一种检疫性寄生杂草——小列当

小列当为检疫性寄生杂草,原产欧洲和中东地区,已在世界各地造成了严重的经济损失,本文阐述了其分类学历史、形态特征、生物学特性、地理分布、传播途径、传播历史及危害性,描述了小列当与其近似种在形态特征上的区别及其防治方法,为小列当的检疫鉴定和综合防治提供理论依据。     

Germination stimulatory activity of bacterial butenolide hormones from Streptomyces albus J1074 on seeds of the root parasitic weed Orobanche minor

Damage caused by Orobanchaceae root parasitic weeds is a substantial agricultural problem for global food security. Many studies have been conducted to establish practical methods of control, but efforts are still required for successful management. Seed germination of root parasitic weeds requires host-derived germination stimulants including strigolactones (SLs). Studies on SLs have revealed that a butenolide ring is the essential moiety for SL activity as a germination stimulant. Interestingly, recent studies have revealed that butenolide hormones regulate the biosynthesis of secondary metabolites and mediate communication in actinomycete bacteria. Because of the structural similarity between SLs and the bacterial butenolides, we evaluated the germination stimulatory activity of butenolides isolated from Streptomyces albus J1074 on root parasitic weeds. These butenolides were found to specifically induce seed germination of Orobanche minor. Our findings contribute to understanding the molecular mechanisms of germination stimulant perception and to the development of a method for their biological control.     

我国向日葵列当发生危害现状调查

向日葵列当是危害我国向日葵最严重的杂草。为明确我国向日葵田列当的发生危害情况及防治现状,采用对角线5点取样法对新疆、内蒙古、吉林和河北等主要向日葵种植区进行调查,对向日葵列当的寄生率和寄生强度等数据进行分析。结果表明,向日葵列当在向日葵产区广泛分布,严重危害向日葵的生产,其对食葵的寄生率高于油葵,对抗性品种的寄生率较低。在所有调查地区中内蒙古地区向日葵列当发生最严重,寄生率高达100%,寄生强度达到38.5,单株寄生数量最高,达118株;新疆地区的向日葵列当寄生率居中,吉林、河北向日葵列当发生相对较轻。通过实地调研结合文献报道,对目前国内外向日葵列当的研究进展进行了综述,研究结果为指导向日葵列当防治提供参考。     

列当杂草及其防除措施展望

根寄生杂草列当Orobanche spp.每株可产生大量细小的种子,易于传播,且在出苗前已经对寄主作物造成危害,使列当的防除成为一个世界性难题。本文详述了列当的生活史、为害现状以及防除措施,并突出了生物防除的生态效益与经济效益。基于＂诱捕＂作物及＂捕获＂作物诱导列当种子＂自杀发芽＂理论的防除机制,本文提出了新型可持续生态防除思想,为列当科杂草防除提供参考。     

分枝列当种子萌芽生物学特性

以寄生于番茄的分枝列当种子为试验材料,研究预培养阶段温度、时间、渗透势以及培养阶段温度、萌发刺激物(独月却金内酯类似物GR24)的浓度和渗透势对种子萌发的影响,以期找到种子萌发的最适条件,从而可以人为创造控制分枝列当生长的环境,以达到有效防治的目的。结果表明:预培养阶段的最适培养温度为25℃,最适培养时间为6 d,最适的渗透势为0 MPa;培养阶段的最适培养温度为25℃,最适GR24浓度为1μmol/L,最适的渗透势为-1 MPa。     

Effect of tillage, cover crop and crop rotation on the composition of weed flora in a sandy soil

The development of integrated weed management strategies requires knowledge of mechanisms that influence compositional changes in weed flora. A 9-year study was initiated in 1988 at Delhi, Canada, on a loamy sand soil to evaluate the effect of tillage systems [conventional (CT) and no-till (NT)] and cover crops (only in NT) on weed density, species composition and associations, and crop yield in a winter wheat ( Triticum aestivum L.)/bean/winter wheat rotation. Three bean types: soyabean ( Glycine max L. Merr.), white bean ( Phaseolus vulgaris L.) and kidney bean ( P . vulgaris L.) were included. The NT system included variations: rye ( Secale cereale L.) or maize ( Zea mays L.) cover crop, volunteer wheat disked after harvest and wheat stubble. Data were collected in 1994, 1995 and 1996. Tillage systems, cover crops and crop type had differential effects on weed densities, species composition and associations. Weed densities were not affected by tillage or cover crops in wheat but, in the beans, densities were greater in the CT than in the NT systems. Various associations of weed species with tillage system, cover crop and crop type were observed. Crop yields were not affected by tillage type or cover crop, except that soyabean yields were highest in plots with cover crops.     

