树脂吸附法分离瓜果腐霉毒素中的除草活性物质

本试验以对禾本科杂草具有除草活性的瓜果腐霉菌株PAM1为试验材料,研究了X-5、AB-8,H-103和S-8等4种大孔吸附树脂对其除草活性物质的吸附性能,结果表明X-5树脂能够较好地吸附该除草活性物质.选用50%乙醇、95%乙醇、乙酸乙酯和丙酮4种溶剂为供试洗脱溶剂,采用2种洗脱方案,对其最佳洗脱溶剂进行了选择,生长抑制作用和种子萌发试验结果表明,以方案1洗脱为最佳.     

Cavity spot of carrots: Interactions between the host and pathogen, related to the cell wall

This study investigates the structural aspects of cavity spot pathogenesis. Different Pythium spp. isolated from infected carrots, apples and melons were cultured on agar in Petri dishes and used for inoculation of uninfected carrots. Only slow-growing Pythium spp. (< 15 mm day^-1), such as P. violae and P. sulcatum caused cavity spot lesions. It is suggested that slow-growing species are able to penetrate, albeit slowly, into the plant tissue for 3 to 4 days before a hypersensitive reaction develops. Fast-growing species, however, did not cause lesions. Based on ultrastructural observations, we suggest that the following sequence of events occurs between the plant and the pathogen: The fungus infects the walls and grows for several days, during which time small amounts of wall-degrading enzymes are secreted. Phenylalanine ammonia lyase (PAL) activity and phenols increase linearly immediately upon inoculation. There was a lag phase of about 5 days before lignin began to increase linearly for about a month. Dissolution of wall components decreases the solute potential and water potential in the apoplast. Thus, water moves from the symplast into the apoplast, the turgor pressure gradually dissipates, and the cells shrink and eventually die.     

Polymorphic microsatellite markers for the human oomycete pathogen Pythium insidiosum

We describe the development and characterization of microsatellite loci from the human oomycete pathogen Pythium insidiosum. Nine of 15 microsatellite loci were shown to be appropriate for population genetic study. All loci were polymorphic with observed heterozygosities ranging from 0.241 to 0.912 and from five to 18 alleles per locus among 65 individuals in Thailand. These markers are being used to ascertain multilocus genotypes for molecular epidemiological and population genetic analyses of this little known human pathogen.     

Transmission of Pythium aphanidermatum to greenhouse cucumber by the fungus gnat Bradysia impatiens (Diptera: Sciaridae)

The fungus gnat (Bradysia impatiens) was examined for its ability to transmit Pythium aphanidermatum to cucumber plants. Larvae that had ingested oospores and mycelium, and then fed on the roots of young cucumber plants growing in rockwool readily introduced the fungus to them. Trans-stadial transmission of oospores from the larval to the adult stage of B. impatiens was demonstrated, although decreasing to a very low level (1.67%) in adults. However, external transmission of P. aphanidermatum on the surface of adults could not be shown. These results suggest that the larval stages of fungus gnats play a role in the dissemination of the fungus between cucumber plants but that adults probably play only a minor role.     

Biocontrol of a root rot of kale by <Emphasis Type="Italic">Muscodor albus</Emphasis> strain MFC2

Pythium ultimum is an oomycetous root rot pathogen that causes significant crop production losses on many crops including kale (Brassica oleracea), an economically important vegetable in Thailand. An endophytic fungus from Thailand designated Muscodor albus MFC2 controlled P. ultimum both in vitro and on kale seedlings grown under outdoor conditions via the production of volatile antibiotics. Ten-day old M. albus MFC2 PDA cultures killed P. ultimum in vitro. Thoroughly mixing three PDA plates of 10-day old M. albus MFC2 into a 500 g mixture of commercial soil and field soil did not adversely affect kale seed germination. The same amount of M. albus MFC2 could restore seedling emergence in P. ultimum inoculated soil to a level close to that of a non-infested control. In addition, M. albus MFC2 did not cause any disease symptoms, but rather seemed to promote the growth of kale in the presence or absence of P. ultimum for up to eight weeks after planting.     

Biocontrol activity of the extract prepared from Zingiber zerumbet for the management of rhizome rot in Zingiber officinale caused by Pythium myriotylum

Zingiber zerumbet Smith or wild ginger is remarkable for its inherent resistance to Pythium spp., which cause soft rot disease in Zingiber officinale Rosc. In the present study, various concentrations of extract prepared from Z. zerumbet were screened for its activity against Pythium myriotylum. Microscopic observation of P. myriotylum in presence of Z. zerumbet extract has confirmed the complete lysis of pathogen within 10 h. However, the same treatment with Z. officinale extract was found to have partial antifungal effect even after 24 h due to inability of its metabolites to prevent the growth of P. myriotylum. Due to the antifungal activity, extract from Z. zerumbet was subjected to GC–MS and LC-QTOF-MS which has identified Zerumbone with m/z 219 as the major compound. Further, in vivo study and the subsequent microscopic analysis have confirmed the applicability of extract from Z. zerumbet as a phytomedicine to control rhizome rot in ginger.     

