THE SUSCEPTIBILITY OF POTATO VARIETIES TO INFESTATION BY THE EELWORMS DITYLENCHUS DESTRUCTOR AND D. DIPSACI

Twenty-five varieties of potato in common commercial cultivation were found to be susceptible to tuber attack by potato-derived populations of Ditylenchus destructor under field and pot experimental conditions. Stunting and leaf deformation may also be caused by the eelworms but appear less consistently. A race of D. destructor from mushroom spawn had almost no effect on potatoes. Various races of D. dipsaci can reproduce in the shoot tissue of potato, sometimes causing damage. One population of this stem eelworm produced lesions on the tubers.     

Genetic-physiological compatibility and karyotypes of stem nematode]

The paper presents literary and the authors own data. The potato stem eelworm Ditylenchus destructor has a set of chromosomes 2n=44-48 and does not cross with the close species D. dipsaci from onion, garlic, parsley and parsnip. Most stem eelworms of the collective species D. dipsaci have n=12 and cross with each other producing fertile progeny. Some forms of stem eelworms, e.g. those of broad beans, plantain, dandelion and falcaria are polyploid. Intraspecies and intrapopulation polymorphism according to the number of chromosomes was recorded. Some races do not cross, some cross but unilaterally, some races produce sterile, non-viable or little viable hybrids. The species D. dipsaci should be regarded not only as a complex of species but as a group of forms at different stages of intraspecies differentiation.     

OBSERVATIONS ON THE ATTACK BY THE STEM EELWORM, DITYLENCHUS DIPSACI, ON STRAWBERRY

Four biologic races of Ditylenchus dipsaci can cause stem eelworm disease on twelve varieties of strawberry, all but one cultivated in Great Britain. The course of attack on strawberry, host reaction and the ways in which the disease originates and is disseminated are described.     

细胞和分子技术在甘薯茎线虫病抗病育种中的应用

甘薯茎线虫病是我国北方甘薯薯区的重要病害之一。为进一步研究甘薯茎线虫病育种中线虫和甘薯的抗感关系,利用细胞培养技术建立发根农杆菌转化甘薯发根,用该发根培养马铃薯腐烂线虫,构建植物寄生线虫培养和抗性鉴定的技术平台;用聚合酶链式反应(polymerase chain reaction,PCR)分子标记技术筛选甘薯茎线虫病抗感品种的分子标记,并对发根培养马铃薯腐烂线虫体系和分子标记辅助选择抗甘薯茎线虫病品种技术进行了展望。     

INVESTIGATIONS ON RESISTANCE OF OATS TO STEM EELWORM, DITYLENCHUS DIPSACI KÜHN

A procedure adopted for testing many varieties of oats and segregating progenies for reaction to attack by stem eelworm ( Ditylenchus dipsaci Kühn) is described, and its merits and limitations discussed in relation to the breeding of resistant varieties.
A study of some 250 forms of oats revealed new sources of resistance in cultivated and wild species. New sources of resistance in the cultivated species Avena sativa were found only in winter types, and in the other hexaploid species in forms belonging to A. byzantina (C) Koch, and the winter wild oat A. ludoviciana Dur.
Segregate progenies in advanced generations could be selected in the field by their reaction in a single drill in the first year followed by a head-row progeny test in the next season. Reaction was sufficiently well defined to identify the truebreeding resistant and susceptible lines.
The inheritance of reaction to stem eelworm in crosses involving Grey Winter and susceptible types depended on a single factor pair with resistance dominant.     

基于发根培养体系的甘薯品种抗线虫特性鉴定研究

利用发根农杆菌诱导的甘薯发根体系,鉴定甘薯品种抗线虫的特性。试验在甘薯品种徐薯18、栗子香和鲁78066诱导的发根体系上,接种马铃薯腐烂线虫,六周后调查发根繁殖线虫情况及线虫侵染发根情况,然后评价它们的抗线虫特性。结果表明:培养六周后,线虫在徐薯18、栗子香和鲁78066发根上繁殖倍数分别为8.82,0.76和0.70;在徐薯18发根上观察到多处线虫侵入位点,在栗子香和鲁78066发根上只观察到一处线虫侵入位点;基于以上结果,鉴定徐薯18为易感线虫病品种,栗子香和鲁78066为抗线虫病品种,徐薯18和鲁78066的鉴定结果和发病地自然诱发鉴定结果相一致,栗子香不同于发病地自然诱发鉴定结果。鉴定结果表明:用不同品种的甘薯发根作鉴定其抗线虫特性,具有体系简单、直观方便、重复性好以及不受自然环境影响等优点,进一步完善可以作为植物对线虫病抗性鉴定新的体系。     

