Classification of Plants Resistant to Heterodera avenae1

Differentiation of barley plants resistant to Heterodera avenae is simple when they are completely without cysts and the number of cysts is high on a susceptible control cultivar. Problems with classification are discussed.     

The Effect of Environment on Survival and Hatching of Heterodera avenae1

Eggs within cysts of Heterodera avenae are able to survive long periods of desiccation and can be held for several years at 5oC when stored at low relative humidity. While this provides an excellent means of storing the nematode for use in laboratory experiments, field experiments show that desiccated eggs are readily dispersed by wind. Tolerance to desiccation is similar in free and encysted eggs, which hatch at the same rate. When eggs are desiccated, water is withdrawn from the larva within the egg shell. If cysts are exposed to conditions favouring eclosion, subsequent desiccation reduces egg viability and larval emergence. The importance of defining pre-test conditions in survival studies is emphasized, and differences in the physiological state of eggs may explain different observations in Australian and European studies.     

The Status of Heterodera avenae on Cereals in New Zealand1

The cereal cyst nematode (Heterodera avenae) was discovered in New Zealand in 1975 on wheat and oats. It was not at that time causing appreciable economic losses in yield, presumably because usual management practice incorporated a good crop rotation with lucerne. However, now that the growing of cereals has become more profitable, farmers are tending to grow consecutive cereal crops and more damage from H. avenae is being experienced. On one farm, up to 9 % of an oat crop was lost due to this nematode. The biotype has not yet been determined.     

Heredity of Heterodera avenae Resistance Originating from two Barley Cultivars and one Spring Wheat Cultivar1

Two spring barley cultivars Bajo Aragon-1-1 and Martin 403-2 from the cyst nematode test assortment were each crossed with a susceptible, a pathotype-11 -resistant, and a pathotype-11 and 12-resistant cultivar, as well as with each other. A spring wheat cultivar, AUS 10894, from the cyst nematode test assortment was crossed with a susceptible and a resistant cultivar. From these crosses F! and F₂ single plants were tested against pathotype 12 and/or pathotype 11 of Heterodera avenae in Denmark. Some plants of the spring barley cultivar Bajo Aragon-1-1 have two resistance genes, which probably are both dominant, but it is not out of the question that one might be recessive. Each gene is inherited independently of the other or with low linkage frequency. Neither gene is the same as or allelic to the resistance gene in the cultivar Ortolan, but one gene is allelic to or the same as the 191 gene in the cultivar Siri. The spring barley cv. Martin 403-2 has one dominant resistance gene which is not allelic to or the same as the resistance gene in Ortolan but is the same as or allelic to the 191 gene in the cultivar Siri. It is possible that there is one more gene, which might be recessive against pathotype 11. The spring wheat cv. AUS 10894 has one dominant resistance gene which might be the same as or allelic to the Loros gene.     

Development of two species-specific primer sets to detect the cereal cyst nematodes Heterodera avenae and Heterodera filipjevi

Twelve Heterodera species are of major economic significance in wheat and barley. Of these, H. avenae, H. filipjevi and H. latipons are among the most important ones, and sometimes coexist. The identification of Heterodera species using morphological characteristics is time consuming, requires specialized skill and can be imprecise, especially when they occur mixed in field populations. Molecular techniques can provide a more accurate way for nematode identification. This study reports the results of experiments targeting the mitochondrial cytochrome oxidase subunit 1 (COI) gene to develop species-specific primers that could be used for the identification of H. avenae and H. filipjevi. The COI gene of 9 Heterodera spp. and Punctodera punctata was partially sequenced and the resultant sequences were aligned to find unique sites suitable for the design of primers. The alignment showed variability between H. avenae, H. filipjevi and other Heterodera species. Two sets of species-specific primers were identified for the identification of both species and the conditions for their use in PCR were optimised. The specificity of the designed primers was checked by comparison with one population of P. punctata and populations of 14 other Heterodera species, nine populations of H. avenae and 10 populations of H. filipjevi originating from different countries. To test the sensitivity, the PCR was run with DNA extracted from five second-stage juveniles (J2) of H. avenae or five J2 of H. filipjevi mixed with DNA extracted from varying numbers of J2 of H. latipons. It was possible to detect as few as five J2 of H. avenae or H. filipjevi among 100 J2 of H. latipons. The two primers sets allow the detection of H. avenae and H. filipjevi where they occur in mixed populations with other Heterodera spp.     

