Potato brown rot incidence and severity under different management and amendment regimes in different soil types

Ralstonia solanacearum race 3 biovar 2, the causative agent of potato brown rot (bacterial wilt), is an economically important disease in tropical, subtropical and temperate regions of the world. In view of previous reports on suppression of the disease by organic amendments, and the expansion of organic agriculture, it was timely to compare the effects of organic and conventional management and various amendments on brown rot development in different soils (type: sand or clay; origin: Egypt or the Netherlands). Brown rot infection was only slightly reduced in organically compared to conventionally managed sandy soils from Egypt, but organic management significantly increased disease incidence and pathogen survival in Dutch sandy and clay soils, which correlated with high DOC contents in the organic Dutch soils. There was no correlation between disease incidence or severity and bacterial diversity in the potato rhizosphere in differently managed soils (as determined by 16S DGGE). NPK fertilization reduced bacterial wilt in conventional Egyptian soils but not in Dutch soils. Cow manure amendment significantly reduced disease incidence in organic Dutch sandy soils, but did not affect the bacterial population. However, cow manure did reduce densities of R. solanacearum in Egyptian sandy soils, most probably by microbial competition as a clear shift in populations was detected with DGGE in these and Dutch sandy soils after manure amendment. Amendment with compost did not have a suppressive effect in any soil type. The absence of a disease suppressive effect of mineral and organic fertilization in Dutch clay soils may be related to the already high availability of inorganic and organic nutrients in these soils. This study shows that the mechanism of disease suppression of soil-borne plant pathogens may vary strongly according to the soil type, especially if quite different types of soil are used.     

Isolation and characterization of lectins from the AG-D group of binucleate <Emphasis Type="Italic">Rhizoctonia</Emphasis> species

Isolates from 18 anastomosis groups (AGs) of binucleate Rhizoctonia were screened for lectin activity. Eight AGs (AG-B, AG-D, AG-F, AG-G, AG-H, AG-I, AG-R and AG-U) had low to moderate lectin activities. Among these, members of AG-D and AG-I had the highest activity. Partially purified lectins from AG-D preferentially agglutinated human blood type A to type B and O. Mucin and galactose were the most potent inhibitors among the tested carbohydrates. The molecular masses of these lectins ranged from 12.7 kDa for the monomer to 62 kDa for the pentamer type. Proline, alanine, glutamic acid, aspartic acid, leucine, threonine, serine and tyrosine were the major amino acid components of these lectins. Lectins from AG-D were stable at 4–50°C and from pH 6.0 to 10.0. When assayed with isoelectric focusing, these lectins gave bands at pI 9.30. Specificity of lectins from AG-D to galactose and its derivatives suggest a possible recognition role in this fungal species.     

Ineffectiveness of pruning to control citrus huanglongbing caused by <Emphasis Type="Italic">Candidatus</Emphasis> Liberibacter americanus

The huanglongbing (HLB) disease of citrus trees, caused by Candidatus Liberibacter asiaticus and Ca. Liberibacter americanus, was first reported in Brazil in March, 2004. The presence of the disease has caused serious concerns among growers. Pruning experiments were conducted to determine if removal of symptomatic branches or the entire canopy (decapitation) would eliminate infected tissues and save HLB-affected trees. Pruning was done in five blocks on a total of 592 3- to 16 year-old ‘Valência’, ‘Hamlin’ or ‘Pêra’ sweet orange trees showing no symptoms or with two levels of symptom severity. Ten decapitated trees per block were caged and all trees were treated with insecticides to control the psyllid vector, Diaphorina citri. Mottled leaves reappeared on most symptomatic (69.2%) as well on some asymptomatic (7.6%) pruned trees, regardless of age, variety, and pruning procedure. Presence of the pathogen (Ca. Liberibacter americanus) in all symptomatic trees was confirmed by PCR. In general, the greater the symptom severity before pruning the lower the percentage of trees that remained asymptomatic after pruning.     

