A search for the ideal flavor of strawberry - Comparison of consumer acceptance and metabolite patterns in <i>Fragaria</i> × <i>ananassa</i> Duch.

in strawberry. Despite numerous investigations of the metabolic composition of strawberries, the description of the relationship between flavor pattern and consumer acceptance is inconsistent. The aim of the present study was to correlate overall liking (acceptance), the intensity of important sensory parameters, which were evaluated by a consumer panel, and data of instrumental analyses like soluble solids content, titratable acidity and volatile organic compound patterning. The data were collected over a period of three harvest years. They are suitable to reveal the relationships and interactions between the metabolite patterns of strawberry and the sensory properties due to the use of a high diversity of the gene pool and due to a special sample preparation with representative sample sizes for both human sensory and instrumental analysis. A high genetic diversity was considered including genotypes from cultivar crossing and from wild species introgression. It was found that the volatile compounds methyl 2-methylbutanoate, (Z)-3-hexenyl acetate, linalool and decanoic acid correlate positively with the attribute ‘sweet’ and, therefore, can act as sweetness enhancers. Furthermore, compounds were identified with positive (linalool, lactones) and negative impact (some esters, furanones) on the sensory quality. From these findings, strategies towards improved, sensorially valuable strawberry cultivars with a high consumer acceptance can be deduced.   The online version of this article (doi: 10.5073/JABFQ.2016.089.029) contains supplementary files

Diversity of volatile patterns in sixteen Fragaria vesca L. accessions in comparison to cultivars of Fragaria ×ananassa

Fragaria vesca is the most distributed wild species in the genus Fragaria. Due to this biogeography a high diversity is to expect. During two harvest seasons sixteen accessions from different locations from the most eastern habitat at Lake Baikal in Siberia, from Middle and Southern Europe and Northern Europe with Scandinavia and Iceland were investigated as well as two of the three described North American subspecies and three F. vesca cultivars. Five very distinct European F. ×ananassa cultivars were chosen to serve as a comparison. Beside brix value and acid contents the aroma patterns including 67 volatile compounds were quantified by stir bar sorptive extraction followed by gas chromatography with mass spectrometric detection. The diversity of important volatiles of Fragaria vesca and F. ×ananassa is discussed regarding biogeography, domestication, breeding and the so-called funnel effect

Spontaneous polyploidisation of interspecific and intersectional Pelargonium hybrids during embryo rescue

Modern Pelargonium crispum hybrids (section Pelargonium) show low genetic and phenotypic variation due to the domestication effect. Species of the sections Cortusina, Ligularia, and Pelargonium are potential breeding partners at the diploid level (2n = 2x = 22). Five P. × crispum cultivars were used as seed parents and pollinated with one genotype of P. grandiflorum (section Pelargonium) and three genotypes of P. fulgidum (section Ligularia). In both combinations, embryo rescue was necessary. Embryos were rescued and cultured on Murashige &amp; Skoog medium supplemented with phytohormones. After callus and adventitious shoot regeneration 15 viable interspecific hybrids were obtained from crossbreeding with P. grandiflorum and 11 intersectional hybrids from crossings with P. fulgidum, respectively. The hybrids were cultivated in the greenhouse until flowering. Their hybrid character was evident due to the intermediate morphological traits. Molecular investigations using dp-RAPD analysis confirmed this. Within the F1 population P. × crispum with P. grandiflorum three hybrids and after crossing with P. fulgidum one hybrid possessed larger flowers and fully developed anthers, respectively. Their ploidy level was confirmed as tetraploid using flow cytometry. Therefore, a spontaneous polyploidisation occurred during in vitro regeneration. The tetraploid F1 hybrids are fertile and could be used for further breeding

Natural Variation in the Control of Flowering and Shoot Architecture in Diploid Fragaria Species

In perennial fruit and berry crops of the Rosaceae family, flower initiation occurs in late summer or autumn after downregulation of a strong repressor TERMINAL FLOWER1 (TFL1), and flowering and fruiting takes place the following growing season. Rosaceous fruit trees typically form two types of axillary shoots, short flower-bearing shoots called spurs and long shoots that are, respectively, analogous to branch crowns and stolons in strawberry. However, regulation of flowering and shoot architecture differs between species, and environmental and endogenous controlling mechanisms have just started to emerge. In woodland strawberry (Fragaria vesca L.), long days maintain vegetative meristems and promote stolon formation by activating TFL1 and GIBBERELLIN 20-OXIDASE4 (GA20ox4), respectively, while silencing of these factors by short days and cool temperatures induces flowering and branch crown formation. We characterized flowering responses of 14 accessions of seven diploid Fragaria species native to diverse habitats in the northern hemisphere and selected two species with contrasting environmental responses, Fragaria bucharica Losinsk. and Fragaria nilgerrensis Schlecht. ex J. Gay for detailed studies together with Fragaria vesca. Similar to F. vesca, short days at 18 degrees C promoted flowering in F. bucharica, and the species was induced to flower regardless of photoperiod at 11 degrees C after silencing of TFL1. F. nilgerrensis maintained higher TFL1 expression level and likely required cooler temperatures or longer exposure to inductive treatments to flower. We also found that high expression of GA20ox4 was associated with stolon formation in all three species, and its downregulation by short days and cool temperature coincided with branch crown formation in F. vesca and F. nilgerrensis, although the latter did not flower. F. bucharica, in contrast, rarely formed branch crowns, regardless of flowering or GA20ox4 expression level. Our findings highlighted diploid Fragaria species as rich sources of genetic variation controlling flowering and plant architecture, with potential applications in breeding of Rosaceous crops.Peer reviewe

