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Tropical fruits are in high demand for their flavor and for their functional composition because these compounds are considered nutraceuticals. Passion fruit production is of economic importance to Ecuador; however, several Passiflora species are grown and each has to be analyzed to identify their phytochemical composition. In this study, the polyphenol, flavonoid, carotenoid, vitamin C, sugar and organic acid contents were determined. Six different Passiflora spp. germplasms were analyzed, coming from Passiflora edulis f. flavicarpa, Passiflora alata, Passiflora edulis f. edulis and unidentified Passiflora species (local germplasm). Measurement techniques included reflectometry for vitamin C, spectrophotometry for antioxidant compounds and HPLC for sugars and organic acids. Data were analyzed by principal component analysis, correlation and analysis of variance. Results showed that INIAP 2009 and P10 showed a high amount of polyphenols, antioxidant activity and citric content. Sweet passion fruit had the lowest vitamin C content while Gulupa showed the highest content. In terms of the local germplasm, POR1 showed the lowest content of flavonoids while PICH1 had high flavonoid and carotenoid content. Polyphenols were the main compounds that influenced antioxidant activity. This phytochemical information adds value to passion fruit as a nutraceutical source.

Background Passion fruit ( Passiflora edulis Sims) is an important horticultural crop in the tropics and subtropics, where it has great commercial potential due to high demand for fresh edible fruits and processed juice as well as source of raw materials in cosmetic industries. Genetic engineering shows great potential in passion fruit improvement and can compensate for the limitations of conventional breeding. Despite the success achieved in genetic modification of few passion fruit varieties, transgenic passion fruit production is still difficult for farmer-preferred cultivars. Therefore, it is important to establish a simple and fast Agrobacterium -mediated cell transformation of commercial hybrid passion fruit KPF4 ( Passiflora edulis f. edulis  ×  Passiflora edulis f. flavicarpa ). Results In the present study, we have developed a simple and fast Agrobacterium -mediated transformation system for hybrid passion fruit KPF4 using leaf disc explants. Factors affecting the rate of transient beta (β)-glucuronidase ( gus A) expression and consequently transformation efficiency were optimized as follows: Agrobacterium cell density with an OD 600 of 0.5, 30 min infection time, 3 days of co-cultivation duration and the incorporation of 200 µM acetosyringone into Agrobacterium infection suspension medium. Using the optimized conditions, transgenic plants of KPF4 were produced within 2 months with an average transformation efficiency of 0.67%. The β-glucuronidase (GUS) histochemical staining confirmed the expression and integration of an intron-containing gus A gene into transformed leaf discs and transgenic plant lines of KPF4. The presence of gus A gene in the transgenic plants was confirmed by polymerase chain reaction (PCR). The results confirmed that the gus A gene was efficiently integrated into the passion fruit genome. Conclusions The developed transformation protocol is simple and rapid and could be useful for functional genomic studies and transferring agronomically important traits into passion fruit hybrid KPF4. This study developed a method that can be used to transfer traits such as resistance to viral diseases, low fruit quality and short storage life. To the best of our knowledge, this is the first report on genetic transformation system for commercial passion fruit hybrid KPF4.

