A new Panax notoginseng Leaf Spot Caused by Boeremia linicola in Yunnan, China.

Panax notoginseng-also known as Tianqi and Sanqi-is one of the most highly valued medicinal perennial herbs in the world (Wang et al. 2016). In August 2021, leaf spot was observed on P. notoginseng leaves in Lincang sanqi base (23º43´10˝N, 100º7´32˝E, 13.33 hm2). Symptoms expanded from water soaked areas on the leaves to form irregular round or oval leaf spots with transparent or grayish-brown centers containing black granular matter, with an incidence of 10 to 20%. To identify the causal agent, ten symptomatic leaves were randomly selected from ten P. notoginseng plants. Symptomatic leaves were cut into small pieces (5 mm2) with asymptomatic tissue margins, disinfected in 75% ethanol for 30s and in 2% sodium hypochlorite for 3 min, and rinsed three times with sterile distilled water. The tissue portions were placed on potato dextrose agar (PDA) plates incubated at 20℃ with a 12 h light/dark photoperiod. Seven pure isolates were obtained with similar colony morphology, dark gray (top view) or taupe (back view) coloration, with flat and villous surfaces. Pycnidia were globose to subglobose, glabrous or with few mycelial outgrowths, dark brown to black, 22.46 to 155.94 (av. 69.57) µm × 18.20 to 130.5 (av. 57.65) µm (n=50) in size. Conidia were ellipsoidal to cylindrical, thinwalled, smooth, hyaline, aseptate, and measured 1.47 to 6.81 (av. 4.29) µm long and 1.01 to 2.97 (av. 1.98) µm thick (n=100). The isolated strains were preliminarily identified as Boeremia sp. based on the morphological characteristics of colonies and conidia. (Aveskamp et al. 2010; Schaffrath et al. 2021). To confirm pathogen identity, the total genomic DNA of two isolates (LYB-2 and LYB-3) was extracted using the T5 Direct PCR kit. The internal transcribed spacer (ITS), 28S large subunit nrRNA gene (LSU), and ß-tubulin (TUB2) gene regions were PCR-amplified using primers ITS1/ITS4, LR0Rf/LR5r, and BT2F/BT4R (Chen et al. 2015), respectively. Sequences have been deposited in GenBank (ON908942-ON908943 for ITS, ON908944-ON908945 for LSU, ON929285-ON929286 for TUB2). BLASTn searches of generated DNA sequences from 2 purified isolates (LYB-2 and LYB-3) against GenBank showed high similarity (>99%) with the sequences of Boeremia linicola. Moreover, a phylogenetic tree was constructed based on the neighbor-joining method in MEGA-X (Kumar et al. 2018) and revealed that the 2 isolates were closest to B. linicola (CBS 116.76). Pathogenicity tests were conducted with the 2 isolates (LYB-2 and LYB-3) as described by Cai et al. (2009) with slight modifications. Each isolate was inoculated with three healthy annual P. notoginseng plants, and each leaf was inoculated with three drops of conidia suspension (106 spores/mL). Three P. notoginseng plants inoculated with sterile water were used as controls. All plants were covered with plastic bags incubated in a greenhouse (20℃, 90%RH, 12 h light/dark photoperiod). Fifteen days post-inoculation, all inoculated leaves showed similar lesions, and the symptoms were identical to those in the field. The pathogen was reisolated from symptomatic leaf spots, and the colony characteristics were identical to the original isolates. Control plants remained healthy, and no fungus was re-isolated. Morphological characteristics, sequence alignment and pathogenicity tests confirmed that B. linicola was the cause of P. notoginseng leaf spot disease. This is the first report of B. linicola causing leaf spot on P. notoginseng in Yunnan, China. The identification of B. linicola as the causal agent of the observed leaf spot on P. notoginseng is critical to the prevention and control of this disease in the future.

First Report of Leaf Spot on Panax notoginseng Caused by Caryophylloseptoria pseudolychnidis in Yunnan, China.