Evaluation of the pathogenicity of microorganisms isolated from Egyptian broomrape (Orobanche aegyptiaca) in Israel

Diseased Egyptian broomrape ( Orobanche aegyptiaca ) inflorescences were collected from a heavily broomrape-infested tomato ( Lycopersicon esculentum ) field in Israel. The microorganisms that were isolated from the diseased inflorescences were passed through Koch's postulates on Egyptian broomrape-parasitizing tomato roots in a polyethylene bag system and pots under greenhouse conditions. The fungi, Alternaria alternata , Macrophomina phaseolina , Rhizoctonia solani , and Fusarium solani , and the bacterium, Bacillus sp., were newly isolated from the diseased inflorescences of Egyptian broomrape and were found to be pathogenic to the parasite. Fusarium solani damaged all of the developmental stages of broomrape and prevented the damage that Egyptian broomrape causes to tomato plants. The level of pathogenicity and the damage of M. phaseolina , A. alternata , and Bacillus sp. to Egyptian broomrape in greenhouse experiments were relatively low. All the tested microorganisms are known as pathogens of tomato, yet none caused disease symptoms on the tomato plants grown in the inoculated polyethylene bags or in the pots. Fusarium solani demonstrated the highest potential for further development as a mycoherbicide for Egyptian broomrape control in tomato.     

Long-term management of Striga hermonthica: strategy evaluation with a spatio-temporal population model

The parasitic weed Striga hermonthica poses a serious threat to cereal production in sub-Saharan Africa. Striga hermonthica seedbanks are long-lived; therefore, long-term effects of control strategies on the seedbank only emerge after several years. We developed a spatially explicit, stochastic model to study the effectiveness of control strategies in preventing invasion of S. hermonthica into previously uninfested fields and in reducing established infestations. Spatial expansion of S. hermonthica and decrease in millet yield in a field was slower, on average, when stochasticity of attachment of seedlings to the host was included and compared to the deterministic model. The spatial patterns of emerged S. hermonthica plants 4–7 years after point inoculation (e.g. seeds in a dung patch) in the spatial-stochastic model resembled the distribution typically observed in farmers' fields. Sensitivity analysis showed that only three out of eight life cycle parameters were of minor importance for seedbank dynamics and millet yield. Weeding and intercropping millet with sesame or cowpea reduced the seedbank in the long term, but rotations of millet with trap crops did not. High seedbank replenishment during years of millet monoculture was not sufficiently offset by seedbank depletion in years of trap crop cultivation. Insight from simulations can be employed in a participatory learning context with farmers to have an impact on S. hermonthica control in practice.     

Uptake and translocation of imazethapyr in peas as affected by parasitism of Orobanche crenata and herbicide application methods

[¹⁴C]-Imazethapyr was applied as a seed treatment and at plant pre-emergence and post-emergence to peas ( Pisum sativum L.) parasitized by Orobanche crenata Forsk. Herbicide uptake increased with time regardless of the application method. Uptake reached about 98%, 89%, 81% and 94% of the total herbicide applied for the seed coating, seed soaking, pre-emergence and post-emergence treatments respectively. Herbicide translocation within the host plants consistently differed between O. crenata -infected and non-infected plants. High levels of ¹⁴C activity were accumulated by parasitic plants from the host. In non-infected pea plants, pods were stronger sinks for imazethapyr than the other parts of the plant, regardless of the application method. The herbicide distribution in the pea plant: O. crenata complex showed the same pattern regardless of the application methods. However, accumulation of radioactivity in the parasite was lower with pre-emergence and post-emergence application than with the seed treatments. In addition, radioactivity concentration in O. crenata plants was slightly higher when [¹⁴C]-imazethapyr was applied to pea seeds by coating than by soaking.     

