Diversity of defence mechanisms in plant–oomycete interactions: a case study of <Emphasis Type="Italic">Lactuca</Emphasis> spp. and <Emphasis Type="Italic">Bremia lactucae</Emphasis>

Plant pathogenic oomycetes, including biotrophic downy mildews and hemibiotrophs/necrotrophs such as Phytophthora and Pythium, cause enormous economic losses on cultivated crops. Lettuce breeders and growers face the threat of Bremia lactucae, the causal agent of lettuce downy mildew. This pathogen damages leaf tissues and lettuce heads and is also frequent on wild Asteraceae plants. The interactions of Lactuca spp. with B. lactucae (abbr. lettuce–Bremia) display extreme variability, due to a long co-evolutionary history. For this reason, during the last 30 years, the lettuce–Bremia pathosystem has been used as a model for many studies at the population, individual, organ, tissue, cellular, physiological and molecular levels, as well as on genetic variability and the genetics of host–parasite interactions. The first part of this review summarizes recent data on host–parasite specificity, host variability, resistance mechanisms and genetics of lettuce–Bremia interactions. The second part focuses on the development infection structures. Phenotypic expression of infection, behaviour of B. lactucae on leaf surfaces, the process of penetration, development of primary infection structures, hyphae and haustoria are discussed in relation to different resistance mechanisms. In the third part, the components of host resistance and the variability of defence responses are analysed. The role of reactive oxygen species (ROS), antioxidant enzymes, nitric oxide (NO), phenolic compounds, reorganization of cytoskeleton, electrolyte leakage, membrane damage, cell wall disruption, hypersensitive reaction and plant energetics are discussed in relation to defence responses. In general, the extreme variability of interactions between lettuce and Bremia, and their phenotypic expression, results from diversity of the genetic background. Different mechanisms of resistance are conditioned by an orchestra of defence responses at the tissue, cell, and molecular levels. The various events responsible for defence involve a complex interaction of the processes and reactions mentioned above. This review also provides an overview on the timing of pathogen development, host pathological anatomy, cytology and physiology of lettuce–Bremia associations. The significance of these factors on the expression of different resistance mechanisms (non-host and host resistance, race-specific and race non-specific resistance, field resistance) is discussed.     

Molecular approaches for characterization and use of natural disease resistance in wheat

Wheat production is threatened by a constantly changing population of pathogen species and races. Given the rapid ability of many pathogens to overcome genetic resistance, the identification and practical implementation of new sources of resistance is essential. Landraces and wild relatives of wheat have played an important role as genetic resources for the improvement of disease resistance. The use of molecular approaches, particularly molecular markers, has allowed better characterization of the genetic diversity in wheat germplasm. In addition, the molecular cloning of major resistance (R) genes has recently been achieved in the large, polyploid wheat genome. For the first time this allows the study and analysis of the genetic variability of wheat R loci at the molecular level and therefore, to screen for allelic variation at such loci in the gene pool. Thus, strategies such as allele mining and ecotilling are now possible for characterization of wheat disease resistance. Here, we discuss the approaches, resources and potential tools to characterize and utilize the naturally occurring resistance diversity in wheat. We also report a first step in allele mining, where we characterize the occurrence of known resistance alleles at the wheat Pm3 powdery mildew resistance locus in a set of 1,320 landraces assembled on the basis of eco-geographical criteria. From known Pm3 R alleles, only Pm3b was frequently identified (3% of the tested accessions). In the same set of landraces, we found a high frequency of a Pm3 haplotype carrying a susceptible allele of Pm3. This analysis allowed the identification of a set of resistant lines where new potentially functional alleles would be present. Newly identified resistance alleles will enrich the genetic basis of resistance in breeding programmes and contribute to wheat improvement.     

