Cell wall and metabolite composition of sweet cherry fruits from two cultivars with contrasting susceptibility to surface pitting during storage.

Surface pitting is a serious postharvest physiological disorder in sweet cherries that is observed as skin depressions developed days after bruising. This work aims to compare two cultivars displaying different pitting susceptibilities ('Kordia': relatively resistant; 'Sweetheart': relatively susceptible) using metabolomics profiling and cell wall sugar characterization at different developmental stages and during postharvest storage. Kordia was significantly firmer than Sweetheart, with 1.4-fold more alcohol-insoluble residues (AIRs). A significant correlation was observed between AIRs and deformation, indicating that the highest yields of cell wall material are positively correlated with the resistance to rupture. Additionally, free d-galacturonic acid was higher in pitted Sweetheart samples, likely indicating greater pectin degradation in this susceptible cultivar. Higher contents of the p-coumaric acid derivatives L-5-oxoproline and d-galactose in Sweetheart cherries were found. The metabolic changes during storage and cell wall composition could influence the susceptibility to surface pitting.

Nutrient Storage in the Perennial Organs of Deciduous Trees and Remobilization in Spring - A Study in Almond (Prunus dulcis) (Mill.) D. A. Webb.

The annual dynamics of whole mature almond tree nutrient remobilization in spring and the accumulation of nutrients in perennial tissues during the year were determined by sequential coring, tissue sampling, nutrient analysis, whole tree excavation and biomass estimation for trees grown under four nitrogen rate treatments 140 kg ha-1 N (N140), 224 kg ha-1 N (N224), 309 kg ha-1 N (N309), and 392 kg ha-1 N (N392) over 2 years. Whole tree perennial organ N content was greatest in dormancy then declined through bud swell, flowering and fruit set, achieving the lowest total whole tree nutrient content of perennial organs by March 12 [12-14 days after full bloom (DAFB)] coincident with 60-70% leaf expansion. During this period no net increment in whole tree N content (annual plus perennial N) was observed indicating that tree demand for N for bud break, flowering, fruit set and leaf out was met by remobilized stored N and that there was no net N uptake from soil. Remobilizable N increased with increasing N application up to N309 and was maximal at 44.4 ± 4 kg ha-1 and 37.5 ± 5.7 kg ha-1 for the optimally fertilized N309 in 2012 and 2013 respectively. Net increases in perennial organ N (stored N) commenced 41 DAFB and continued through full leaf abscission at 249 DAFB. Total annual N increment in perennial organs varied from 25 to 60 kg ha-1 and was strongly influenced by N rate and tree yield. N remobilized from senescing leaves contributed from 11 to 15.5 ± 0.6 kg ha-1 to perennial stored N. Similar patterns of nutrient remobilization and storage were observed for P, K, and S with maximal whole tree perennial storage occurring during dormancy and remobilization of that stored P, K, S to support annual tree demands through to fruit set and 70-100% leaf development. Net annual increment in perennial organ P, K, S commenced 98 DAFB and continued through full leaf abscission at 249 DAFB. Organ specific contribution to remobilizable and stored nutrients changes over the growing season are presented. Details of the pattern of perennial organ nutrient allocation, storage, and remobilization provides a framework for the optimal management of nutrients in almond with relevance for other deciduous tree species.

A Comparison of Immediate and Short-Term Defensive Responses to Phytophthora Species Infection in Both Susceptible and Resistant Walnut Rootstocks.

Clonal rootstocks are one alternative used by the walnut industry to control damage caused by Phytophthora species, traditionally using plants grafted on susceptible Juglans regia rootstock. Vlach, VX211, and RX1 are clonal rootstocks with a degree of resistance to Phytophthora species. The resistance to pathogens in these rootstocks depends on the resistance mechanisms activated by the presence of the pathogen and subsequent development of responses in the host. In this work, we analyzed how plants of J. regia, Vlach, VX211, and RX1 responded to inoculation with Phytophthora cinnamomi or Phytophthora citrophthora isolates obtained from diseased English walnut plants from Chilean orchards. After inoculation, plants of Vlach, VX211, and RX1 showed canopy and root damage indexes that did not differ from noninoculated control plants. In contrast, plants of J. regia, which is susceptible to P. cinnamomi and P. citrophthora, died after inoculation. Vlach, VX211, and RX1 plants inoculated with P. cinnamomi or P. citrophthora showed greater root weight and volume and greater root growth rates than their respective controls. These results suggest that short-term carbohydrate dynamics may be related to the defense mechanisms of plants; they are immediately activated after inoculation through the production of phenolic compounds, which support the further growth and development of roots in walnut clonal rootstocks. To our knowledge, this is the first study that comprehensively characterizes vegetative and radicular growth and the dynamics of sugars and phenols in response to infection with P. cinnamomi or P. citrophthora in walnut rootstocks.

Characterization of Oomycete Species Associated With Root and Crown Rot of English Walnut in Chile.

English (Persian) walnut (Juglans regia) trees affected by root and crown rot were surveyed in five regions of central Chile between 2015 and 2017. In each region, nine orchards, ranging from 1 to 21 years old, were randomly selected and inspected for incidence and severity of tree decline associated with crown and root rot. Soil and symptomatic crown and root tissues were collected and cultured in P5ARP semiselective medium to isolate potential oomycete pathogens, which were identified through morphology and molecularly using ITS sequences in the rDNA gene and beta tubulin gene. The most frequently isolated species was Phytophthora cinnamomi. Pathogenicity tests were conducted with representative oomycete isolates. P. cinnamomi, P. citrophthora, and Pythium ultimum were all pathogenic in J. regia. Nevertheless, only P. cinnamomi and P. citrophthora were pathogenic to English walnut. Py. ultimum caused limited levels of root damage to English walnut seedlings. Our research indicates that as the Chilean walnut industry has expanded, so have walnut crown and root rots induced by oomycetes.