A novel strain of Fusarium oxysporum from Germany and its potential for biocontrol of Orobanche ramosa

A newly isolated Fusarium oxysporum strain was investigated for its biocontrol potential against the root parasitic weed Orobanche ramosa (branched broomrape). The fungus was found to affect all developmental stages of the parasite. Orobanche seed germination was reduced by 40% in the presence of fungal conidia in vitro . The number of underground tubercles and shoots of the weed was reduced by the fungus by 55% compared with the control and 92% of tubercles were recorded as diseased in root chambers. In pot experiments, soil application of a granular formulation of the fungus resulted in a reduction of number and dry matter of Orobanche shoots by more than 90%. Spraying of a conidial suspension on aboveground Orobanche shoots caused the death of 75% of them within 2 weeks. Data from initial host-range experiments indicate that the isolate is very host-specific, not even attacking shoots of other Orobanche species. Because of these promising results, we conclude that the fungal isolate should be investigated under field conditions and be compared with other Fusarium isolates proposed for biocontrol of O. ramosa .     

Revisiting strategies for reducing the seedbank of Orobanche and Phelipanche spp.

Weedy Orobanche and Phelipanche species are important in Southern and Eastern Europe, the Middle East and North Africa, and have recently been reported in the USA, Australia and some countries in South America. Rather than being controlled, the Orobanche and Phelipanche problem is increasing, both in intensity and in acreage. Large areas of new territory are at risk of invasion, if care is not immediately taken to limit the introduction of parasitic seeds and to educate farmers and others to be alert for new infestations. There is an urgent need to re-evaluate novel integrated Orobanche and Phelipanche management programmes that will allow a better control of the parasite species and limit their distribution. The main obstacle in the long-term management of Orobanche and Phelipanche infested fields is the durable seedbank, which may remain viable for decades in the field. Large quantities of long-lived seeds give the parasite genetic adaptability to changes in host resistance and cultural practices. As long as the seedbank is not controlled, the need to control the parasite will persist whenever a susceptible host is grown in the infested field. We discuss strategies for seedbank reduction, paying particular attention to cultural practices, whereas chemical and biological control methods are covered by other reviews in this issue.     

The use of an alternative food source (red clover) as a means of reducing slug pest damage to winter wheat: towards field implementation

Slugs are major pests of many crops in the UK, including winter wheat, yet current methods of control are often unreliable. The aim of this study was to investigate three issues key to the successful field implementation of a control strategy that uses red clover as an alternative food source to reduce the amount of damage caused to winter wheat by the field slug, Deroceras reticulatum (Müller). A series of three experiments was designed to assess this aim. Firstly, under laboratory conditions, red clover was consumed in greater quantities than wheat, even when wheat was presented as a novel food. Secondly, red clover had no significant effects on the emergence and early growth of wheat in a polytunnel experiment. Both these results are crucial to the successful implementation of a strategy that uses red clover as an alternative food source. Lastly, the results of a field experiment were consistent with the results of the polytunnel experiment, in that red clover did not significantly affect wheat emergence. However, plots in which red clover was left to grow until the time of wheat harvest resulted in significantly lower (43%) wheat yields than plots without red clover. These results suggest that red clover must be removed from the field after the wheat has passed its vulnerable seedling stage. Recommendations for the potential use of red clover as an alternative food source for reducing damage to winter wheat in field conditions are discussed and opportunities for further work are suggested.     

诱集植物在农业害虫综合治理中的应用

诱集植物作为害虫综合治理的重要措施已经越来越引起关注。本文介绍了诱集植物利用的原理和历史,简述了诱集植物的优点,讨论了诱集植物在害虫治理中的应用,并展望了诱集植物的应用前景。     

Genetic diversity of Moroccan populations of Orobanche foetida: evolving from parasitising wild hosts to crop plants

Orobanche foetida is widely distributed in western Mediterranean countries infecting wild legumes. Recently it has been reported in Morocco infecting common vetch, presenting a further constraint for legume production in this area. Comparative studies between Orobanche populations attacking wild species and Orobanche populations growing on crops from the same region may help to clarify whether a host specialisation process occurred. In the present study, the genetic variability of five O. foetida populations, four infecting wild plants and one infecting cultivated vetch in Morocco was characterised using amplified fragment‐length polymorphism (AFLP) markers to elucidate the existing genetic relationship between populations and to suggest a potential origin for the recently detected vetch‐infecting population. Analysis of molecular variance suggested the existence of genotypic differentiation among populations. The most genetic divergent population by cluster analysis was the population collected on Ornithopus sativus. The vetch‐infecting O. foetida population was closer to the three populations infecting Scorpiurus muricatus. The possibility of the presence of a reservoir of diversity is balanced against direct genetic adaptation and completely new introduction. The potential for this Orobanche species to shift host and become a threat to agriculture exists and has to be taken into account for future legume breeding for these areas.     

