Photooxidative stress activates a complex multigenic response integrating the phenylpropanoid pathway and ethylene,leading to lignin accumulation in apple(Malus domestica Borkh.)fruit

Photooxidative stress,when combined with elevated temperatures,triggers various defense mechanisms leading to physiological,biochemical,and morphological changes in fruit tissue.Furthermore,during sun damage,apple fruit undergo textural changes characterized by high flesh firmness compared to unexposed fruit.Fuji and Royal Gala apples were suddenly exposed to sunlight on the tree and then sampled for up to 29 days.Cell wall components and lignin biosynthetic pathway analyses were carried out on the fruit tissue.At harvest,Fuji apples with different sun exposure levels,such as exposed to direct sunlight(Exp),shaded(Non-Exp),and with severe sun damage(Sev),were also characterized.In fruit suddenly exposed to sunlight,the expression levels of phenylpropanoid-related genes,phenylalanine ammonia lyase(MdPAL),chalcone synthase(MdCHS),and flavanone-3-hydroxylase(MdF3H),were upregulated in the skin and flesh of Exp and Sev.Exposure had little effect on the lignin-related genes caffeic acid Omethyltransferase 1(MdCOMT1)and cinnamyl alcohol dehydrogenase(MdCAD)in the skin;however,the expression of these genes was highly induced in the flesh of Exp and Sev in both cultivars.Lignin deposition increased significantly in skin with sun injury(Sev);in flesh,this increase occurred late during the stress treatment.Additionally,the ethylene biosynthesis genes 1-aminocyclopropane-1-carboxylate synthase(MdACS)and 1-aminocyclopropane-1-carboxylate oxidase(MdACO)were highly expressed in the skin and flesh tissues but were more upregulated in Sev than in Exp during the time-course experiment,which paralleled the induction of the phenylpropanoid pathway and lignin accumulation.At harvest,flesh from Sev fruit exhibited higher firmness than that from Non-Exp and Exp fruit,although no differences were observed in the alcohol-insoluble residues(AIR)among groups.The fractionation of cell wall polymers revealed an increase in the uronic acid contents of the water-soluble pectin fraction(WSF)in Exp and Sev tissues compared to Non-Exp tissues,while the other pectin-rich fractions,that is,CDTA-soluble(CSF)and Na2CO3-soluble(NSF),were increased only in Sev.The amount of hemicellulose and cellulose did not differ among fruit conditions.These findings suggest that increases in the flesh firmness of apples can be promoted by photooxidative stress,which is associated with the induction of lignin accumulation in the skin and flesh of stressed fruit,with the involvement of stress phytohormones such as ethylene.

Non-invasive sensing techniques to phenotype multiple apple tree architectures

Tree fruit architecture results from combination of the training system and pruning and thinning processes across multiple growth and development years.Further,the tree fruit architecture contributes to the light interception and improves tree growth,fruit quality,and fruit yield,in addition to easing the process of orchard management and harvest.Currently tree architectural traits are measured manually by researchers or growers,which is labor-intensive and time-consuming.In this study,the remote sensing techniques were evaluated to phenotype critical architectural traits with the final goal to assist tree fruit breeders,physiologists and growers in collecting architectural traits efficiently and in a standardized manner.For this,a consumer-grade red–green–blue(RGB)camera was used to collect apple tree side-images,while an unmanned aerial vehicle(UAV)integrated RGB camera was programmed to image tree canopy at 15 m above ground level to evaluate multiple tree fruit architectures.The sensing data were compared to ground reference data associated with tree orchard blocks within three training systems(Spindle,V-trellis,Biaxis),two rootstocks(‘WA 38 trees grafted on G41 and M9-Nic29)and two pruning methods(referred as bending and click pruning).The data were processed to extract architectural features from ground-based 2D images and UAV-based 3D digital surface model.The traits extracted from sensing data included box-counting fractal dimension(DBs),middle branch angle,number of branches,trunk basal diameter,and tree row volume(TRV).The results from ground-based sensing data indicated that there was a significant(P<0.0001)difference in DBs between Spindle and V-trellis training systems,and correlations between DBs with tree height(r=0.79)and total fruit yield per unit area(r=0.74)were significant(P<0.05).Moreover,correlations between average or total TRV and ground reference data,such as tree height and total fruit yield per unit area,were significant(P<0.05).With the reported findings,this study demonstrated the potential of sensing techniques for phenotyping tree fruit architectural traits.