Spring bud growth depends on sugar delivery by xylem and water recirculation by phloem Münch flow in Juglans regia.

MAIN CONCLUSION: During spring, bud growth relies on long-distance transport of remotely stored carbohydrates. A new hypothesis suggests this transport is achieved by the interplay of xylem and phloem. During the spring, carbohydrate demand of developing buds often exceeds locally available storage, thus requiring the translocation of sugars from distant locations like limbs, stems and roots. Both the phloem and xylem have the capacity for such long-distance transport, but their functional contribution is unclear. To address this ambiguity, the spatial and temporal dynamics of carbohydrate availability in extension shoots of Juglans regia L. were analyzed. A significant loss of extension shoot carbohydrates in remote locations was observed while carbohydrate availability near the buds remained unaffected. This pattern of depletion of carbohydrate reserves supports the notion of long-distance translocation. Girdling and dye perfusion experiments were performed to assess the role of phloem and xylem in the transport of carbohydrate and water towards the buds. Girdling caused a decrease in non-structural carbohydrate concentration above the point of girdling and an unexpected concurrent increase in water content associated with impeded xylem transport. Based on experimental observations and modeling, we propose a novel mechanism for maintenance of spring carbohydrate translocation in trees where xylem transports carbohydrates and this transport is maintained with the recirculation of water by phloem Münch flow. Phloem Münch flow acts as a pump for generating water flux in xylem and allows for transport and mobilization of sugars from distal locations prior to leaves photosynthetic independence and in the absence of transpiration.

Colour and in vitro quality attributes of walnuts from different growing conditions correlate with key precursors of primary and secondary metabolism.

Walnuts (Juglans regia L.) are well known for their flavour, nutritional and health properties. The light colour of walnuts is a quality attribute that leads to consumer preference. The aim of this study was to correlate attributes such as colour and antioxidant capacity with the precursors of primary and secondary metabolism. Two growing areas and four different colours of walnuts cv. Chandler from the central region of Chile were evaluated. Walnuts grown in the zone with Andes Mountains influence showed higher (p<0.05) sugar and unsaturated fatty acid contents, which could be attributed to lower minimum temperatures during seed filling. Extra light walnuts had higher (p<0.05) total phenolic compounds, antioxidant capacity and arbutin levels than amber walnuts. To the best of our knowledge, this is the first time that arbutin has been reported in walnuts and could provide the first insight into how enzymatic browning is prevented in the Chandler cultivar.

Foliar application of microbial and plant based biostimulants increases growth and potassium uptake in almond (Prunus dulcis [Mill.] D. A. Webb).

The use of biostimulants has become a common practice in agriculture. However, there is little peer-reviewed research on this topic. In this study we tested, under controlled and replicated conditions, the effect of one biostimulant derived from seaweed extraction (Bio-1) and another biostimulant derived from microbial fermentation (Bio-2). This experiment utilized 2-years-old almond plants over two growing seasons in a randomized complete design with a full 2 × 4 factorial structure with two soil potassium treatments (125 µg g(-1) of K vs. 5 µg g(-1)) and four foliar treatments (No spray, Foliar-K, Bio-1, Bio-2). Rubidium was utilized as a surrogate for short-term potassium uptake and plant growth, nutrient concentration, and final plant biomass were evaluated. There was a substantial positive effect of both biostimulant treatments on total shoot leaf area, and significant increases in shoot length and biomass under adequate soil potassium supply with a positive effect of Bio-1 only under low K supply. Rubidium uptake was increased by Bio-1 application an effect that was greater under the low soil K treatment. Though significant beneficial effects of the biostimulants used on plant growth were observed, it is not possible to determine the mode of action of these materials. The results presented here illustrate the promise and complexity of research involving biostimulants.

Fruit presence negatively affects photosynthesis by reducing leaf nitrogen in almond.

Fruit presence often positively and seldom negatively affects leaf carbon assimilation rate in fruit-trees. In almond (Prunus dulcis (Mill.) DA Webb) the presence of fruit often results in the death of the fruit bearing spurs. The mechanism of this effect is unclear, but may be a consequence of diminished carbon assimilation rate in leaves adjacent to fruit and the subsequent depletion of nutrient and carbohydrates reserves. This study evaluated the influence of fruit on leaf carbon assimilation rate and leaf nitrogen throughout the season. Carbon assimilation rate (Aa), rubisco carboxylation capacity at leaf temperature (Vcmax@Tleaf), maximum rate of RubP regeneration at leaf temperature (Jmax@Tleaf), leaf nitrogen on a mass basis (N%) and area basis (Na), and specific leaf weight data were recorded. Fruit presence negatively affected leaf nitrogen concentration by a reduction in specific leaf weight and leaf nitrogen content. The impact of fruit presence on carbon assimilation rate was predominantly associated with the negative effect of fruit on Na and resulted in a significant reduction in Jmax@Tleaf and therefore in Aa, especially after full leaf and fruit expansion. The reduction in leaf area, leaf nitrogen, reduced Jmax@Tleaf and decreased carbon assimilation rate in the presence of fruit explains the negative effects of fruit presence on spur vitality.