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Yu Cui, Jinsheng Wang, Xingchun Wang and Yiwei Jiang

Perennial ryegrass (Lolium perenne L.) is a popular cool-season forage and turfgrass in temperate regions. Due to its self-incompatible and out-crossing nature, perennial ryegrass may show a high degree of heterozygosity. Perennial ryegrass generally is susceptible to drought stress, but variations of drought response of individual genotypes within a particular accession or cultivar are not well understood. The objective of this study was to characterize phenotypic diversity of drought tolerance within and among accessions in relation to genetic diversity in perennial ryegrass. Five individual genotypes from each of six accessions varying in origin and growth habits were subjected to drought stress in a greenhouse. Leaf wilting, plant height, chlorophyll fluorescence (Fv/Fm) and leaf water content (LWC) differed significantly among accessions as well as among genotypes within each accession under well-watered control and drought stress conditions. Fv/Fm was highly correlated with LWC under drought stress. Genetic diversity among and within accessions were identified by using previously characterized 23 simple sequence repeat markers. Across accessions, the mean major allele frequency, gene diversity, and heterozygosity values were 0.66, 0.43, and 0.66, respectively. Accessions with closer genetic distance generally had similar drought responses, while accessions with greater genetic distance showed distinct drought tolerance. Significant differences in drought tolerance among and within accessions, especially for individual genotypes within one accession, indicated that variations of drought response could be used for enhancing breeding programs and studying molecular mechanisms of stress tolerance in perennial ryegrass.

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Yu Bai, Ying Zhou, Xiaoqing Tang, Yu Wang, Fangquan Wang and Jie Yang

The appropriate timing of bolting and flowering is one of the keys to the reproductive success of Isatis indigotica. Several flowering regulatory pathways have been reported in plant species, but we know little about flowering regulatory in I. indigotica. In the present study, we performed RNA-seq and annotated I. indigotica transcriptome using RNA from five tissues (leaves, roots, flowers, fruit, and stems). Illumina sequencing generated 149,907,857 high-quality clean reads and 124,508 unigenes were assembled from the sequenced reads. Of these unigenes, 88,064 were functionally annotated by BLAST searches against the public protein databases. Functional classification and annotation assigned 55,991 and 23,072 unigenes to 52 gene ontology (GO) terms and 25 clusters of orthologous group (COG) categories, respectively. A total of 19,927 unigenes were assigned to 124 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and 80 candidate genes related to plant circadian rhythm were identified. We also identified a number of differentially expressed genes (DEG) and 91 potential bolting and flowering-related genes from the RNA-seq data. This study is the first to identify bolting and flowering-related genes based on transcriptome sequencing and assembly in I. indigotica. The results provide foundations for the exploration of flowering pathways in I. indigotica and investigations of the molecular mechanisms of bolting and flowering in Brassicaceae plants.

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Ling Yu, Hongwei Chen, Peipei Hong, Hongli Wang and Kefeng Liu

Salvia splendens is a widely used ornamental bedding plant; however, the limited propagation method has decreased its quality and yield. Through years of selection, we have obtained a new variety of S. splendens with weak apical dominance and named it as ‘Cailinghong’. To establish an effective method for regeneration of S. splendens ‘Cailinghong’, different explants, including leaves, receptacles, petioles, stem nodes, and stem segments were used for adventitious bud induction. Next, various combinations of plant growth regulators (PGRs) were selected for bud and root induction, which were assessed by adventitious bud initiation rate and proliferation rate, as well as root induction rate. Meanwhile, the survival rate of transplanted plantlets was also calculated. As a result, stem nodes were found easy to be induced to form buds, and the optimum medium component was 1/2 Murashige and Skoog (MS) medium supplemented with 0.45 µM naphthalene acetic acid (NAA), 8.88 µM 6-benzylaminopurine (6-BA), and 2.46 µM 3-indolebutyric acid (IBA) for plantlets induction, whereas 1/4 MS medium supplemented with 2.23 µM NAA for root induction. Furthermore, the survival rate of transplanted plantlets was up to 80%, and all regenerated plantlets were normal in phenotype. Therefore, cultured in 1/2 MS medium with combined PGRs, whole plantlet of S. splendens ‘Cailinghong’ could be regenerated directly from stem node.

