This article discusses the needs and challenges of developing good, science-based, simple methods for postharvest handling that can be made available in developing countries. Some of the traditional challenges have been successfully met (i.e. identifying causes and sources of losses for key crops, identifying many potential postharvest technologies of practical use for reducing losses), but many challenges remain. These include the characterization of indigenous crops in terms of their unique postharvest physiology (e.g. respiration rate, susceptibility to water loss, chilling sensitivity, ethylene sensitivity), ascertaining the differences between handling recommendations made for well-known varieties and the needs of local varieties of crops, and determining cost effectiveness of scale-appropriate postharvest technologies in each locale and for each crop. Key issues include building capacity at the local level in postharvest science, university teaching and extension, and continued adaptive research efforts to match emerging postharvest technologies to local needs as these continue to change over time. Development of appropriate postharvest technology relies upon many disciplines that are relevant to the overall success of horticulture, i.e. plant biology, engineering, agricultural economics, food processing, nutrition, food safety, and environmental conservation. The expanding pool of new information derived from postharvest research and outreach efforts in these areas can lead in many directions which are likely to have an impact on relieving poverty in developing countries.

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Postharvest technology for developing countries: challenges and opportunities in research, outreach and advocacy

Testing how populations are locally adapted and predicting their response to their future environment is of key importance in view of climate change. Landscape genomics is a powerful approach to investigate genes and environmental factors involved in local adaptation. In a pooled amplicon sequencing approach of 94 genes in 71 populations, we tested if >3'500 single nucleotide polymorphisms (SNPs) in the three most common oak species in Switzerland (Quercus petraea, Q. pubescens, Q. robur) show an association with abiotic factors related to local topography, historical climate, and soil characteristics. In the analysis including all species, the most frequently associated environmental factors were those best describing the habitats of the species. In the species-specific analyses, the most important environmental factors and associated SNPs greatly differed among species. However, we identified one SNP and seven genes that were associated to the same environmental factor across all species. We finally used regressions of allele frequencies of the most strongly associated SNPs along environmental gradients to predict the risk of non-adaptedness (RONA), which represents the average change in allele frequency at climate-associated loci theoretically required to match future climatic conditions. RONA is considerable for some populations and species (up to 48% in single populations) and strongly differs among species. Given the long generation time of oaks, some of the required allele frequency changes might not be realistic to achieve based on standing genetic variation. Hence, future adaptedness requires gene flow or planting of individuals carrying beneficial alleles from habitats currently matching future climatic conditions.

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Signatures of local adaptation in candidate genes of oaks (Quercus spp.) with respect to present and future climatic conditions.

The aerial parts of land plants are covered by a hydrophobic layer called cuticle that limits non-stomatal water loss and provides protection against external biotic and abiotic stresses. The cuticle is composed of polymer cutin and wax comprising a mixture of very-long-chain fatty acids and their derivatives, while also bioactive secondary metabolites such as triterpenoids are present. Fleshy fruits are also covered by the cuticle, which has an important protective role during the fruit development and ripening. Research related to the biosynthesis and composition of cuticles on vegetative plant parts has largely promoted the research on cuticular waxes in fruits. The chemical composition of the cuticular wax varies greatly between fruit species and is modified by developmental and environmental cues affecting the protective properties of the wax. This review focuses on the current knowledge of the cuticular wax biosynthesis during fleshy fruits development, and on the effect of environmental factors in regulation of the biosynthesis. Bioactive properties of fruit cuticular waxes are also briefly discussed, as well as the potential for recycling of industrial fruit residues as a valuable raw material for natural wax to be used in food, cosmetics and medicine.

/pdf/developmental-and-environmental-regulation-of-cuticular-wax-4ftgcd1azr.pdf

Developmental and Environmental Regulation of Cuticular Wax Biosynthesis in Fleshy Fruits