Cultural Practices and their Effects on Heterodera avenae and Grain Yields of Wheat in Victoria, Australia1

The effects of various cultural practices on cereal cyst nematode (Heterodera avenae) populations, and the subsequent yield of wheat, have been studied over many seasons in Victoria, Australia. Crop rotations which include periods of fallow, or of non-host crop reduce population levels and improve yields. The inclusion of a legume has the additional advantage of improving soil nitrogen levels. Early sown crops (April/May) are less severely damaged, and produce better yields, than late sown crops (June/July). The resowing of damaged wheat crops with either wheat or barley is not effective in improving yields, although cyst numbers are lower on resown crops. Nitrogenous fertilisers are not generally applied to cereals, and although small increases in yield are sometimes obtained, they are rarely economic. Sulphate of ammonia applications increase cyst numbers, especially when applied at seeding, but urea has only a marginal effect on cyst numbers.     

Suggestions for Determination and Terminology of Pathotypes and Genes for Resistance in Cyst-forming Nematodes, especially Heterodera avenae1

A short review of differentiation into pathotypes is given. Use of the word ≪ pathotype ≫ is recommended when a very clear difference is established between virulence of nematode populations. Our present knowledge makes it possible to differentiate between 10 pathotypes of Heterodera avenae. It is suggested that the pathotypes are given numbers, and corresponding terms should be used for genes for resistance in plants, e.g. a gene Hal on the barley chromosome gives resistance to nematode pathotypes 11,21,31,41 etc. Some proposals for improvement of pathotype identification are given.     

Chemical Control of Heterodera rostochiensis Woll.1)

In Dutch field experiments with Heterodera rostochiensis Woll. systemic nematicides at low and high nematode densities resulted in unfavourable cost/ benefit relations, as compared to other control procedures; on average, a 50 % reduction of the maximum multiplication of the nematode was observed. In England, better results were obtained at high nematode densities when higher dosages of nematicides were worked into the soil at a depth of 15 cm. In order to obtain a better effect of the mostly used contact nematicide DD-mixture at a moderate dosage, a special treatment of the soil surface with the non-fumigant dazomet was combined with the fumigation. On clay soil more than 99 % kill of stem nematodes was obtained with 30 g dazomet + 50 ml DD-mixture per m When 10 g dazomet was added a 80% kill of Rolylenchus uniformis (Thorne) could be obtained on sandy soil; this was equivalent to 2 applications of the DD-mixture alone. The combined treatment offers the great advantage of increasing the chances by 3 times to make the appropriate choice of the year for the treatment. Eggs of R. uniformis and H. rostochiensis are less susceptible to DD-mixture than free living larvae and adults.     

Biological Suppression and Natural Population Decline of Heterodera schachtii in a California Field

ABSTRACT Soil suppressiveness to Heterodera schachtii was demonstrated in a field at the research station of the University of California, Riverside. In two field trials planted to Swiss chard (Beta vulgaris), introduced H. schachtii multiplied 2.7 and 1.7 times more in preplant metam sodium-fumigated plots than in nontreated plots in 1994 and 1995, respectively. In greenhouse experiments, preplant treatments with metam sodium, methyl bromide, methyl iodide, formaldehyde, and aerated steam reduced suppressiveness of soil against H. schachtii to undetectable levels. H. schachtii multiplied significantly less in nontreated soil than in treated soil on Swiss chard. At harvest, the number of infective second-stage juveniles in suppressive soil was close to the lowest detection level, whereas high numbers were encountered in soils initially treated. In a crop rotation trial with host crops of H. schachtii, introduced H. schachtii populations were monitored for five cropping periods over 30 months in initially fumigated versus nontreated suppressive field plots. In fumigated plots, H. schachtii population levels increased in the first and second cropping periods and then declined in the third cropping period. In the fourth and fifth cropping periods, the nematode reproduction factor in the initially fumigated plots was not significantly different from that in suppressive plots.     

