IntroductionThe strawberry industry in South Korea has witnessed a significant 65% growth over the past decade, surpassing other fruits and vegetables in production value. While sweetness and acidity are well-recognized flavor determinants, the role of volatile organic compounds (VOCs) in defining the desirable flavor profiles of strawberries is also crucial. However, existing research has predominantly concentrated on a limited range of commercial cultivars, neglecting the broader spectrum of strawberry varieties.MethodsThis study embarked on developing a comprehensive VOC database for a diverse array of strawberry cultivars sourced both domestically and internationally. A total of 61 different strawberry cultivars from Korea (45), the USA (7), Japan (8), and France (1) were analyzed for their VOC content using Tenax TA Thermo Desorption tubes and Gas Chromatography-Mass Spectrometry (GC-MS). In addition to VOC profiling, heritability was assessed using one-way ANOVA to compare means among multiple groups, providing insights into the genetic basis of flavor differences.Results and discussionThe analysis identified 122 compounds categorized into esters, alcohols, terpenes, and lactones, with esters constituting the majority (46.5%) of total VOCs in Korean cultivars. ‘Arihyang’, ‘Sunnyberry’, and ‘Kingsberry’ exhibited the highest diversity of VOCs detected (97 types), whereas ‘Seolhong’ showed the highest overall concentration (57.5mg·kg-1 FW). Compared to the USA cultivars, which were abundant in γ-decalactone (a peach-like fruity aroma), most domestic cultivars lacked this compound. Notably, ‘Misohyang’ displayed a high γ-decalactone content, highlighting its potential as breeding germplasm to improve flavor in Korean strawberries. The findings underscore the importance of a comprehensive VOC analysis across different strawberry cultivars to understand flavor composition. The significant variation in VOC content among the cultivars examined opens avenues for targeted breeding strategies. By leveraging the distinct VOC profiles, particularly the presence of γ-decalactone, breeders can develop new strawberry varieties with enhanced flavor profiles, catering to consumer preferences for both domestic and international markets.

Strawberry aroma, crucial for determining quality, involves complex volatile compounds which are challenging to identify. This study explores strawberry aroma analysis using Gas Chromatography-Mass Spectrometry (GC-MS) and the Automated Mass Spectral Deconvolution and Identification System (AMDIS). Central to our research is the creation of a bespoke strawberry Volatile Organic Compounds (VOCs) user library using AMDIS, specifically for analyzing strawberry aromas. The library contains VOCs from 61 strawberry cultivars, integrating information on 104 VOCs, including mass spectra, retention index, chemical class, CAS number, formula, odor threshold, and odor description. This custom library significantly outperformed a commercial library by reducing potential false hits by 200, decreasing the size of report files by over 96%, and, most importantly, shortening AMDIS analysis processing time from 31 s to 9 s, representing an approximate 71% reduction. Further, the study demonstrates the library’s practical application by contrasting the aroma profiles of strawberries harvested in winter and spring. This comparison revealed significant VOC variations depending on seasonal temperature changes, offering insights into environmental influences on strawberry aroma. In conclusion, this research marks a significant advance in strawberry aroma quality analysis. The strawberry VOC library developed in this study is expected to greatly aid targeted metabolomics and flavor research in strawberry breeding.

The objective of a strawberry nursery is to produce numerous runners and improve the quality of the runner plants, ensuring their uniformity and health. About 80% of the strawberry nurseries in Wanju-gun, Republic of Korea, are cultivated by the growers themselves, which results in variations in the cultivation techniques. Different methods are employed to reduce the nitrogen levels to promote floral bud initiation in the later nursery stage, and these methods vary between farms. This study was conducted on the ‘Sulhyang’ cultivar (Fragaria × ananassa Dutch. cv. Sulhyang) to measure the nutrient content in runner plants obtained from eight growers using various cultivation methods, supply EC levels, nutrient solution termination times, etc., and to correlate the nutrient levels with floral bud initiation during the nursery period. Four investigations were conducted at 15-day intervals from Julian day 214 (2 August) to Julian day 259 (16 September) in 2022, focusing on nutrient management during the nursery period, runner plant growth, petiole nitrate nitrogen content (NO3-N), and soluble solid content (SSC). The NO3-N content decreased, and the SSC/NO3-N ratio increased near the transplanting period, as assessed using a rapid inorganic nutrient diagnostic device. The proportion of runner plants that had advanced to stage 3 or above in floral bud initiation was investigated using a stereomicroscope. As a result, differences in the percentage of floral bud initiation were confirmed based on the varying nutrient management among the farms. In this study, on Julian day 243 (31 August 2022), there was a strong negative correlation (r = −0.86, r2 = 0.73) between the NO3-N content in the runner plants and the percentage of floral bud initiation. These results emphasize the importance of nutrient management during the nursery period, especially for strawberry self-propagating growers, and demonstrate a strong correlation between nutrient content and floral bud initiation in strawberries.

