香蕉炭疽菌菌株亲缘关系的RAPD分析

应用筛选的8个Operon随机引物对供试菌株的DNA进行扩增,所产生的RAPD图谱揭示了香蕉炭疽菌具有丰富的种内遗传多样性。UPGMA聚类分析的结果表明：26个香蕉炭疽菌被分为两个与地理来源相关的RAPD聚类群,它们分别由广东菌株和海南菌株为主组成。在两个香蕉菌群的外侧,两个胶胞炭疽菌菌株聚为一个小的外群。这些结果表明香蕉炭疽菌存在有与地域相关的种下类群分化。     

Mycelial elongation and sporulation of two fungi on amended media in light or dark

Botrytis allii andCollectotrichum dematium are onion pathogens which can infect in the field and cause decay in storage. Some phenolics can hinder development of these fungi, but the effect of cytokinins is not clear. Cytokinins (kinetin or 6-benzyladenine) or phenolics (caffeic or chlorogenic acids) were added to agar at concentrations of 0 to 10^–3 M. Cultures were continuously irradiated with fluorescent light or maintained in the dark for 6 days. On unamended media, final mycelial elongation was 45 or 17.8 mm and sporulation was 28 or 10.6 × 10⁴ spores/ml forBotrytis andColletotrichum, respectively. ForBotrytis, mycelial elongation was slightly (5%) but significantly increased and sporulation increased by 21% by incubation on phenolics as compared to cytokinins. Mycelial extension ofColletotrichum was not affected by amendment. Sporulation ofColletotrichum on kinetin was 16 to 28% greater than on the other amendments. As amendments concentration increased elongation of mycelia of both fungi decreased. Sporulation ofBotrytis increased by 60% as amendment concentration increased from 0 to 10^–5 M and then decreased 25% at 10^–3 M. As amendment concentration increased from 0 to 10^–3 M, sporulation ofColletotrichum increased by 45%. Incubation in light increased mycelial extension 3 to 17% forBotrytis andColletotrichum respectively, and sporulation was increased approximately 78% for both fungi. These compounds do not appear to inhibit development of theseBotrytis orColletotrichum species in culture.     

Role of foliar hemibiotrophic and fruit resistance in anthracnose‐resistant strawberry genotypes for annual hill plasticulture systems

Anthracnose fruit rot (AFR) caused by Colletotrichum acutatum is one of the most devastating diseases of strawberry (Fragaria × ananassa) in plasticulture systems in the Southeast US. Host resistance offers the best option to limit crop losses in both nursery and fruiting fields. To evaluate levels of anthracnose resistance and elucidate the role of foliar and fruit resistance in overall field AFR resistance, we tested 14 strawberry genotypes including numerous selections from the North Carolina State University strawberry breeding programme. Inoculations of plug plants with three representative C. acutatum isolates prior to field‐set indicated that the commercially standard cultivar Chandler was highly susceptible, with an average fruit rot incidence of over 72% the following spring. In contrast, breeding lines such as NC C99‐13 and NC C02‐63 showed superior resistance with AFR incidence values of 23.6% and 11.1%, respectively, and showed superior marketable yields. An average hemibiotrophic infection (HI) severity on foliage (percent leaf area covered with acervular growth after paraquat treatment and incubation) did not correlate (r = 0.57) well with in vitro AFR severity on detached fruit, indicating different mechanisms may be operative for resistance to foliar HI and fruit rot resistance. Multiple regression analysis indicated that in vitro fruit rot resistance expressed by lesion diameter and severity of foliar hemibiotrophic infections may be utilized to predict field AFR incidence. Strawberry genotypes bred for resistance against both fruit rot and foliar HI could be effectively selected by using rank‐sum classification methods and this process offers an effective strategy to advance selections for superior AFR field resistance.     

Der mit der Versuchsdauer anwachsende Resistenzfaktor

Abstract

Pseudomonas spp. strains capable of inducing systemic resistance were applied to sugarcane by sett treatment followed by soil applications in the field. Later the fungal pathogen Colletotrichum falcatum causing red rot disease of sugarcane was inoculated in the treated canes and its colonization was assessed by ELISA at different nodal positions above the point of inoculation. Studies with three cvs showed a significant variation in pathogen colonization only in disease susceptible cv CoC 671 and not with cvs Co 8021 and BO 91, moderately susceptible and moderately resistant to the disease, respectively. In further studies when pathogen colonization was assessed on the entire stalks of cv CoC 671, the pathogen titre was significantly reduced from three nodes upwards in the treated canes. In the upper nodes no pathogen colonization was noticed in bacteria-treated canes, whereas in the control all the nodes recorded higher titre for pathogen infection. Incorporation of chitin in the talc formulation caused further reduction in fungal colonization in the stalks.     

Reaction of Some Coffea arabica Genotypes to Strains of Colletotrichum kahawae, the Cause of Coffee Berry Disease

Pathogenicity tests were performed on 11 genotypes of Coffea arabica using single‐isolate suspensions of Colletotrichum Kahawae obtained from 90 monoconidial isolates. The objective of this study was to estimate the proportion of pathogenic variation corresponding 10 differences in aggressiveness and virulence (races). A large part of the variation in the pathogen population was due to aggressiveness. The differential effects were too small to suggest conclusively that races exist. This paper discusses the possible causes for the observed small differential interaction and suggests breeding strategies that not only prevent possible adaptation of the pathogen to resistant varieties but also limit variation for resistance due to differences in aggressiveness of the pathogen.     