Panax notoginseng is a unique traditional medicinal plant in China, which has the effects of improving myocardial ischemia, protecting liver and preventing cardiovascular diseases (Jiang, 2020). In July 2021, gray-brown round spots were found on the leaves of P. notoginseng in the plantations of Lincang City (23º43´10˝N, 100º7´32˝E). By September, the symptoms were observed on more P. notoginseng plants, with incidence reaching 31%. Initial symptoms on leaves were small, brown spots that expanded, with black granular bulges on the lesions, often surrounded with yellow halo. As the disease progressed, multiple lesions merged, leaves became yellow, and abscission occurred. To isolate the causal pathogen, twelve symptomatic leaves were randomly obtained from twelve P. notoginseng plants. Small pieces of infected leaf tissues (about 5 mm2) were disinfected with 75% ethanol for 30 s, soaked in 2% sodium hypochlorite for 3 min, and then rinsed 3 times with sterile water and blotted dry. Sample tissues were plated on potato dextrose agar (PDA) plates incubated at 25℃ for 5 days with 12 h light/dark photoperiod. Hyphal-tips from the growing edge of colonies were transferred to fresh PDA to obtain pure cultures. Eight isolates were obtained with similar colony morphology, gray (top view) or black (back view) coloration, with a villous surface, and slow-growing on PDA. Conidia were hyaline, slender and obtuse to subobtuse at both ends, 10.3 to 52.62 (av. 25.2) µm × 1.4 to 4.0 (av. 2.4) µm (n=200) in size. Characteristics of the colonies and conidia were consistent with Caryophylloseptoria pseudolychnidis as described by Quaedvlieg et al. (2013) and Verkley et al. (2013). Genomic DNA of three representative isolates (LINC-4 to LINC-6) was extracted, and the rDNA-ITS region, ACT, and LSU gene regions were amplified and sequenced using the primer pairs ITS4/ITS5, 512F/783R, and LSU1Fd/LR5, respectively. Sequences have been deposited in GenBank (OK614104-OK614106 for ITS, OK614109-OK614111 for LSU, OK628350-OK628352 for ACT). BLAST search showed that all sequences were 98% to 100% homology with the corresponding sequences of C. pseudolychnidis. ITS sequences of the three isolates (LINC-4 to LINC-6) showed 99.21% identity (500/504 bp) to C. pseudolychnidis strain CBS 128630 (GenBank accession no. NR156266). LSU sequences of the three isolates showed 99.76% identity (823/825 bp) to C. pseudolychnidis strain CBS 128630 (MH876481). For ACT sequences, LINC-4 and LINC-5 showed 98.53% identity (201/204 bp) to C. pseudolychnidis strain 128614 (KF253599); LINC-6 showed 99.02% identity (202/204 bp) to C. pseudolychnidis strain 128614 (KF253599). Further, the neighbor-joining and maximum-likelihood method were used for multilocus phylogenetic analysis of the obtained sequences using MEGA-X (Kumar et al. 2018). The three isolates were clustered in the same clade with two C. pesudolychidis from database. Three isolates (LINC-4 to LINC-6) were tested for pathogenicity to confirm Koch's postulates. Annual potted P. notoginseng was inoculated with spore suspension (105 spores.mL-1). Each isolate was inoculated onto two leaves each of five P. notoginseng plants. The controls were similarly mock-inoculated with sterile water. To maintain high humidity (>90% RH), all plants were placed in transparent plastic boxes in a greenhouse at 25℃ with a 12 h light/dark photoperiod. Fifteen days post-inoculation, inoculated leaves showed similar symptoms to those observed in the field, and control plants remained healthy. The pathogen were reisolated from symptomatic leaf spots, and the colony characteristics were the same as those of the original isolates. Morphological characteristics, molecular data, and Koch's postulates tests confirmed C. pseudolychnidis as the cause of P. notoginseng leaf spot disease. To our knowledge, this is the first report of C. pseudolychnidis causing leaf spot on P. notoginseng in Yunnan, China. The spread of this disease might pose a serious threat to the production of P. notoginseng. The occurrence and spread of this pathogen should be further studied in order to formulate reasonable control measures.

