Identification and pathogenicity analysis of Fusarium spp. on peach in China.

BACKGROUND: Vascular system is affected by diseases that can seriously damage plant health by inducing browning and death of branches. This study aimed to identify and analyze the pathogenicity of Fusarium spp. isolates obtained from diseased peach branches in several peach-producing areas of China. RESULTS: We obtained and confirmed nine Fusarium isolates based on morphological and molecular characteristics. Phylogenetic relationships using a combination of rDNA-internal transcribed spacer (ITS), elongation factor (EF)-1α, and mitochondrial small subunit (mtSSU) gene sequences were analyzed. GJH-Z1, GJH-6, and GJH-1 were identified as F. avenaceum; HYR-Z3, and ZLZT-6 as F. concentricum, HH-2020-G2, and HYTZ-4 as F. solani, GG-2020-1 as F. asiaticum, SYGZ-1 as F. equiseti. Through acupuncture comparison, the pathogenicity of F. equiseti (SYGZ-1) was highest amongst nine strains. Meanwhile, F. concentricum (HYR-Z3 and ZLZT-6), and F. solaini (HYTZ-4) had a higher level of pathogenicity as revealed by impregnation. CONCLUSIONS: Our study shed light on the findings that Fusarium spp. can inflict vascular bundle browning of peach plants. Our results will extend the understanding of pathogenic diseases in China's peach industry.

Identification of Susceptibility Genes for Fusarium oxysporum in Cucumber via Comparative Proteomic Analysis.

Fusarium wilt (FW) in cucumber (Cucumis sativus L.), caused by Fusarium oxysporum f. sp. cucumerinum (Foc), poses a major threat to cucumber growth and productivity. However, lack of available natural resistance resources for FW restricts the breeding of resistant cultivars via conventional approaches. Susceptibility (S) genes in susceptible host plants facilitate infection by the pathogen and contribute to susceptibility. Loss of function of these S genes might provide broad-spectrum and durable disease resistance. Here, we screened S genes via comparative proteomic analysis between cucumber cultivars Rijiecheng and Superina, which exhibited resistance and high -susceptibility to FW, respectively. We identified 210 and 243 differentially regulated proteins (DRPs) in the Rijiecheng and Superina, respectively, and further found that 32 DRPs were predominantly expressed in Superina and significantly up-regulated after Foc inoculation. Expression verification found that TMEM115 (CsaV3_5G025750), encoding a transmembrane protein, TET8 (CsaV3_2G007840), encoding function as a tetraspanin, TPS10 (CsaV3_2G017980) encoding a terpene synthase, and MGT2 (CsaV3_7G006660), encoding a glycosyltransferase, were significantly induced in both cultivars after Foc infection but were induced to a higher expression level in Superina. These candidate genes might act as negative regulators of FW resistance in cucumber and provide effective FW-susceptibility gene resources for improving cucumber FW resistance through breeding programs.

Identification of miRNA-Target Gene Pairs Responsive to Fusarium Wilt of Cucumber via an Integrated Analysis of miRNA and Transcriptome Profiles.

Fusarium wilt (FW) of cucumber (Cucumis sativus L.) caused by Fusarium oxysporum f. sp. cucumerinum (Foc) is a destructive soil-borne disease that severely decreases cucumber yield and quality worldwide. MicroRNAs (miRNAs) are small non-coding RNAs (sRNAs) that are important for regulating host immunity because they affect target gene expression. However, the specific miRNAs and the miRNA/target gene crosstalk involved in cucumber resistance to FW remain unknown. In this study, we compared sRNA-seq and RNA-seq data for cucumber cultivar 'Rijiecheng', which is resistant to FW. The integrated analysis identified FW-responsive miRNAs and their target genes. On the basis of verified expression levels, we detected two highly expressed miRNAs with down-regulated expression in response to Foc. Moreover, an analysis of 21 target genes in cucumber inoculated with Foc indicated that JRL3 (Csa2G362470), which is targeted by miR319a, and BEE1 (Csa1G024150), DAHP1 (Csa2G369040), and PERK2 (Csa4G642480), which are targeted by miR6300, are expressed at high levels, but their expression is further up-regulated after Foc inoculation. These results imply that miR319a-JRL3, miR6300-BEE1, miR6300-DAHP1 and miR6300-PERK2 regulate cucumber defenses against FW, and provide the gene resources that may be useful for breeding programs focused on developing new cucumber varieties with enhanced resistance to FW.

