Effects of kaolin application on light absorption and distribution, radiation use efficiency and photosynthesis of almond and walnut canopies

Climate change impacts on temperate fruit and nut production: a systematic review

Temperate fruit and nut crops require distinctive cold and warm seasons to meet their physiological requirements and progress through their phenological stages. Consequently, they have been traditionally cultivated in warm temperate climate regions characterized by dry-summer and wet-winter seasons. However, fruit and nut production in these areas faces new challenging conditions due to increasingly severe and erratic weather patterns caused by climate change. This review represents an effort towards identifying the current state of knowledge, key challenges, and gaps that emerge from studies of climate change effects on fruit and nut crops produced in warm temperate climates. Following the PRISMA methodology for systematic reviews, we analyzed 403 articles published between 2000 and 2023 that met the defined eligibility criteria. A 44-fold increase in the number of publications during the last two decades reflects a growing interest in research related to both a better understanding of the effects of climate anomalies on temperate fruit and nut production and the need to find strategies that allow this industry to adapt to current and future weather conditions while reducing its environmental impacts. In an extended analysis beyond the scope of the systematic review methodology, we classified the literature into six main areas of research, including responses to environmental conditions, water management, sustainable agriculture, breeding and genetics, prediction models, and production systems. Given the rapid expansion of climate change-related literature, our analysis provides valuable information for researchers, as it can help them identify aspects that are well understood, topics that remain unexplored, and urgent questions that need to be addressed in the future.

Effects of regulated deficit irrigation and foliar kaolin application on quality parameters of almond [Prunus dulcis (Mill.) D.A. Webb]

BACKGROUND

Water stress during the growing season of the almond tree is the factor that most limits its yield. Different strategies have been studied in recent years to reduce its negative effects, such as deficit irrigation and the application of reflective spray compounds. A 3-year experiment (2019-2021) was set in a factorial design in which the effect of regulated deficit irrigation and foliar kaolin spray was evaluated on morphological characteristics (weight, length, width, and thickness of the nut and kernel, shell thickness, kernel yield, double kernels, and damaged kernels), color properties, nutritional value (carbohydrates, fat, proteins and ash) and chemical parameters (free sugars and fatty acids profiles).

RESULTS

In general, the significant differences between the treatments did not have a similar trend in the 3 years of the study. Regulated deficit irrigation and kaolin had no detrimental impact on almond morphological and color characteristics. The almond free sugars concentration was relatively stable under deficit irrigation and kaolin application. On the other hand, kaolin application positively affected the synthesis of linoleic acid.

CONCLUSION

Reducing the amount of irrigation water applied to almonds contributes to the sustainability of production without negatively affecting quality and even improving some quality parameters. In general, the foliar application of kaolin did not show significant differences in the evaluated morphological parameters. However, in terms of chemical composition, kaolin led to an increase in the concentration of linoleic acid and sucrose. © 2023 Society of Chemical Industry.

Assessing temperature-based adaptation limits to climate change of temperate perennial fruit crops

Temperate perennial fruit and nut trees play varying roles in world food diversity-providing edible oils and micronutrient, energy, and protein dense foods. In addition, perennials reuse significant amounts of biomass each year providing a unique resilience. But they also have a unique sensitivity to seasonal temperatures, requiring a period of dormancy for successful growing season production. This paper takes a global view of five temperate tree fruit crops-apples, cherries, almonds, olives, and grapes-and assesses the effects of future temperature changes on thermal suitability. It uses climate data from five earth system models for two CMIP6 climate scenarios and temperature-related indices of stress to indicate potential future areas where crops cannot be grown and highlight potential new suitable regions. The loss of currently suitable areas and new additions in new locations varies by scenario. In the southern hemisphere (SH), end-century (2081-2100) suitable areas under the SSP 5-8.5 scenario decline by more than 40% compared to a recent historical period (1991-2010). In the northern hemisphere (NH) suitability increases by 20% to almost 60%. With SSP1-2.6, however, the changes are much smaller with SH area declining by about 25% and NH increasing by about 10%. The results suggest substantial restructuring of global production for these crops. Essentially, climate change shifts temperature-suitable locations toward higher latitudes. In the SH, most of the historically suitable areas were already at the southern end of the landmass limiting opportunities for adaptation. If breeding efforts can bring chilling requirements for the major cultivars closer to that currently seen in some cultivars, suitable areas at the end of the century are greater, but higher summer temperatures offset the extent. The high value of fruit crops provides adaptation opportunities such as cultivar selection, canopy cooling using sprinklers, shade netting, and precision irrigation.