A laboratory-based comparison of a molluscicide and an alternative food source (red clover) as means of reducing slug damage to winter wheat

Slugs are major pests of many crops in the UK, including winter wheat, yet current methods of control are often unreliable. This study investigates the potential use of red clover, as an alternative food source, to reduce the amount of damage caused to winter wheat by the field slug, Deroceras reticulatum (Müller). Two laboratory-based studies, each conducted over a 7-day period, investigated the effects of red clover seedlings and commercial metaldehyde pellets on damage to winter wheat seeds and seedlings. The results indicate that metaldehyde applications, in the form of commercially available pellets, resulted in significantly greater protection to wheat seeds compared with red clover, whereas metaldehyde and red clover were equally as effective in reducing damage to wheat seedlings. A further laboratory experiment investigated the effect of two slug population densities (48 and 16 adults m(-2)) and high and low red clover seed rates (125% and 75% of a standard rate) on damage to wheat seeds. Results showed that, at the highest slug population density, red clover sown at 125% of the standard rate gave 99% protection to wheat seeds, compared with the 75% seed rate which gave 55%. At the lower slug population density, both seed rates of red clover resulted in similar levels of protection. Implications for the potential use of red clover as an alternative food source for reducing damage to winter wheat in field conditions are discussed.     

Sheep as vectors for branched broomrape (Orobanche ramosa subsp. mutelii [F.W. Schultz] Cout.) seed dispersal

Sheep can be vectors for the long‐distance dispersal of weeds when seed becomes attached and retained in wool or survives the gastrointestinal tract. This study aimed to determine an appropriate quarantine period for sheep that minimized the risk of the long‐distance dispersal of the seeds of branched broomrape (Orobanche ramosa L. subsp. mutelii [F.W. Shultz] Cout.), a parasitic weed. Experiments with penned sheep found that the seeds that were placed on the soil surface adhered to the wool on the thigh and belly of the sheep, with most of the seeds attaching to the feet. Most of the seeds that were applied to the belly and thigh wool detached within 2 days, although a small proportion was present after 7 days. The seeds that were introduced to the digestive tract via drenching had a peak voidance 2 days later and no seed was detected on Day 8. It is suggested that a 7 day quarantine period for sheep would be sufficient in order to reduce the risk of the internal transport of seed to acceptable levels, but a small risk of the external transport of seed on the fleece remains.     

Dormancy and viability of Phalaris minor seed in a rice–wheat cropping system

Seed placement, soil temperature and soil moisture content influenced the process of after-ripening in Phalaris minor seeds. Seeds of P. minor collected from the soil just after wheat harvesting exhibited higher germination than seeds from P. minor threshed directly. There was a pronounced impact of periodic inhabitation of seed into the soil on germination after its dispersal. Germination was strongly inhibited when the seed was kept in soil at more than field capacity (FC) or in water. Maximum germination of seed incubated in soil at FC occurred at 30°C while a temperature of 40°C favoured after-ripening of seed when mixed with dry soil or kept dry without any medium. Release from conditional dormancy was quicker in the seed retrieved from the soil kept at 20°C than at 10°C. Seed release from conditional dormancy and germination increased with a rise in temperature from 30 to 40°C when the seed was retrieved from incubation in soil at FC for 70 days. The seed kept immersed in water was least responsive to a rise in temperature. Seed recovered from dry soil, or kept without any medium, responded quickly at both temperatures. Light enhanced the germination of Phalaris minor seed. The seedbank subjected to rice (Oryza sativa) field management conditions lost vigour in comparison with the seed stored in laboratory. There was significant variability in seed viability when exposed to differential water management conditions in rice.     

Effects of winter wheat cultivars and seed rate on the biological characteristics of naturally occurring weed flora

Summary Differential competitive ability of six winter wheat cultivars and traits that confer such attributes were investigated for a range of seed rates in the presence or absence of weeds for a naturally occurring weed flora in two successive years in split-plot field experiments. Crop height and tillering capacity were considered suitable attributes for weed suppression, although competitiveness is a relative rather than an absolute characteristic. Maris Huntsman and Maris Widgeon were the most competitive cultivars whereas Fresco was the least competitive. Manipulation of seed rate was a more reliable factor than cultivar selection for enhancement of weed suppression, although competitiveness of cultivars Buster, Riband and Maris Widgeon was not enhanced by increased seed rate. Crop densities ranging between 125 and 270 plants m⁻² were found to offer adequate weed suppression. Linear relationships were observed between individual and total weed species dry weight and reproductive structures per unit area.