Horticulture, Environment, and Biotechnology

Substantial progress has been made in the micropropagation of orchid species using biotechnological interventions, but the commercial viability of the technique has been hindered by increased mortality of plantlets out of culture vessels. This is attributed to the development of in vitro-induced structural and physiological abnormalities in the plantlets. This research investigated the chronological series of foliar microstructural and histochemical responses at the microscopic level during various stages of plantlet development in Spathoglottis plicata, an important terrestrial orchid. Plants that were grown under in vitro heterotrophic conditions displayed underdeveloped foliar anatomical and histochemical traits such as a thin cuticle, unorganized epidermal cells, and fewer mesophyll tissue density and vascular elements with reduced deposition of lignins, cutin, pectin, tannins, and polyphenolic compounds. Ex vitro hardening of the plantlets in a mixotrophic environment improved the development of the cuticle and histochemical traits, created a uniform epidermal layer, increased mesophyll and vascular elements. The field-developed plants had well-developed dermal, ground, and vascular tissue systems along with increased deposition of primary and secondary metabolites. These gradual changes positively impacted the microstructural and physiological status of in vitro-propagated plantlets of S. plicata to withstand biotic and abiotic stresses in field conditions. This study suggests that subsequent hardening and an acclimatization period would enhance the structural and histochemical parameters of in vitro-propagated S. plicata plants resulting in the production of healthy regenerants with 100% survival success.

Increasing demand for high quality mangoes has increased the need for enhanced fruit quality and longer shelf life. The concentrations of calcium (Ca) and boron (B) in fruit can affect its quality and shelf life and physiochemical composition. However, these effects have not been investigated in postharvest mango. The effects of Ca and B concentration on mango fruit quality and shelf life were investigated by spraying a 40% Ca(NO3)2·4H2O and 0.3% H3BO3 solution at 1, 2, 3 and 4 mL L−1 concentration on mango fruits for 60 and 90 days after anthesis compared with water control treatment. Mango fruits were subsequently harvested 110 days after anthesis and stored at 15 °C. Chemical and physical properties were then observed every three days. When fruit were sprayed with a 1 mL L−1 Ca–B solution, the size of the mango fruit and cells in the exocarp and the mesocarp increased, which was increased concentrations of Ca and B in the fruit. In addition, we found that pre-harvest application of Ca and B by spraying improved the tissue structure of the segment membrane, as well as increased fruit firmness, which was consistently delayed as much as nine to 21 days after harvest. Moreover, fruit that had been sprayed with a 1 mL L−1 Ca and B solution had an extended storage life at 15 °C of 24 days. Vitamin C concentration and SS/TA were higher at this treatment concentration compared to the other treatments. Furthermore, Hunter L, a, and b values of the peel were lower than those from fruit in other treatments groups. Additionally, the activities of pectin methylesterase and polygalacturonase in the treated pulp were reduced.

Radish (Raphanus sativus L.) is a representative root crop of the Brassicaceae family and is important to the vegetable seed industry in East Asia. Due to its agronomic importance, various molecular markers, genetic maps, genomic resources, and genome assemblies of radish have been developed during the past decade. Marker integration and comparative mapping using these resources will accelerate genetic improvements in radish cultivars. With the goal of establishing a marker-based high-throughput genetic analysis tool, we integrated 3765 nonredundant genetic markers into the Rs1.0 reference genome and converted them into 1182 single nucleotide polymorphism (SNP) markers via whole-genome resequencing data of the mapping parents ‘WK10039’ and ‘WK10024’. A genetic map covering 721.3 cM with 768 framework loci was constructed by analyzing these SNP conversion markers in the F2 mapping population, which was composed of 93 individuals. Comparison of this map with the Rs1.0 reference genome and other linkage maps showed the physical and genetic correlations of the markers. To develop a high-throughput genotyping system for large accessions or populations with smaller numbers of SNPs, 674 Fluidigm and 68 kompetitive allele-specific PCR (KASP) markers were validated. Application of the 68 KASP assays to 127 commercial cultivars enabled successful identification and classification of genotypes; 11 KASP markers constituted the minimum marker set. The SNP markers used to construct the genetic maps will be a useful resource in research on radish and should lead to low-cost, accurate, and high-throughput genotyping platforms.