Defaecation in the stem nematode, Ditylenchus dipsaci

The process of defaecation in the stem nematode, Ditylenchus dipsaci , has been analysed using cinemicrography. During feeding regular shortenings of the hind end of the body are accompanied by groups of a few defaecation periods. Each period begins as the shortened hind body re-elongates, and consists of several defaecation cycles. In each cycle the posterior rectum becomes dorsally bowed and, as it straightens, the rectal valve, rectum and anus open. Faeces pass out irregularly while the rectum remains open and are forcibly expelled as it closes. Defaecation in D. dipsaci is intermediate between that of the high-pressure nematode Aphelenchoidzs blastophthorus and the low-pressure passive feeder Hexatylus viviparus. We suggest that the main function of defaecation in plant nematodes is to excrete excess water.     

DNA polymorphism in the stem nematode Ditylenchus dipsaci: development of diagnostic markers for normal and giant races.

DNA polymorphism in the Ditylenchus dipsaci complex was investigated using amplified fragment length polymorphism (AFLP) to determine the relationships among populations growing mainly on Vicia faba and to develop diagnostic markers. Twenty-two populations of D. dipsaci originating from different geographical areas and one population of Ditylenchus myceliophagus were used. AFLP proved to be a powerful method to reveal intraspecific polymorphism even within the giant type. The analysis showed a clear distinction between the giant and normal populations, with genetic distances similar to those observed between normal populations and D. myceliophagus or giant populations and D. myceliophagus, strengthening the hypothesis that these two nematode types could be considered distinct species. Two specific AFLP markers differentiating the two types were converted into sequenced characterized amplified region (SCAR) markers. Used in a multiplex PCR, the SCAR primers proved to be a rapid and efficient tool to identify the giant and the normal types of D. dipsaci.     

Population increase of Ditylenchus dipsaci (Kühn) in the narcissus and the spread of the nematode through the soil

A bioassay technique, using forty onion seedlings per pot, was used to determine the soil population of the narcissus race of Ditylenchus dipsaci .
In experiments with narcissus, a progressive increase of D. dipsaci populations was shown, reaching a peak at the end of the growing season. This rise in population in May/June was associated with a rise in temperature. Increase in inoculum gave a significantly larger population in the foliage but not in the bulbs. Nematodes moved actively and were transported passively both up and down within the host plant. The presence of spikkels was associated with nematodes in the active intercalary meristem.
Migration from the plant into the soil and back into the plant, mostly via the base of the bulb, was continuous throughout the growing season and related to the population increase within the plant. Migration of nematodes from wetted dried leaf tissue continued over 60 days. Spread of the nematode through the soil was slow in the absence of external agencies, such as water run-off and methods of cultivation.     

甘薯茎线虫乙酰胆碱酯酶基因Dd-ace-2全长cDNA的克隆和序列分析

利用RT-PCR、RACE技术克隆了甘薯茎线虫(Ditylenchus destructor)乙酰胆碱酯酶基因(Dd-ace-2) cDNA (GenBank 登录号EF583058), 用DNAMAN5.0、MEGA3.0进行了序列分析。克隆的Dd-ace-2 基因cDNA全长2425 bp, 包含一个2205 bp的开放阅读框, 编码734个氨基酸。Dd-ace-2基因推导的氨基酸序列与南方根结线虫(Meloidogyne incognita)、秀丽小杆线虫(Caenorhabditis elegans)和动物寄生线虫胎生网尾线虫(Dictyocaulus viviparous)ace-2的氨基酸序列同源性分别达48.0%、42.7%和42.1%。在推导的734个氨基酸残基的前体蛋白中, 前面的701个氨基酸残基是成熟的乙酰胆碱酯酶序列, 其预测的分子量为79240.38 D。在一级结构中, 形成催化活性中心的3个氨基酸残基(Ser291, Glu442和His574)、胆碱结合位点Trp(177), 以及在亚基内形成二硫键的6个半胱氨酸完全保守; 在电鳐乙酰胆碱酯酶分子的催化功能域中存在14个保守的芳香族氨基酸残基, 其中10个在甘薯茎线虫乙酰胆碱酯酶中完全保守。与其它线虫和物种乙酰胆碱酯酶的聚类分析显示, 甘薯茎线虫的乙酰胆碱酯酶与其它线虫乙酰胆碱酯酶ACE-2同属一个支系。     