陇南山区小麦白粉病流行程度预测模型

调查分析1990~2005年陇南山区小麦白粉病发生、流行资料,发现:陇南白龙江流域为小麦白粉病常发重发生区,徽成盆地为小麦白粉病易发区,西汉水流域为小麦白粉病轻发区;小麦感病品种面积、上年秋苗平均病叶率和病田率、当年早春平均病田率、上年7、10月和当年5月平均气温、当年4月和上年7、8、11月降水量与全市春季小麦白粉病流行程度相关十分显著,上年9月到次年3月平均气温和4~8月降水量与小麦白粉病流行程度呈正相关,4~8月平均气温和9月到次年3月降水量与小麦白粉病流行程度呈反相关。由此建立的预报模型,历史拟合率可达93.75%,2006年业务应用预报准确率100%。     

我国小麦地方品种蚂蚱麦、小白冬麦、游白兰、红卷芒抗白粉病性遗传分析

我国地方品种是小麦白粉病抗性的重要来源之一,为了对地方品种抗源的利用奠定基础,采用常规杂交方法,以感病品种Chancellor分别与我国小麦抗病地方品种蚂蚱麦、小白冬麦、游白兰、红卷芒进行正交和反交,获得F₁、F₂代。根据白粉菌菌株的毒谱选用E09菌株对Chancellor与小白冬麦、游白兰、红卷芒的杂交后代进行苗期抗性鉴定和统计分析,选用E30菌株对Chancellor与蚂蚱麦的杂交后代进行苗期抗性鉴定和统计分析。结果表明4个品种在正、反交情况下均表现出由一对隐性基因控制的抗性,说明这4个地方品种属于核遗传,其抗性是由一对隐性基因控制的。     

白粉病菌重寄生物——粉霉芽枝孢

寄生于枫杨白粉病菌上的重寄生物,经过调查研究,确定为芽枝孢(Cladosporium)的一个种。经与近似的重寄生芽枝孢比较,存在形态上和培养特性方面的区别,因此,确定应另立新种,称为粉霉芽枝孢(C.erysiphicola sp.nov.)。该菌不但能寄生于枫杨白粉病菌上,还能侵染枸杞白粉病菌及小麦白粉病菌等。对上述几种白粉病菌分生孢子的侵染,出现穿入孢子、缠绕菌丝、腐蚀孢子及使孢子萎缩等现象,有希望作为一种生物防治剂。该菌在培养基PSA及PDA上生长繁殖良好,其分生孢子除在不同营养液中萌发外,在蒸馏水中也能萌发。萌发的温度在27℃左右。     

小麦抗白粉病基因Pm21 的抑制基因

 小麦-簇毛麦6VS. 6AL 易位染色体含有抗白粉病基因Pm21,在我国的小麦育种中被广泛应用。近年来,一些含有Pm21 基因的小麦品种(系)开始感染白粉病。为探索含Pm21 的品种(系)感染白粉病的原因,本研究在6VS. 6AL 易位系与小麦品系(种)R14 和川农12 的杂交后代中利用分子标记CINAU17-1086 和CINAU18-723 辅助选择的遗传背景相对简单的F7 和F8 近等基因系为材料,研究了小麦抗白粉病基因Pm21 的抗病性表达。结果发现,在3 个含有6VS. 6AL 易位染色体的感病F6 植株繁殖的F7 近等基因系中发生了白粉病抗性的分离,分离比率符合13 感病︰ 3 抗病的理论值。在随机选取的F7 感病小麦单株所繁殖的F8 近等基因系中,有7 / 13 的株系一致地重感白粉病,有6 / 13 的株系发生了抗白粉病的分离,其中2 / 13 的株系分离比符合3 感病︰ 1 抗病、4 / 13 的株系分离比符合13 感病︰ 3 抗病的分离模式。这一结果指出,小麦株系中的抗白粉病基因Pm21 的抗性表达受小麦基因组中的一对显性抑制基因所控制,该基因来源于小麦品种(系)川农12或R14,建议命名为SuPm21。本研究指出,在把外源基因引入小麦的研究中,有利的外源基因与不含抑制基因的受体遗传资源同等重要。     

A data-driven model simulating primary infection probabilities of cucumber downy mildew for use in early warning systems in solar greenhouses

