玉米茎腐病研究进展

系统综述了玉米茎腐病的发病症状、分级标准、致病菌、致病机理、抗性遗传规律、抗性基因定位和抗病机理的研究进展,并提出了抵御玉米茎腐病的综合防治措施。     

党参根腐病病原菌鉴定及其室内毒力测定

为明确引起甘肃省渭源县党参根腐病的病原菌,并筛选防治该病害的最佳杀菌剂,试验采用组织分离法和单孢分离法对引起党参根腐病的病原菌进行了分离纯化,通过致病性测定、形态学特征、编码转录延伸因子区序列(TEF-1α)聚类分析对病原菌进行了鉴定,并采用生长速率法进行药剂毒力测定.病原鉴定结果表明,引起甘肃省渭源县党参根腐病的病原...     

寄生玉米的6种腐霉及其致病性研究

 从国内12省、自治区、直辖市玉米植株上分离出腐霉菌菌株,依据形态特征、培养性状、生长抑制温度,以及产生的有性与无性器官,鉴别出6个腐霉种:棘腐霉(Pythium acanthicum Drechsler),瓜果腐霉(P.aphanidermatum(Edson)Fitzpatrick),强雄腐霉(P. arrhenomanes Drechsler),禾生腐霉(P.graminicola Subramaniam),肿囊腐霉(P.inflatum Matthews),寡雄腐霉(P.oligandrum Drechsler),其中肿囊腐霉出现频率高,分布广泛。回接玉米表明,腐霉能够侵染玉米并引起病害,肿囊腐霉、禾生腐霉、强雄腐霉、棘腐霉是玉米青枯病的重要致病菌;瓜果腐霉能够引起玉米中部茎节腐烂;寡雄腐霉虽寄生玉米,但对玉米成株无致病力。     

Ribosomal DNA Sequence Comparisons of Colletotrichum Graminicola from Turfgrasses and other Hosts

The 5.8S ribosomal gene and the flanking internal transcribed spacers (ITS) 1 and 2 from Colletotrichum graminicola isolates causing anthracnose disease of Agrostis palustris and Poa species were sequenced. Although bootstrap support was not high, two major groups were observed with both UPGMA and parsimony algorithms, one containing isolates from A. palustris and another with isolates from Poa spp. The ITS sequences were also compared with those of isolates of C. graminicola and C. sublineolum from Sorghum spp., Zea mays and Rottboellia cochinchinesis as well as other Colletotrichum species. Except for one isolate from P. annua in Texas, the ITS1 and ITS2 sequences of turfgrass isolates always grouped separately from C. graminicola or C. sublineolum from non-turfgrass hosts with high bootstrap support. ITS sequences of the turfgrass isolates were more similar to those of other species of Colletotrichum, such as C. coccodes and C. dematium, than they were to C. graminicola isolates from other hosts. Turfgrass isolates have ITS sequences which are not identical to those of isolates from Zea mays and Sorghum species demonstrating diversity among fungi conventionally classified as C. graminicola.     

Specificity of polycllonal and monoclonal antibodies for the identification of Xanthomonas campestris pv. campestris

Polyclonal and monoclonal antibodies (PCAs and MCAs), produced to whole cells and flagellar extracts ofXanthomonas campestris pv.campestris (Xcc), respectively, were tested for specificity. In immunofluorescence microscopy (IF) the three PCAs tested, reacted at low dilutions with all Xcc strains, some other xanthomonads and non-xanthomonads. At higher dilutions most cross-reactivity with non-xanthomonad strains disappeared. However, the cross-reactivity with strains ofX. c. pv.vesicatoria (Xcv),X. c. pv.amoraciae (Xca) andX. c. pv.phaseoli var. fuscans (Xcpf) remained.Six MCA-producing cell clones viz. 20H6, 2F4, 18G12, 10C5, 17C12 and 16B5 were selected for specificity tests with an enzyme immunoassay (EIA), IF and a dot-blot immunoassay (DBI). None of the MCAs reacted with all Xcc strains in IF and EIA. In DBI, only MCAs 17C12 and 16B5 reacted with all Xcc strains. All six MCAs tested, cross-reacted in one of either tests with other pathovars ofX. campestris, such as Xcv or Xca. The MCAs were also tested in immunoblotting experiments using total bacterial extracts, cell envelope and flagellar extracts. MCAs 20H6, 2F4, 18G12 and 10C5 reacted with the lipopolysaccharide (LPS) of Xcc. MCAs 16B5 and 17C12 reacted with a 39 kilodalton and a 29 kilodalton protein, respectively.It is concluded that the PCAs and MCAs discussed in this study may be used for routine identification and differentiation of (a group of) Xcc strains. The significance of the cross-reactions with other pathovars ofX. campestris needs to be determined by testing seed lots.     