Efficacy of Selected Nonvolatile Nematicides on Control of Ditylenchus destructor in Iris

Greenhouse and field tests established that fenamiphos at 6.7 and 13.4 kg ai/ha applied in a 30-cm band directly on iris bulbs at planting effectively controlled Ditylenchus destructor. Aldicarb at rates of 5.6 to 11.2 kg ai/ha was less effective. Carbofuran, fensulfothion, and oxamyl at 6.7 to 13.4 kg ai/ha were ineffective. When applied on the bulbs, fenamiphos (granular or liquid) reduced nematode infection from 31 to 0.6% as determined by visual inspection of bulbs at harvest. Populations of D. destructor were reduced from 5.7 nematodes/g of fresh weight of bulb tissue to 0.04, 0.05, and 0.14 with applications of 13.4, 6.7, and 3.3 kg ai/ha fenamiphos, respectively. The most effective treatment was fenamiphos (granular or liquid) applied in a 30-cm band directly on the bulbs at time of planting.     

Feeding of the stem nematode, Ditylenchus dipsaci on leaf tissue of field bean, Vicia faba

The behaviour of Ditylenchus dipsaci before, during and after feeding on leaf tissue of Vicia faba is described. Short-term reactions of the food cells and functions of different regions of the pharynx are described and discussed in relation to the changing pressure relationships between nematode and cell.     

Ultrastructural changes during recovery from anabiosis in the plant parasitic nematode, Ditylenchus

Ultrastructural changes after desiccation and rehydration of the anabiotic fourth-stage juveniles of the plant parasitic nematode Ditylenchus dipsaci (Kuhn) Filipjev are described and quantified. Anabiotic juveniles retain their structural integrity, although the cuticle decreases in thickness and the muscle cell sarcoplasm condenses. In contrast the structure of the non-anabiotic nematode Panagrellus silusae is completely disorganized by desiccation. Following rehydration of D. dipsaci there is a lag phase of 2-3 hr before the nematodes become active. During this period the juveniles undergo an ordered series of morphological changes. The lipid droplets within the intestinal cells coalesce and the cuticle increases in thickness. The muscle cell sarcoplasm expands, the spacing of the thick myofilaments increases and the mitochondria swell before recovering a more normal appearance. These morphological changes, together with earlier metabolic studies, indicate that repair occurs during the lag phase prior to recovery. This may involve membrane repair and the re-establishment of the ionic gradients essential for normal muscle and nerve function.     

甘薯、胡萝卜发根单寄主培养体系繁殖马铃薯腐烂线虫的研究

利用发根农杆菌A4转化甘薯品种徐薯18和胡萝卜品种天红2号的发根,建立甘薯茎线虫病病原线虫(马铃薯腐烂线虫)的单寄主培养体系。通过该体系对马铃薯腐烂线虫的行为进行观察以及繁殖情况进行调查。结果表明:(1)马铃薯腐烂线虫在甘薯和胡萝卜发根上都能正常发育和繁殖,完成其生活周期;(2)培养4周和8周后,在甘薯发根上线虫繁殖倍数分别为2.6和50.6倍;在胡萝卜发根上线虫繁殖倍数分别为1.7和9.9倍;相同培养时间内,线虫在甘薯发根上的繁殖数极显著高于在胡萝卜发根上的繁殖数。(3)利用发根系统繁殖马铃薯腐烂线虫,便于研究其行为,在显微镜下可以直接观察到线虫在发根上活动情况,这对研究发根和线虫相互关系十分有利。基于上述结果,初步证实构建甘薯发根单寄主培养体系繁殖马铃薯腐烂线虫是可行的,且优于胡萝卜发根繁殖马铃薯腐烂线虫体系。     

Field studies of potato-root eelworm, Heterodera rostochiensis Wollenweber, 1938-40