Enhancing Yield and Physiological Performance by Foliar Applications of Chemically Inert Mineral Particles in a Rainfed Vineyard under Mediterranean Conditions

One of the biggest environmental challenges that most of the traditional and modern grape-growing areas are facing is the frequency, severity, and unpredictability of extreme weather events as a result of climate change. Sustainable tools such as chemically inert mineral particles could be a valid alternative for the promotion of environmentally-friendly viticultural techniques to enhance yield, improve physiological processes, and increase tolerance to biotic/abiotic stressors and grape quality. In regard to this concept, the effects of kaolin (KL) and zeolite (ZL) application was tested in the rosé grapevine cultivar Roditis, field-and rainfed, under the Mediterranean conditions of central Greece. In a two-year trial, the whole vine canopy was sprayed with kaolin and zeolite until runoff at a dose of 3% (w/v) twice throughout the growing season; the first at the beginning of veraison and the second one week later; treatment of the untreated control plants was also performed (C). The assimilation rate in morning and midday, the stomatal conductance, and the WUEi of the leaves of the treated and untreated plants were monitored one day after each application and at harvest. During the same time period of the day (i.e., morning and midday) in July, August, and September, the leaf temperature near the fruit zone was also recorded. At harvest, the yield parameters, cluster characteristics, grape composition, and incidence (%) of sunburned and dehydrated berries as well as berries infected by Plasmopara viticola and Lobesia botrana were recorded. The results showed that KL and ZL application decreased leaf temperature during the growing season until harvest compared to the control treatment, which resulted in an improvement in physiological parameters such as net photosynthesis and intrinsic water use efficiency. At harvest, the KL- and ZL-treated vines showed increased yield due to an increasing cluster and berry fresh weight. On the other hand, the KL and ZL application did not affect the sugar concentration and pH of the must and increased the total acidity and decreased the total phenolic compound content, but only in the first year of the experiments. Furthermore, the incidence of sunburn necrosis, dehydrated berries, and infected berries was significantly lower in the treated vines compared to the control vines. These results confirm the promising potential of kaolin and zeolite applications as a stress mitigation strategy during the summer period, with the ability to protect grapevine plants, enhance yield, and maintain or improve fruit quality in rainfed Mediterranean vineyards.

Distinct Particle Films Impacts on Olive Leaf Optical Properties and Plant Physiology

The olive fruit fly is worldwide considered a major harmful pest of the olive agroecosystem. In Italy, the fruit fly infestation is traditionally countered by spraying chemical insecticides (e.g., dimethoate), but due to the recent ban of dimethoate by the Reg EU2019/1090 and the increasing awareness of consumers of food sustainability, the interest in developing chemical-free alternatives to pesticides, such as the use of particle-films, is rising. A field experiment was conducted to assess the effect of different particle films (kaolin-base and zeolitite-base) on leaf gas exchanges and leaf optical properties. Results showed that with the dust accumulation on the leaves’ surface, photosynthesis, stomatal conductance, transpiration and water use efficiency were significantly lower in kaolin-treated olive trees compared to those treated with zeolitite and to the control, while olive trees treated with zeolitite showed physiological parameters similar to the untreated plants. Microstructural differences of different particle film on the leaf and olive surfaces emerged by ESEM observations also influenced leaf optical properties. Oils produced by zeolitite-treated plants show higher intensities of gustatory and olfactory secondary flavors compared to kaolin and test oils.

Salicylic acid and kaolin effects on pomological, physiological, and phytochemical characters of hazelnut (Corylus avellana) at warm summer condition

Climate change and population increase are two challenges for crop production in the world. Hazelnut (Corylus avellana L.) is considered an important nut regarding its nutritional and economic values. As a fact, the application of supporting materials as foliage sprays on plants will decrease biotic and abiotic stresses. In this study, the effects of salicylic acid (0, 1 mM and 2.5 mM) and kaolin (0, 3% and 6%) sprays were investigated on morphological, physiological, pomological, and biochemical characteristics of hazelnut. The results showed that 1 mM salicylic acid and 6% kaolin had the best effects on nut and kernel weight compared to control. Biochemical parameters such as chlorophyll a, b, a + b, and carotenoid contents showed that salicylic acid and kaolin improved pigment concentration. Proline and antioxidant contents such as phenolic acids, SOD, APX, and CAT enzyme activities increased by these applications. On the other hand, lipid peroxidation, protein content, and H₂O₂ content were decreased. Based on the tolerance index result, Merveille de Bollwiller cultivar showed the highest tolerance while 'Fertile de Coutard' had the lowest value. Therefore, hazelnut performance may be improved through exogenous application of the signaling (salicylic acid) and particle film (Kaolin) compounds in warmer climates.

