed that the effect on flooded (T2) on apple stock was greater than that of waterlogged (T1), Short-term (7 d) waterlogging (T1) did not affect the growth of seedlings but was conducive to the accumulation of dry matter. Furthermore, the initial stress was be imprinted on the plants, which could directly affect their response to later stress. The results of principal component analysis (PCA) revealed that PC1, PC2, and PC3 explained 26.92%, 17.46%, and 13.03% of the physiological changes under water stress, respectively. By calculating the weight of each indicator, we concluded that high-frequency resistance r, relative chlorophyll content (SPAD) and maximum photochemical efficiency Fv/Fm are important parameters for apple rootstocks affected by water stress.

Molecular and Enzymatic Characterization of Flavonoid 3′-Hydroxylase of Malus × domestica

Malus × domestica (apple) accumulates particularly high amounts of dihydrochalcones in various tissues, with phloridzin (phloretin 2′-O-glucoside) being prevalent, although small amounts of 3-hydroxyphloretin and 3-hydroxyphloridzin are also constitutively present. The latter was shown to correlate with increased disease resistance of transgenic M. × domestica plants. Two types of enzymes could be involved in 3-hydroxylation of dihydrochalcones: polyphenol oxidases or the flavonoid 3′-hydroxylase (F3′H), which catalyzes B-ring hydroxylation of flavonoids. We isolated two F3′H cDNA clones from apple leaves and tested recombinant Malus F3′Hs for their substrate specificity. From the two isolated cDNA clones, only F3′HII encoded a functionally active enzyme. In the F3′HI sequence, we identified two putatively relevant amino acids that were exchanged in comparison to that of a previously published F3′HI. Site directed mutagenesis, which exchanged an isoleucine into methionine in position 211 restored the functional activity, which is probably because it is located in an area involved in interaction with the substrate. In contrast to high activity with various flavonoid substrates, the recombinant enzymes did not accept phloretin under assay conditions, making an involvement in the dihydrochalcone biosynthesis unlikely.

Effect of Nozzle Type and Adjuvants on Spray Coverage on Apple Leaves

Three non-ionic adjuvants, Agral, Silwet, and Greemax, at three concentrations, were applied on apple leaves with the use of hollow cone nozzles (TR) and air-induction nozzles (ID) to verify the assumption that adjuvants may improve spray coverage obtained by coarse droplets, and thereby ensure both satisfactory application quality and an environmental advantage. Spray coverage and droplet density were measured on both sides of the leaves. The adjuvants enhanced the spray coverage when applied at a certain concentration level. In general, the adjuvant coverage produced by the ID nozzles equaled the pure water coverage produced by the TR nozzles, thereby showing the adjuvants’ potential to compensate for the lower spray coverage usually obtained by coarse spray. A higher spray coverage was obtained on the lower side of leaves, which is discussed in terms of leaf surface properties. In the experiment with the mixture of Silwet and the fungicide Delan (dithianon), the product interacted with the adjuvant, resulting in the reversed picture of spray coverage and droplet density on the upper and lower leaf sides compared to the results obtained for the adjuvant alone. The combination of coarse spray nozzles with adjuvants may reduce environmental pollution without compromising the quality of spray applications in fruit growing.