Dwarfism is an important trait which is closely related to the efficiency of fruit orchard management and production.  However, dwarfing cannot be widely applied in the cultivation of pears, especially Asian pears.  Developing varieties with dwarf characteristics is a goal of paramount importance in pear breeding.  In the present study, dwarf phenotype pears (DPPs) and arborescent phenotype pears (APPs) were obtained from the offspring of a cross between ‘Aiyuxiang’ and ‘Cuiguan’ pear cultivars, which exhibited dwarfed and arborescent statures, respectively.  When compared with APPs, the heights of DPPs showed a 62.8% reduction, and the internode lengths were significantly shorter.  Cross-grafting between DPPs and APPs demonstrated that the dwarfed phenotype of DPPs was primarily induced by the aerial portions of the plant, and independent of the root system.  Observations of stem tissue sections showed that DPP cells were arranged chaotically with irregular shapes, and the average length was larger than that of the APP cells.  A total of 1 401 differently expressed genes (DEGs) in shoot apices between DPPs and APPs were identified by RNA-sequencing (RNA-Seq), and these DEGs were mainly enriched in the ‘phytohormone-related pathways, cell wall metabolism and cell division’ categories.  Moreover, 101 DEGs were identified as transcription factors (TFs).  In DPPs, several brassinosteroids (BR) signaling and cell cycle-related genes were significantly down-regulated, while genes involved in BR and GA degradation were up-regulated.  Comprehensive analysis of RNA-Seq data and stem tissue sections suggested that the dwarfed phenotype of DPPs could be primarily attributed to deficiencies in cell division.  Previous work using simple sequence repeat (SSR) markers narrowed the location of the gene responsible for the dwarf phenotype of ‘Le Nain Vert’.  Through combined analysis of our transcriptomic data with the SSR results, we identified four genes as promising candidates for the dwarf phenotype, among which, a DELLA gene could be the most promising.  The results presented in this study provide a sound foundation for further exploration into the genetic and molecular mechanisms underlying pear dwarfing.

Pakchoi (Brassica campestris L. ssp. chinensis) is an important leafy vegetable.  Various light spectra, especially red and blue light, play vital roles in the regulation of nitrate metabolism.  Information on the effects of red and blue light on nitrate metabolism at the transcriptome level in pakchoi is still limited, so this study used RNA sequencing technology to explore this molecular mechanism.  Through pairwise comparisons with white LED light, 3 939 and 5 534 differentially expressed genes (DEGs) were identified under red and blue light, respectively.  By Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, these unigenes were found to be involved in nitrate assimilation, plant–pathogen interaction, biosynthesis of secondary metabolites, and phenylpropanoid biosynthesis.  The differential effects of light spectra on the nitrate concentration and metabolism-related enzyme activities were also confirmed at the physiological level.  Several signal transduction modules, including Crys/Phys-COP1-HY5/HY5-like, were found to be involved in red and blue light-induced nitrate metabolism, and the transcript levels for this complex were consistent with the observed degree of nitrate assimilation.  The expression patterns of 15 randomly selected DEGs were further validated using qPCR.  Taken together, the results of this study could help improve our understanding of light spectrum-regulated nitrate metabolism in pakchoi at the transcriptome level.

The potato minitubers have been widely used for the elite seed propagation to improve the seed potato system in China. However, little information is available for an efficient production of the minitubers with high plant density in the protected growing conditions like plastic houses. In present research, the minitubers of a wide-grown potato variety, Favorita, were produced with the microtubers from tissue culture and the tip-cuttings of the microtuber plants. Three plant densities, 200, 400 and 600 microtubers or plants m-2 were set up with the randomized block design of 3 replications and the experiment was repeated in 4 seasons in 2009-2010. The canopy development, light interception, dry weight production and partitioning, tuberization and tuber weight were investigated to elucidate the mechanism by which the plant density affects the formation and growth of the minitubers. The results showed that the number of the tubers formed per unite area was in line with the increase in plant density. The difference in leaf area index (LAI) between the plant densities, especially in early stage of the plant growth, resulted in more radiation interception and dry weight producing in higher plant density than in lower one. However, our analysis demonstrated that the conversion coefficient of the cumulative intercepted radiation to plant weight and the dry weight partition rate to the tubers were constant between plant densities, suggesting that less amount of the photoassimilates partitioned to individual tubers is causal for more small tubers in high plant density. A negative exponential curve model, determined by total number of tubers produced per unit area and the mean tuber weight, fitted well to the tuber size distribution pattern. The optimum plant density could be estimated from this model for a maximum production of the minitubers with desired size.

Cultivated potato with high level of horizontal resistance against late blight is one of the most important goals of potatobreeding. The recurrent selection has been adopted to increase the level of potato horizontal resistance and a B3C1population without R1-R11 dominant genes has been released by the International Potato Center at the short-day conditionof Peru. The present research was carried out to further improve the resistance and the agronomic traits of B3C1population under long-day condition of Hubei, China, with maximized retention of its genetic diversity. Twenty-sevenindividual clones of B3C1 were used to generate population B3C2 by in-population crossing with the bulk pollens aimingto elevate the frequency of late blight resistance genotypes and to improve the adaptation to local long-day conditions.The late blight resistance and the main agronomic traits including the maturity, the plant characters and the tuber traitswere evaluated for the foreground selection in three years, by which 130 pedigrees were maintained as the basic populationof B3C2 for further selection. A total of 312 polymorphic loci detected by 9 AFLP marker combinations were used tomonitor the genetic diversity of the populations for the background selection. The B3C2 population of 51 clones wasfinally selected, of which the frequency of resistant genotypes increased by 23.8% points and the genetic diversity wasmaintained by about 96% as referred to B3C1. Our results strongly suggested that combination of the foregroundselection for target traits and the background selection for the genetic diversity is an efficient strategy in the recurrentselection of tetraploid potato to improve quantitative traits.