Chitinase Chi 2 Positively Regulates Cucumber Resistance against Fusarium oxysporum f. sp. cucumerinum.

Cucumber (Cucumis sativus L.) is an important vegetable crop worldwide, and Fusarium wilt (FW), caused by Fusarium oxysporum f. sp. cucumerinum (Foc), severely restricts cucumber growth and yield. Accumulating lines of evidence indicate that chitinases play important roles in attacking the invading fungal pathogens through catalyzing their cell wall degradation. Here, we identified the chitinase (Chi) genes in cucumber and further screened the FW-responsive genes via a comparative transcriptome analysis and found that six common genes were predominantly expressed in roots but also significantly upregulated after Foc infection. Expression verification further conformed that Chi2 and Chi14 were obviously induced by Foc as well as by hormone treatments, compared with the controls. The purified Chi2 and Chi14 proteins significantly affected the growth of Foc in vitro, compared with the controls. Knockdown of Chi2 in cucumber by virus-induced gene silencing (VIGS) increased susceptibility to FW, compared with the Chi14-silenced and control plants, and silencing of Chi2 drastically impaired gene activation in the jasmonic acid pathway, suggesting that the Chi2 gene might play positive roles in cucumber FW defense and, therefore, can provide a gene resource for developing cucumber-FW-resistance breeding programs.

Induced resistance in nectarine fruit by Bacillus licheniformis W10 for the control of brown rot caused by Monilinia fructicola.

Brown rot caused by Monilinia fructicola has led to considerable preharvest and postharvest losses in all major nectarine fruit-growing areas. In our previous study, we successfully identified a biocontrol strain of bacteria, Bacillus licheniformis W10, that can be used to control brown rot. However, the possible mechanism of the control of brown rot by B. licheniformis W10 is still unclear. Therefore, the objectives of this study were to determine whether B. licheniformis W10 induces resistance by activating defense-related enzymes including antioxidant enzymes in nectarine. Treatment of nectarine fruit with B. licheniformis W10 reduced both M. fructicola-induced oxidative damage and reactive oxygen species (ROS) production. Furthermore, application of B. licheniformis to nectarine fruit resulted in a significant increase in the activity of antioxidant and defense-related enzymes and increase in the expression of the corresponding genes. Overall, our results verified the proposed mechanism of B. licheniformis W10 in controlling M. fructicola via regulation of ROS levels and activation of antioxidant and defense-related enzymes.

Transcriptome analysis reveals ethylene-mediated defense responses to Fusarium oxysporum f. sp. cucumerinum infection in Cucumis sativus L.

BACKGROUND: Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (Foc), is a severe disease affecting cucumber (Cucumis sativus L.) production worldwide, but mechanisms underlying Fusarium wilt resistance in cucumber remain unknown. To better understand of the defense mechanisms elicited in response to Foc inoculation, RNA sequencing-based transcriptomic profiling of responses of the Fusarium wilt-resistant cucumber line 'Rijiecheng' at 0, 24, 48, 96, and 192 h after Foc inoculation was performed. RESULTS: We identified 4116 genes that were differentially expressed between 0 h and other time points after inoculation. All ethylene-related and pathogenesis-related genes from the differentially expressed genes were filtered out. Real-time PCR analysis showed that ethylene-related genes were induced in response to Foc infection. Importantly, after Foc infection and exogenous application of ethephon, a donor of ethylene, the ethylene-related genes were highly expressed. In response to exogenous ethephon treatment in conjunction with Foc inoculation, the infection resistance of cucumber seedlings was enhanced and endogenous ethylene biosynthesis increased dramatically. CONCLUSION: Collectively, ethylene signaling pathways play a positive role in regulating the defense response of cucumber to Foc infection. The results provide insight into the cucumber Fusarium wilt defense mechanisms and provide valuable information for breeding new cucumber cultivars with enhanced Fusarium wilt tolerance.