Kaolin Reduces ABA Biosynthesis Through the Inhibition of Neoxanthin Synthesis in Grapevines Under Water Deficit

In many viticulture regions, multiple summer stresses are occurring with increased frequency and severity because of warming trends. Kaolin-based particle film technology is a technique that can mitigate the negative effects of intense and/or prolonged drought on grapevine physiology. Although a primary mechanism of action of kaolin is the increase of radiation reflection, some indirect effects are the protection of canopy functionality and faster stress recovery by abscisic acid (ABA) regulation. The physiological mechanism underlying the kaolin regulation of canopy functionality under water deficit is still poorly understood. In a dry-down experiment carried out on grapevines, at the peak of stress and when control vines zeroed whole-canopy net CO₂ exchange rates/leaf area (NCER/LA), kaolin-treated vines maintained positive NCER/LA (~2 µmol m^-2 s^-1) and canopy transpiration (E) (0.57 µmol m^-2 s^-1). Kaolin-coated leaves had a higher violaxanthin (Vx) + antheraxanthin (Ax) + zeaxanthin (Zx) pool and a significantly lower neoxanthin (Nx) content (VAZ) when water deficit became severe. At the peak of water shortage, leaf ABA suddenly increased by 4-fold in control vines, whereas in kaolin-coated leaves the variation of ABA content was limited. Overall, kaolin prevented the biosynthesis of ABA by avoiding the deviation of the VAZ epoxidation/de-epoxidation cycle into the ABA precursor (i.e., Nx) biosynthetic direction. The preservation of the active VAZ cycle and transpiration led to an improved dissipation of exceeding electrons, explaining the higher resilience of canopy functionality expressed by canopies sprayed by kaolin. These results point out the interaction of kaolin with the regulation of the VAZ cycle and the active mechanism of stomatal conductance regulation.

Silicates of Potassium and Aluminium (Kaolin); Comparative Foliar Mitigation Treatments and Biochemical Insight on Grape Berry Quality in Vitis vinifera L. (cv. Touriga National and Touriga Franca)

Grapevine physiology is influenced by several environmental factors, such as temperature, precipitation, potential evapotranspiration, and sunshine hours. Due to climatic changes, effects in grapevine physiology and consequently on the grape berry composition and quality have been observed. This work aims to make a comparative study of the effect of foliar mitigation treatment with kaolin (5%) and potassium silicates (0.1% and 0.05%) on the grape berry quality; namely on berry weight, pH, probable alcohol, total phenolics, tannins, total anthocyanins, monomeric anthocyanins, calcium, potassium, and magnesium composition from Portuguese grapevines (Vitis vinifera L. cv. Touriga Nacional and Touriga Franca). The results suggested that the phenolic composition and anthocyanin content differs between treatments while other parameters showed distinct behavior among the different applications. Qualitative parameters observed in the present study suggested non-significant changes upon both the applications.

Influence of Foliar Kaolin Application and Irrigation on Photosynthetic Activity of Grape Berries

Climate changes may cause severe impacts both on grapevine and berry development. Foliar application of kaolin has been suggested as a mitigation strategy to cope with stress caused by excessive heat/radiation absorbed by leaves and grape berry clusters. However, its effect on the light micro-environment inside the canopy and clusters, as well as on the acclimation status and physiological responses of the grape berries, is unclear. The main objective of this work was to evaluate the effect of foliar kaolin application on the photosynthetic activity of the exocarp and seeds, which are the main photosynthetically active berry tissues. For this purpose, berries from high light (HL) and low light (LL) microclimates in the canopy, from kaolin-treated and non-treated, irrigated and non-irrigated plants, were collected at three developmental stages. Photochemical and non-photochemical efficiencies of both tissues were obtained by a pulse amplitude modulated chlorophyll fluorescence imaging analysis. The maximum quantum efficiency (Fv/Fm) data for green HL-grown berries suggest that kaolin application can protect the berry exocarp from light stress. At the mature stage, exocarps of LL grapes from irrigated plants treated with kaolin presented higher Fv/Fm and relative electron transport rates (rETR200) than those without kaolin. However, for the seeds, a negative interaction between kaolin and irrigation were observed especially in HL grapes. These results highlight the impact of foliar kaolin application on the photosynthetic performance of grape berries growing under different light microclimates and irrigation regimes, throughout the season. This provides insights for a more case-oriented application of this mitigation strategy on grapevines.