Although hydroponic techniques enable intensive and effective crop management, controlling the watering for each crop type and growth stage is challenging using the commonly used timed watering system. Therefore, excessive and insufficient watering occurs frequently. Hydroponic technology that considers the drainage rate can minimize the amount of drainage, thereby reducing environmental pollution and fertilizer consumption. This study compared the drainage rate and the timed watering methods in a strawberry hydroponic system and determined the optimal drainage rate. As the drainage rate increased, the amount of water supplied increased. A significantly negative correlation was found between the amount of water supplied and the total nitrogen content. Drainage electrical conductivity (EC) level was the highest in the 10% drainage rate group. In the 20% drainage rate treatment, leaf length and width increased compared to the four applications timer-supplying method. The yield of fruits weighing more than 27 g was the highest in the 20% drainage rate treatment. Therefore, the 20% drainage rate treatment was the most appropriate. We propose that it is possible to reduce unnecessary fertilizer consumption and increase productivity by controlling the water supply using the drainage rate for precise water supply management of strawberries.

The genus Fragaria encompass fruits with diverse colors influenced by the distribution and accumulation of anthocyanin. Particularly, the fruit colors of strawberries with different ploidy levels are determined by expression and natural variations in the vital structural and regulatory genes involved in the anthocyanin pathway. Among the regulatory genes, MYB10 transcription factor is crucial for the expression of structural genes in the anthocyanin pathway. In the present study, we performed a genome wide investigation of MYB10 in the diploid and octoploid Fragaria species. Further, we identified seven quantitative trait loci (QTLs) associated with fruit color in octoploid strawberry. In addition, we predicted 20 candidate genes primarily influencing the fruit color based on the QTL results and transcriptome analysis of fruit skin and flesh tissues of light pink, red, and dark red strawberries. Moreover, the computational and transcriptome analysis of MYB10 in octoploid strawberry suggests that the difference in fruit colors could be predominantly influenced by the expression of MYB10 from the F. iinumae subgenome. The outcomes of the present endeavor will provide a platform for the understanding and tailoring of anthocyanin pathway in strawberry for the production of fruits with aesthetic colors.

Strawberry is an allo-octoploid crop with high genome heterozygosity and complexity, which hinders the sequencing and the assembly of the genome. However, in the present study, we have generated a chromosome level assembly of octoploid strawberry sourced from a highly homozygous inbred line ‘Wongyo 3115’, using long- and short-read sequencing technologies. The assembly of ‘Wongyo 3115’ produced 805.6 Mb of the genome with 323 contigs scaffolded into 208 scaffolds with an N50 of 27.3 Mb after further gap filling. The whole genome annotation resulted in 151,892 genes with a gene density of 188.52 (genes/Mb) and validation of a genome, using BUSCO analysis resulted in 94.10% complete BUSCOs. Firmness is one of the vital traits in strawberry, which facilitate the postharvest shelf-life qualities. The molecular and genetic mechanisms that contribute the firmness in strawberry remain unclear. We have constructed a high-density genetic map based on the ‘Wongyo 3115’ reference genome to identify loci associated with firmness in the present study. For the quantitative trait locus (QTL) identification, the ‘BS F 2 ’ populations developed from two inbred lines were genotyped, using an Axiom 35K strawberry chip, and marker positions were analyzed based on the ‘Wongyo 3115’ genome. Genetic maps were constructed with 1,049 bin markers, spanning the 3,861 cM. Using firmness data of ‘BS F 2 ’ obtained from 2 consecutive years, five QTLs were identified on chromosomes 3-3, 5-1, 6-1, and 6-4. Furthermore, we predicted the candidate genes associated with firmness in strawberries by utilizing transcriptome data and QTL information. Overall, we present the chromosome-level assembly and annotation of a homozygous octoploid strawberry inbred line and a linkage map constructed to identify QTLs associated with fruit firmness.

Chlorophyll is an important factor facilitating plants to capture, allocate and transforms light energy and plays a major role in yield formation. Strawberry is one of the most important fruit crops worldwide. Breeding strawberry for better light utilization by improving photosynthetic efficiency can improve the yield potential. In strawberry, genetic studies have been done for several traits, but no reports on the genetic mapping of chlorophyll content in leaves. In the present study, we used two independent F2 mapping populations (BS-F2 and BC-F2) and, Axiom 35 K strawberry chip and genotyping-by-sequencing derived single nucleotide polymorphisms based linkage maps to identify the quantitative trait loci (QTLs) controlling leaf chlorophyll content. SPAD values were used to estimate the leaf chlorophyll content of parental lines and F2 populations. A total of seven QTLs, including major and minor effects, common and specific to populations, were identified across the strawberry genome explaining phenotypic variation (R2) ranging from 1.4 to 26.4%. Candidate genes associated with the photosynthesis and chlorophyll content were inferred in commonly detected QTLs. This work thus provides not only information for novel loci controlling chlorophyll content in strawberry leaves but also forms the basis for future marker assisted breeding in strawberry to select the plants for required chlorophyll content.