A 9-year monitoring study of diseases on potato seed tubers imported to Israel

Potato seed tubers are imported annually to Israel from northern Europe. Although the seed is registered as certified, a survey carried out over a 9-year period indicated that most lots were affected by latent or active bacterial and fungal infections. Latent infection byErwinia carotovora subsp.atroseptica, the causal agent of blackleg, at a level of 10³ cells/g peel, was present in 30% of the lots in most years. Black scurf caused byRhizoctonia solani was present in 20–70% of the imported lots, with a moderate to high level of infection in all years except 1985. In contrast, although many lots were affected by powdery scab, common scab, and Fusarium dry rot in most years, disease incidence within lots was generally low. The gangrene pathogen (Phoma exigua) was rarely detected. The survey findings are of marked importance, due to the extensive use of soil fumigation in Israeli agriculture.     

Enzymatic Maceration of Witloof Chicory by the Soft Rot Bacteria Erwinia carotovora Subsp. carotovora: The Effect of Nitrogen and Calcium Treatments of the Plant on Pectic Enzyme Production and Disease Development

Disease incidence of bacterial soft rot caused by Erwinia carotovora subsp. carotovora and activities of bacterial pectolytic enzymes were studied in witloof chicory. Disease incidence after forcing of the chicory heads was enhanced by the nitrogen treatment and reduced by the calcium treatment of the chicory plants prior to forcing. Significant differences in susceptibility to bacterial soft rot were found for the tested chicory cultivars. Disease severity after 96h ranged from 6% in Clause R2 to 100% in Bea and Tabor. Chicory cultivars Rumba and Salsa showed a final average severity of 65–70%. Activity of the pectolytic enzymes, polygalacturonase and pectate lyase increased in artificially inoculated chicory heads of cultivar Rumba and was not affected by calcium and nitrogen treatments of the plants. Polygalacturonase showed highest activity 48h after inoculation while pectate lyase activity increased throughout 72h of incubation. Maceration of the chicory tissue and bacterial growth increased continuously until 96h after inoculation, when more than 60% of the chicory heads was macerated by pectolytic enzymes of the bacteria. Enzyme activity of Erwinia carotovora subsp. carotovora grown on chicory cell wall extracts was influenced by nitrogen and calcium treatments of the chicory plants. The activity of polygalacturonase reached its highest level at 48h after incubation and pectate lyase activity peaked at 24h followed by a continuous decrease until 72h after inoculation.     

Isolation and characterization of Pseudomonas aeruginosa from sheep with fleece rot in northern and middle Jordan

A total of 162 sheep fleece samples were collected from 2315 sheep clinically examined for evidence of dermatitis. The sheep belonged to 32 flocks raised in northern and middle Jordan. Eighty-three samples showed no obvious abnormalities, whereas the remainder showed exudation (79 samples), fleece discoloration (18) and fleece roughness (40) and abscesses (7). Seventeen Pseudomonas aeruginosa isolates were obtained from these samples. Antibacterial resistance in vitro was common; resistance to tetracycline, amoxycillin, erythromycin and cotrimoxazole was shown by > 90% of the isolates. Resistance to norfloxacin (29.4% of isolates), ciprofloxacin (17.6%) and amikacin (17.6%) was also demonstrated. Fourteen isolates were serum resistant when assessed after 1-3 h incubation in sheep and calf sera, and their count increased by 2-2.9 and 2.5-3.5 respectively.     

Armillaria species on tea in Kenya identified using isozyme and DNA sequence comparisons

The aim of this study was to identify seven Armillaria isolates obtained from diseased tea bushes in Kenya using pectic enzyme profiles, PCR-RFLP and IGS-I DNA sequence data. The combination of these identification methods confirmed the presence of three distinct Armillaria groups. One of these groups resembled Zimbabwean group I ( A. fuscipes ). The second group was phylogenetically closely related to A. mellea ssp. nipponica . The third group was different from all other African isolates examined, but had isozyme patterns, especially of pectin methylesterases (PMEs), similar to those of isolates related to A. mellea ssp. nipponica. Analyses of sequence data suggested that this group is phylogenetically closely related to A. hinnulea from Australia and New Zealand.