Control of blast and sheath blight diseases of rice using antifungal metabolites produced by Streptomyces sp. PM5

Two antifungal aliphatic compounds, SPM5C-1 and SPM5C-2 with a lactone and ketone carbonyl unit, respectively obtained from Streptomyces sp. PM5 were evaluated under in vitro and in vivo conditions against major rice pathogens, Pyricularia oryzae and Rhizoctonia solani. These compounds were dissolved in distilled water/medium to get the required concentrations. The well diffusion bioassay indicated that the of SPM5C-1 remarkably inhibited the mycelial growth of P. oryzae and R. solani in comparison to SPM5C-2. Though SPM5C-2 showed low antifungal activity against P. oryzae, it was not active against R. solani. Further, SPM5C-1 completely inhibited the growth of P. oryzae and R. solani at concentrations of 25, 50, 75 and 100 μg/ml. Greenhouse experiments revealed that spraying of SPM5C-1 at 500 μg/ml on rice significantly decreased blast and sheath blight development by 76.1% and 82.3%, respectively, as compared to the control with a corresponding increase in rice grain yield.     

Characterization of Bacillus strains from apple and pear trees in South Africa antagonistic to Erwinia amylovora

In order to find reasons for the absence of fire blight in most countries of the Southern hemisphere, bark samples from apple and pear trees in orchards of the Western Cape region in South Africa were extracted for bacteria which could be antagonistic to Erwinia amylovora. Screening was done in the late growth season and mainly Gram-positive bacteria were isolated. Approximately half of them produced growth inhibition zones on a lawn of E. amylovora. Most isolates were classified as Bacillus megaterium by microbiological assays and in API 50 test systems. They were visualized in the light microscope as non-motile large rods. These strains may not be responsible for the absence of fire blight in orchards, but they may indicate unfavourable climatic conditions for Gram-negative bacteria including E. amylovora. They may reduce the ability of E. amylovora to establish fire blight and could also be useful for application in biological disease control.     

Curtobacterium flaccumfaciens pv. flaccumfaciens on Soybean in Germany – A Threat for Farming

Plant diseases caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) are distributed in North and South America as well as in South and East Europe and occur mostly on beans (Phaseolus vulgaris). This is the first report of Cff on soybean in Germany. Cff was detected in complex with Pseudomonas syringae pv. glycinea on field‐grown soybeans that were not treated with pesticides. Cff, the causal agent of bacterial tan spot disease, was identified by 16S rDNA sequencing and by artificial infection and re‐isolation from the host plants soybean (Glycine max) and bush bean (Phaseolus vulgaris).     

The feruloyl esterase gene family of Fusarium graminearum is differentially regulated by aromatic compounds and hosts

Feruloyl esterases can liberate ferulic acid (FA) from plant cell wall polymers. They are expressed by plant pathogenic fungi and could play a role in pathogenicity, although this question has not been addressed yet. The fungus Fusarium graminearum is the principal causal agent of fusarium head blight (FHB) and gibberella ear rot (GER), major diseases of wheat, barley, and maize in all temperate regions of the world. The F. graminearum genome contains seven genes with strong homology to feruloyl esterase (FAE) sequences. Phylogenetic analysis showed that these included three type B, three type C, and one type D FAE genes. Expression profiling of the seven FAE genes showed complex regulation patterns unique to each gene. In F. graminearum-infected plant tissues, the FAE genes exhibited host-specific gene expression. On wheat, FAEB1 and FAED1 were strongly expressed while FAEB2, FAEB3, and FAEC1 were expressed at more modest levels. On maize, only FAEB3, FAEC1, and FAED1 were expressed and at low levels. When growing F. graminearum in liquid culture, only FAEB1 and FAEC1 were expressed. Both genes were induced by a small group of related aromatic compounds including FA, caffeic acid, and p-coumaric acid. FAEB1 was induced by xylose, while repressed by glucose and galactose. FAEC1 was constitutively expressed at low levels in the presence of those sugars. Expression of the other five FAE genes was not detected in the culture conditions used. To determine if FAE genes were important for pathogenicity of F. graminearum, mutant strains inactivated for faeB1?, faeD1? or both genes were constructed and tested on wheat plants. No statistically significant change in pathogenicity and no compensatory expression of the other FAE genes were observed in the fae gene mutants. Our results show that FAEB1 and FAED1 are not required for pathogenicity of F. graminearum on wheat.     