Phenotyping 172 strawberry genotypes for water soaking reveals a close relationship with skin water permeance.

Water soaking is a commercially important disorder of field-grown strawberries that is exacerbated by surface wetness and high humidity. The objective was to establish the effect of genotype on susceptibility to water soaking. Three greenhouse-grown model ‘collections’ were used comprising a total of 172 different genotypes. Potential relationships between water soaking and water uptake characteristics, depth of the achene depressions, fruit firmness, cuticle mass and strain relaxation and microcracking were investigated. Further, the effect of downregulating the polygalacturonase genes (FaPG1 and FaPG2) on the susceptibility to water soaking was investigated. The collection of wild species was most susceptible to water soaking. Susceptibility to water soaking was strongly correlated with water uptake rate (mass of water, per fruit, per time). For the pooled dataset of 172 genotypes, 46% of the variability in water soaking was accounted for by the permeance of the skin to osmotic water uptake. Susceptibility to water soaking was not, or was only poorly correlated with measurements of fruit surface area or of the osmotic potential of the expressed fruit juice. The only exceptions were the wild Fragaria species which were highly variable in fruit size and also in fruit osmotic potential. For genotypes from the F2 and the wild species collections, firmer fruit were less susceptible to water soaking than softer fruit. There were no relationships between fruit firmness and susceptibility to water soaking in transgenic plants in which FaPG1 and FaPG2 were down-regulated. Susceptibility to water soaking was not related to cuticle mass per unit fruit surface area, nor to strain relaxation of the cuticle upon isolation, nor to achene position. In summary, strawberry’s susceptibility to water soaking has a significant genetic component and is closely and consistently related to the skin’s permeance to osmotic water uptake.This work was funded by a grant from the Deutsche Forschungsgemeinschaft (DFG KN402/19-1

Hybridization between Pelargonium acetosum L’Hér. and Pelargonium xpeltatum

Pelargonium acetosum L’Hér. is a wild species from South Africa with decorative bluish foliage. Only few reports describe crossings between P. acetosum and P. peltatum L’Hér. (or P. ×peltatum). Therefore, information about hybridization barriers is limited. In this study, two different genotypes of Pelargonium acetosum (AC1 and AC2) were crossed with the diploid P. ×peltatum ‘Tornado Fuchsia’ (PTF). Embryos and F1 hybrids from the combination AC1 × PTF were hampered by chlorophyll deficiencies. Embryos and seeds of the combination AC2 × PTF were underdeveloped. The reciprocal combination PTF × AC1 did not show any fruit set. The combination PTF × AC2 resulted in low numbers of seeds, which were normally developed. Hybrids from seeds were only obtained from the combinations AC1 × PTF and PTF × AC2. Embryo rescue of the combinations AC1 × PTF and AC2 × PTF resulted in few but viable hybrids. Flowers of all hybrids had shrivelled anthers and proved to be sterile. The occurrence of most hybridization barriers varied strongly between the different combinations and depended on both the genotype and the direction of cross-breeding. The bluish leaf colour did not appear among the F1. To overcome hybrid sterility a polyploidization is suggested

Strawberry Accessions with Reduced Drosophila suzukii Emergence From Fruits

Drosophila suzukii is threatening soft fruit production worldwide due to the females’ ability to pierce through the intact skin of ripe fruits and lay eggs inside. Larval consumption and the associated microbial infection cause rapid fruit degradation, thus drastic yield and economic loss. Cultivars that limit the proliferation of flies may be ideal to counter this pest; however, they have not yet been developed or identified. To search for potential breeding material, we investigated the rate of adult D. suzukii emergence from individual fruits (fly emergence) of 107 accessions of Fragaria species that had been exposed to egg-laying D. suzukii females. We found significant variation in fly emergence across strawberries, which correlated with accession and fruit diameter, and to a lesser extent with the strawberry species background. We identified accessions with significantly reduced fly emergence, not explained by their fruit diameter. These accessions constitute valuable breeding material for strawberry cultivars that limit D. suzukii spread.Peer Reviewe

A strawberry accession with elevated methyl anthranilate fruit concentration is naturally resistant to the pest fly Drosophila suzukii