Calcium ion promotes successful penetration of powdery mildew fungi into barley cells

To determine whether Ca²⁺ promotes powdery mildew penetration, Ca²⁺-treated barley coleoptiles were inoculated with conidia of pathogenic and nonpathogenic fungi. Penetration efficiency of the pathogenic powdery mildew Blumeria graminis was enhanced by Ca²⁺ treatment, but that of the necrotrophic pathogen Helminthosporium sp. remained unaffected. Similarly, when actin-dependent penetration resistance is suppressed with cytochalasin A, Ca²⁺ treatment specifically enhanced penetration of the nonpathogenic powdery mildew Erysiphe pisi but not that of other nonpathogens. Calmodulin inhibitors suppressed the promotive effect of Ca²⁺ on B. graminis penetration. These results suggest that barley powdery mildew specifically requires Ca²⁺ and calmodulin for penetration.     

Molecular characterization of <Emphasis Type="Italic">Phoma tracheiphila</Emphasis>, causal agent of Mal secco disease of citrus,in Israel

Mal secco disease of citrus caused by Phoma tracheiphila is a devastating disease in the Mediterranean basin. Susceptible citrus species include lemon, citron, lime and others. Trees attacked by the fungus show characteristic symptoms; the smallest twigs die first, followed by the larger branches. Eventually, the whole tree is killed. The symptoms are clear in the orchards but by the time they are visible the disease is already well established. The need for a sensitive, reliable and rapid diagnostic method for the early identification of the fungus in trees and fruit exists. We have developed a PCR-based method for the identification of P. tracheiphila from plant tissues including fruit. Any such method must take into account the genetic variability in the pathogen population. Molecular methods were used to compare different isolates of P. tracheiphila. This study found no significant differences between different isolates from different citrus species from different parts of Israel.     

不同食料植物对安婀珍蝶幼虫生长发育影响

恒温条件下用薇甘菊、香泽兰、野茼蒿、菜苔和青菜为食料饲养安婀珍蝶,测定各龄幼虫的体长、体重和头壳宽度,研究不同食料植物饲养对安婀珍蝶幼虫生长发育的影响。结果表明:安婀珍蝶取食野茼蒿、菜苔和青菜虽然程度有不同,但生长发育受到影响,高龄幼虫体长、体重和头壳宽度明显低于薇甘菊饲养的试虫,不能完成生活世代。     

Cloning of DNA fragments specific to the pathotype and race of <Emphasis Type="Italic">Verticillium dahliae</Emphasis>

Japanese isolates of Verticillium dahliae, a causal agent of wilt disease in many plants, are classifiable into pathotypes based on their pathogenicity. Because these pathotypes are morphologically indistinguishable, establishing a rapid identification method is very important for the control of this pathogen in Japan. For cloning DNA fragments that are useful for identification and specific detection of V. dahliae pathotypes, we performed random amplified polymorphic DNA (RAPD) analyses using various isolates. One polymerase chain reaction (PCR) product, E10-U48, was specific to isolates pathogenic to sweet pepper. The other product, B68-TV, was specific to race 1 of isolates pathogenic to tomato. The specificity of these sequences was confirmed by genomic Southern hybridization. Further analyses revealed that the region peripheral to B68-TV obtained from the genomic DNA library includes the sequence specific to all isolates pathogenic to tomato (races 1 and 2). Moreover, sequence tagged site (STS) primers designed from B68-TV and its peripheral region showed race-specific and pathotype-specific amplification in a PCR assay. The probes and primers obtained in this study are likely to be useful tools for the identification and specific detection of pathotypes and races of V. dahliae. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession number AB095266.     

试论宾馆、酒店动物性食品安全控制程序

动物产品是人类赖以生存的重要物质基础,如肉、蛋、禽、奶等动物产品是人类食物构成的重要组织部分,社会越发达,经济越发展,社会文明程度越高,人类对动物产品的依赖性越强,     

生猪屠宰中放血不良产生因素的分析

在生猪屠宰过程中,时常发生放血不良的现象,由于肉中含血过多,使肉色不佳,易于腐败变质,缩短了肉品保鲜时间,影响了肉品卫生质量,而且上市后,往往被消费者误认为是病死猪肉,