Histological studies of the expression of the Lr9, Lr20 and Lr28 alleles for resistance to leaf rust in wheat

The development of the leaf rust fungus ( Puccinia recondita f.sp. tritici ) in a susceptible cultivar and three other cultivars possessing the Lr9, Lr20 and Lr28 alleles for resistance was studied by light and fluorescence microscopy. Formation of the substomatal vesicle, intercellular hypha and the first haustorial mother cell was unaffected by resistance. Lr9 and Lr28 expression was rapid, first seen as early initiation of hyphal branching at 16 h after inoculation, then reduced haustorial diameters at 19 h. Limited host cell necrosis was seen immediately afterwards. Elongation of intercellular hyphae was reduced between 20 and 24 h, and virtually ceased by about 30 h. Numbers of infection sites with a second haustorial mother cell were briefly higher at 24 h. Reduced hyphal branching and haustorial mother cell numbers were seen at 20–24 h and 36 h respectively. Lr20 expression was not seen until 36 h when reduced hyphal branching was observed, accompanied by extensive host cell necrosis. Reduced haustorial mother cell numbers were detected at 48 h. Findings suggested a secondary role for host cell necrosis in the expression of the Lr9 and Lr28 alleles. Host necrosis may play a determinant role in Lr20- based expression.     

Comparative microscopic and molecular analysis of Thatcher near‐isogenic lines with wheat leaf rust resistance genes Lr2a,Lr3, LrB or Lr9 upon challenge with different Puccinia triticina races

Thatcher near‐isogenic lines (NILs) of wheat carrying resistance gene Lr2a, Lr3, LrB or Lr9 were inoculated with Puccinia triticina races of virulence phenotype BBBD, MBDS, SBDG and FBDJ. Puccinia triticina infection structures were analysed under the fluorescence microscope over a course of 14 days after inoculation (dai). The relative proportion of P. triticina and wheat genomic DNA in infected leaves was estimated with a semiquantitative multiplex PCR analysis using P. triticina‐ and wheat‐specific primers. The occurrence of a hypersensitive response (HR), cellular lignification and callose deposition in inoculated plants was investigated microscopically. In interactions producing highly resistant infection type (IT) ‘0;’, a maximum of two haustorial mother cells per infection site were produced, and there was no increase in the proportion of P.  triticina genomic DNA in infected leaves, indicating the absence of P. triticina growth. In comparison, sizes of P. triticina colonies increased gradually in interactions producing moderately resistant IT ‘1’ and ‘2’, with the highest proportion of P. triticina genomic DNA found in leaves sampled at 14 dai. In interactions producing susceptible IT ‘3–4’, the highest proportion of P. triticina genomic DNA was found in leaves sampled at 10 dai (45·5–51·5%). HR and cellular lignification were induced in interactions producing IT ‘0;’ and ‘1’ at 1 dai but they were not observed in interactions producing IT ‘2’ until 2 dai. No HR or cellular lignification were induced in interactions producing susceptible IT ‘3–4’. Furthermore, a strong deposition of callose was induced in Lr9 + BBBD and Lr9 + FBDJ (IT ‘0;’), whereas this defence response was not induced in resistant or susceptible interactions involving Lr2a, Lr3 or LrB, indicating that Lr9 mediated resistance was different from that conditioned by Lr2a, Lr3 or LrB.     

四川省17个主栽小麦品种中Lr26和Lr19检测

正小麦叶锈病是一种重要的小麦病害,培育和种植抗病品种是最为经济有效的防治方法。我国在小麦抗病育种工作中引入了1BL/1RS易位系,已知小麦抗病基因Lr26、Pm8、Yr9和Sr31均位于1BL/1RS易位系上~([1])。然而目前Lr26已丧失抗性~([2]),所以育种过程中需要谨慎考虑Lr26的使用。Lr19来源于长穗偃麦草~([3]),在我国目前为有效的     

Genetic Variation and Virulence on Lr26 in Puccinia triticina

ABSTRACT The genetic relationships between isolates of Puccinia triticina virulent on wheat with the Lr26 resistance gene were studied. The diversity within and between isolates of P. triticina from Israel, Europe, and the United States was determined by virulence on near-isogenic Thatcher lines and by random amplified polymorphic DNA. According to the molecular markers, isolates that were virulent on Lr26 had diversity levels similar to those of Lr26 nonpathogenic isolates. Distances between subpopulations of isolates virulent and avirulent on Lr26 varied and were unrelated to the Lr26 virulence phenotype. Cluster analysis suggested four groups, three of which were closely associated with the geographical origin of the isolates-Israel, the United States, and Europe. All four groups included both Lr26 virulent and avirulent pathotypes. The results showed that Lr26 virulent rust pathotypes are as genetically dissimilar as the rest of the population. The cluster analysis showed that the rust population in Israel includes at least two different subpopulations, both of which contain Lr26 virulent and Lr26 avirulent isolates.     