Treatment during the primary infection phase is essential for controlling cucumber downy mildew in solar greenhouses. An early warning model applicable to this phase would represent a foundation for early warning systems for managing the disease and reducing pesticide usage. Based on the input parameters that were both readily available and appropriately limited in number, EWMPICDW (early warning model for primary infection of cucumber downy mildew in solar greenhouses) was developed based on monitoring data, early warning theory and plant disease epidemiology. The elaboration of this model included clarification of the meaning of warning, monitoring the warning indicators, forecasting the warning situation, tracing the warning sources and controlling the warning situation. The definition of warning included disease occurrence (yes or no) and probability. Because the leaf wetness duration (LWD) played an important role in disease warning systems for crops in solar greenhouses and was difficult to monitor, the leaf wetness sensor and RH threshold model were investigated and combined to form a practical estimation solution for LWD. Within the warning situation forecasting model system, the infection condition and incubation early warning submodels received the most attention. The infection condition early warning submodel was developed by using a threshold method based on the combination of LWD and mean temperature in LWD. The temperature was chosen as the warning indicator for incubation, and the incubation early warning submodel was defined using nonlinear regression methods. The warning sources traceability algorithm was developed in relation to expert knowledge and in terms of a mode of disaster mitigation that involved cutting the disaster chain from the headstream. The method for controlling the warning situation was based on good agricultural practices (GAP). The early warning model was implemented as a system and was evaluated using data for 4 years at two sites in Beijing, China. The warnings can be provided more than 2 d before symptoms appear. Using EWMPICDW, a positive early warning is associated with a change in the chance of disease occurrence from 0.68 to 0.96. Accordingly, the probability of disease occurrence calculated for the early warning model was 96%. These results demonstrate that the data-driven model will support the development of early warning systems for primary infection by cucumber downy mildew in solar greenhouses.     

黄瓜白粉病抗性基因的QTL定位

 【目的】对黄瓜高抗白粉病材料K8进行研究,明确其抗性遗传规律,并完成抗性基因的QTL定位分析,为探索抗病机理和分子标记辅助选择（MAS）育种提供理论依据。【方法】利用黄瓜白粉病致病菌Podosphaera xanthii (syn. Sphaerotheca fuliginea）对K8×K18（感白粉病）杂交后代F2:3家系人工接种鉴定,进行抗白粉病遗传分析。以完成抗病性鉴定的F2和F2:3家系组成的抗感分离群体为研究对象,应用BSA法和2360对黄瓜SSR引物进行SSR分析,采用JoinMap 4.0作图软件和MapInspect软件构建连锁群并完成连锁群与染色体的对应。利用MapQTL4.0软件对白粉病抗性基因进行QTL定位分析。【结果】试材K8所含有的黄瓜白粉病抗性基因符合数量性状遗传的特点。本研究共检测到4个白粉病抗性基因的QTL位点pm5.1、pm5.2、pm5.3和pm6.1,其中,pm5.1、pm5.2、pm5.3在两年中被重复检出,pm5.2位点的贡献率最大,在其所在区域预测到了4个NBS类抗病基因。pm6.1位于黄瓜Chr.6上,是个微效的QTL位点。【结论】位于Chr.5上的pm5.2是黄瓜白粉病抗性基因的主效QTL位点,该抗性基因可能属于NBS类抗病基因。本研究结果为抗性基因主效QTL的精细定位和克隆及MAS抗病育种奠定了良好基础。     

新疆甜瓜(Cucumis melo L.)白粉病抗性育种研究

【目的】选育具有白粉病抗性的新疆甜瓜育种材料。【方法】以1个肉质松脆、高感白粉病的新疆甜瓜品种与高抗白粉病的美国Cantaloupe类型甜瓜品种为原始亲本进行杂交,采用植株田间自然抗性筛选结合果实品质鉴定的方法,经回交和自交,转育肉质松脆、高抗白粉病的新疆甜瓜育种材料。【结果】选育出个3高抗白粉病新疆甜瓜类型纯系材料。【结论】利用引进抗性资源进行新疆甜瓜白粉病抗性转育是必要且可行的途径。     

保鲜剂MY系列在小麦白粉病菌种保存中的应用

主要进行了离体条件下用保鲜剂MY系列保存小麦白粉病菌的应用研究。结果表明,在设定温度为4℃冰箱中以保鲜剂MY-02浓度为60μg·mL-1保湿保存的方法最佳。在第40天其叶片绿色仍可达到近67.0%,孢子萌发率可达26.7%。