Powdery mildew (PM), which is caused by the pathogen Erysiphe necator (Schw.) Burr., is the single most damaging disease of cultivated grapes (Vitis vinifera) worldwide. However, little is known about the transcriptional response of grapes to infection with PM. RNA-seq analysis was used for deep sequencing of the leaf transcriptome to study PM resistance in Chinese wild grapes (V. pseudoreticulata Baihe 35-1) to better understand the interaction between host and pathogen. Greater than 100 million (M) 90-nt cDNA reads were sequenced from a cDNA library derived from PM-infected leaves. Among the sequences obtained, 6541 genes were differentially expressed (DEG) and were annotated with Gene Ontology terms and by pathway enrichment. The significant categories that were identified included the following: defense, salicylic acid (SA) and jasmonic acid (JA) responses; systemic acquired resistance (SAR); hypersensitive response; plant–pathogen interaction; flavonoid biosynthesis; and plant hormone signal transduction. Various putative secretory proteins were identified, indicating potential defense responses to PM infection. In all, 318 putative R-genes and 183 putative secreted proteins were identified, including the defense-related R-genes BAK1, MRH1 and MLO3 and the defense-related secreted proteins GLP and PR5. The expression patterns of 16 genes were further illuminated by RT-qPCR. The present study identified several candidate genes and pathways that may contribute to PM resistance in grapes and illustrated that RNA-seq is a powerful tool for studying gene expression. The RT-qPCR results reveal that effective resistance responses of grapes to PM include enhancement of JA and SAR responses and accumulation of phytoalexins.

A program for producing new seedless table and raisin grape cultivars was initiated using embryo culture methods. F 1 descendants of the cross Delight × Ruby Seedless (DRs) were used as the female parent and crossed with various seedless cultivars. The berries of DRs have excellent table traits but they retain small seed traces at maturity. Blush Seedless and DRs were used as female parents, and 354 ovules from five crosses were tested. The percentage of embryos that developed using DRs as the female parent was higher (26.7-35.8%) than when a seedless cultivar was the female parent (5.9-6.7%). The best ovule excision time [days after flowering (DAF)] for ovule inoculation was tested in another set of crosses and found to be DAF 48, 50, and 50 for DR1 × Monukka, DR6 × Thompson Seedless, and DR7 × Zhengguo Seedless, respectively. A total of 569 hybrid progeny were obtained from 13 hybrid combinations; 311 of these survived and were established in soil after hardening. We used three molecular markers (SCC8, SCF27, and GSLP1) to analyze 15 parents used in the hybrid combinations. SCC8 had a 1018-bp band in the seedless parents and in some of the DR parents, while SCF27 had a 2000-bp band in all seedless and DR parents. GSLP1 had a 569-bp band in all of the seedless parents tested, whereas the seeded and DR parents had no bands of this size. Therefore, GSLP1 was used to screen the progeny for possible seedlessness. Eight strains had the 569-bp band; these were preliminarily identified as being seedless since they are in juvenile phase, but they have not yet been evaluated for fruiting characteristics. If the strains identified by using GSLP1 are confirmed to be seedless, this marker will be a valuable tool in breeding for seedlessness in grape.

Summary Seedlessness in grapes is one of the features most appreciated by consumers. However, the mechanisms underlying seedlessness in grapes remain obscure. Here, we observe small globular embryos and globular embryos in Pinot Noir and Thompson Seedless from 20 to 30 days after flowering (DAF). From 40 to 50 DAF, we observe torpedo embryos and cotyledon embryos in Pinot Noir but aborted embryos and endosperm in Thompson Seedless. Thus, RNA‐Seq analyses of seeds at these stages from Thompson Seedless and Pinot Noir were performed. A total of 6442 differentially expressed genes were identified. Among these, genes involved in SA biosynthesis, VvEDS1 and VvSARD1, were more highly expressed in Thompson Seedless than in Pinot Noir. Moreover, the content of endogenous SA is at least five times higher in Thompson Seedless than in Pinot Noir. Increased trimethylation of H3K27 of VvEDS1 and VvSARD1 may be correlated with lower SA content in Pinot Noir. We also demonstrate that VvHDZ28 positively regulates the expression of VvEDS1. Moreover, over‐expression of VvHDZ28 results in seedless fruit and increased SA contents in Solanum lycopersicum. Our results reveal the potential role of SA and feedback regulation of VvHDZ28 in seedless grapes.

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