Bioherbicidal enhancement and host range expansion of a mycoherbicidal fungus via formulation approaches

Eastern black nightshade (Solanum ptycanthum; EBN) is a problematic weed partly due to its tolerance or resistance to certain herbicides. We examined the effects of an invert emulsion (IE) on the host range and weed control efficacy of the fungus Colletotrichum coccodes (NRRL strain 15547) for biocontrol of EBN. Greenhouse tests demonstrated that several other solanaceous weeds were also infected and killed, and field tests revealed >90% EBN control and dry weight reduction in plants treated with the fungus-IE formulation. These results demonstrate that this IE formulation can promote the efficacy of this bioherbicidal pathogen.     

Hydroponic Seedling Bioassay for the Bioherbicides Colletotrichum truncatum and Alternaria cassiae

A rapid bioassay was developed to measure the bioherbicidal efficacy of spore preparations of the pathogens Colletotrichum truncatum (Schwein.) Andrus and W. D. Moore and Alternaria cassiae Jurair and Khan on hemp sesbania (Sesbania exaltata) and sicklepod (Cassia obtusifolia), respectively. The system uses 4-day-old dark-grown seedlings (grown hydroponically in paper towel cylinders) which were sprayed with spore suspensions. Shoot lengths were monitored non-destructively, and recorded over time under conditions of dark growth, 90-100% relative humidity and 25 C. Shoot growth inhibition and stem collapse (mortality) were directly related to the spore concentration applied. Generally, at 10 3 - 10 4 spores ml-1, these pathogens caused significant shoot growth inhibition within 25-30 h and seedling death within 40-50 h. This bioassay has been used to study herbicide-pathogen interactions, and may be extended to determine the bioherbicidal efficacy of different pathogen isolates, pathovars or spore formulations. This technique is more rapid, uses a lower inoculum volume, requires less space and is performed under more controlled conditions than conventional greenhouse bioassay methods. The data obtained are more quantitative than those obtained from bioassays relying on visual rating systems.     

浙江无核柿炭疽病菌鉴定及附着胞形成过程中的核相变化

浙江无核柿炭疽病近年来在浙江淳安地区严重发生,根据形态学特征病原菌鉴定为胶孢炭疽菌ColletotrichumgloeosporioidesPenz.,在枝条病斑上的分生孢子盘通常不产生刚毛,分生孢子顶端顶部钝圆,基部平截,分生孢子盘中的孢子包埋在基质中,紧密结合在一起。分生孢子在自然寄主和人工培养条件下形态特征相似。6个柿树炭疽菌菌株的rDNAITS序列联配显示,其序列是相同的。用UPGMA方法分析ITS1-ITS2序列构建的炭疽菌系统发育树把6个柿树炭疽菌菌株和其它寄主上的胶孢炭疽菌或其有性型围小丛壳菌菌系分入同一个组,与根据形态学的鉴定结果一致。在附着胞形成过程中,用DAPI荧光染色观察到核相发生两次有丝分裂变化。第一次有丝分裂发生在分生孢子固着聚苯乙烯塑料培养皿3-4h后,随后,分生孢子中部形成一个隔膜,把它分成两个细胞;6~7h后,分生孢子发生第二次有丝分裂。分裂后,一个核通过芽管移入附着胞中。     

Responses of embryogenic mango cultures and seedling bioassays to a partially purified phytotoxin produced by a mango leaf isolate of Colletotrichum gloeosporioides penz

Summary Colletotrichum gloeosporioides Penz., the causal agent of mango anthracnose, produces a phytotoxin in vitro. The partially purified phytotoxin, presumably colletotrichin, caused anthracnose-like symptoms on young mango leaves, was toxic to embryogenic suspension cultures of two mango cultivars, ‘Hindi’ and ‘Carabao,’ and inhibited in vitro seed germination of two nonhosts, lettuce and tobacco. There were linear relationships between concentration of the partially purified phytotoxin and mortality of mango embryogenic cultures. Embryogenic cultures grown in the presence of the partially purified phytotoxin showed significantly lower growth rates than the controls. Similarly, embryogenic cultures grown in the presence of 40% (vol/vol) fungal culture filtrate showed significantly lower growth rates than unchallenged controls. Medium containing 40% (vol/vol) Czapek-Dox fungal broth did not reduce growth of embryogenic cultures, indicating the production of phytotoxin in vitro. The results suggest that either fungal culture filtrate or purified phytotoxin can be used as in vitro selection agents to screen for resistance to this fungus.     

Bacillus velezensis strain HYEB5-6 as a potential biocontrol agent against anthracnose on Euonymus japonicus

Anthracnose is a foliar disease of the Euonymus shrub caused by Colletotrichum gloeosporioides. In this study, the bacterium HYEB5-6 was isolated from inside one-year-old branches of healthy Euonymus japonicus and showed significant antifungal activities against various phytopathogenic fungi, including C. gloeosporioides s.s. HYCG2-3, in dual culture experiments. The HYEB5-6 isolate significantly decreased lesion diameter and disease index caused by C. gloeosporioides inoculation on detached leaves of E. japonicus. The effects of HYEB5-6 metabolites on the invading structure of the fungus were investigated. Bacterial metabolites inhibited conidial germination, the growth of the germ tube and appressorium formation, possibly through protease and glucanase of HYEB5-6 by managing the mycelial cell wall. The HYEB5-6 isolate also produced a massive biofilm, which might facilitate leaf colonisation. These results indicate that HYEB5-6 has the potential for use as a biological control agent against C. gloeosporioides. The HYEB5-6 isolate was identified as Bacillus velezensis based on its biochemical characteristics and its 16S rRNA gene sequence.