Genetic relationship between the adult plant resistance gene Lr12 and the complementary gene Lr31 for seedling resistance to leaf rust in common wheat

A resistant phenotype similar to that conferred in wheat by the complementary genes Lr27  +  Lr31 was produced in the progeny of intercrosses of cultivars carrying Lr27 and a line possessing Lr12 . This confirms that Lr12 is either completely linked with Lr31 or is the same gene. On the basis of these findings and that Lr31 is located on chromosome 4BS, it is concluded that Lr12 must also be located on 4BS. Adult-plant genetic tests confirm that the Australian wheat cultivar Timgalen carries Lr12 , and stocks with Lr12 alone were established from this cultivar.     

116个小麦品种（系）抗叶锈基因Lr9-Lr26、Lr19-Lr20的复合PCR检测

[目的]建立简单、快速、有效的小麦抗叶锈基因复合PCR体系,从而提高分子标记辅助选择效率。[方法]以28个‘Thatcher’为背景的近等基因系和16个已知基因载体品系作为试材,测试了小麦抗叶锈病基因Lr9、Lr26、Lr19和Lr20的STS标记特异性,通过优化PCR反应体系和循环条件,构建了抗叶锈基因Lr9-Lr26和Lr19-Lr20的复合PCR检测体系。对116个小麦品种(系)所含有的抗叶锈病基因进行了分子检测。[结果]供试品种均不含有Lr9和Lr20,47个品种含有Lr26(基因频率为40.5%),‘中梁22’含有Lr19。经反复验证,Lr9-Lr26和Lr19-Lr20复合PCR技术检测结果可靠,且与上述单个分子标记检测结果一致。[结论]建立的Lr9-Lr26和Lr19-Lr20的复合PCR检测体系可以准确、稳定、高效地检测小麦抗叶锈基因Lr9、Lr26、Lr19和Lr20。     

小麦抗叶锈基因Lr 38的AFLP标记

 小麦叶锈病是小麦的重要病害之一,几乎在所有小麦种植区都有发生,严重时可造成5%~15%甚至更大的产量损失^[1]。小麦抗叶锈基因Lr38发现位于中间偃麦草(Agropyron intermedium)第7组的一条染色体上,并被标定在6 DL上^[2],是抗性很强的抗叶锈病基因,国内外至今尚未发现对Lr38有毒性的菌株,是一个应用潜力很大的抗病基因。     

Lr46: a gene conferring slow-rusting resistance to leaf rust in wheat

ABSTRACT Wheat (Triticum aestivum) cultivar Pavon 76 carries slow-rusting resistance to leaf rust that has remained effective in Mexico since its release in 1976. 'Pavon 76' was crossed with two leaf rust-susceptible wheat cultivars, Jupateco 73S and Avocet S, and between 118 and 148 individual F(2) plant-derived F(3) and F(5) lines were evaluated for adult-plant leaf rust resistance at two field sites in Mexico during different seasons. Evaluation of F(1) plants and parents indicated that the slow-rusting resistance was partially dominant. Segregation in the F(3) and F(5) indicated that the resistance was based on two genes with additive effects. Monosomic analysis was carried out to determine the chromosomal locations of the resistance genes. For this purpose, two or three backcross-derived cytogenetic populations were developed by crossing 'Pavon 76' with a monosomic series of adult-plant leaf rust-susceptible cultivar Lal-bahadur. Evaluation of such BC(2)F(3) and BC(3)F(3) lines from 16 confirmed 'Lalbahadur' monosomics indicated that one slow-rusting gene was located in chromosome 1B of 'Pavon 76'. This gene, designated as Lr46, is the second named gene involved in slow-rusting resistance to leaf rust in wheat.     