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Yu Hong, D. Creech, Wang Chuanyong, Gu Yin and He Shanan

Blueberries are now the hot point of fruit development in China. Researches conducted in the past since 1980s include mainly introduction and propagation. More than 30 cultivars of rabbiteye blueberries and southern highbush blueberries were introduced successfully in the Nanjing Botanical garden in late 1980s. For dormant cuttings of 4 rabbiteye blueberry cultivars Gardenblue, Tifblue, Climax, and Premier the rooting percentage could reach 84%, 52%, 62%, and 79% respectively under interrupted misting. Lignification of the cuttings seemed the key point for rooting. For soft cuttings the rooting percentage can reach 90% to 95% with chemical treatments. Seedling selection has been conducted and some promising individuals are under observation. So far, there were little experiments on cultural practice under taken. But looking at the difference of soils between the blueberry growing areas in the US and China it seems that there are a series of aspects should be researched in the future.

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Yu Hong, D. Creech, Wang Chuanyong, Gu Yin and He Shanan

The native species of Vaccinium are distributed in both northeast and south of China but more species are in the South. Ecologically, there is a vast territory in the South with acidic soils and plenty of precipitation and warm weather. On the other hand in the northeast regions temperature in winter is usually a problem for cultivated blueberries and protection from freezing is necessary for young plantations. Based on the result of introduction of cultivars, including rabbiteye, southern highbush and lowbush blueberries, in both northern and southern parts in China during the last 2 decades authors suggested that the most prospective regions for blueberry growing could be mostly in south of China. In the between of the two regions the natural ecological conditions are not appropriate for blueberry growing but plantations under plastic film appeared relatively vigorous. 12 rabbiteye blueberry cultivars have been tested in the south and the performance of growth and fruiting are good. It is expected that the average of yield could reach about 15 t·ha–1. The quality of fruits is similar to that of the natives in North America. Up to now there are less insects and diseases damages. It seems that the regions in the south of Changjiang (Yangtze) River provide good conditions for blueberry commercial growing.

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Xuefei Ning, Xianlei Wang, Zhijie Yu, Simeng Lu and Guan Li

Hami melon ‘Queen’ (Cucumis melo ssp. melo var. ameri Pangalo) is the most widely cultivated and exported type of melon in Xinjiang Province, Northwest China. We previously found the unique traits of Hami melon ‘Queen’ for wave seeds and tight-placenta fruits. An analysis of the inheritance showed that these traits were controlled by two recessive genes wave seed (ws) gene and tight-placenta (tp) gene, respectively. Here, to identify these two traits and melon seed–related traits, segregation populations including BC1 and F2 derived from a cross between ‘Queen’ (P1) and MR-1 (P2) were used as mapping populations. Eighty-seven simple sequence repeat (SSR) markers were used in map construction of BC1P1 population, and as a result, ws and tp were identified on linkage group 1. Analysis of quantitative trait locus (QTL) referring seed traits showed that QTL ss1.1 for seed shape (SS) and QTL sl1.1 for seed length (SL) were located at LG 1, supported by likelihood of odds (LODs) of 15.6 and 13.4, respectively, and both linked with ws. Subsequently, the genetic linkage and parental re-sequence analysis were constructed for fine mapping ws and tp. Genetic analysis showed that ws and tp were located in CM3.5_scaffold00060 on LG 1, flanked by InDelchr1-3241 and InDelchr1-3233. The 80.9-kb physical distance of this region included 11 candidate genes. Among them, MELO3C023549 and MELO3C023551 could be candidates for ws and tp by sequence alignment and allelic variation survey in parental lines. MELO3C023549 was predicted to encode an MYB46-like transcription factor related to positive regulation of secondary cell wall biogenesis. MELO3C023551 was annotated to encode a cellulose synthase A (CESA) associated with cellulose biosynthetic process.

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Libin Wang, Elizabeth A. Baldwin, Zhifang Yu and Jinhe Bai