Flavonoids play a key role as a secondary antioxidant defense system against different biotic and abiotic stresses, and also act as coloring compounds in various fruiting plants. In this study, fruit samples of purple (Passiflora edulis f. edulis) and yellow (Passiflora edulis f. flavicarpa) passion fruit were collected at five developmental stages (i.e., fruitlet, green, veraison, maturation, and ripening stage) from an orchard located at Nanping, Fujian, China. The contents of flavonoid, anthocyanin, proanthocyanin, and their metabolites were determined using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), activities of key enzymes involved in flavonoid metabolism were measured, and expression profiling of related genes was done using quantitative real-time PCR (qRT-PCR). The results revealed that total flavonoids, anthocyanins, and procyanidins were found to be increased in the fruit peel of both cultivars with fruit maturity. Total flavonoids, anthocyanins, procyanidins, flavonoid metabolites (i.e., rutin, luteolin, and quercetin), and anthocyanin metabolites (i.e., cyanidin-3-O-glucoside chloride, peonidin-3-O-glucoside, and pelargonidin-3-O-glucoside) were found abundant in the peel of purple passion fruit, as compared to yellow passion fruit. Principle component analysis showed that the enzymes, i.e., C4H, 4CL, UFGT, and GST were maybe involved in the regulation of flavonoids metabolism in the peel of passion fruit cultivars. Meanwhile, PePAL4, Pe4CL2,3, PeCHS2, and PeGST7 may play an important role in flavonoid metabolism in fruit peel of the passion fruit. This study provides new insights for future elucidation of key mechanisms regulating flavonoids biosynthesis in passion fruit.

Colombia is the country with the greatest genetic diversity in passion fruit species, some of which are cultivated on an area of approximately 13,673 ha. Each variety must be planted at a suitable altitude under optimal conditions to obtain the best quality. Regarding plant nutrition, potassium has the greatest influence due to the effect of its application on the yield increase, ascorbic acid content and lifecycle to harvest. Adequate water increases the percentage of the marketable quality and amount of fruit juice, and the use of rootstocks does not significantly change the fruit quality. Ensuring a pollination of the flowers in cultivation is decisive for the fruit formation and its juice content. The species differ greatly in their quality, as purple passion fruit (Passiflora edulis f. edulis) is a fruit that develops the highest content of ascorbic acid, while sweet calabash (P. maliformis) forms the maximum amount of phenols and total antioxidant activity. The maturation and ripening of passion fruit is determined by the skin coloration, during which the Brix grades and the maturity index increase and the titratable acidity diminishes. Fruits harvested early in physiological maturity and with unripe peel color can be treated with ethylene in post-harvest, matching fruits that ripened in the plant. More research is needed in the improvement of the quality of the Passifloraceae. Giant granadilla (P. cuadrangularis) and sweet calabash have been studied less than banana passion fruit (P. tripartita var. mollissima), purple passion fruit, yellow passion fruit and sweet granadilla (P. ligularis). The last three species are the most exported fruits in the country.

In vitro grafting is one of the promising techniques for fruit crop breeding. This study was performed to produce in vitro vigorous passion fruit rootstocks and developed a simple in vitro grafting protocol with the support of nylon microtubes—a low cost, wide availability, non-toxic and reusable material. The results showed that stem-lTCL explants (longitudinal thin cell layers) cultured on MS medium containing 0.5 mg/L BA and 0.5 mg/L NAA gave the highest shoot regeneration, and these shoots were initial materials for micropropagation of passion fruit rootstock. MSM medium containing 5 mg/L AgNPs increased shoot multiplication twofold higher than that of control and significantly reduced leaf yellowing and leaf drop during this stage. Rooting rate and quality of the plantlets were optimal on MSM medium contained with 2.5 mg/L IBA as well as their survival rate was enhanced in nursery. Nylon microtubes improved the efficiency of passion fruit in vitro grafts to 73.33% with yellow passion fruit as rootstock and purple passion fruit nodal segments as scion. In addition, the use of nylon microtubes significantly improved the in vitro growth of in vitro grafted plants resulting in increased survival rate and plantlet growth in the nursery stage. The present results provide an efficient protocol for micropropagation of yellow passion fruit for rootstock and production of purple passion fruit via nylon microtubule-mediated in vitro grafting.Key messageAn efficient protocol was established for multiplication of in vitro vigorous passion fruit rootstock via the application of thin cell layer culture techniques, nanotechnology and modification of the culture medium. Nylon microtubes enhanced the success rate of in vitro grafting and ex vitro grafted plant growth.