偃麦草属E染色体组特异SCAR标记对Lr19的特异性和稳定性研究

 小麦抗叶锈基因Lr19来源于长穗偃麦草,表现优良的抗叶锈性,国内外发现对Lr19有毒性的小麦叶锈菌菌株的报道较少。本研究以TcLr19和Thatcher亲本以及TcLr19×Thatcher F₂代单株构建的分离群体为材料,建立了与Lr19共分离的稳定的SCAR分子标记,命名为Y₁₉SCAR₉₈₂。对49个小麦抗叶锈近等基因系材料的稳定性检测结果表明,其重复性好且为Lr19特异的分子标记。对120个小麦品种检测的结果表明,该标记可有效应用于小麦抗叶锈分子辅助选择育种。     

High and low pre-inoculation temperatures decrease the effectiveness of the Lr 20 and Sr 15 rust resistance genes in wheat

Spring wheat seedlings containing Lr 20 and Sr 15 resistance alleles were raised at 30° C, prior to inoculation with leaf rust ( Puccinia recondita race 76–2,3) and stem rust ( Puccinia graminis f.sp, tritici race 343–1,2,3,5,6) pathogens, respectively. Infected plants were then grown at one of seven temperatures in the range 18–30 C and infection types were scored at 10 days post-inoculation. These results were compared with those obtained for plants raised at a pre-inoculation temperature of 18° C. In both 18° C and 30° C pre-grown plants, a progressive increase in infection type was observed on resistant lines as post-inoculation temperature increased. However, resistant lines raised at 30°C had significantly higher infection types than plants raised at 18° C at all post-inoculation temperatures for which some degree of resistance was still evident in the plants raised at 18°C, The maximum temperature for expression of resistance was significantly higher for Lr 20 than for Sr 15. irrespective of pre-inoculation temperature. A lowering of the resistance expression was also evident in Sr 15 -bearing lines raised at a very low pre-inoculation temperature (4°C). The effects of low pre-inoculation temperature on resistance were assessed in both winter and spring wheat lines. These results are discussed in the light of current ideas concerning the host membrane location of pathogen recognition events.     

Suppression subtractive hybridization and microarray analysis reveal differentially expressed genes in the <Emphasis Type="Italic">Lr39/41</Emphasis>-mediated wheat resistance to <Emphasis Type="Italic">Puccinia triticina</Emphasis>

Wheat leaf rust caused by Puccinia triticina (Pt) is one of the most severe fungal diseases threatening the global wheat production. The use of leaf rust resistance (Lr) genes in wheat breeding programs is the major solution to solve this issue. Wheat isogenic line carrying the Lr39/41 gene has shown a moderate to high resistance to most of the Pt pathotypes detected in China. In the present study, a typical hypersensitive response (HR) was observed using microscopy in leaves of the Lr39/41 isogenic line inoculated with the avirulent Pt pathotype THTT from 48 h-post inoculation. Two Lr39/41 resistance-associated suppression subtractive hybridization (SSH) libraries with a total of 6000 clones were established. Microarray hybridizations were performed on all obtained SSH clones using RNAs extracted from leaves of the Pt-inoculated and non-inoculated Lr39/41 isogenic lines, and leaves of the Pt-inoculated and non-inoculated Thatcher susceptible lines. Differentially expressed clones were analyzed by significance analysis of microarrays (SAM), followed by further sequencing. A total of 36 Lr39/41-resistance-related differentially expressed genes (DEGs) were identified, many of which had been previously reported to be involved in the plant defense response. The expression levels of eight selected DEGs during different stages of the Lr39/41-mediated resistance were further quantified by a qRT-PCR assay. Several pathogenesis-related (PR) and HR-related genes seem to be crucial for the Lr39/41-mediated resistance. In general, a brief profile of DEGs associated with the Lr39/41-mediated wheat resistance to Pt was drafted.     

Using leaf tip necrosis as a phenotypic marker to predict the presence of durable rust resistance gene pair <Emphasis Type="Italic">Lr34</Emphasis>/<Emphasis Type="Italic">Yr18</Emphasis> in wheat

Fifty wheat varieties along with Jupateco-73 and Morocco were studied for the expression of leaf tip necrosis (LTN), a trait linked with the durable rust resistance gene pair Lr34/Yr18. LTN was frequent (i.e., ≥6) in nine replications of a field experiment over 3 years in 17 genotypes, and the varieties were considered positive for LTN. In molecular analyses of these varieties, having relative severity values up to 78 for yellow rust and 45 for leaf rust, the 150-bp Lr34/Yr18-linked allele was consistently amplified. Expression of LTN in six of nine replications is an appropriate threshold for predicting the presence of Lr34/Yr18 gene pair, and genotypes can be selected using this trait.     