Comparing Kaolin and Pinolene to Improve Sustainable Grapevine Production during Drought

Viticulture is widely practiced in dry regions, where the grapevine is greatly exposed to water stress. Optimizing plant water use efficiency (WUE) without affecting crop yield, grape and wine quality is crucial to limiting use of water for irrigation and to significantly improving viticulture sustainability. This study examines the use in vineyards of particle film technology (engineered kaolin) and compares it to a film-forming antitranspirant (pinolene), traditionally used to limit leaf water loss, and to an untreated control. The trial was carried out under field conditions over three growing seasons, during which moderate to very severe plant water stress (down to -1.9 MPa) was measured through stem water potential. Leaf stomatal conductance (gs) and photosynthesis rate (An) were measured during the seasons and used to compute intrinsic WUE (WUEi, defined as An/gs ratio). Leaf temperature was also recorded and compared between treatments. Bunch quantity, bunch and berry weight, sugar accumulation, anthocyanin and flavonoid contents were measured. Finally, microvinifications were performed and resultant wines subjected to sensory evaluation.Results showed that the use of kaolin increased grapevine intrinsic WUE (+18% on average as compared to unsprayed vines) without affecting berry and bunch weight and quantity, or sugar level. Anthocyanin content increased (+35%) in kaolin treatment, and the wine was judged more attractive (p-value <0.05) and slightly more appreciated (p-value < 0.1) than control. Pinolene did not increase WUEi, limiting An more than gs; grapes with this treatment contained lower sugar and anthocyanin content than control, and the obtained wine was the least appreciated. This study demonstrates that particle film technology can improve vine WUEi and wine quality at the same time, while traditional antitranspirants were not as effective for these purposes. This positive effect can be used in interaction with other already-demonstrated uses of particle film technology, such as pest control and sunburn reduction, in order to achieve more sustainable vineyard management.

Potential and actual uses of zeolites in crop protection

In this review, it is demonstrated that zeolites have a potential to be used as crop protection agents. Similarly to kaolin, zeolites can be applied as particle films against pests and diseases. Their honeycomb framework, together with their carbon dioxide sorption capacity and their heat stress reduction capacity, makes them suitable as a leaf coating product. Furthermore, their water sorption capacity and their smaller particle sizes make them effective against fungal diseases and insect pests. Finally, these properties also ensure that zeolites can act as carriers of different active substances, which makes it possible to use zeolites for slow-release applications. Based on the literature, a general overview is provided of the different basic properties of zeolites as promising products in crop protection.

Effects of kaolin on Ophelimus maskelli (Hymenoptera: Eulophidae) in laboratory and nursery experiments

Although recent research has demonstrated that clays provide satisfactory control of some agricultural insect pests, the effect of clays on gall wasps that damage forest trees has not been previously reported. The aim of the current study is to evaluate the effectiveness of the clay kaolin in the laboratory and in the field in reducing the damage caused by the eulophid Ophelimus maskelli (Ashmead) on seedlings of eucalyptus (Eucalyptus L'Hér.) species. In the laboratory, kaolin + wetting agent significantly reduced the percentage of infested leaves and the number of galls per leaf. In the nursery, gall number per leaf was not correlated with leaf area with kaolin + wetting agent but was related to leaf area for all other treatments (wetting agent alone, imidacloprid, and untreated control). In the nursery, gall number per leaf was lower with kaolin + wetting agent and with imidacloprid than with the other two treatments. Overall, kaolin effectively reduced eulophid infestations, and its effect was more persistent than that of imidacloprid. Although application of kaolin might not be feasible on large forested areas, kaolin could represent a valuable control method in nurseries, where the repeated application with more toxic chemicals can result in high concentrations of residual pesticides in the soil.