Identification, characterization, and expression of lipoxygenase genes in sweet cherry (Prunus avium L.) cv. Regina and their relationship with the development of an herbaceous off-flavor during fruit ripening.

Flavor is an essential characteristic of fruit quality and is significant for consumers. Off-flavors have been reported in several fruits, including sweet cherry. This fruit has been reported to show an herbaceous/grassy-like flavor. The herbaceous off-flavor in sweet cherries detected in cultivar Regina has been related to the differential development of aroma compounds such as short-chain aldehydes and esters. One of the main biosynthesis pathways for these compounds is the fatty acid oxidation mediated by lipoxygenases (LOX). In order to have a better understanding of the biological basis of the differences in the volatile profile, the LOX gene expression profile was characterized during fruit development with and without herbaceous off-flavor. A genome-wide analysis of LOX in sweet cherry was carried out and compared to other species such as Arabidopsis, tomato, apple, prunus and strawberry. The structural features of 9-LOX and 13-LOX genes, encoded protein domains and their synteny were examined. Moreover, we analyzed the LOX expression at four developmental stages along ripening by RT-qPCR. Thirteen LOX gene candidates (six 9-LOX and seven 13-LOX) were identified. The 13-LOXs, PaLOX10, PaLOX11, and PaLOX12 were differentially expressed in herbaceous sweet cherries. Furthermore, their expression profile positively correlated with key volatile compounds linked to the herbaceous off-flavor. Overall, this study involves the genome-wide characterization of the LOX family in Prunus avium cv. Regina and provides information that can aid in studying LOX-related fruit deterioration in sweet cherries and associated species.

Study of Mineral Composition and Quality of Fruit Using Vascular Restrictions in Branches of Sweet Cherry.

Calcium (Ca) and carbohydrate (CHO) supply in sweet cherry have been associated with fruit quality at harvest and during storage. There is little published information integrating CHO and Ca availability and distribution in sweet cherry and their effects on fruit quality. Accordingly, in the 2019-20 season, vascular restrictions were imposed on the phloem (girdling, G, stopping phloem flow) and xylem (transverse incision, S, cutting 50% of xylem cross-section area) of individual vertical branches of the sweet cherry combination 'Lapins'/Colt trained as Kym Green Bush system to modify mineral and CHO composition in fruit and associate such changes with quality at harvest and storage. The girdling to the phloem was used to induce changes in CHO distribution. The transverse incision to the xylem was a tool to modify Ca distribution. Five treatments (TR) were implemented: TR1-CTL = Control (without vascular restriction), TR2-G, at its base, TR3-G + G: at its base, and G further up at the change of year between the second and the third years of growth TR4--S and TR5-S + G. The vegetative (i.e., shoot and leaf growth), reproductive (i.e., fruit set and yield) development and stomatal conductance were monitored. Each branch was divided into the upper (1-and 2-year-old wood) and the lower (3-and 4-year-old wood) segments of the restriction applied. The quality and mineral composition (Ca, Mg, K, and N) of fruit borne on each segment were measured at harvest. The upper segment of TR3-G + G branches were harvested 10 d before the lower segment. The fruit from the upper segment of TR3-G + G was the largest, the sweetest, and had the higher titratable acidity concentration. However, fruits of this segment were the softest, had the lowest Ca concentrations, and had the highest ratios of N:Ca and K:Ca, compared with the other TRs. TR3-G + G branches developed the highest number of lateral current season shoots including shoots below the second girdling in the lower segment of the branch. This vegetative flow of growth would explain the mineral unbalance produced in the fruit from the upper segment of the branch. TR2-G did not register changes in fruit quality and mineral concentration compared with TR1-CTL. Surprisingly, the fruit from the branches with xylem restriction did not show changes in Ca concentration, suggesting that the xylem stream was enough to supply the fruit in branches without lateral shoot development. Fruit firmness was positively related to fruit Ca concentration and negatively related to the ratios of K:Ca and N:Ca.

Estimation of Soluble Solids for Stone Fruit Varieties Based on Near-Infrared Spectra Using Machine Learning Techniques.

The quality control for fruit maturity inspection is a key issue in fruit packaging and international trade. The quantification of Soluble Solids (SS) in fruits gives a good approximation of the total sugar concentration at the ripe stage, and on the other hand, SS alone or in combination with acidity is highly related to the acceptability of the fruit by consumers. The non-destructive analysis based on Visible (VIS) and Near-Infrared (NIR) spectroscopy has become a popular technique for the assessment of fruit quality. To improve the accuracy of fruit maturity inspection, VIS−NIR spectra models based on machine learning techniques are proposed for the non-destructive evaluation of soluble solids in considering a range of variations associated with varieties of stones fruit species (peach, nectarine, and plum). In this work, we propose a novel approach based on a Convolutional Neural Network (CNN) for the classification of the fruits into species and then a Feedforward Neural Network (FNN) to extract the information of VIS−NIR spectra to estimate the SS content of the fruit associated to several varieties. A classification accuracy of 98.9% was obtained for the CNN classification model and a correlation coefficient of Rc>0.7109 for the SS estimation of the FNN models was obtained. The results reported show the potential of this method for a fast and on-line classification of fruits and estimation of SS concentration.

