Effects of sowing date and vernalisation on the growth of winter barley and its resistance to powdery mildew (Erysiphe graminis f.sp. hordei)

Detailed studies on the production of individual leaves, and the development of powdery mildew on them, were made in field plots of winter barley sown on different dates. The greater severity of the disease on early-sown than on later-sown seedlings during the autumn and winter can probably be explained mainly by changes in the abundance of inoculum and the suitability of the weather for infection. Results from glasshouse experiments suggest that the differences may be reinforced by direct effects of vernalisation on the susceptibility of seedlings to the disease. Contrary effects of sowing date on mildew severity during summer are probably due to the progressively greater resistance to mildew of the later-formed than of seedling leaves, and the earlier appearance of corresponding leaves on early-sown than on later-sown plants. Early sowing can also increase the total number of leaves produced per stem. Therefore, because resistance of the leaves increases progressively, the maximum degree of resistance expressed by the later-formed (e.g. flag) leaves will often be greater on early-sown than on later-sown plants.     

禾谷多粘菌游动孢子超微结构观察

本文描述了寄生在大麦根部的禾谷多粘菌Polymyxa graminis Led.的次生游动孢子的超微结构,包括核、内质网、高尔基体、线粒体、脂质粒、排泄泡、小囊、具膜小囊、核糖体以及鞭毛基体(Kinetosome)和鞭毛杆等细胞器。游动孢子中未见微体。同时也在电镜下观察了游动孢子接触和穿透根细胞时所形成的管腔(Rohr)和棘杆(Stachel)以及游动孢子穿透细胞壁的详细过程。     

受白粉菌诱导大麦抗感等基因系蛋白质变化的双向电泳分析

分别对接种与否的大麦抗—感白粉病等基因系—叶期幼苗取材进行蛋白质双向电泳分析。结果表明,病原的侵入使抗—感两系在30Kd以下的低分子量区域的蛋白质发生了明显变化。接种48小时之后,抗病系在pH5.5、6.0、6.8及8.8附近出现了对照中所没有的蛋白质,而在pH6.0和8.8附近的蛋白质则较对照有减小的趋势;感病系在pH6.0附近蛋白质明显增多,在pH8.8处不仅在量上有大幅度提高,而且种类也有增加。结果还表明,抗—感系间在未接种的情况下双向电泳图谱也有差异,接种之后由于感病系在pH8.8处蛋白质的特异性合成,使抗—感两系间的差异缩小。     

Comparison of natural and artificial epidemics of take-all in sequences of winter wheat crops

Winter wheat was grown for six successive years (Expt 1) and for three successive years (Expt 2) in field experiments on different soil types. Artificial inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici cultured on autoclaved oat grains) was incorporated in the soil of some of the plots just before, or at, sowing of the first winter wheat crop. Expt 1 tested the incorporation of similar amounts of inoculum (212 kg ha^-1) at different depths. Expt 2 tested different amounts of inoculum at the same, shallow depth. Early sowing (September), late sowing (October) and spring inoculation were additional treatments, applied to the first crop only, in Expt 2. Seasonal factors apart, the disease outcome in the first year after inoculation depended on amounts and placement of applied inoculum, as well as date of sowing. Deeper inoculum resulted in less disease (Expt 1). Severe take-all was produced in Expt 2 by incorporating inoculum shallowly in sufficient quantities (400 kg ha^-1 or more). Less inoculum (200 kg ha^-1) generated less disease, especially in earlier-sown plots. Differences in disease amongst inoculum treatments were greatest in the first year and diminished subsequently, particularly where sowing had been early in the first year. In Expt 1, where first crops exposed to artificial inoculum developed moderate-to-severe disease, disease in subsequent second and/or third crops was less. In the fourth crop a second peak of disease occurred, coinciding with a first peak in sequences without added inoculum. Take-all decline (TAD) appeared to be expressed in all sequences thereafter. In Expt 2 in sequences without added inoculum, TAD occurred after a peak of disease in the second crop. Where 400 kg ha^-1 or more of inoculum were added, disease was severe in the first year and decreased progressively in successive years. Disease was less patchy in plots that received artificial inoculum. However, it remains uncertain mat severe disease caused by artificial inoculation achieved an early onset of true TAD. The infectivity of the top 12 cm of soil in the first 3 yr of Expt 1, determined by bioassay, depended on the depth of added inoculum and amount of disease in subsequent crops. However, at the time of the naturally occurring peak of disease severity (in either inoculated or non-inoculated plots) it did not predict either disease or TAD. Differences and similarities amongst epidemics developing naturally and those developing from different amounts and placement of applied inoculum have been revealed. The epidemiological implications of adding inoculum and the potential value of artificially-created epidemics of take-all in field trials are discussed.