Inheritance and Quantitative Trait Locus Mapping of Fusarium Wilt Resistance in Cucumber.

Fusarium wilt (FW) is a very serious soil-borne disease worldwide, which usually results in huge yield losses in cucumber production. However, the inheritance and molecular mechanism of the response to FW are still unknown in cucumber (Cucumis sativus L.). In this study, two inbred cucumber lines Superina (P1) and Rijiecheng (P2) were used as the sensitive and resistant lines, respectively. A mixed major gene plus polygene inheritance model was used to analyze the resistance to FW in different generations of cucumber, namely, P1, P2, F1 (P1×P2), B1, and B2, obtained by backcrossing F1 plants with Superina (B1) or Rijiecheng (B2), and F2, obtained by self-crossing the F1 plants. After screening 18 genetic models, we chose the E-1 model, which included two pairs of additive-dominance-epistatic major genes and additive-dominance polygenes, as the optimal model for resistance to FW on the basis of fitness tests. The major effect quantitative trait locus (QTL) fw2.1 was detected in a 1.91-Mb-long region of chromosome 2 by bulked-segregant analysis. We used five insertion/deletion markers to fine-map the fw2.1 to a 0.60 Mb interval from 1,248,093 to 1,817,308 bp on chromosome 2 that contained 80 candidate genes. We also used the transcriptome data of Rijiecheng inoculated with Fusarium oxysporum f. sp. cucumerinum (Foc) to screen the candidate genes. Twelve differentially expressed genes were detected in fw2.1, and five of them were significantly induced by FW. The expression levels of the five genes were higher in FW-resistant Rijiecheng inoculated with Foc than in the control inoculated with water. Our results will contribute to a better understanding of the genetic basis of FW resistance in cucumber, which may help in breeding FW-resistant cucumber lines in the future.

Variation of genetic diversity in a rapidly expanding population of the greater long-tailed hamster (Tscherskia triton) as revealed by microsatellites.

Genetic diversity is essential for persistence of animal populations over both the short- and long-term. Previous studies suggest that genetic diversity may decrease with population decline due to genetic drift or inbreeding of small populations. For oscillating populations, there are some studies on the relationship between population density and genetic diversity, but these studies were based on short-term observation or in low-density phases. Evidence from rapidly expanding populations is lacking. In this study, genetic diversity of a rapidly expanding population of the Greater long-tailed hamsters during 1984-1990, in the Raoyang County of the North China Plain was studied using DNA microsatellite markers. Results show that genetic diversity was positively correlated with population density (as measured by % trap success), and the increase in population density was correlated with a decrease of genetic differentiation between the sub-population A and B. The genetic diversity tended to be higher in spring than in autumn. Variation in population density and genetic diversity are consistent between sub-population A and B. Such results suggest that dispersal is density- and season-dependent in a rapidly expanding population of the Greater long-tailed hamster. For typically solitary species, increasing population density can increase intra-specific attack, which is a driving force for dispersal. This situation is counterbalanced by decreasing population density caused by genetic drift or inbreeding as the result of small population size. Season is a major factor influencing population density and genetic diversity. Meanwhile, roads, used to be considered as geographical isolation, have less effect on genetic differentiation in a rapidly expanding population. Evidences suggest that gene flow (Nm) is positively correlated with population density, and it is significant higher in spring than that in autumn.