Nutrient-containing nanomaterials have been developed as fertilizers to foster plant growth and agricultural yield through root applications. However, if applied through leaves, how these nanomaterials, e.g. γ-Fe2O3 nanoparticles (NPs), influence the plant growth and health are largely unknown. This study is aimed to assess the effects of foliar-applied γ-Fe2O3 NPs and their ionic counterparts on plant physiology of Citrus maxima and the associated mechanisms. No significant changes of chlorophyll content and root activity were observed upon the exposure of 20–100 mg/L γ-Fe2O3 NPs and Fe3+. In C. maxima roots, no oxidative stress occurred under all Fe treatments. In the shoots, 20 and 50 mg/L γ-Fe2O3 NPs did not induce oxidative stress while 100 mg/L γ-Fe2O3 NPs did. Furthermore, there was a positive correlation between the dosages of γ-Fe2O3 NPs and Fe3+ and iron accumulation in shoots. However, the accumulated iron in shoots was not translocated down to roots. We observed down-regulation of ferric-chelate reductase (FRO2) gene expression exposed to γ-Fe2O3 NPs and Fe3+ treatments. The gene expression of a Fe2+ transporter, Nramp3, was down regulated as well under γ-Fe2O3 NPs exposure. Although 100 mg/L γ-Fe2O3 NPs and 20–100 mg/L Fe3+ led to higher wax content, genes associated with wax formation (WIN1) and transport (ABCG12) were downregulated or unchanged compared to the control. Our results showed that both γ-Fe2O3 NPs and Fe3+ exposure via foliar spray had an inconsequential effect on plant growth, but γ-Fe2O3 NPs can reduce nutrient loss due to their the strong adsorption ability. C. maxima plants exposed to γ-Fe2O3 NPs and Fe3+ were in iron-replete status. Moreover, the biosynthesis and transport of wax is a collaborative and multigene controlled process. This study compared the various effects of γ-Fe2O3 NPs, Fe3+ and Fe chelate and exhibited the advantages of NPs as a foliar fertilizer, laying the foundation for the future applications of nutrient-containing nanomaterials in agriculture and horticulture.

Interaction of γ-Fe2O3 nanoparticles with Citrus maxima leaves and the corresponding physiological effects via foliar application

Improving crop performance under water-limiting conditions is essential for achieving environmentally sustainable food production. This requires significant progress in both the identification and characterization of key genetic and physiological processes involved in water uptake and loss. Plants regulate water uptake and loss through both developmental and environmental responses. These responses include: root morphology and architecture, cuticle development, stomatal development, and guard cell movements in response to the environment. Genes controlling root traits and stomatal development and guard cell movements strongly impact water use efficiency (WUE), and represent the best targets for molecular breeding programs. This article provides an overview of the complex networks of genes involved in water uptake and loss. These traits represent novel opportunities and strategies for genetic improvement of WUE and drought tolerance in crops.

Improving Plant Water Use Efficiency through Molecular Genetics

Increasing cuticular wax accumulation in plants has been associated with improving drought tolerance in plants. In this study, a cDNA clone encoding the SlSHN1 transcription factor, the closest ortholog to WIN/SHN1 gene in Arabidopsis, was isolated from tomato plant. Expression analysis of SlSHN1 indicated that it is induced in response to drought conditions. The over-expression of SlSHN1 in tomato under the control of the constitutive CaMV 35S promoter produced plants that showed mild growth retardation phenotype with shiny and dark green leaves. Scanning electron microscopy showed that the over-expression of SlSHN1 in tomato resulted in higher cuticular wax deposition on leaf epidermial tissue when compared to non-transformed plants. Expression analysis in transgenic lines over-expressing SlSHN1 indicated that several wax-related synthesis genes were induced. Transgenic tomato plants over-expressing SlSHN1 showed higher drought tolerance when compared with wild type plants; this was reflected in delayed wilting of transgenic lines, improved water status and reduced water loss rate when compared with wild type plants. In conclusion, the SlSHN1 gene can modulate wax accumulation and could be utilized to enhance drought tolerance in tomato plant.

https://www.mdpi.com/1422-0067/15/11/19499/pdf

Over-expression of SlSHN1 gene improves drought tolerance by increasing cuticular wax accumulation in tomato.

Technical and economical evaluation of traditional vs. advanced handling of tomatoes in Jordan.