Characterization and functional analysis of clpB gene from Acidovorax avenae subsp. avenae RS‐1

The type VI secretion system (T6SS) has been reported to be highly associated with various cellular activities in strain RS‐1 of Acidovorax avenae subsp. avenae (Aaa), the pathogen of bacterial brown stripe of rice. However, the role of the clpB gene that presents in the T6SS gene cluster in Aaa pathogenicity has not been clarified. The aim of the current study was to characterize the function of clpB and to investigate its contribution to bacterial pathogenesis using insertional deletion mutation and complementation approaches. The results indicated that mutation of clpB significantly affected bacterial growth, virulence, exopolysaccharide (EPS) production, biofilm formation and expression of 13 other T6SS genes of Aaa RS‐1. The reduction of virulence may be also partially due to the change in EPS composition, which was characterized by the Fourier transform infrared (FTIR) spectra. Furthermore, analysis of protein homology modelling showed that the structure of ClpB is different from those of the other T6SS components. In addition, structural difference was observed between ClpB and Type IV pili (TFP) as well as Type IV pilus biogenesis proteins (PilP), whose functions are similar to ClpB. Taken together, this study demonstrated that the clpB gene plays a key role in Aaa bacterial virulence.     

The impact of resistant and susceptible wheat cultivars on the multiplication of Heterodera filipjevi and H. avenae in parasite‐infested soil

Cereal cyst nematode (CCN) severely threatens wheat production in many regions of China. Cultivars susceptible to CCN are the main reason for its spread. This study was initiated to determine whether wheat cultivars conferring different resistance levels are the dominant determinants of CCN populations in the rhizospheric soil. Field experiments were conducted at two locations in Henan province, China, where high populations of Heterodera filipjevi or H. avenae have occurred, during the growing seasons of 2010/11 and 2011/12. Conventional enumeration of white female nematodes on the plant roots, reproductive factor (Rf) and a molecular diagnostic approach, PreDicta B test, a soil testing service based on a sensitive quantitative PCR technique, were used to determine the nematode populations in the rhizospheric soils of seven common wheat and durum wheat cultivars with different reactions to CCN. The resistant responses to CCN conferred by durum wheat Wascana and Wakooma and common wheat Madsen were effective against both H. filipjevi and H. avenae and resulted in significantly fewer nematodes (<5 females) on the roots, and lower Rf. Those cultivars were effective in limiting nematode propagation, resulting in fewer CCN eggs in their rhizospheric soils. Taikong 6 conferred moderate resistance (5–10 females) to both Heterodera species. Tianmin 668 only showed resistance to H. avenae. Aikang 58 and Wenmai 19 were susceptible to both CCN species, which facilitated increases in the nematode populations. These results demonstrate that the reactions to CCN of wheat genotypes have obvious impact on the propagation of nematodes.     

阿拉善荒漠区东部的残遗植物-四合木(Tetraena mongolica Maxim.)种群动态的分析-运用Leslie矩阵的讨论

用 Leslie矩阵对内蒙古与宁夏的西鄂尔多斯残遗分布的特有植物 -四合木(Tetraena mongolica)种群动态在张慧荣等人研究工作的基础上再作探讨。从调查数据中提取信息 ,构造新的 Leslie矩阵 ,对四合木种群年龄分级提出合理的划分。可以认为四合木种群动态有微小波动的特点。各龄级个体数的变化趋势不同 ,但种群动态在总体上呈衰退趋势。     

棉田棉蚜种群动态及瓢虫对棉蚜种群数量的影响

根据新疆尉犁县4种棉花品种的棉田调查,利用棉蚜数量和时间进行回归分析,探讨其种群动态,应用棉蚜数量和瓢虫数量进行相关分析,研究棉田棉蚜种群与瓢虫种群的关系。结果表明,在不同品种的棉田中,棉蚜种群数量基本呈指数规律上升与下降。在尉犁县孔雀农场的中棉35和军棉1棉田中,从2001年5月31日至6月28日棉蚜种群数量呈指数增长,从6月28日至7月26日棉蚜种群数量呈指数下降。在尉犁县达西村的抗虫棉9和新陆中11棉田中,棉蚜种群数量开始发生和发生高峰期均比中棉35和军棉1推迟1周左右,其中抗虫棉9棉田的棉蚜发生高峰期数量最多,而新陆中11棉田的棉蚜发生期数量最少。在不同品种的棉田中,瓢虫是棉田棉蚜的主要天敌,对棉蚜起控制作用,它与棉蚜种群数量呈显著的跟随关系,发生期比棉蚜滞后1周左右。     

