Biocontrol potential of Pseudomonas azotoformans,Serratia marcescens and Trichoderma virens against Fusarium wilt of Dalbergia sissoo

Wilt disease caused by Fusarium solani is a serious constraint to Dalbergia sissoo (shisham) plantations in northern India. In this study, the antagonistic potential of 40 bacterial isolates recovered from rhizophere soil of healthy shisham trees, and a well‐characterized Trichoderma species (Trichoderma virens) were tested for their possibility as biocontrol agents for F. solani. Two promising isolates (S1 and S15) were identified which inhibited pathogen growth, caused chitin degradation, produced siderophores and solubilized phosphate in vitro. Isolate S15 scored highest for hydrogen cyanide (HCN) production while isolate S1 was a non‐HCN producer. These two isolates were identified as Serratia marcescens (S1) and Pseudomonas azotoformans (S15) following sequence analysis of 16S rDNA. In dual culture assays, T. virens caused 80% inhibition of mycelial growth of the test fungus. The three selected antagonists when tested in planta in the glasshouse completely suppressed production of wilt symptoms on 12‐month‐old shisham plants. Further work is needed to ascertain the potential of these isolates to be used as biocontrol agents to manage shisham wilt under field conditions.     

番茄青枯病抑病土壤根际微生物群落特征及其抑制性传递机制

根际微生物在宿主植物抵御土传病害发生过程中发挥着重要作用。为探究抑病土壤与感病土壤根际微生物群落特征及其微生物群落构建机制,分别采集抑病土和感病土中的番茄根际土壤,采用实时荧光定量PCR技术检测两种根际土壤中的病原菌含量,并利用16SrRNA基因扩增子高通量测序技术分析抑病和感病土中番茄根际土壤微生物群落多样性、组成、结构以及基于零模型的微生物群落构建机制的差异。结果表明,与感病土相比,抑病土壤中番茄的青枯病病情指数明显降低（病情指数分别为47.5和22.5）,其根际中细菌群落具有更高的alpha多样性、更丰富的放线菌门、厚壁菌门以及芽孢杆菌科和链霉菌科等有益微生物,较低的青枯病菌丰度（病原菌丰度降低了12.22倍）并伴随着较高的随机性过程,因此抑病土壤受病害胁迫的适应性较强。将感病土壤与抑病土壤按照一定比例进行混合,形成了仅有感病土D10H0、感病土与抑病土质量比为1︰1的D5H5以及仅有抑病土D0H10这三种处理以进一步检测抑病土壤抑病特性的可传递性。结果表明,随着抑病土比例的增加,番茄青枯病病情指数逐步降低,D10H0、D5H5和D0H10的病情指数分别为41.67、29.17与...     

保水剂在香蕉枯萎病药剂防治上的运用效果

香蕉枯萎病化学防治的理论和应用研究,是香蕉枯萎病综合防治体系的重要内容之一。试验研究中,采用在香蕉枯萎病杀菌剂掺入农用保水剂,并用于接种了FOC4的香蕉盆栽中,进行保水剂对杀菌剂的药效保持情况的试验研究,通过盆栽试验和田间药效试验得到使用保水剂和不使用保水剂的杀菌剂在香蕉枯萎病防治效果上具有显著的差异。结果表明保水剂能够较好的保持住杀菌剂药效,延长有效期,从而为香蕉枯萎病的防治工作提供了另一有效的防治措施。     

百合枯萎病发生规律及防治研究

百合枯萎病是甘肃省百合产区近年来新发生的一种重要病害。研究证明,百合枯萎病系由尖孢镰刀菌(Fusarium oxysporum Schlecht.)、串珠镰刀菌(F.moniliform Sheldon)和茄病镰刀菌[F.solani(Mart.)Sacc.]侵染所致。病菌以菌丝体在种球内,或以菌丝体、厚垣袍子及菌核随病残体在土壤中越冬,成为翌年的主要初侵染源。病害的发生与连作、线虫、栽培技术及气候因素等密切相关。多菌灵对此病有显著防治效果。     

土壤添加剂防治细菌性青枯病初报

１９９２～１９９３年在四川用一种土壤添加剂对烟草和番茄青枯病进行了小区防治试验，当剂量分别为７５克／株和１００克／株时，防治效果分别达５９．６％和７８．９％，显著优于同时参试的农药。盆栽试验结果显示，添加剂的防病机制主要是通过土壤中有益微生物群体而实现的，施用添加剂的土壤比对照土壤中的放线菌和芽孢杆菌的数量增加１０～１０３倍     

Correlation of molecular markers and biological properties in Verticillium dahliae and the possible origins of some isolates