Orphan crops, which include many of the tropical fruit species used in the juice industry, lack genomic resources and breeding efforts. Typical of this dilemma is the lack of commercial cultivars of purple passion fruit, Passiflora edulis f. edulis, and of information on the genetic resources of its substantial semiwild gene pool. In this study, we develop single-nucleotide polymorphism (SNP) markers for the species and show that the genetic diversity of this fruit crop has been reduced because of selection for cultivated genotypes compared to the semiwild landraces in its center of diversity. A specific objective of the present study was to determine the genetic diversity of cultivars, genebank accession, and landraces through genotyping by sequencing (GBS) and to conduct molecular evaluation of a broad collection for the species P. edulis from a source country, Colombia. We included control genotypes of yellow passion fruit, P. edulis f. flavicarpa. The goal was to evaluate differences between fruit types and compare landraces and genebank accessions from in situ accessions collected from farmers. In total, 3820 SNPs were identified as informative for this diversity study. However, the majority distinguished yellow and purple passion fruit, with 966 SNPs useful in purple passion fruits alone. In the population structure analysis, purple passion fruits were very distinct from the yellow ones. The results for purple passion fruits alone showed reduced diversity for the commercial cultivars while highlighting the higher diversity found among landraces from wild or semi-wild conditions. These landraces had higher heterozygosity, polymorphism, and overall genetic diversity. The implications for genetics and breeding as well as evolution and ecology of purple passion fruits based on the extant landrace diversity are discussed with consideration of manual or pollinator-assisted hybridization of this species.

This study evaluated P. edulis f. edulis intraspecific variation at DNA level using AFLPs and SSRs. About 60 specimens were collected from Colombian commercial plantations in the departments of Antioquia, Boyaca ´, Cundinamarca, Huila, Quindı ´o and Tolima. Ten specimens were also included from Corpoica's La Selva research center Passiflora germplasm bank. A non-commercial purple passion fruit plant and three species from the Passiflora genus (Passiflora maliformis, Passiflora edulis f. flavicarpa and Passiflora ligularis) were included as controls. The six most informative ones were selected from the initial screening of 49 different AFLP primer combinations; 52-92 DNA fragments for each combination in each genotype (total 419 fragments) were obtained by using these six combinations. 17 SSR primers reported in P. edulis f. flavicarpa and Passiflora alata were tested on purple passion fruit. Eight of them were successfully amplified but none showed polymorphism. Relationships among individuals were assessed on AFLP data using cluster analysis by Dice coefficient, UPGMA algorithm and the multiple correspondence analysis ordination method based on Greenacre measurement. The similarity coefficients ranged from 0.75 to 1.00 giving an average of 0.96 within the different purple passion fruit materials, showing low genetic variability for the purple passion fruit material used in this study.

Passiflora edulis is an exotic fruit found in limited parts of India. The pulp of the fruit is mainly consumed while the rind and seeds are discarded. Thus, the present study aimed to investigate the physicochemical, nutritional, antioxidant and antibacterial properties of unused rind and seeds from yellow passion fruit (YPF) and purple passion fruit (PPF) collected from Northeast India. Physical investigation of biomass showed low ash and moisture content. Elements like K, Ca and Mg were the major macro elements present in both YPF and PPF rind and seed. A significant quantity of vitamin C, carbohydrate and reducing sugar was observed in the rinds, whereas total protein content was predominant in seeds. Methanolic extract of the rind of YPF showed the highest TPC and TFC followed by acetone extracts. High antioxidant activity (DPPH scavenging, ABTS (2,2-azinobis-3-ethylbenzothiazoline-6-sulphonic acid) and metal chelating) were displayed by methanolic and acetone extracts from rinds and seeds. The global antioxidant score was mathematically calculated to classify the best extract among the rind and seed samples. The presence of gallic acid, p-coumaric acid, ferulic acid, quercetin, myercetin and kaempferol in different extracts of YPF and PPF was confirmed from HPLC analysis. Gallic acid was found ranging from 17.52–83.00 mg/g, where flavonol glycosides were found ranging from 1.64–10.84 mg/g in both YPF and PPF rind and seed extract. Methanolic extracts of seeds showed the best antibacterial activity against gram-positive and gram-negative bacteria, followed by rind extracts. The obtained findings could help understand the nutritional and therapeutic values of passion fruit from Northeast India for their food and pharmaceutical applications.