Plastic house experiments were conducted to evaluate the effect of different cucurbit rootstocks on growth and yield of cucumber under the impact of root-knot nematode. Three cucurbit rootstocks (Strongtosa, Shintosa supreme and Tetsukabuto) were selected to test their graft success rate with cucumber plant and their possible resistance against soil-borne pathogens. Cucumber cultivar Zezia was grafted on these rootstocks either by tongue approach or by top grafting (hole-insertion) methods. The grafted plants were transplanted along with non-grafted plants in greenhouse and their performance was evaluated. Results indicated that plants grafted on Strongtosa, Shintosa supreme and Tetsukabuto had 100% survival rate as compared to non-grafted plants where 32-43% were infected with Rhizoctonia solani and Pythium. On the other hand, graft success rate was 100% from plants grafted on Shintosa supreme and Strongtosa whereas it was 76.66% for plants grafted on Tetsukabuto once top-grafting method was used. In addition, these two rootstocks resulted in more vigorous cucumber plants. For instance, the total dry weight of vegetative parts was 112-123% higher than nongrafted plants in the first season and 131-152% in the second season. The more vigorous growth resulted in higher marketable yield ranging from 37% to 134% of that in non-grafted plants. In addition, both rootstocks showed a significant increase in fruit yield when compared to plants grafted on the Tetsukabuto rootstock. However, Tetsukabuto rootstock showed a higher marketable yield ranged from 22% to 85% than that of non-grafted plants. All plants were severely infested with nematodes with no significant differences in galling index, even though Strongtosa had the lowest galling index and showed enhanced resistance against the root knot nematode. Therefore, it is recommended to use Strongtosa and Shintosa supreme as rootstocks for ‘Zezia’ cucumber that improves plant vigor and yield, which confer tolerance to root knot nematode.

Influence of different rootstocks on growth and yield of cucumber (Cucumis sativus L.) under the impact of soil-borne pathogens in Jordan

Utilization of treated wastewater (TWW) for agricultural purposes has grown over the past few years because of limited available water resources. This study was performed to assess the long-term irrigation of treated wastewater from the Wadi-Musa region on the accumulation of heavy metals in soil and their uptake and translocation to various parts of olive trees. Fifteen year old trees that had been grown and irrigated with treated wastewater resources since their establishment were used in this study. Irrigation water, soil, and plant samples (root, stem bark, leaves, fruits) were collected and chemically analyzed for their heavy metal content. Accumulation of heavy metals in irrigation water and soil were found to be within the acceptable range for the safe use of treated wastewater according to the standards of the WHO. However, long-term and continuous irrigation with TWW resulted in significant accumulation of heavy metals in plant parts when compared to their levels in irrigation water and soil. Uptake of metals was consistent among plant parts with the highest concentrations for Fe, Mn, Pb and Zn, and the lowest concentrations for Ni, Cr and Cd. Assessment of the bioaccumulation factor (BFC) and translocation factors (TF) of heavy metals into different plant parts indicated selective absorption and partitioning of these heavy metals into different plant parts. High BCF values were observed for Fe, Cu and Ni in roots and fruits, and Fe, Mn, Cd and Pb in leaves. Translocation factors of metal ions were variable among plant parts. Fruits had the highest TF for Cu, Cd and Zn metals, and the lowest for Mn and Fe, while leaves have the highest TF for Fe, Zn and Mn and the lowest for Cd and Pb. The results of this study indicate that olive trees are heavy metal accumulators, caution should be considered in long-term use of TWW and periodic assessment of possible hazards, especially on fruits and oil quality is required.

Long-Term Irrigation with Treated Municipal Wastewater from the Wadi-Musa Region: Soil Heavy Metal Accumulation, Uptake and Partitioning in Olive Trees

The complete nucleotide sequences of two Jordanian isolates of Tomato Yellow Leaf Curl Virus (TYLCV) were determined and compared with other reported TYLCV isolates. Sequence analysis revealed that one isolate belonged to the mild strain, TYLCV-Mld, while the other isolate belonged to the Israel strain, TYLCV-IL. Agrodrench inoculation of tomato (Solanum lycopersicum L.) plants with a 1.8-mer infectious clone of TYLCV-IL[JO:Ju:08] resulted in the development of severe symptoms, while tomato plants infected with a 1.8-mer infectious clone of the isolate TYLCV-Mld[JO:Ju:08] resulted in milder symptoms. The infectious clones can be an important tool for improved understanding of TYLCV-tomato interactions.

https://journals.ju.edu.jo/JJAS/article/viewFile/2458/2306

Hmoud S. Al-Debei

Papers

Over-expression of SlSHN1 gene improves drought tolerance by increasing cuticular wax accumulation in tomato.

Technical and economical evaluation of traditional vs. advanced handling of tomatoes in Jordan.

Influence of different rootstocks on growth and yield of cucumber (Cucumis sativus L.) under the impact of soil-borne pathogens in Jordan

Long-Term Irrigation with Treated Municipal Wastewater from the Wadi-Musa Region: Soil Heavy Metal Accumulation, Uptake and Partitioning in Olive Trees

Complete Nucleotide Sequences and Construction of Infectious Clones of Two Jordanian Isolates of Tomato Yellow Leaf Curl Virus