Both refrigeration and blanching of red-stage tomatoes are common practices in Japan home kitchens and in food service operations. However, little is reported on the impact of such practices on aroma profiles in tomato fruits. In this study, ‘FL 47’ tomatoes at red stage were dipped in 50 °C hot water for 5 minutes or exposed to 5 °C for 4 days to simulate consumer handling of tomato in food service or home kitchens, respectively. Of the 42 volatile compounds detected, refrigeration generally suppressed production of aldehydes, alcohols, oxygen-containing heterocyclic compounds, and nitrogen- and oxygen-containing heterocyclic compounds, including the following abundant and/or important volatiles: pentanal, 3-methylbutanal, 2-methylbutanal, hexanal, cis-3-hexenal, trans-2-hexenal, 2-phenylacetaldehyde, pentanol, 3-methylbutanol, 2-phenylethanol, 1-penten-3-one, geranial, and geranylacetone. On the other hand, the production of aldehydes, alcohols, hydrocarbons, oxygen-containing heterocyclic compounds, and nitrogen- and oxygen-containing heterocyclic compounds was reduced by blanching, associated with low concentrations of 2-methylbutanal, pentanal, cis-3-hexenal, trans-2-hexenal, 2-phenylacetaldehyde, pentanol, 2-methylbutanol, and 2-phenylethanol. These results indicate that a short blanching or refrigeration of tomatoes substantially impacts tomato aroma quality.

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Zhan Shu, Xue Zhang, Dianqiong Yu, Sijia Xue and Hua Wang

Hybridization between species of the genus Juglans is common because of weak reproductive isolation mechanisms between closely related species with sympatric distributions. In this research, we investigated the possibility of naturally occurring interspecific hybrids between two species in the genus Juglans: persian walnut (Juglans regia) and chinese walnut (Juglans cathayensis). We used 12 pairs of microsatellite markers to analyze introgression between the two species. All amplified microsatellites were polymorphic in the two species. The result of Bayesian admixture analyses showed that introgression between the two species is rare; only three of nine individuals tentatively identified as hybrids, based on intermediate morphological characteristics, were defined as mixed genotypes. The other six putative hybrids and 156 morphologically pure individuals showed no sign of introgression.

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Xiyan Yu, Xiufeng Wang, Jide Fan, Hongmei Tian and Chengchao Zheng

Sucrose phosphate synthase [SPS (EC 2.4.1.14)] is thought to play a critical role in sucrose accumulation in muskmelon (Cucumis melo L.) fruit. A full-length cDNA clone encoding sucrose phosphate synthase was isolated from muskmelon by reverse transcriptase–polymerase chain reaction and rapid amplification of cDNA ends. The clone, designated CmSPS1, contains 3377 nucleotides with an open reading frame of 3162 nucleotides. The deduced 1054 amino acids sequence showed high identities with other plant sucrose phosphate synthases. Northern blot analysis indicated that CmSPS1 was expressed in leaves, stems, and mature fruit, but was not detected in roots or flowers. Moreover, the mRNA accumulation of CmSPS1 started at 25 days after pollination (DAP) and reached highest level in mature fruit. Interestingly, both sucrose content and SPS activity increased dramatically between 20 and 30 DAP during fruit development, suggesting that sucrose accumulation may be linked to the CmSPS1 transcript level in muskmelon fruit.

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Hongmei Du, Zhaolong Wang, Wenjuan Yu and Bingru Huang

The accumulation of different types of metabolites may reflect variations in plant adaptation to different severities or durations of drought stress. The objectives of this project are to examine changes in metabolomic profiles and determine predominant metabolites in response to short-term (6 days) and long-term (18 days) drought stress with gas chromatography–mass spectrometry analysis in a C4 perennial grass species. Plants of hybrid bermudagrass (Cynodon dactylon × C. transvaalensis cv. Tifdwarf) were unirrigated for 18 days to induce drought stress in growth chambers. Physiological responses to drought stress were evaluated by visual rating of grass quality, relative water content, photochemical efficiency, and electrolyte leakage (EL). All parameters decreased significantly at 6 and 18 days of drought stress, except EL, which increased with the duration of drought stress. Under short-term drought stress (6 days), the content did not change significantly for most metabolites, except methionine, serine, γ-aminobutyric acid (GABA), isoleucine, and mannose. Most metabolites showed higher accumulation under long-term drought stress compared with that under the well-watered conditions, including three organic acids (malic acid, galacturonic acid, and succinic acid), 10 amino acids (proline, asparagine, phenylalanine, methionine, serine, 5-hydroxynorvaline, GABA, glycine, theorine, valine), seven sugars (sucrose, glucose, galactose, fructose, mannose, maltose, xylose), one nitrogen compound (ethanolamine), and two-sugar alcohol (myo-inositol). The accumulation of those metabolites, especially malic acid, proline, and sucrose, could be associated with drought adaptation of C4 hybrid bermudagrass to long-term or severe drought stress.