Identification and Pathogenicity of Diplodia, Neofusicoccum, Cadophora, and Diaporthe Species Associated with Cordon Dieback in Kiwifruit cultivar Hayward in Central Chile.

Dieback symptoms associated with fungal trunk pathogens cause significant economic losses for farmers of kiwifruit and other woody fruit trees worldwide. This study represents the first attempt to identify and characterize the fungal trunk pathogens associated with cordon dieback disease of kiwifruit in central Chile. Field surveys were conducted throughout the main kiwifruit-growing regions in central Chile to determine the incidence and characterize the fungal trunk pathogens associated with cordon dieback of kiwifruit cultivar Hayward through morphological, molecular, and pathogenicity studies. A total of 250 cordon samples were collected and isolations were performed on 2% acidified potato dextrose agar (APDA) plus antibiotics and Igepal. The incidence of kiwifruit cordon dieback ranged between 5% and 85% in all surveyed areas in central Chile. A total of 246 isolates were isolated and identified using culture and morphological features belonging to three fungal taxa: Diaporthaceae spp. (Diaporthe ambigua and D. australafricana; n = 133 isolates); Botryosphaeriaceae spp. (Diplodia seriata and Neofusicoccum parvum; n = 89 isolates); and Ploettnerulaceae spp. (Cadophora luteo-olivacea and C. malorum; n = 24 isolates). These were identified using phylogenetics studies of the internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2) of the rDNA, part of the ß-tubulin gene (tub2), and part of the translation elongation factor 1-α gene (tef1-α). Isolates of N. parvum and D. seriata were the most virulent, causing internal brown lesions and dieback symptoms in attached green shoots, attached lignified canes, and young inoculated kiwifruits. This report is the first to describe D. seriata and C. luteo-olivacea associated with kiwifruit cordon dieback in Chile. It presents the first description of N. parvum causing kiwifruit dieback worldwide.

Characterization of Botrytis cinerea and B. prunorum From Healthy Floral Structures and Decayed 'Hayward' Kiwifruit During Post-Harvest Storage.

Gray mold is the primary postharvest disease of 'Hayward' kiwifruit (Actinidia deliciosa) in Chile, with a prevalence of 33.1% in 2016 and 7.1% in 2017. Gray mold develops during postharvest storage, which is characterized by a soft, light to brown watery decay that is caused by Botrytis cinerea and B. prunorum. However, there is no information on the role of B. prunorum during the development and storage of kiwifruit in Chile. For this purpose, asymptomatic flowers and receptacles were collected throughout fruit development and harvest from five orchards over two seasons in the Central Valley of Chile. Additionally, diseased kiwifruits were selected after storage for 100 days at 0°C and 2 days at 20°C. Colonies of Botrytis sp. with high and low conidial production were consistently obtained from apparently healthy petals, sepals, receptacles, and styles and diseased kiwifruit. Morphological and phylogenetic analysis of three partial gene sequences encoding glyceraldehyde-3-phosphate dehydrogenase, heat shock protein 60, and DNA-dependent RNA polymerase subunit II were able to identify and separate B. cinerea and B. prunorum species. Consistently, B. cinerea was predominantly isolated from all floral parts and fruit in apparently healthy tissue and diseased kiwifruit. During full bloom, the highest colonization by B. cinerea and B. prunorum was obtained from petals, followed by sepals. In storage, both Botrytis species were isolated from the diseased fruit (n = 644), of which 6.8% (n = 44) were identified as B. prunorum. All Botrytis isolates grew from 0°C to 30°C in vitro and were pathogenic on kiwifruit leaves and fruit. Notably, B. cinerea isolates were always more virulent than B. prunorum isolates. This study confirms the presence of B. cinerea and B. prunorum colonizing apparently healthy flowers and floral parts in fruit and causing gray mold during kiwifruit storage in Chile. Therefore, B. prunorum plays a secondary role in the epidemiology of gray mold developing in kiwifruit during cold storage.

Postharvest Incidence of Stem End Rot in 'Hayward' Kiwifruit Is Related to Preharvest Botrytis cinerea Colonization of Floral Parts and Latent Infection.

Stem end rot (SER) caused by Botrytis cinerea is the primary postharvest disease in the Chilean kiwifruit industry. Relationships between the postharvest occurrence of SER in 'Hayward' kiwifruit and the temporal dynamics of earlier B. cinerea colonization of the floral parts (petals, sepals, receptacles, styles) was studied in five orchards over two consecutive seasons in Chile. Weather conditions in the first season favored B. cinerea infection with roughly constant colonization of floral parts up to about 120 days after full bloom, but colonization then increased up until harvest. In the second season, colonization was roughly constant throughout. Latent infections of the fruit occurred in both seasons but were high in the first season and low in the second. Incidence of latent infections at harvest were the best predictors (r > 0.8) of postharvest SER. The number of preharvest infection periods calculated using temperature, leaf wetness, and relative humidity satisfactorily predicted SER incidence by an exponential model, R2 = 0.90, P < 0.001. Results indicated environmental variables play key roles in the temporal dynamics of B. cinerea colonization. Quantification of latent B. cinerea infections in asymptomatic fruit close to harvest, is a practicable way to predict later incidence of SER during storage.