Whole-Cell Fatty Acid Composition to Characterize and Differentiate Isolates of Rhizoctonia Species Associated with Turfgrass Diseases in Japan

Cellular fatty acids were analyzed to characterize and differentiate 34 isolates of Rhizoctonia species representing binucleate Rhizoctonia AG-D (I), AG-D (II), R. solani AG 2-2 IIIB, AG 2-2 LP, R. circinata var. circinata and var. oryzae associated with turfgrass diseases in Japan. Myristic, pentadecanoic, palmitic, palmitoleic, stearic, oleic, linoleic and linolenic acids were consistently present in varying quantities in all isolates. Heptadecanoic and 9-heptadecenoic acids were present in isolates of Rhizoctonia AG-D (I), AG-D (II), R. solani AG 2-2 IIIB and AG 2-2 LP but not in isolates of R. circinata var. circinata and var. oryzae. Palmitic, oleic and linoleic acids were the major fatty acids found, constituting 88.30-98.37% of the whole-cell fatty acid content. The remaining fatty acids were present in smaller amounts. Isolates within a single group were closely clustered, whereas isolates from different groups were clearly distinguishable based on average linkage cluster analysis of cellular fatty acids. Principal component analysis, based on all fatty acids detected, confirmed the distinct separation of isolates representing the six groups of Rhizoctonia species obtained from turfgrasses. These results suggested that fatty acid analysis is useful for the characterization and differentiation of isolates of Rhizoctonia species associated with turfgrass diseases. Received 21 May 2001/ Accepted in revised form 28 September 2001     

Aromatic Substances Inhibiting Wheat Powdery Mildew Produced by a Fungus Detected with a New Screening Method for Phylloplane Fungi

Microorganisms isolated from wheat leaf surfaces were screened for inhibition of wheat powdery mildew. A new screening method, in which wheat leaves were inoculated with Blumeria graminis f. sp. tritici and incubated with the cultured microorganisms under non-contact conditions, was developed in the present study. Using this method, 10 phylloplane fungi that inhibited wheat powdery mildew were selected from 408 microorganisms isolated from wheat leaf surfaces. Among these 10 strains, a fungus designated as Kyu-W63 had an especially strong inhibitory effect. Kyu-W63 produced white colonies without spores when cultivated on PDA. Kyu-W63 had a strong aromatic odor when being cultured. Wheat powdery mildew was suppressed even though a membrane filter with a pore size of 0.45 μm was placed between the mycelial colony and wheat leaf segment. However, when activated charcoal was introduced, Kyu-W63 did not inhibit growth of B. graminis. It was presumed that volatile substances were involved in the inhibitory effect of Kyu-W63. GC-MS analysis was used to identify two substances produced by Kyu-W63 with molecular weights of 164 and 166. Kyu-W63 also inhibited the in vitro growth of four plant pathogenic fungi other than B. graminis. Received 19 September 2001/ Accepted in revised form 7 February 2002     

Ultrastructural Localization of Hydrogen Peroxide in Host Leaves Treated with AK-toxin I Produced by Alternaria alternata Japanese Pear Pathotype

The rapid generation of reactive oxygen species (ROS), called the oxidative burst, is one of the earliest host responses to pathogen infection or elicitor treatments. Therefore, we looked for the induction of ROS generation in Japanese pear leaves by the host-specific toxin, AK-toxin I using a cytochemical method for detecting H₂O₂. A small amount of non-specific generation of H₂O₂ was found in the cell walls in toxin- and water-treated susceptible and resistant leaves. Thus, the generation of H₂O₂ at cell walls appears to be caused by wounding stress during sampling. Specific generation of ROS, however, was found only in the membrane fragments and extended desmotubules characteristic of modified sites of the plasma membrane in the toxin-treated susceptible leaves. In addition, generation of H₂O₂ at plasma membranes was observed with higher frequency in toxin-treated susceptible leaves. This result indicates that the H₂O₂ generation was associated with damaged sites in the plasmalemma after toxin treatment and perhaps with the formation of membrane fragments from altered portions of the invaginated plasma membrane. Received 21 September 2001/ Accepted in revised form 25 October 2001     