苹果链格孢菌与寄主叶片互作的超微结构研究

以苹果杂交组合(‘华脆’ב金冠’)F1代杂种实生苗群体易感病株系为材料,通过扫描电镜、透射电镜等观察方法,对苹果链格孢菌与寄主叶片互作过程进行了细胞学观察,分析苹果链格孢菌侵染寄主的动态过程和变化规律,以揭示苹果病害发生机制。结果表明,苹果链格孢菌侵染寄主叶片时,多数在表皮分枝扩展,很少通过气孔器或其他方式入侵细胞内部。互作后期,寄主叶细胞内叶绿体和质膜变化显著,多数细胞器降解,表明病原菌已分泌AM毒素作用于寄主。     

中国板栗EST-SNP和抗栗疫病候选基因分析及同源比对

从壳斗科基因组数据库下载中国板栗的Unigene序列和基于这些Unigene序列开发获得的EST-SNP数据,分析发现,中国板栗EST-SNP的发生频率为4个/kb,在碱基置换类型上,C-T置换发生的频率最高,C-G置换发生频率最低,转换和颠换的比值为1.74∶1.对211个在中国板栗健康组织和感染栗疫病的染病组织中差异表达的基因进行基因注释和蛋白质结构域分析,结果表明,参与蛋白质代谢、对胁迫、生物和非生物刺激发生响应的基因所占的比例较多,并发现了大量的跨膜结构、信号肽、卷曲螺旋和蛋白激酶相关结构域.对这211个中国板栗抗栗疫病相关的候选基因和其Unigene序列进行同源比对,统计整理定位在具有同源性的Unigene序列上的EST-SNP,共有3023个EST-SNP标记.这批EST-SNP标记可为今后开展基于候选基因途径的中国板栗抗栗疫病居群基因组学研究和关联作图研究奠定重要的基础.     

水稻对白叶枯病和细菌性条斑病的抗性遗传研究进展

水稻白叶枯病和水稻细菌性条斑病是由稻黄单胞细菌(Xanthomonas oryzae)不同致病变种引起的两种最重要的水稻细菌性病害。发掘和利用抗性基因,培育抗病品种是防治这两种病害的最有效手段之一。本文分别综述了这两种高度相关的病害的抗性遗传研究进展,包括已发掘和利用的主效抗性基因特点及目前国内外对这两种病害的抗性QTL定位研究进展,为水稻抗白叶枯病和细菌性条斑病育种研究提供有用信息。     

Susceptibility to <Emphasis Type="Italic">Fusarium </Emphasis>head blight is associated with the <Emphasis Type="Italic">Rht-D1b</Emphasis> semi-dwarfing allele in wheat

Fusarium head blight (FHB) is an important disease of wheat worldwide. The cultivar Spark is more resistant than most other UK winter wheat varieties but the genetic basis for this is not known. A mapping population from a cross between Spark and the FHB susceptible variety Rialto was used to identify quantitative trait loci (QTL) associated with resistance. QTL analysis across environments revealed nine QTL for FHB resistance and four QTL for plant height (PH). One FHB QTL was coincident with the Rht-1D locus and accounted for up to 51% of the phenotypic variance. The enhanced FHB susceptibility associated with Rht-D1b is not an effect of PH per se as other QTL for height segregating in this population have no influence on susceptibility. Experiments with near-isogenic lines supported the association between susceptibility and the Rht-D1b allele conferring the semi-dwarf habit. Our results demonstrate that lines carrying the Rht-1Db semi-dwarfing allele are compromised in resistance to initial infection (type I resistance) while being unaffected in resistance to spread within the spike (type II resistance).     

Highly polymorphic microsatellite loci in the rice- and maize-infecting fungal pathogen Rhizoctonia solani anastomosis group 1 IA

Ten polymorphic microsatellite loci were isolated and characterized from the rice- and maize-infecting Basidiomycete fungus Rhizoctonia solani anastomosis group AG-1 IA. All loci were polymorphic in two populations from Louisiana in USA and Venezuela. The total number of alleles per locus ranged from four to eight. All 10 loci were also useful for genotyping soybean-infecting R. solani AG-1 isolates from Brazil and USA. One locus, TC06, amplified across two other AG groups representing different species, showing species-specific repeat length polymorphism. This marker suite will be used to determine the global population structure of this important pathogenic fungus.     

Combined expression of chitinase and β-1,3-glucanase genes in indica rice (Oryza sativa L.) enhances resistance against Rhizoctonia solani

Agrobacterium-mediated transformation of rice was done using the binary vector pNSP3, harbouring the rice chitinase (chi11) gene under maize ubiquitin promoter and the tobacco β-1,3-glucanase gene under CaMV 35S promoter in the same T-DNA. Four of the six T₀ plants had single copies of complete T-DNAs, while the other two had complex integration patterns. Three of the four single-copy lines showed a 3:1 segregation ratio in the T₁ generation. Northern and western blot analyses of T₁ plants revealed constitutive expression of chitinase and β-1,3-glucanase genes. Homozygous T₂ plants of the single-copy lines CG20, CG27 and CG53 showed 62-, 9.6- and 11-fold higher chitinase activity over the control plants. β-1,3-Glucanase activity was 1.1- to 2.5-fold higher in the transgenic plants. Bioassay of homozygous T₂ plants of the three single-copy transgenic lines against Rhizoctonia solani revealed a 60% reduction in sheath blight Disease Index in the first week. The Disease Index increased from 61.8 in the first week to 90.6 in the third week in control plants, while it remained low (26.8–34.2) in the transgenic T₃ plants in the corresponding period, reflecting the persistence of sheath blight resistance for a longer period.