The Interactions between Two Fungal Endophytes Epicoccum layuense R2-21 and Alternaria alternata XHYN2 and Grapevines (Vitis vinifera) with De Novo Established Symbionts under Aseptic Conditions.

In this study, we focused on grapevine-endophyte interactions and reprogrammed secondary metabolism in the host plant due to defense against the colonization of endophytes. Thus, the transcriptional responses of tissue cultured grapevine seedlings (Vitis vinifera L. cv.: Cabernet Sauvignon) to two fungal endophytes Epicoccum layuense R2-21 (Epi R2-21) and Alternaria alternata XHYN2 (Alt XHYN2) at three different time points (6 h, 6 d, 15 d) were analyzed. As expected, a total of 5748 and 5817 differentially expressed genes (DEGs) were separately initiated in Epi R2-21 and Alt XHYN2 symbiotic tissue cultured seedlings compared to no endophyte treatment. The up-regulated DEGs at all time points in Epi R2-21- or Alt XHYN2-treated seedlings were mainly enriched in the flavonoid biosynthesis, phenylpropanoid biosynthesis, phenylalanine metabolism, stilbenoid, diarylheptanoid and gingerol biosynthesis, and circadian rhythm-plant pathways. In addition, the up-regulated DEGs at all sampling times in Alt XHYN2-treated tissue cultured seedlings were enriched in the plant-pathogen interaction pathway, but appeared in Epi R2-21 symbiotic seedlings only after 15 d of treatment. The down-regulated DEGs were not enriched in any KEGG pathways after 6 h inoculation for Epi R2-21 and Alt XHYN2 treatments, but were enriched mainly in photosynthesis-antenna proteins and plant hormone signal transduction pathways at other sampling times. At three different time points, a total of 51 DEGs (all up-regulated, 1.33-10.41-fold) were involved in secondary metabolism, and 22 DEGs (all up-regulated, 1.01-8.40-fold) were involved in defense responses in endophytic fungi symbiotic tissue cultured seedlings. The protein-protein interaction (PPI) network demonstrated that genes encoding CHS (VIT_10s0042g00920, VIT_14s0068g00920, and VIT_16s0100g00910) and the VIT_11s0065g00350 gene encoding CYP73A mediated the defense responses, and might induce more defense-associated metabolites. These results illustrated the activation of stress-associated secondary metabolism in the host grapevine during the establishment of fungi-plant endophytism. This work provides avenues for reshaping the qualities and characteristics of wine grapes utilizing specific endophytes and better understanding plant-microbe interactions.

2,3-Butanediol from the leachates of pine needles induces the resistance of Panax notoginseng to the leaf pathogen Alternaria panax.

Compared with the use of monocultures in the field, cultivation of medicinal herbs in forests is an effective strategy to alleviate disease. Chemical interactions between herbs and trees play an important role in disease suppression in forests. We evaluated the ability of leachates from needles of Pinus armandii to induce resistance in Panax notoginseng leaves, identified the components via gas chromatography-mass spectrometry (GC-MS), and then deciphered the mechanism of 2,3-Butanediol as the main component in the leachates responsible for resistance induction via RNA sequencing (RNA-seq). Prespraying leachates and 2,3-Butanediol onto leaves could induce the resistance of P. notoginseng to Alternaria panax. The RNA-seq results showed that prespraying 2,3-Butanediol onto leaves with or without A. panax infection upregulated the expression of large number of genes, many of which are involved in transcription factor activity and the mitogen-activated protein kinase (MAPK) signaling pathway. Specifically, 2,3-Butanediol spraying resulted in jasmonic acid (JA) -mediated induced systemic resistance (ISR) by activating MYC2 and ERF1. Moreover, 2,3-Butanediol induced systemic acquired resistance (SAR) by upregulating pattern-triggered immunity (PTI)- and effector-triggered immunity (ETI)-related genes and activated camalexin biosynthesis through activation of WRKY33. Overall, 2,3-Butanediol from the leachates of pine needles could activate the resistance of P. notoginseng to leaf disease infection through ISR, SAR and camalexin biosynthesis. Thus, 2,3-Butanediol is worth developing as a chemical inducer for agricultural production.