Paphiopedilum pacific shamrock is an orchid with high ornamental value. Understanding the mechanisms responsible for leaf color in albino mutants is important for ornamental development and breeding. In this study, we compared the leaf photosynthetic pigment content and transcriptome of albino mutants ppa01 and wild-type P. pacific shamrock. Photosynthetic pigment in mutants was less than 2% of the wild type and chl a/b was 60% less than the wild type. Transcriptome sequencing yielded 6.27 Gb and 5.67 Gb clean data from the mutant and wild-type leaves, respectively. De novo assembly yielded 104,763 unigenes with 15,400 greater than 1 kb in length. In unigene expression analysis, 3170 differentially expressed genes (DEGs) were identified with 2231 (70.38% of total DEGs) down-regulated. Results from GO and KEGG enrichment analysis, KEGG pathway analysis and qPCR suggest that the reduction of chloroplast biosynthesis and division in the mutant was due to low expression levels of ppGLK1 and ppFtsz. Mutants were associated with fewer chloroplasts in leaf cells, abnormal chloroplast structures, impaired chlorophyll biosynthesis, and thus reduced total chlorophyll and carotenoid contents. Furthermore, down-regulated expression of ppNYC1 reduced transformation of chlorophyll b into chlorophyll a, leading to a chl a/b decline. The research will guide future studies of leaf pigment mutations and the breeding of P. pacific shamrock.

A three-locus model for rind phenotypes in watermelon (Citrullus lanatus) was previously proposed based on genetic analysis. These three loci, S (foreground stripe pattern), D (depth of rind color), and Dgo (background rind color), segregate in a Mendelian manner. Whole genome sequencing of watermelon offers a new strategy for marker development in these rind phenotype-related loci. A genotype analysis using subsets of 188, 273, 287 and 113 probes was performed for the ‘0901’, ‘10909’, ‘109905’ and ‘90509’ rind trait-segregating F2 populations, respectively. A total of 26, 34, 30 and 15 linkage groups with 175, 254, 269 and 79 probes were constructed for the ‘0901’, ‘10909’, ‘109905’ and ‘90509’ populations, respectively. The genetic order of the probes was mostly collinear with the physical order on the reference genome, except for some probes on chromosomes 1, 3 and 11. The three rind-related loci, S, D, and Dgo were anchored near chr6_25767 on chromosome 6, chr8_26061 on chromosome 8 and chr4_150/chr4_249 on chromosome 4, respectively. The three loci are located on different chromosomes, and the three-locus model was therefore verified through molecular genetic analysis. We suggest a rapid and practical marker development strategy that can be used not only for rind traits but also for other agriculturally important traits in watermelon and applied for conventional breeding.

Rapid, economical, and reliable genotyping is an important requirement for germplasm analysis and cultivar identification in crop species. Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt) originated in China and is now an economically important vegetable crop worldwide, especially in East Asia. In this study, we evaluated 1167 single nucleotide polymorphisms (SNPs) among 166 representative Chinese cabbage inbred lines using a KASP genotyping assay. On the basis of polymorphisms and principal component analysis, we selected 60 core SNPs distributed on all Brassica rapa chromosomes with allele frequencies sufficiently balanced so as to provide adequate information for genetic identification. The core set of SNPs was used for construction of a neighbor-joining dendrogram, in which the 166 inbred lines were clustered into spring, summer, and autumn ecotype groups. Clustering of the ecotype groups was better resolved than that achieved with 1167 and 360 polymorphic SNP datasets. Stability and resolution of the core SNP markers were tested using 178 commercial hybrid Chinese cabbage cultivars to confirm their utility in genetic identification. The set of 60 informative and stable SNP markers showed high discriminatory power and relatively uniform genomic distribution (4–9 markers per chromosome). The SNPs represent a cost-efficient and accurate marker set for germplasm analysis and cultivar identification and are suitable for molecular marker-assisted breeding in Chinese cabbage.

