Although it is usually latent on citrus, apple, and pear, apple stem grooving virus (ASGV) poses a great risk to many sensitive cultivars.  Since severe leaf yellow mottle mosaic (LYMM) symptoms have been observed on Huangjinmiyou (HJY) pummelos (Citrus grandis cv. Huangjinmiyou), a commercial variety that is widely cultivated in South China, high throughput sequencing (HTS) was used to find potential pathogens and only three divergent ASGV variants were identified.  The three ASGV variants shared 81.03–82.34% genome-wide pairwise identities with each other, and were separately closest to other ASGV variants from different hosts and/or geographical regions, as indicated by viral phylogenies.  However, these new variants may have developed from viral interstrain interactions, based on the results of recombination analysis.  A large-scale survey using reverse transcription-PCR (RT-PCR) protocols designed for the three ASGV variants revealed a high incidence (92.7–100%) of ASGV in symptomatic HJY trees from 11 major citrus-producing regions in China.  None of ASGV were detected in asymptomatic trees.  Temperature treatments applied to the symptomatic HJY plants showed that ASGV is sensitive to high temperatures (30–35°C), at which not only the plants recovered, but also the viruses were not detected by RT-PCR, while at low temperatures (20–24°C), both the symptoms and viruses remained detectable.  These data show that ASGV is associated with the LYMM disease prevalent on HJY in China, and this is the significant basis especially of taking appropriate measures timely to manage the disease.  

Citrus leaf blotch virus (CLBV) is a member of the genus Citrivirus, in the family Betaflexiviridae.  It has been reported CLBV could infect kiwi, citrus and sweet cherry in China.  Of 289 citrus samples from six regions of China, 15 were detected to be infected with CLBV in this study.  The complete genome of four isolates of CLBV was obtained from Reikou in Sichuan (CLBV-LH), Yura Wase in Zhejiang (CLBV-YL), Bingtangcheng in Hunan (CLBV-BT), Fengjie 72-1 in Chongqing (CLBV-FJ), respectively.  While they all represented 8 747 nucleotides in monopartite size, excluding the poly(A) tail, each of the isolates coded three open reading frames (ORFs).  Identity of the four isolates ranged from 98.9 to 99.8% to each other and from 96.8 to 98.1% to the citrus references in GenBank by multiple alignment of genomes.  A phylogenetic tree based on the genome sequences of available CLBV isolates indicated that the four isolates were clustered together, suggesting that CLBV isolates from citrus in China did not have obvious variation.  This is the first report of the complete nucleotide sequences of CLBV isolates infecting citrus in China.

The ecological effect of reclaimed water irrigation and fertilizer application on the soil environment is receiving more attention.  Soil microbial activity and nitrogen (N) levels are important indicators of the effect of reclaimed water irrigation on environment.  This study evaluated soil physicochemical properties and microbial community structure in soils irrigated with reclaimed water and receiving varied amounts of N fertilizer.  The results indicated that the reclaimed water irrigation increased soil electrical conductivity (EC) and soil water content (SWC).  The N treatment has highly significant effect on the ACE, Chao, Shannon (H) and Coverage indices.  Based on a 16S ribosomal RNA (16S rRNA) sequence analysis, the Proteobacteria, Gemmatimonadetes and Bacteroidetes were more abundant in soil irrigated with reclaimed water than in soil irrigated with clean water.  Stronger clustering of microbial communities using either clean or reclaimed water for irrigation indicated that the type of irrigation water may have a greater influence on the structure of soil microbial community than N fertilizer treatment.  Based on a canonical correspondence analysis (CCA) between the species of soil microbes and the chemical properties of the soil, which indicated that nitrate N (NO₃^–-N) and total phosphorus (TP) had significant impact on abundance of Verrucomicrobia and Gemmatimonadetes, meanwhile the pH and organic matter (OM) had impact on abundance of Firmicutes and Actinobacteria significantly.  It was beneficial to the improvement of soil bacterial activity and fertility under 120 mg kg^–1 N with reclaimed water irrigation.

Mung bean (Vigna radiata L.) has the potential to establish symbiosis with rhizobia, and symbiotic association of soil micro flora may facilitate the photosynthesis and plant growth response to elevated [CO2]. Mung bean was grown at either ambient CO2 400 μmol mol–1 or [CO2] ((550±17) μmol mol–1) under free air carbon dioxide enrichment (FACE) experimental facility in North China. Elevated [CO2] increased net photosynthetic rate (Pn), water use efficiency (WUE) and the non-photochemical quenching (NPQ) of upper most fully-expanded leaves, but decreased stomatal conductance (Gs), intrinsic efficiency of PSII (Fv´/Fm´), quantum yield of PSII (ΦPSII) and proportion of open PSII reaction centers (qP). At elevated [CO2], the decrease of Fv´/Fm´, ΦPSII, qP at the bloom stage were smaller than that at the pod stage. On the other hand, Pn was increased at elevated [CO2] by 18.7 and 7.4% at full bloom (R2) and pod maturity stages (R4), respectively. From these findings, we concluded that as a legume despite greater nutrient supply to the carbon assimilation at elevated [CO2], photosynthetic capacity of mung bean was still suppressed under elevated [CO2] particularly at pod maturity stage but plant biomass and yield was increased by 11.6 and 14.2%, respectively. Further, these findings suggest that even under higher nutrient acquisition systems such as legumes, nutrient assimilation does not match carbon assimilation under elevated [CO2] and leads photosynthesis down-regulation to elevated [CO2].

Humankind has been through different periods of agricultural improvement aiming at enhancing our food supply and the performance of food crops. In recent years, whole genome sequencing and deep understanding of genetic and epigenetic mechanisms have facilitated new plant breeding approaches to meet the challenge of growing population, dwindling resources, and changing climate. Here we proposed a simple and fast molecular breeding method, marker-assisted reverse breeding (MARB), which will revert any maize hybrid into inbred lines with any level of required similarity to its original parent lines. Since all the pericarp DNA of a hybrid is from the maternal parent, whereas one half of the embryo DNA is from the maternal parent and the other half from the paternal parent, so we firstly extract DNA from seed embryo and pericarp of a selected elite hybrid separately and then we derived the genotypes of the two parents with high-density single nucleotide polymorphism (SNP) chips. The following marker-assisted selection was performed based on an Illumina low-density SNP chip designed with 192 SNPs polymorphic between the two parental genotypes, which were uniformly distributed on 10 maize chromosomes. This method has the advantages of fast speed, fixed heterotic mode, and quick recovery of beneficial parental genotypes compared to traditional pedigree breeding using elite hybrids. Meanwhile, MARB has the advantage of not requiring sophisticated transformation and double haploid (DH) technologies over RNA interference (RNAi)-mediated reverse breeding. In addition, MARB can also be used with feed corn harvested from big farms, which is often similar to F2 populations, and the relevant transgenes in the population can be eliminated by marker-assisted selection. As a result, the whole global commercial maize hybrids can be utilized as germplasm for breeding with MARB technology. Starting with an F2 population derived from an elite hybrid, our experiment indicates that with three cycles of marker-assisted selection, selected lines could recover over 80% of the parental genotypes and associated beneficial genes in a fixed heterotic mode. The success application of MARB in maize suggests that this technology is applicable to any hybrid crop to breed new inbreds with improved hybrid performance but the same heterotic mode. As chip technology becomes cheap, it would be expected that polymorphism screening and following marker-assisted selection could be done with one all-purpose high density chip.Several issues associated with MARB were discussed, including its rationale, efficiency and advantages, along with food/ feed and environmental safety issues and applications of MARB in variety protection and marker-assisted plant breeding.