[Mechanism on biodiversity managing crop diseases].

Reasonable utilization of natural resource and protection of ecological environment is the foundation for implementing agricultural sustainable development. Biodiversity research and protection are becoming an important issue concerned commonly in the world. Crop disease is one of the important natural disasters for food production and safety, and is also one of the main reasons that confine sustainable development of agricultural production. Large-scale deployment of single highly resistant variety results in reduction of agro-biodiversity level. In this case, excessive loss of agro-biodiversity has become the main challenge in sustainable agriculture. Biodiversity can not only effectively alleviate disease incidence and loss of crop production, but also reduce pollution of agricultural ecological environment caused by excessive application of pesticides and fertilizers to the agricultural ecological environment. Discovery of the mechanism of biodiversity to control crop diseases can reasonably guide the rational deployment and rotation of different crops and establish optimization combinations of different crops. This review summarizes recent advances of research on molecular, physiological, and ecological mechanisms of biodiversity managing crop diseases, and proposes some research that needs to be strengthened in the future.

The symbioses of endophytic fungi shaped the metabolic profiles in grape leaves of different varieties.

Endophytic fungi produce many novel bioactive metabolites that are directly used as drugs or that function as the precursor structures of other chemicals. The metabolic shaping of endophytes on grape cells was reported previously. However, there are no reports on the interactions and metabolic impact of endophyte symbiosis on in vitro vine leaves, which may be examined under well-controlled conditions that are more representative of the natural situation of endophytes within grapevines. The present study used an in vitro leaf method to establish endophyte symbiosis of grapevines and analyze the effects on the metabolic profiles of grape leaves from two different cultivars, 'Rose honey' (RH) and 'Cabernet sauvignon' (CS). The effects of endophytic fungi on the metabolic profiles of grape leaves exhibited host selectivity and fungal strain specificity. Most of the endophytic fungal strains introduced novel metabolites into the two varieties of grape leaves according to the contents of the detected metabolites and composition of metabolites. Strains RH49 and MDR36, with high or moderate symbiosis rates, triggered an increased response in terms of the detected metabolites, and the strains MDR1 and MDR33 suppressed the detected metabolites in CS and RH leaves despite having strong or moderate symbiosis ability. However, the strain RH12 significantly induced the production of novel metabolites in RH leaves due to its high symbiosis ability and suppression of metabolites in CS leaves.

[Low-background and high-resolution contracted silver-stained method in polyacrylamide gels electrophoresis].

The disadvantage of time-consuming and fussy steps of conventional silver-stained method for polyacrylamide gels is evident, and has become the choke point in its application. In this paper, a low-background and high-resolution contracted silver-stained method for polyacrylamide gels was established. Compared with the conventional banding method, this contracted method has fewer steps and needs fewer reagents, in particular, lower NaOH concentration. It is rapid and economic, especially for mass silver-staining.

[Computational analysis of signal peptide-dependent secreted protein in Caenorthaditis elegans ws123].