The odor-active compounds of the conventional yellow passion fruit influence the aroma during ripeness and the acceptance of the juice. HS–GC–MS and GC–OSME analysis and sensory acceptance of the conventional passion fruit from different stages of ripeness were studied to characterize the aroma of the fruit and, aroma and flavor of the juice. Ethyl butanoate, ethyl hexanoate and propyl acetate showed high odoriferous importance in the passion fruit from the 1/3 yellow skin color. C is -3-hexen-1-ol and diethyl carbonate plus the odor-active compounds from the 1/3 yellow skin color showed high odoriferous importance in the 2/3 yellow skin color, and butyl acetate and alpha-terpineol plus the same odor-active compounds from 2/3 were the most important for the 3/3 yellow skin color. There was difference in the aroma and flavor of the juices, with higher acceptance means for the passion fruit from the 3/3 yellow skin color. The passion fruit volatile compounds peak area, odoriferous intensity and sensory acceptance of the juices increased during ripeness, indicating that the conventional passion fruit characteristic aroma is completely expressed when the fruit reaches the whole maturation, at the 3/3 yellow skin color.

Passion fruit has a difficult natural fruiting process and low yield due to its approach herkogamy. Understanding the molecular mechanism of passion fruit style bending is crucial as it enhances pollination efficiency by optimizing stigma-anther alignment, overcoming herkogamy and improving fruit yield. In this study, we used the purple passion fruit variety ‘Tainong 1’ as experimental material. We observed that its style bends into an “S”-shape after flowering. As development progresses, the degree of this S-shaped curvature gradually weakens. Simultaneously, the style also exhibits a spatial bending from top to bottom during this process. In order to identify the genes specifically induced during the style bending process, transcriptome analysis was conducted on styles at T 1 (flowering), T 2 (30 min post-flowering), and T 5 (120 min post-flowering). 226 DEGs were identified to be specifically expressed in the T 1 to T 2 stages, mainly enriched in the “Protein processing in endoplasmic reticulum” pathway, involving heat shock proteins and DnaJ family proteins, suggesting that heat stress response is involved in early style movement regulation. The enriched 18 DEGs were all heat shock protein family proteins and DnaJ family proteins, which may be due to the stress response of the style to environmental heat stimulation. At the same time, 1,080 DEGs were specifically expressed in the T 2 to T 5 stages, mainly enriched in the “Phenylpropanoid biosynthesis” pathway and involved in the lignin biosynthesis pathway. Physiological testing confirmed that as the S-shaped of the style weakens, lignin accumulates significantly, increasing by 60% from T 1 to T 2 and by 43% from T 2 to T 5 , which is consistent with the trend of transcriptome data. In addition, differential expression of hormone metabolism related genes (abscisic acid, brassino steroids, jasmonic acid, and gibberellin pathways) was observed. Endogenous hormone quantification further confirmed hormonal regulation of style bending, revealing distinct accumulation patterns: ABA showed a biphasic trend with an initial 30% increase (T 1 to T 2 ) followed by a 9% rise (T 2 to T 5 ), while jasmonic acid exhibited a sharper 30% (T 1 to T 2 ) to 22% (T 2 to T 5 ) escalation. In summary, our results indicate that lignin accumulation enhances the mechanical strength of the style and reduces its inherent S-shaped bending. Thermal stimulation and hormone synthesis metabolism may also play a role in the process of style bending, but further research is needed to determine the specific mechanisms by which the response is regulated.