Dormancy release of variegated Solomon’s seal (Polygonatum odoratum Druce var. pluriflorum Ohwi for. variegatum Y.N.Lee) was studied by varying the transferring date from the field to greenhouse and by cold storage in order to identify their precise chilling requirement. Bud emergence and flowering did not occur throughout the experiment when dormant rhizomes were transferred until a calendar date November 22, 2009, in which natural cumulative chill unit (NCU) was 75 h. Days to sprouting, flowering, and flower abscission were shortened with delayed transferring dates. Percent sprouting and flowering showed an increasing tendency since rhizomes were transferred on December 7 (= 241 h NCU), but emergence date was not uniform. However, uniform percent sprouting was maintained since rhizomes were transferred on December 22 (= 492 h NCU). No or 1 week of cold storage at 0 or 5°C did not induce sprouting, which meant bud dormancy was not released when rhizomes were stored ≤ 1 week. When they were stored for more 2 weeks at 0 or 5°C, percent sprouting was increased to ≥ 91% in the heated greenhouse. Cumulative chill unit (CCU) was 336 h at 0°C and 225 h at 5°C. However, bud emergence date after 2 weeks of cold storage was not uniform at both storage temperatures, whereas bud emergence after 4 weeks of cold storage at 0°C was more uniform than that at 5°C. Therefore, at least 492 h NCU, 4 weeks of cold storage at 0°C (= 672 h CCU), or 6 weeks at 5°C (= 675 h CCU) is recommended for forcing and normal growth afterward of variegated Solomon’s seal.

To promote the stress resilience of sweet pepper crops (Capsicum annuum L.) and phase out the use of pesticides and other environmentally harmful materials, grafting has been used to integrate biotic or abiotic stress-resistance characteristics with sustainable crop production. This study aimed to determine the changes in the morphological characteristics, physiological features and low-temperature resistance of the sweet pepper cultivar ‘Hongxing No. 2’ grafted onto five rootstocks (‘No. 14’, ‘No. 15’, ‘No. 16’, ‘Jiaozhen108’, and ‘J4-908’) and itself. The morphological features of the aerial organs and roots of the different graft combinations were monitored, as were the activities of active oxygen-scavenging enzymes. Most morphological and physiological characteristics were significantly improved in the graft combination No. 2/Jiaozhen108, which indicated that Jiaozhen108 had a higher graft affinity with Hongxing No. 2 than the other rootstocks. No. 2/Jiaozhen108 also had a higher resistance to low temperatures. Therefore, the Jiaozhen108 rootstock is considered a quality candidate for grafting with the sweet pepper cultivar Hongxing No. 2, providing a theoretical basis for the screening and greenhouse production of low-temperature resistant stocks.

Lagerstroemia indica is a summer ornamental flowering tree, belonging to the Lythraceae family. Its flower color is a key ornamental characteristic. Recent research indicates that WRKY and bZIP transcription factors play important role in flower color formation. Based on the transcriptome database of L. indica, this study identified 85 LibZIPs and 61 LiWRKYs from the L. indica transcriptome database and analyzed their expression profiles using qRT-PCR. Phylogenetic analysis divided LibZIPs into 11 subfamilies and LiWRKYs into six subfamilies. Nine LibZIPs and four LiWRKYs were found to have higher expression in colored samples compared to the white sample. LibZIP31, LibZIP65, LibZIP34, LiWRKY16, LiWRKY25, LiWRKY40, and LiWRKY67 may play important roles in flower color formation in L. indica. These results provide valuable information for further functional analysis of the bZIP and WRKY genes families in L. indica and help clarify their roles in flower color formation.