Urocystis tranzscheliana,a newly recorded smut fungus onPrimula sieboldii from Japan

A smut fungus onPrimula sieboldii was newly found in Japan and identified asUrocystis tranzscheliana by comparative morphology. This species causes systemic infection ofP. sieboldii and produces sori in its ovaries.Contribution No. 121, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

高粱丝黑穗病菌种内分化的RAPD分析

应用随机引物对来自不同地理来源、不同寄主和经寄主致病力测定的高粱丝黑穗病菌2、3号生理小种的10个菌株的DNA进行分析,所产生的RAPD结果表明,丝黑穗病菌S.reilianum具有丰富的种内遗传多样性,存在明显的分化现象。经聚类分析可将供试菌株大致分成两组,辽宁清原H2和黑龙江绥化H9菌株为一组。辽宁沈阳(H3)、阜新(H1)、营口(H10),山西榆次(H4),吉林四平(H5),黑龙江哈尔滨(H6),河北张家口(H8)等高粱丝黑穗病菌株以及辽宁沈阳的玉米丝黑穗病菌株(H7)为另一组,并且同一组内的DNA多态性亦有差异。高粱丝黑穗病菌2号生理小种和3号小种间在分子水平上存在差异明显。     

Evaluation of improved and local/landrace/sorghum varieties for covered kernel smut

Twelve varieties of improved and local (landrace) sorghum were tested under artificial inoculation conditions. Out of 12 sorghum varieties evaluated with covered kernel smut, notably local cultivar ‘Tetron’ was found to be highly resistant. Disease incidence and severity on the rest of the cultivars varied from 21 to 47% and 40 to 53% respectively. Differences among cultivars in yield loss were also observed. The highest yield loss (40%) was recorded on 97 MW 6129 (NVT-11 4) and for Tetron yield loss was nil. The effect of disease on germination was noticed but cannot be considered as conclusive due to moisture stress at the time of germination.     

抗、感黑穗病谷子品种几种酶活性的比较研究

本文对7个不同抗、感黑穗病的谷子品种在不同时期进行了超氧化物歧化酶、过氧化物酶、多酚氧化酶活性的比较研究。结果表明,谷子感染黑穗病后,体内超氧化物歧化酶、过氧化物酶、多酚氧化酶活性均显著增强。抗病品种的酶活性明显地高于感病品种。这些酶活性的变化能够削弱或消除病菌对谷子的毒害作用,在谷子抗黑穗病过程中发挥重要作用。     

Double chitin synthetase mutants from the corn smut fungus Ustilago maydis

Using genetic crosses between single chs mutants of Ustilago maydis inoculated into maize ( Zea mays ) seedlings, two classes of double mutants affected in genes coding for chitin synthetases were isolated: chs3 / chs4 , and chs4 / chs5 . Analysis of the mutants showed almost no change in their phenotype compared with wild-type strains. Growth rate, effect of stress conditions, dimorphic transition and mating were not affected. The only salient differences were increased sensitivity to osmotics at acid pH, and decrease in chitin synthetase activity, especially when measured with CO²⁺, and in chitin content. Most significant was a decrease in virulence, although this appeared to be due a factor unrelated to CHS genes. These data can be taken as further evidence that multigenic control of chitin synthetase in fungi operates as a safety mechanism to guarantee fungal viability in changing and hostile environmental conditions.     

Rate of resistance evolution and polymorphism in long‐ and short‐lived hosts

Recent theoretical work has shown that long‐lived hosts are expected to evolve higher equilibrium levels of disease resistance than shorter‐lived hosts, but questions of how longevity affects the rate of resistance evolution and the maintenance of polymorphism remain unanswered. Conventional wisdom suggests that adaptive evolution should occur more slowly in long‐lived organisms than in short‐lived organisms. However, the opposite may be true for the evolution of disease‐resistance traits where exposure to disease, and therefore the strength of selection for resistance increases with longevity. In a single locus model of innate resistance to a frequency‐dependent, sterilizing disease, longer lived hosts evolved resistance more rapidly than short‐lived hosts. Moreover, resistance in long‐lived hosts could only be polymorphic for more costly and more extreme resistance levels than short‐lived hosts. The increased rate of evolution occurred in spite of longer generation times because longer‐lived hosts had both a longer period of exposure to disease as well as higher disease prevalence. Qualitatively similar results were found when the model was extended to mortality‐inducing diseases, or to density‐dependent transmission modes. Our study shows that the evolutionary dynamics of host resistance is determined by more than just levels of resistance and cost, but is highly sensitive to the life‐history traits of the host.     