Localization of metabolic sites of action of herbicides

Time- and concentration-course studies were conducted to determine the effect of thirteen herbicides on photosynthesis, respiration, RNA synthesis, protein synthesis, and lipid synthesis using isolated single leaf cells. Each herbicide was from a different chemical class. Appropriate ¹⁴C-substrates and product purification procedures were used for each process prior to liquid scintillation counting. The most sensitive metabolic site of inhibition was photosynthesis for atrazine, bromacil, dichlobenil, monuron, and paraquat; RNA synthesis for dalapon and dinoseb; protein synthesis for chlorpropham; and lipid synthesis for CDAA, chloramben, 2,4-D, EPTC, and trifluralin. However, with several herbicides, one or more process was almost as sensitive as the one mentioned above. All herbicides inhibited more than one process, and the most sensitive site of inhibition may not be the same process that was inhibited the greatest at the maximum concentration and maximum exposure time used. Therefore, a concept of metabolic sites of action, rather than a primary site of action, appears to be more meaningful for herbicides.     

百合地下害虫主要种类调查及生物（源）农药筛选

调查了甘肃省临洮县为害百合的地下害虫种类, 并以主要发生为害种类为供试对象, 采用拌土法测定了几种生物（源）农药对主要害虫的室内毒力和致死中时。调查发现小云斑鳃金龟Polyphylla gracilicornis、棕色鳃金龟Holotrichia titanis为主要发生及为害种类, 不同时间发生种类存在差异, 9月份以小云斑鳃金龟幼虫发生为害为主, 发生量占地下害虫总数的66.16%, 平均种群密度为10.48头/m2, 10月份, 则以棕色鳃金龟幼虫发生为主, 发生量占地下害虫总数的96.86%, 平均种群密度为7.79头/m2, 主要取食百合根系和鳞茎, 造成根系数量减少, 鳞茎出现不规则褐色缺口或凹陷斑。药剂筛选结果表明, 1.8%阿维菌素乳油、200亿孢子/g球孢白僵菌粉剂对两种蛴螬均具有较高的杀虫活性和速效性, 药后7 d时, 校正死亡率在82.22%以上, 对小云斑鳃金龟幼虫和棕色鳃金龟幼虫的LC50分别为0.161、0.060 mg/g和5.558×107、0.362×107孢子/g, LT50分别为2.237 d（2.2 mg/g）、1.393 d（2.2 mg/g）和6.645 d（40.0×107孢子/g）、4.940 d（2.0×107孢子/g）, 这两种生物（源）农药对两种蛴螬的LC50和LT50值均略大于两种化学农药25%二嗪磷乳油、40%辛硫磷乳油处理的, 且对小云斑鳃金龟幼虫的杀虫活性均低于对棕色鳃金龟幼虫的杀虫活性, 致死中时则长于对棕色鳃金龟幼虫的致死中时。     

Effects of timing and method of application of Penicillium oxalicum on efficacy and duration of control of Fusarium wilt of tomato

The effects of timing and method of application of Penicillium oxalicum on the control of fusarium wilt of tomato were investigated. Application of P. oxalicum to tomato seedlings in seedbeds reduced disease caused by Fusarium oxysporum f.sp. lycopersici in a growth chamber by 45–49% and in glasshouse experiments by 22–69%. Disease suppression was maintained for 60–100 days after inoculation with the pathogen in the glasshouse. No disease reduction was observed in tomato plants where P. oxalicum was applied to seeds. Treatment with P. oxalicum did not affect the population of F. oxysporum f.sp. lycopersici in the rhizosphere.     

福寿螺配偶个体大小选择性初步观察

通过野外观察与实验研究,掌握了福寿螺的婚配体制及其配偶选择性规律。福寿螺与多数低等动物一样,其婚配属于乱交制,无固定配偶;雌螺对与其交配的雄螺个体大小没有选择性,而雄螺对雌螺的个体大小有选择性,倾向于与较大个的雌螺交配。     

Systems of designation of pathotypes of plant pathogens12

A variety of systems of designation has evolved to name pathotypes of plant pathogens. The systems were evaluated to determine those best suited for particular purposes. Virulence and avirulence/virulence formulae of pathotypes have advantage over the use of consecutive numbers or letters given in chronological order of pathotype discovery. As soon as pathotype information exceeds a certain level of complexity, mathematical codes are most advantageous, in particular two codes, octal notation and coded triplets. A more universal adoption of the most appropriate codes is recommended to ease communication and comparisons of results.     

Investigation of the Mode of Action of Nematode Neuropeptides

The neuropeptide AF2 has a complex set of actions on the dorsal muscle strip of Ascaris suum, including a potentiation of the acetylcholine-stimulated muscle contraction. Caffeine at 100 μm and 5 mm inhibited this potentiation, as did 100 μm theophylline in two out of six studies. The cyclic-AMP-potentiating compounds IBMX, dibutyryl cAMP and forskolin had no effect on the AF2-induced potentiation of the acetylcholine-stimulated muscle contraction. These preliminary data suggest that the potentiating action of AF2 is not mediated by a cAMP pathway.