The internet-based softwares SignalP v3.0, TargetP v1.01, big-PI predictor and TMHMM v2.0 were combined to predict the signal peptides and the signal peptide-dependent secreted proteins from the 19,855 ORFs in Caenorthaditis elegans ws123 genome. 1,990 proteins were predicted to be secreted and to contain signal peptides among 19,855 proteins, among which 1,936 have SignalPase I signal peptide (containing 41 with RR-motif signal peptide), 53 have SignalPase II signal peptide and one has SignalPase IV signal peptide. The signal peptides of 742 secreted proteins include only H-domain and C-domain, but no typical N-domain; the signal peptides of other 1,248 secreted proteins include all three domains. Although the amino acids constitution of the SignalPase I signal peptides were similar in general between Caenorthaditis elegans and prokaryote, there were apparently small differences, and the amino acid composition of Caenorthaditis elegans are more diverse and less conserved. But there are distinct differences on the amino acid composition of SignalPase II signal peptides. The signal peptides of Caenorthaditis elegans were more diverse than unicellular eukaryotic organism. The signal peptides of a few proteins were exactly the same. We used the BLAST 2 SEQUENECES aligning method to compare the homology among the secreted proteins with the same signal peptides. The alignment results indicated that the genes sharing the same signal peptide sequences were homologous to each other and were likely to have arisen from gene duplication.

Panicle blast and canopy moisture in rice cultivar mixtures.

ABSTRACT Glutinous rice cultivars were sown after every fourth row of a nonglutinous, hybrid cultivar in an additive design. The glutinous cultivars were 35 to 40 cm taller and substantially more susceptible to blast than was the nonglutinous cultivar. Interplanting of glutinous and nonglutinous rice reduced the incidence and severity of panicle blast on the glutinous cultivars by >90%, and on the nonglutinous cultivar by 30 to 40%. Mixing increased the per unit area yield of glutinous rice by 80 to 90% relative to pure stand, whereas yield of the nonglutinous cultivar was essentially unaffected by mixing. To determine whether the different plant heights and canopy structures may contribute to a microclimate that is less favorable to blast infection, we monitored the moisture status of the glutinous cultivars in pure stand and mixture at 0800 h by measuring relative humidity at the height of the glutinous panicles using a swing psychrometer and by visually estimating the percentage of leaf area covered by dew. Averaged over the two seasons, the number of days of 100% humidity at 0800 h was 20.0 and 2.2 for pure stands and mixtures, respectively. The mean percentage of glutinous leaf area covered by dewwas 84 and 36% for the pure stands and mixtures, respectively. Although other mechanisms also were operative, reduced leaf wetness was likely a substantial contributor to panicle blast control in the mixtures.

[Analysis of the coding region for signal peptide-containing proteins in Pseudomonas syringae pv. tomato genome].

The completed 5 615 ORFs of chromosome sequence of Pseudomonas syringae pv. tomato were analyzed by SignalP 3.0. The result revealed that 679 ORFs consisted of putative secretary proteins with signal peptides. 107 ORFs of signal peptides have been named. The length of most signal peptides was different from 19 amino acids to 31 amino acids, and the most dominant one was 23 amino acids in length. The size of most ORFs varied between 101 ~ 400 amino acids. The frequency of particular amino acids in signal peptides by statistical approach was 48.54% for hydrophobic, 18.67% for uncharged, 24.54% for negative and 8.00% for positive amino acids. The most frequent amino acid was alanine, and the least was isoleucine. Three classes of signal peptides were found in the genome of P. syringae pv. tomato: 501 ORFs belong to secretary signal peptides, 36 ORFs belong to twin-arginine signal peptides, and 15 ORFs belong to lipoprotein signal peptides. Type IV pilin signal peptide and bacteriocins and pheronoes signal peptide was not found in the genome.

[Isolation and identification of root endophytic and rhizosphere bacteria of rice landraces in Yuanyang Terrace, China].

ABSTRACT: To reveal root endophytic and rhizosphere bacteria constitution of rice landraces in Yuanyang Terrace, isolation was carried out by tissue isolation method and soil dilution plate method for two landraces of Yuelianggu and Hongjiaolaojing. A total of 399 bacterial strains isolated were identified by morphological characteristics, physiological and biochemical identification. The results showed that there were 8 genera isolated from the root of Yuelianggu and 5 genera from its rhizosphere soil, and 5 genera were same. For Hongjiaolaojing, there were 10 genera isolated from its root and 7 genera from its rhizosphere soil, and 6 genera were same. By molecular biology, identification, a total of 11 species and 5 genera were isolated from the root of Yuelianggu, 8 species and 4 genera from its rhizosphere soil, and 5 species and 4 genera were same. As for Hongjiaolaojing, there were 9 species and 5 genera isolated from its root, and 10 species and 3 genera from its rhizosphere soil, and 4 species and 2 genera were same. The results of physiological and biochemical characteristics identification method and molecular identification method were basically same at the genus level, while most of the strains could be identified to species by molecular identification. There were certain species homology and specificity in the root endophytic and rhizosphere bacteria of Yuanyang rice landraces.