Intraspecific competition and mating between fungal strains of the anther smut Microbotryum violaceum from the host plants Silene latifolia and S. dioica

Abstract We studied intraspecific competition and assortative mating between strains of the anther smut fungus Microbotryum violaceum from two of its host species, Silene latifolia and S. dioica . Specifically, we investigated whether strains from allopatric host populations have higher competitive ability on their native host species and show positive assortative mating. In general, strains isolated from S. latifolia outcompeted strains isolated from S. dioica on both host species, but in female hosts, heterotypic dikaryons (i.e., dikaryons composed of a haploid strain originating from S. latifolia and a haploid strain originating from S. dioica ) were most successful in competition. Furthermore, the latency period was significantly shorter for heterokaryons that contained at least one strain originating from S. latifolia , compared to heterokaryons that only contained strains originating from S. dioica . The frequencies of conjugations between strains originating from S. latifolia were much higher than conjugation frequencies between strains originating from S. dioica . A significant positive correlation was detected between the relative success of strains in competition and in conjugation, suggesting that success of a strain in competition might be partly determined by its swiftness of mating. In addition, reciprocal differences within heterotypic crosses revealed a significant effect of fungal mating type, with mating type a₁ being the main determinant of mating pace. The observed differences in infection success, conjugation rate, and latency period in favor of strains from S. latifolia relative to strains from S. dioica on both host species are discussed in an evolutionary context of opportunities for the maintenance of differentiation between different formae speciales upon secondary contact.     

稻绿核菌(稻曲病菌)分离方法的比较研究

作者对不同情况下稻曲病菌的分离方法进行了比较研究。结果表明成熟早期稻曲球上的绝大多数新鲜的厚垣孢子具有萌发能力,及时进行分离培养是病原菌成功分离的关键。随保存时间的延长,厚垣孢子萌发能力急剧下降;消毒处理可杀死大部分的厚垣孢子。菌核可长期保存并保持极高的萌发生长能力,是稻曲病菌分离最为理想的材料。稻曲球中部的致密菌丝组织分离难度较大,只能作为稻曲病菌分离的一种补救方法。     

Precise Disease Severity Assessment for False Smut Disease of Rice

False smut is a disease of rice inflorescence. The existing systems of disease severity assessment for rice false smut disease are not very sensitive as the ball quality and also the impact of false smut on filled grain number and grain‐filling were not under consideration. Here, a precise assessment method to evaluate the severity of the disease was developed. The ‘yield representative’ (YR) based on ‘mean floret wt.’ and ‘filled grain %’ was simulated for the precise disease severity assessment of rice false smut disease. The single floret weight envisages major yield components irrespective of the type of panicle. Correlation between YR and major yield attributes was studied, and it was observed that YR had significant correlation with ‘filled grain %’ (0.77–0.95) and ‘single spikelet weight’ (0.88–0.98). Significant negative correlation of YR was observed with the chaff percentage, false smut ball number and ball weight. This YR‐based methodology was utilized to assess the disease severity in nine rice cultivars. The disease severity in those nine cultivars was evaluated by the already existing methodologies also. The disease severity measured by the present technique was compared with the disease severity assessed by the old methodologies. The procedure adapted here for disease severity measurement was found to be more informative and useful. It was observed that in case of mild infection, the false smut was enhancing yield attributes. The high‐yielding rice varieties Savitri and Gayatri were found to be tolerant to false smut and may be used as resistant donors.