Fusarim oxysporum에 의한 덩굴쪼김병은 수박 재배에 큰 피해를 일으키는 중요한 병이다. 이 병을 방제하기 위해 덩굴쪼김병 저항성 박 대목을 이용하는 것이 가장 좋은 방법이다. 본 연구는 박 덩굴쪼김병 저항성 자원을 선발할 수 있는 방법을 확립하기 위해 수행하였다. 효과적인 접종법을 개발하기 위해 접종 후 온도(15, 20, 25, 30°C), 접종 농도(1 X 105, 5 X 105, 1 X 106 and 5 X 106 conidia･mL-1), 접종 시기(파종 7, 10, 13, 16일 후)를 조사하였다. 박 덩굴쪼김병을 접종하였을 때 접종 후 배양 온도나 파종 후 접종 시기의 영향이 적었다. 그러나, 덩굴쪼김병에 저항성인 박의 경우 접종농도가 높을수록 발병이 심하게 나타났다. 따라서, 박 덩굴쪼김병에 대한 효과적인 접종법으로 파종 10일 된 유묘 뿌리를 1 X 105 - 1 X 106 conidia･mL-1 농도로 30분간 접종한 후 감염되지 않은 토양에 옮겨 심고 25°C에서 3주 동안 재배하는 것을 제안한다.

This work assessed the percent germination according to seed storage duration and influence on F1 hybrid progeny by individual plants of inbred lines, used as parents in crosses, in the F1 hybrid strawberry cultivar ‘Seeberry’. Seed germination was the highest, at approximately 90%, when seeds were sown in the year of crossing. Percent germination dropped to 40-50% after 1-2 years of storage, with further substantial decreases in percent germination after 3, 4, and 5 years of storage. For stored seed, therefore, the optimal storage duration was about 2 years. However, germination of stored seed could be substantially improved, up to approximately 90% germination, with the application of a priming treatment such as MgCl2. The degree of uniformity of F1 hybrid progeny with advancement of selfing generation of cross parents showed no significant differences both in crosses between the S9 or S10 generation. However, when individual F1 crosses of the S9 generation were considered, one of nine crosses exhibited reduced plant vigor and yield. Overall, for optimal germination, F1 hybrid seed strawberry should be sown in the same year as crossing. Where storage is required, seeds should be sown within 2 years, preferably with a priming treatment to improve germination. Furthermore, vegetative propagation of each individual of inbred lines using crossing parents appears preferable to seed propagation for maintaining the purity of the F1 hybrid cultivar.

The octoploid strawberry (Fragaria × ananassa Duch.) is one of the most important horticultural crops in the world. However, few genomic studies have been performed in this plant due to its polyploidy nature and complex genome. In this work, we developed diallelic single-nucleotide polymorphism (SNP) markers using next-generation resequencing data and high-resolution melting (HRM) analysis. We also constructed a genetic linkage map using an F1 segregating population derived from a cross between two cultivars, F. × ananassa ‘Sulhyang’ and ‘Senga-sengana’. A previous study revealed 20,848 SNP positions that can be developed into HRM markers. In this study, 576 SNP-based and 34 simple sequence repeat (SSR)-based HRM markers were developed using 832 newly designed and 461 previously reported primer sets, respectively. In addition, a strawberry genetic linkage map covering a total genetic distance of 1504.7 cM and consisting of 759 loci on 35 linkage groups was constructed. The linkage groups were assigned to corresponding chromosomes using the informative SSR-based markers and a BLAST search to the diploid strawberry genome, Fragaria vesca ver. 2.0.a1. Furthermore, the genome-wide HRM markers were applied to analyze the homozygosity of the inbred strawberry line ‘Wongyo 3115’, which showed a homozygosity of 96.6%. This marker and map information will be useful for future genomic and genetic research of the octoploid strawberry.