Genetic analysis of rice varietal diversity for rice blast control.

Two Indica hybrid rice of Shanyou63 (A) and Shanyou22 (B), two glutinous landraces of Huanghenuo (C) and Zinuo (D) and three improved Japonica rice of Hexi41 (E), Chujing12 (F) and 8126 (G) were selected and their genetic resistance relationship was estimated using resistance gene analogue (RGA). The results showed that there were similar genetic relationships between hybrid varieties at the genetic similarity (GS) of 0.86,and among improved Japonica varieties at the GS of 0.84, while highly genetic diversifications between traditional varieties, Indica and Japonica varieties, traditional and modern variety ( GS:0.45). The results also showed that clustering analysis based on RGA data were generally corresponded to known pedigrees and blast field resistances of the varieties. Based on varietal differences in RGA data and agronomic traits, plot experiments of five mixed-planting combinations of A/C, A/D, B/C, B/D and A/B and two combinations of E/C and E/F/G were conducted in Jianshui and Shiping counties ( Indica rice growing region) and Luxi County (warm Japonica region) in Yunnan Province in past two years, respectively. The results demonstrated that rice blast management was more effective in five mixed-planting combinations of varieties with different genetic backgrounds (GS: 0.45-0.77) than in two combinations with similar genetic relationships (GS: 0.84-0.90), compared with their monocultures. It is evident for the highly susceptible landraces in mixed-planting to achieve disease control, with significant decreases both in incidence and severity. The blast control efficiencies of landraces in different mixture combinations reached to 54.47%-92.18%. The control efficiencies of improved varieties varied from 15.12% to 25.54% in mixture combinations with closed genetic relationship. In addition,the total yield of 5 varietal combinations with distant genetic relationship increased 539.0-904.0 kg/ha in the mixed-planting plots, at increase rates of 5.6%-10.2%. Mixed rice varieties with similar genetic background did not achieve significant yield increase. Otherwise, the yield of E/F/G decreased 2.7%-4.0% compared with pure stand. The results can provide scientific basis of varietal combinations in diversification experiments for blast control.

[Relationship between genetic lineage and pathotype of Pyricularia grisea in Yunnan Plateau].

Rice blast caused by Pyricularia grisea is the most destructive disease in Yunnan Plateau, China. In order to elucidate the relationship between genetic lineage and pathotype of P. grisea of Yunnan Plateau as well as the variability of the fungus at DNA level,the repetitive element-based PCR (rep-PCR) of Pot2, an element found in approximately 100 copies in the fungus genome,was exploited. Two hundred and thirty-six isolates of P. grisea collected from 15 main rice-growing counties of Yunnan Plateau were fingerprinted by using rep-PCR. A linkage graph of the rep-PCR fingerprints from 134 representative isolates was generated using an unweighted pair-grouped average program (UPGMA) of the STATISTICAL 5.0 software. The isolates were classified into 8 genetic lineages (G1 approximately G8) at the level of 1.75 genetic linkage distance, of which the G1, G2 and G4 were the dominant lineages. The isolates in a certain area generally belonged to one correspondent genetic lineage and the isolates from the same plot and host rice variety mostly shared one linkage group though different genetic lineages within one lesion. Furthermore, 29 isolates representing the eight genetic lineages were inoculated on 33 rice cultivars of Yunnan at the stage of 3 approximately 4 leaves in greenhouse. The isolates were divided into 6 pathotype groups (P1 approximately P6) according to its compatibility, which demonstrated that some isolates of one genetic lineage sharing two or three pathotype groups, alternatively, one or four pathotype groups. The isolates from each genetic lineage, however, may share one pathotype group such as P2. The preliminary results implicated that the relationship between genetic lineages and pathotype groups of P. grisea in Yunnan Plateau was complicated rather than simple. On the other hand,2 rice cultivars including HeXi 16 and JingGuo 92 were resistant to the 29 isolates but YunJing 20 and HeXi 30 both susceptible to all of them, which was helpful for deploying the blast-resistant genes in rice production of Yunnan Plateau. Therefore, the rice blast-resistance spectrum of the tentative new rice cultivars should be evaluated before its release considering the blast-resistant rice breeding and the practice of rice production in Yunnan Plateau.