Haploid and amphihaploid Verticillium dahliae isolates were studied using PCR-based molecular markers which: (i) discriminate the defoliating and nondefoliating pathotypes (two primer pairs INTD2f/r and INTND2f/r), and (ii) are species-specific (primer pair 19/22). The results were compared with some known biological and other molecular properties of the isolates. Five discrete sequences of the 19/22 amplicon were found. Sequence 4 was associated with both defoliating isolates from Spain and nondefoliating isolates from Spain and USA; these pathotypes were separated by the primer pairs INTD2f/r and INTND2f/r, but the data showed that the primer espdef01 (derived from the 19/22 amplicon) cannot be used for this purpose. Amplicon sizes and sequences with primers 19/22 divided amphihaploid isolates from crucifers (thought to be interspecific hybrids) into those corresponding to the previously reported α and β groups. The β-group isolates had either sequence 4 or 5 (these two differing by a single base). The distinct amplicon sequence 3 given by the α-group isolates demonstrated that the V. dahliae -like 'parent' of this group was molecularly unlike any haploid isolate yet studied. The overall results are discussed in relation to phytosanitary considerations and the probability of defoliating or crucifer pathotypes arising de novo within Europe, either by selection or by interspecific hybridizations.     

Susceptibility of Commercial Tomato Cultivars to Bacterial Wilt in Hydroponic System

Commercially available tomato cultivars were hydroponically cultured for inoculation, with Ralstonia solanacearum (K-101), which causes bacterial wilt, by pouring an inoculum suspension into the nutrient solution. Cultivar susceptibility to the bacteria was evaluated, based on the highest percentage of wilting. Because the length of time for wilt appearance varied among cultivars, some cultivars appeared to be suppressive to the translocation and/or multiplication of the invading pathogen. Thus, this hydroponic inoculation system is effective for examining levels of susceptibility in tomato cultivars to bacterial wilt. Received 13 December 2000/ Accepted in revised form 27 March 2001     

Extracts of killedPenicillium chrysogenum Induce resistance against Fusarium wilt of melon

Dry fungal biomass ofPenicillium chrysogenum (dry mycelium), a waste product of the pharmaceutical industry, was extracted with water and applied to the roots of melon plants before or after inoculation withFusarium oxysporum f.sp.melonis (Font). Seedlings (4–6 days after emergence) treated with either acidic dry mycelium extract (DME) or neutralized dry mycelium extract (NDME) were protected against challenge infection withFom. A single drench with 2–5% DME applied 12–72 h before inoculation provided significant control of the disease compared with water-drenched, challenged seedlings. No protection was seen in plants treated 0–6 h before inoculation or 0–48 h after inoculation. Neither DME nor NDME (0.5–5%) had any effect on fungal growthin vitro, which implied that disease controlin vivo was mediated by induced resistance. The resistance induced by DME protected melon plants not only against race 1,2, but also against the three other races of the pathogen, indicating a race-non-specific resistance againstFom. Both DME and NDME significantly increased peroxidase activity and free L-proline content in seedlings 12 h and 48 h after soil drench, respectively. Resistance to Fusarium wilt was significantly associated with elevated levels of peroxidase activity but not with free L-proline content. Thus, peroxidase might be involved in the defense mechanisms activated by DME or NDME. http://www.phytoparasitica.org posting Aug. 31, 2001.     

北京地区西瓜枯萎病生理小种分化研究

对在北京大兴、顺义、通县等西瓜主产区采集，经单孢分离得到的８个西瓜枯萎病菌株进行了生理小种分化研究。应用国际通用的３个鉴别寄主ＳｕｇａｒＢａｂｙ、ｃｈａｒｌｅｓｔｏｎＧｒａｙ、ｃａｌｈｏｕｒＧｒａｙ和国内京欣１号、苏蜜１号２个品种，采用全国协作组统一的苗期抗病鉴定方法，进行人工接种鉴定。结果表明北京地区西瓜枯萎病菌株均系同一生理型，为西瓜枯萎病生理小种１号。     

Characterisation ofFusarium oxysporum isolated from carnation in Australia based on pathogenicity,vegetative compatibility and random amplified polymorphic DNA (RAPD) assay

Isolates ofF. oxysporum collected from symptomless carnation cuttings from Australian carnation growers properties, together with isolates from national collections, were screened for pathogenicity and grouped according to vegetative compatibility and random amplified polymorphic DNA (RAPD) patterns. The collection of 82 Australian isolates sorted into 23 different vegetative compatibility groups (VCGs). Of 69 isolates tested for pathogenicity, 24 were pathogenic to carnations, while the remaining 45 were non-pathogenic. All pathogenic isolates were within two VCGs, one of which was also compatible with an isolate obtained from an international culture collection, and which is known to represent VCG 0021 and race 2. Race status of the two pathogenic VCGs remains unknown. The RAPD assay revealed distinct DNA banding patterns which could distinguish pathogenic from non-pathogenic isolates as well as differentiate between isolates from the two pathogenic VCGs.