Effectiveness of Four New Pyrazole-pyrimidines on Phytopathogens: Ultrastructural Evidences on Pythium ultimum

Four newly synthesized molecules derived from pyrazole-pyrimidine were assayed on Botrytis cinerea Micheli, Fusarium moniliforme Sheld and Pythium ultimum Trow. All proved effective in inhibiting the growth of the phytopathogens at all of the test concentrations (10, 20, 50, 100 μg/ml). The most effective compound was 1-(3)nitrophenyl - 6 - trifluoromethylpyrazolo[3,4 - d ]pyrimidine 4(5H)-thione (CF₃3). Ultrastructural studies on P. ultimum treated with CF₃3 revealed alterations in the normal hyphal shape and, at high concentration, plasmolysis and damage to the wall texture was observed. At 20 μg/ml different vesicles were seen in the cytoplasm: some appeared quite dense, and specific cytochemical reactions indicated that they were most likely peroxysomes; other vesicles seem to be vacuoles of varying content. In some cases there was disintegration of the nuclear envelope. The effects on membrane lipids and interference in protein synthesis are hypothesized as possible mechanism of action of the molecule.     

A PCR-RFLP assay for identification and detection of Pythium myriotylum, causal agent of the cocoyam root rot disease

Aim: Development of a PCR‐RFLP assay that could reliably distinguish strains of Pythium myriotylum that are pathogenic to cocoyam from nonpathogens, as well as in planta detection of the pathogen. Methods and Results: Sequences of the internal transcribed spacer regions of nuclear ribosomal DNA (rDNA‐ITS) containing ITS1 and ITS2 of P. myriotylum isolates from cocoyam and other hosts were aligned and a restriction map was generated. rDNA‐ITS alignment report revealed a new single nucleotide polymorphism (SNP; thymine/cytosine) downstream to previously published SNP (guanine/adenine) between isolates of P. myriotylum that are pathogenic to cocoyam and nonpathogenic strains. This new SNP is within the restriction site of the endonuclease AarI. Based on this SNP, a PCR‐RFLP assay was developed for specific detection of P. myriotylum. The PCR amplicons of all isolates of P. myriotylum that infect cocoyam were cleaved by AarI, resulting to two bands (600/400 bp); but those from other hosts showed a single band (1000 bp), confirming the presence and specificity of the AarI restriction site. Also, the assay was effective in in planta detection of the pathogen on infected cocoyam roots without prior isolation of a pure culture. Conclusion: A PCR‐RFLP method was developed that differentiates isolates of P. myriotylum that are pathogenic to cocoyam from nonpathogens as well as from other fungi commonly found in the cocoyam rhizosphere. Significance and Impact of the Study: Early and rapid detection of the pathogen could be of great importance in certifying planting materials as disease‐free, enhancing sustainable management practices and limiting economic losses.     

NaCl溶液对贵阳腐霉菌丝生长、孢子囊产生及灭蚊能力的影响

研究不同浓度NaCl溶液对贵阳腐霉菌丝生长、产孢能力及灭蚊能力的影响,探讨贵阳腐霉对NaCl溶液的耐受性,为其在含盐水体中控制蚊虫种群的应用提供理论依据。结果表明：低浓度NaCl溶液可以促进贵阳腐霉菌丝生长及孢子囊形成,高浓度NaCl溶液则抑制菌丝生长及孢子囊形成。于0.01%浓度NaCl溶液中培养24h菌丝生长速度最快,产孢子囊数量最多,与对照相比差异显著。随着NaCl浓度升高,菌丝及孢子囊形成均受影响。菌丝生长速度降低,孢子囊形成数量减少。在0.75% NaCl溶液中贵阳腐霉的菌丝生长严重受抑制,且产孢子囊能力为零。灭蚊实验表明,0.01% NaCl溶液中贵阳腐霉的灭蚊能力在72–96h时均比蒸馏水对照组强,但二者未有显著差异,120h蒸馏水对照组灭蚊能力均明显高于各浓度NaCl溶液处理组;蚊虫总感染率蒸馏水对照组均显著高于NaCl溶液处理组。     

Rhizobacterial-mediated induction of defense enzymes to enhance the resistance of turmeric (Curcuma longa L) to Pythium aphanidermatum causing rhizome rot

Rhizobacteria isolated from the rhizosphere soil were evaluated for their ability to control rhizome rot in turmeric (Curcuma longa L). These isolates were characterised as Pseudomonas fluorescens and Bacillus subtilis. Under in vitro condition, two isolates, namely P. chlororaphis (PcPA23) and B. subtilis (BsCBE4), showed maximum inhibition of mycelial growth of Pythium aphanidermatum, were found effective in reducing rhizome rot of turmeric both under greenhouse and field conditions and increased the plant growth and rhizome yield. Both the isolates were further tested for its ability to induce production of defense-related enzymes and chemicals in plants. Increased activities of phenylalanine ammonia lyase, peroxidase, polyphenol oxidase, chitinase and β-1,3-glucanase were observed in PcPA23 and BsCBE4 pre-treated turmeric plants challenged with P. aphanidermatum. Moreover, higher accumulation of phenolics was noticed in plants pre-treated with PcPA23 and BsCBE4 challenged with P. aphanidermatum. Thus, the present study shows that in addition to direct antagonism and plant growth promotion, induction of defense-related enzymes involved in the phenyl propanoid pathway collectively contributed to enhance resistance against invasion of Pythium in turmeric.