Genome-wide analysis of microsatellite sequence in seven filamentous fungi.

Abundance of microsatellites with repeated unit lengths of 1-6 base pairs in seven fungi: Aspergillus nidulans, Coprinus cinereus, Cryptococcus neoformans (serotype A), Fusarium graminearum, Magnaporthe grisea, Neurospora crassa and Ustilago maydis were investigated on genomic scale. The results showed that each species has its specific profile for different types and different motifs of SSR loci. Ascomycetes fungi M. grisea, N. crassa and basidiomycete fungus U. maydis adopt much more microsatellites than other fungi examined. Total amount of 15,751, 14,788 and 6,854 SSR loci were observed respectively, average density is 406, 389 and 347 per Mbp sequence; overall length of SSR sequence was 0.82%, 0.95% and 0.79% of genomic sequence respectively. While ascomycetes fungus F. graminearum and A. nidulans contains the least SSRs in the genomic DNA, only 4,679 and 4,837 tracts were observed in 36 Mb and 30 Mb genomic sequence respectively. Microsatellite repeats in protein coding regions are investigated in Aspergillus nidulans, Magnaporthe grisea, and Neurospora crassa also, the results show that the difference of different types and motifs among three fungi is very little than that in whole genomic sequence. For trinucleotide repeats, overrepresent (comparing to the total base pair of protein coding region) of AGC, GGC, AGG, ACG and ACC was observed in coding region, frequencies of AAC and AAG were not difference between coding and non-coding region, AAT, AGT and ATG were underrepresent in coding region excepted for A. nidulans, in which ATG was overrepresentative.

[Effects of nitrogen application rate on rhizosphere microbial community in wheat-faba bean intercropping system].

With field plot experiment, this paper studied the effects of different nitrogen application rate (0, 90, 180 and 270 kg x hm(-2)) on the rhizosphere microbial community and its diversity in wheat-faba bean intercropping ecosystem. The results indicated that the amount of rhizosphere microbes fluctuated with crop growth stages, being the highest at the flowering stage of test crops. Comparing with monocropping, intercropping significantly increased the total amount of microbes and the numbers of bacteria, fungi and actinomyces in the rhizosphere of both wheat and faba bean, but decreased the microbial diversity in the rhizosphere of faba bean at its flowering and maturing stages. Under no nitrogen and low nitrogen application rate, a larger difference was observed in the amount of rhizosphere microbes between intercropping and monocropping. The promotion effect of intercropping in increasing the amount of rhizosphere microbes was more apparent at tillering and flowering stages, but declined significantly at maturing stage. With increasing nitrogen application rate, the amount of microbes in wheat rhizosphere increased first and decreased then, with the peak appeared at 180 kg N x hm(-2), and the effect was more obvious on monocropped wheat than on intercropped one. Nitrogen application rate had no significant effects on the numbers of bacteria, fungi and actinomyces and the microbial diversity in faba bean rhizosphere, but decreased the total amount of microbes in the rhizosphere of intercropped faba bean. Rational nitrogen application could regulate rhizosphere microbial community effectively, and there was an obvious correlation between aboveground plant diversity and belowground microbial community.