Population Dynamics of Biocontrol Agents and Pathogens in Soils and Rhizospheres

Understanding the dynamics between a pathogen and a biocontrol agent (BCA) in soil or in an infection court such as the rhizosphere is crucial for predicting the success of biological control. This is especially true for biological control using the strategy of reduction of initial inoculum prior to infection. By studying the population density fluxes over time, one can observe how the BCA and pathogen influence each other's population and life cycles, and how the biological and physical environment influence this relationship. Methods for quantifying fungi and bacteria in soil, including classical (dilution plating, baiting, bioassays), immunological (ELISA, IFC, immunomagnetic) and molecular (DNA hybridization, PCR, marker and reporter genes) methods, are discussed and critiqued. Finally, the value of mathematical modeling of population dynamics as a means of providing important information about the tripartite relationship between the pathogen, BCA, and host plant is reviewed.     

Problems with the Use of Resistance in Wheat to the Australian Pathotype of Heterodmra avenae1

Problems with the use of resistance in wheat to the Australian pathotype of Heterodera avenae are discussed. Resistance in different cultivars is regarded as a continuous series, and multiplication rates, sex ratios and susceptibility/resistance all measure the same thing. The best source of resistance to the Australian pathotype is in Aus 10894, but this will be of greatest use if incorporated into a tolerant cultivar. Tolerance of wheat cultivars is also a continuous series from poor to good. Cv. Olympic has poor tolerance. Resistance in cv. Festiguay and Portugal 1 31 may also be useful in tolerant cultivars. The Australian pathotype is not more damaging than other pathotypes.     

Characterization of pilP, a gene required for twitching motility, pathogenicity, and biofilm formation of Acidovorax avenae subsp. avenae RS-1

The Gram-negative bacterium Acidovorax avenae subsp. avenae is the causal agent of bacterial brown stripe (BBS), which can cause severe diseases in many plants, including rice, with huge economic importance. Type IV pili (TFP) are hair-like appendages involved in several bacterial activities such as bacterial surface motility, surface adherence, colonization, biofilm formation, and virulence. The aim of our study is to characterize the association of A. avenae subsp. avenae TFP with BBS in rice. We generated a transposon (Tn5) mutant library. Then, an insertional mutagenesis on the background of this bacterium was identified as reduced pathogenicity. The confirmed inserted genetic region was into gene pilP, which encodes a TFP assembly protein. The pilP-deficient mutant strain seriously affected the motility twitching ability, biofilm formation and virulence. Collectively, our results clearly indicated that the pilP gene and TFP in A. avenae subsp. avenae play a key role in plant pathogenicity, twitching motility, and biofilm formation.     

Population Dynamics of the Field Vole (Microtus agrestis [L]): a Model1

The basic hypothesis underlying a population dynamics model for the field vole (Microtus agrestis [L.]) in central Scandinavia is described and discussed. The hypothesis is that most aspects of population dynamics of the field vole may be understood by analyzing the nutritional (energy and matter) balance of individual animals and their differential allocation of available nutrients. Digested nutrients are assumed to be utilized for maintenance cost, M; growth, A S; reproduction, R; and dispersion behaviour (including dispersal), D. The simulation model whose main ideas are described verbally is being developed at present. The model is intended to simulate density, age structure, reproductive activity of different categories of the population and spatial distribution; grazing impact apportioned among the most important potential food species (or group); interaction with sympatric rodents, their predators and parasites. Special emphasis is placed on the spatial heterogeneity of the landscape. The population dynamics model is of the Monte Carlo type and considers the realization of a series of events by calculating average probabilities and “drawing” random numbers. The model simulates individual animals in a large heterogeneous area. Qualitative predictions based on our basic hypothesis are discussed and compared with available field information.     

不同混交模式马尾松林与松墨天牛种群动态的关系

通过调查马尾松纯林、马尾松×杉木混交林、马尾松×火力楠混交林、马尾松×毛竹混交林等5种混交比例模式的马尾松林中诱捕的松墨天牛数量,分析不同混交模式与松墨天牛种群动态的关系。结果表明：不同混交模式的马尾松林诱捕到的松墨天牛成虫数量有差异,马尾松混交林诱捕到松墨天牛成虫数量明显低于马尾松纯林。每年6月和8月为华安县松墨天牛成虫活动的高峰期,应结合生产实际开展松墨天牛综合防控。