Suppression of Verticillium Wilt in Eggplant by Some Fungal Root Endophytes

One hundred and twenty-three fungal isolates were obtained from 225 root segments of eggplants, melon, tomato, strawberry and Chinese cabbage, grown as bait plants in a mixed soil made up of samples from different fields in Shizuoka, Japan. Isolates belonging to Mycelium radicis atrovirens (MRA), including Phialocephala fortinii, were the most prevalent in all the five bait plants. Eleven of the 123 isolates, after being inoculated onto axenically reared eggplant seedlings, almost completely suppressed the pathogenic effects of a post-inoculated, virulent strain of Verticillium dahliae. Seven of these 11 isolates had come from the roots of eggplant and included Heteroconium chaetospira, P. fortinii, and unidentified species of Fusarium, Penicillium, Trichoderma and MRA. P. fortinii, H. chaetospira, a non-sporulating isolate with white mycelium (SWM) and MRA were easily reisolated from root segments. Hyphae of H. chaetospira, P. fortinii and SWM colonized the root tissues of eggplant without causing apparent pathogenic symptoms. The mechanisms by which these endophytes confer resistance to infection by V. dahliae are unknown but the effectiveness of these fungi in a laboratory setting indicates that they have potential as biocontrol agents and merit further investigation.     

The Complete Nucleotide Sequence of a Japanese Isolate of White clover mosaic virus Strain RC

The complete nucleotide sequence was determined for genomic RNA of White clover mosaic virus (WClMV-RC) isolated from red clover (Trifolium pratense) in Japan, It is 5843 nucleotides in length, excluding the poly(A) tail at the 3' terminus. Similar to other potexviruses, it contains five open reading frames (ORFs 1 through 5), which putatively encode an RNA-dependent RNA polymerase (RdRp) (147 kDa), a triple gene block (TGB) (26 kDa/13 kDa/7 kDa), and a coat protein (CP) (22 kDa), respectively. The deduced amino acid sequence of the WClMV-RC CP was identical to that of WClMV-O, one of two New Zealand isolates, but only 85% identical to that of WClMV-M, the other New Zealand isolate, because of heterogeneity in the C-termini of CP amino acid sequences. The implication of this CP heterogeneity is discussed. Received 30 August 2001/ Accepted in revised form 11 January 2002     

甘薯根腐病抗性在不同环境条件下的表现及遗传趋势

结果表明,甘薯根腐病发病轻重与环境条件有很大关系,表现为干旱少雨的年份发病较重,降雨量较多的年份发病较轻;土壤瘠薄的发病较重,肥力条件较好的则发病较轻;通常情况下,年份间品种的抗性表现较为一致,但遇特殊气候则年份间品种的抗性有一定的差异。对1150份甘薯品种资源及育种材料的根腐病抗性鉴定结果表明,高抗型材料占14.6％,抗病型占15.7％,感病型占26.0％,高感型占43.7％。对754份材料及亲本的抗性分析表明,不同的抗性组合后代中均可分离出高抗至高感类型的材料,杂交后代的抗性强弱随双亲抗性水平的提高而提高。中国自1970年以来采用品种间杂交和种间杂交育种技术,先后育成了一批高产、优质的高抗型优良品种。     

棉铃虫性诱剂诱捕器的改进及其应用研究

利用废弃的食用油油壶制成棉铃虫诱捕器,可提高诱蛾的效果。挡板距诱捕器器口的距离以3cm的效果最佳。与常规水钵、水盆诱捕器相比较,全年诱蛾总量分别增加116.3％和减少79.8％,但诱蛾灵敏度均高出18.72％。     

辣椒疫病发病主导因素及综合防治技术研究

通过3a在多年辣椒重茬地的田间试验及调查研究,基本明确了辣椒疫病发生与灌水方法、栽培方式、降水、中心病株的出现等主导因素的关系。提出了栽培防病、化学治疗的综防技术,达到控病增产的目的。     

Effect of take-all root infections on nitrate uptake in winter wheat

The effect of take-all root lesions on nitrate uptake of wheat was investigated in two experiments under controlled conditions. Plants were supplied with a nutrient solution labelled with ¹⁵N during stem elongation and flowering to assess the distribution of the isotopic tracer in the different plant organs, and particularly in root segments located on both sides of take-all lesions. The ¹⁵N atom percentage excess measured in root segments located below lesions longer than 1 cm was reduced on average by half compared with that in healthy roots and root segments above lesions, reflecting a reduction in nitrogen uptake by these root segments. This reduction probably resulted from the invasion and breakdown of phloem vessels by the fungus hyphae, interrupting energy supply and thus the uptake process. Severely infected plants showed an increase in the uptake rate per unit of efficient root, which appeared to be a compensatory response to reduction of efficient root biomass in order to satisfy shoot nitrogen demand. However, this compensatory response was insufficient to ensure nitrogen accumulation equivalent to that of healthy plants, as reductions in nitrogen accumulated in roots and aerial parts at flowering were up to 56 and 49%, respectively, for plants with more than 50% of the root system below lesions longer than 1 cm.