Field studies of potato crops under different soil and fertility conditions and exposed to attack by diverse concentrations of potato-root eelworm led to the following conclusions:
In the north-western agricultural advisory province potato-root eelworm is not a major cause of failure or partial failure of potato crops on land where the viable cyst concentration is low (under 10/10 c.c. of soil). On such land increased yields can be obtained by improving conditions for plant growth, widening the rotation and increasing the fertility of the soil.
The production of satisfactory crops on land with a low eelworm population is likely to be accompanied by considerable increases in the numbers of root eelworms in the soil.
Crops free from signs of 'potato sickness' or 'potato-root eelworm disease' can be grown on land heavily infested with root eelworms (viable cyst concentration exceeding 25/10 c.c.), if no other adverse condition, such as unsuitable weather, lack of available food or incidence of fungus disease, affects the growth of the crop, but yields from heavily infested land are not likely to be more than moderate.
The treatments used against eelworms in the trials described here did not give results commensurate with their cost.
The practical difficulties of incorporating lethal substances with soil in the field are considerable, and this may have contributed to the disappointing results obtained.
The study of the influence of host variety on cyst production suggests that varietal differences in the host plants may influence the numbers of cysts formed on the crop, but the evidence is not conclusive.     

Water uptake and morphological changes during recovery from anabiosis in the plant-parasitic nematode, Ditylenchus dipsaci

The changes in water content and structural organization that occur during the rehydration of the anabiotic 4th-stage juveniles of the plant-parasitic nematode Ditylenchus dipsaci are described. Morphological changes include the coalescence of lipid droplets and the appearance of a hyaline layer beneath the cuticle. Changes in diameter are mainly responsible for volume changes. Changes in the appearance of the hyaline layer suggests that the muscle cells undergo some sort of repair process before activity resumes.     

THE INFLUENCE OF THE HOST ON THE DIMENSIONS OF THE PLANT PARASITIC NEMATODE, DITYLENCHUS DESTRUCTOR

Measurement data and body ratios from eleven populations of Ditylenchus destructor are presented. The data for lengths of males and females have been analysed for variance, and many differences between population means are shown to be significant. The essential importance of structural characters and the care with which sizes and dimensional ratios must be used, in the identification of a species, is emphasized.     

Characteristic Stimulation by Ethylene of Respiration in Dutch Iris Bulbs

The low steady-state basic respiration of iris bulbs (Iris bollandica cv.‘Wedgwood') at 30°C can be enhanced by ethylene. When ethylene is administered continuously a lag period of 4 hours is followed by an increase in the rate of respiration showing two peaks, one after 24 hours and the other after 3 to 4 days. Thereafter, the respiration rate decreases gradually, notwithstanding the presence of ethylene. Concentrations of less than 0.05 microlitre ethylene per litre have no effect, and the maximum effect is observed at concentrations of 3 microlitre per litre and higher. Between 0.2 and 2 microlitre ethylene per litre the peak values of the first maximum are linearly proportional to the logarithm of the ethylene concentration applied. The characteristics of the respiratory response in iris bulbs are probably similar to those described for potato tubers and non-climacteric fruits.     

ON THE STEM AND BULB EELWORM (ANGUILLULINA DIPSACI KUHN) WITH SPECIAL REFERENCE TO ITS OCCURRENCE ON WEEDS OF ARABLE LAND

The importance of wild hosts of Anguillulina dipsaci Kühn as carriers of infection needs no emphasis. The occurrence of the eelworm in the weeds, cleavers ( Galium aparine ) and duckweed ( Stellaria media ) taken in crops of oats and field beans which were themselves suffering from stem eelworm disease, was recorded by Johnson (1936) and Johnson & Thompson (1937); Walton (1937) confirmed the occurrence of infested cleavers plants in eelworm-infested oats. Walton also stated that experiments indicated that seed oats failed to carry eelworm infection, and from circumstantial evidence similar to that recorded by Johnson (1936) stated that "infestations of oat crops which occur, even after the absence of the crop for more than six years, are in all probability attributable to weeds rather than to infested seed". The present writer failed to obtain living eelworms from oat seed from infested crops in Yorkshire. This paper summarizes the results of field observations and experiments accumulated mainly during the past three years.