During the past decade, Drosophila suzukii has established itself as a global invasive fruit pest, enabled by its ability to lay eggs into fresh, ripening fruit. In a previous study, we investigated the impact of different strawberry accessions on the development of D. suzukii eggs, in the search of natural resistance. We identified several accessions that significantly reduced adult fly emergence from infested fruit. In the present study, we aimed at understanding the chemical basis of this effect. We first noted that one of the more resistant accessions showed an unusual enrichment of methyl anthranilate within its fruit, prompting us to investigate this fruit compound as a possible cause limiting fly development. We found that methyl anthranilate alone triggers embryo lethality in a concentration-dependent manner, unlike another comparable organic fruit compound. We also showed that a chemical fraction of the resistant strawberry accession that contains methyl anthranilate carries some activity toward the egg hatching rate. Surprisingly, in spite of the lethal effect of this compound to their eggs, adult females are not only attracted to methyl anthranilate at certain concentrations, but they also display a concentration-dependent preference to lay on substrates enriched in methyl anthranilate. This study demonstrates that methyl anthranilate is a potent agonist molecule against D. suzukii egg development. Its elevated concentration in a specific strawberry accession proven to reduce the fly development may explain, at least in part the fruit resistance. It further illustrates how a single, natural compound, non-toxic to humans could be exploited for biological control of a pest species

Great Cause—Small Effect: Undeclared Genetically Engineered Orange Petunias Harbor an Inefficient Dihydroflavonol 4-Reductase

A recall campaign for commercial, orange flowering petunia varieties in spring 2017 caused economic losses worldwide. The orange varieties were identified as undeclared genetically engineered (GE)-plants, harboring a maize dihydroflavonol 4-reductase (DFR, A1), which was used in former scientific transgenic breeding attempts to enable formation of orange pelargonidin derivatives from the precursor dihydrokaempferol (DHK) in petunia. How and when the A1 cDNA entered the commercial breeding process is unclear. We provide an in-depth analysis of three orange petunia varieties, released by breeders from three countries, with respect to their transgenic construct, transcriptomes, anthocyanin composition, and flavonoid metabolism at the level of selected enzymes and genes. The two possible sources of the A1 cDNA in the undeclared GE-petunia can be discriminated by PCR. A special version of the A1 gene, the A1 type 2 allele, is present, which includes, at the 3′-end, an additional 144 bp segment from the non-viral transposable Cin4-1 sequence, which does not add any functional advantage with respect to DFR activity. This unequivocally points at the first scientific GE-petunia from the 1980s as the A1 source, which is further underpinned e.g., by the presence of specific restriction sites, parts of the untranslated sequences, and the same arrangement of the building blocks of the transformation plasmid used. Surprisingly, however, the GE-petunia cannot be distinguished from native red and blue varieties by their ability to convert DHK in common in vitro enzyme assays, as DHK is an inadequate substrate for both the petunia and maize DFR. Recombinant maize DFR underpins the low DHK acceptance, and, thus, the strikingly limited suitability of the A1 protein for a transgenic approach for breeding pelargonidin-based flower color. The effect of single amino acid mutations on the substrate specificity of DFRs is demonstrated. Expression of the A1 gene is generally lower than the petunia DFR expression despite being under the control of the strong, constitutive p35S promoter. We show that a rare constellation in flavonoid metabolism—absence or strongly reduced activity of both flavonol synthase and B-ring hydroxylating enzymes—allows pelargonidin formation in the presence of DFRs with poor DHK acceptance.Peer Reviewe

Independent mutations in a single locus, the transcriptional factor MYB10, control natural variation in fruit color among Fragaria species

External and internal fruit color are important traits in strawberry (Fragaria spp.) breeding programs, where different preferences are sought depending on whether the fruits are produced for fresh consumption or processing. Therefore, there is a great interest in the development of predictive markers that effectively speed the development of new cultivars with increased consumer acceptance and/or which address processed fruit industry´s preferences. In order to identify loci controlling fruit color variation, two mapping populations were generated: one crossing diploid F. vesca parentals and another interspecific population between two octoploid species: the cultivated and the Chilean strawberry, F. x ananassa and F. chiloensis. Both populations allowed the detection of a QTL spanning a region of the F. vesca linkage group 1 (LG I) that includes the MYB10 gene, a known key regulator of anthocyanin biosynthesis. Mapping by sequencing in the F. vesca population revealed an LTR retrotransposon inserted in the third exon of FvMYB10, which produces a premature stop codon, and co-segregates with white fruits in the entire population. Genotyping by Sanger sequencing of additional white-fruited F. vesca accessions resulted in the identification of another three independent mutations in MYB10, two of them not previously described1. In octoploid strawberry, a mayor QTL on LG I-3 controls about 55% variation in internal flesh color and is associated with an insertion in the promoter region of FcMYB10. Similar insertions have been detected in other F. chiloensis accessions bearing white fruits. In all cases, transient over-expression of FvMYB10 restored anthocyanin biosynthesis and red color in fruit flesh and skin, indicating that lack of function of MYB10 was the underlying cause of white fruits in all analyzed cases