Myeong Cheoul Cho, Jung-Ho Kwak, Hyo Bong Jeong, Suk Woo Jang, Su Hyoung Park, Young Seok Kwon, Chul Woo Kim, Min Seon Choi, Ji Won Han, Ji Hye Moon, Dae Young Kim, Sun Yi Lee, Oak Jin Lee, Do Sun Kim, Hye Eun Lee, Yun Chan Huh, and Eun Young Yang*. Korean J. Breed. Sci. 2020;52:112-43. https://doi.org/10.9787/KJBS.2020.52.S.112

The ‘common’ strawberry (Fragaria × ananassa) is a popular fruit in Korea and is often consumed fresh. Polyploidy is common in horticultural crops, and Fragaria × ananassa is octoploid, having 8 sets of each chromosome; however, the molecular genetic information of octoploid strawberry is still insufficient to develop effective markers for agronomic traits. In this study, a set of high-quality single nucleotide polymorphisms (SNPs) was collected via the genotyping-by-sequencing (GBS) method to genotype the strawberry inbred lines developed in Korea. We used a population of 89 strawberry inbred lines, which were derived from nine strawberry cultivars. The FANhybrid_r1.2 octoploid assembly was used as a reference genome. The average length of reads was 87,458,702 bp, and a total of 437,058 SNPs were collected. Several filtering criteria (SNP quality, read depth, and genotype quality) were used to identify 20,923 potential SNPs. Finally, 2863 high-quality SNPs were selected for the study. The genetic diversity of the inbred lines was analyzed by phylogenetic tree and structure analysis using the SNP genotype data. This is the first report of genotyping strawberry inbred lines using the GBS technique, and can be used to accelerate strawberry molecular breeding.

Modern cultivated strawberry is propagated vegetatively using stolons and crowns, but this clonal propagation of strawberry makes propagation labor-intensive and time-consuming, and introduces the risk of the virus and pathogen transfer from the mother plant to the nursery plant. Therefore, there has long been a need for seed–propagated strawberry cultivars. We tested the genetic similarity of seed-propagated F1 hybrids strawberry using seven simple sequence repeat markers. We detected high (> 0.90) genetic similarity among individuals of F1 hybrids developed by crossbreeding between these inbred lines and individuals of S9 or S11 inbred lines derived from ‘Benihoppe’, ‘Toyonoka’, and ‘Akihime’, original cultivars. The genetic similarity among inbred lines increased with the advancement of selfing generations, and that of F1 hybrids produced through hybridization between inbred lines was also very high. Although the genetic similarity among these individual of inbred lines and F1 hybrids was very high, some variation was detected, but it did not result in morphological differences. With the advancement of selfing generations, the yield and fruit weight tended to decrease in the F1 hybrids. To develop commercially useful seed-propagated cultivars, the effects of different cross combinations or crossing among and within selfing generations should be investigated.

A strawberry variety ‘Arihyang’ was derived as an artificial cross between ‘Tochiotome’ and ‘Seolhyang’ in 2014. The seedling and line selections were conducted from 2014 to 2015. Preliminary and advanced yield trials of ‘14-5-5,’ which was the final selected line, were conducted from 2015 to 2017. ‘Arihyang’ is suitable for forced cultivation and has strong plant vigor, uniformly large-sized fruit, and a high yield compared to those of the check variety, ‘Seolhyang’ and ‘Maehyang.’ Especially, vitamin C was at a significant level, which was approximately 15% higher than that of ‘Seolhyang.’ The average number of flowers per first flower cluster was 10.5, which could reduce the labor of thinning fruit. Its fruit has a conical shape, dark red color, and glossy skin. The fruit was of good quality but has recommendations for harvest at the fully ripened stage. ‘Arihyang’ has intermediate resistant to phytophthora crown rot, but is susceptible to powdery mildew, gray mold, anthracnose, and fusarium wilt. It is reguired to manage major diseases and pests using optimum cultivation techniques and chemical control.

American/European strawberry cultivars are morphologically different from Asian cultivars with American cultivars generally having higher yields, fruit weight, and fruit hardness and Asian cultivars tending to have higher sugar content. In this study, we performed backcrossing to improve the fruit qualities of Asian varieties of strawberries using American cultivars as the donor parent. The F1 progeny derived from crosses between Asian and American cultivars tended to have lower sugar content and higher fruit weight and yield than Asian cultivars, but fruit hardness did not differ between the Asian cultivars and the progenies. The percent germination and survival ratio were not significantly different between the BC1F1 and BC2F1 generations, whereas the percent germination decreased rapidly with advancing backcross generations. The BC1F1 generation had slightly higher sugar content and the sugar content of the BC2F1 generation increased significantly over the BC1F1 generation, but fruit weight and yield decreased. However, there was variability among individual progeny from the same cross. With advancing generations of backcrossing (BC3F1, BC4F1, BC5F1), sugar content tended to improve while fruit weight and yield tended to decrease, and hardness tended not to change. Therefore, to develop new cultivars with the combined qualities of Asian and American cultivars, we concluded that generations beyond the BC2F1 are not necessary, and that the selection efficiency of superior individual plants can be improved if the number of seedlings is increased in generations before the BC1F1 or BC2F1.