Population dynamics of the potato cyst nematode,Globodera pallida,in relation to temperature,potato cultivar and nematicide application

The impact of increasing temperatures on the population dynamics of the soil-dwelling nematode Globodera pallida, a persistent and economically important pest of potatoes, was investigated. The reproductive factor (final population⁄initial population) and length of life cycle were found to be temperature sensitive. Pot experiments performed over 4 months allowed comparison of the effect on development of G. pallida of two temperature regimes: an average temperature comparable to current field conditions (14.3 °C) and an average temperature above current field conditions (17.3 °C). A larger second generation of juveniles was observed at 17.3 °C compared to 14.3 °C. Multiplication of G. pallida at field sites in Shropshire and East Lothian (average soil temperatures of 15.5 and 14.1 °C, respectively, during potato cropping) was also examined. A quantitative PCR assay and visual examination of roots were used to monitor the dynamics of the G. pallida populations in both field sites at 4-weekly intervals. Four cultivars, Desirée, Cara, Maris Piper and Estima, were grown with and without nematicide treatments. Nematicide treatments suppressed population increases at both sites. Females were observed on the roots of cvs Cara and Desirée at the end of the growing season in Shropshire, but not at East Lothian, and are likely to represent a second generation.     

Quantification of Globodera rostochiensis and G. pallida in mixed populations using species-specific thermostable proteins

A method has been developed to quantify species ratios in mixed populations. The method is based on the separation of species-specific thermostable proteins by SDS-PAGE. Densitometric analyses of the 17 kD protein ofGlobodera pallida and the 18 kD protein ofG. rostochiensis revealed a high correlation (R ²=0.93) with the species ratio in the mixed samples. Within the limits of 10 to 90% of each species, one can estimate with 95% reliability the species composition with 3 to 6% deviation.Samenvatting Een methode is ontwikkeld om de samenstelling van soortenmengsels vanGlobodera rostochiensis enG. pallida te kwantificeren. Bij deze methode wordt gebruik gemaakt van de soort-specifieke thermostabiele eiwitten die met behulp van SDS-PAGE gescheiden worden. De kleurintensiteit van het 17 kD eiwit vanG. pallida en het 18 kD eiwit vanG. rostochiensis is per gel-laan bepaald m.b.v. een densitometer en heeft een lineair verband met de soortsverhouding in de mengsels (R ²=0.93). Binnen het bereik van 10 tot 90% van elke soort kan men met deze ijklijn met 95% betrouwbaarheid de soortsamenstelling bepalen op 3 tot 6% nauwkeurig.     

警惕检疫性有害生物马铃薯孢囊线虫(Globodera rostochiensis和G. pallida)入侵我国

马铃薯孢囊线虫包括马铃薯金线虫Globodera rostochiensis和马铃薯白线虫G. pallida, 是马铃薯生产上危害最为严重的植物寄生线虫, 一般造成30%的产量损失, 在热带发病严重地区, 产量损失高达80%~90%, 甚至绝收?由于其危害严重性, 包括我国在内的100多个国家将其列为重要检疫性有害生物?我国目前尚无马铃薯金线虫和白线虫的发生报道, 但随着贸易全球化, 马铃薯孢囊线虫传入我国的风险日趋增高?本文主要对马铃薯孢囊线虫的发生分布?危害症状?经济损失?生物学特性?传入我国的潜在风险和预防控制措施进行综述, 旨在为防止马铃薯孢囊线虫入侵我国提供参考?     

Consistent action of two partially effective loci conferring resistance to Globodera pallida Pa2/3 across multiple nematode field populations

The potato cyst nematodes (PCN) Globodera rostochiensis and Globodera pallida are significant pests of potatoes worldwide. The most effective control methods are crop rotation and the deployment of resistant varieties. Complete resistance to G. rostochiensis based on a single resistance gene has successfully been integrated into many varieties. However, resistance to G. pallida has not been as successful to date, with current varieties only exhibiting partial resistance. Combining partially effective quantitative trait loci (QTLs) for resistance can increase the strength and breadth of the resistance. An additive effect on resistance has previously been demonstrated on combining two QTLs from Solanum tuberosum subsp. andigena (GpaIV^s_adg) and Solanum vernei (Gpa5). However, populations of G. pallida can be quite divergent and it was unclear whether the relative effects of the individual QTLs and the combined additive effect would be consistent across different G. pallida Pa2/3 populations. Using a mapping population segregating for both QTLs, the effect of the QTLs individually and combined was examined on four UK‐derived field populations of G. pallida pathotype Pa2/3, and the relative effects of the individual QTLs and the additive effect of the combination found to be consistent across all populations.     

The effect of the presence of R-genes for resistance to late blight (Phytophthora infestans) of potato (Solanum tuberosum) on the underlying level of field resistance

The differential genotypes R₁, R₁₀ and R₁₁, as originally defined by Black, were crossed with R-gene-free cultivars and the progenies divided into two subpopulations comprising those which had inherited the R-gene and those which had not. The underlying level of field resistance of the two groups was compared in a field trial in which they were inoculated with an isolate that could overcome the relevant R-genes. The R-gene-bearing group was significantly ( P  < 0·001) more resistant than the R-gene-free group, with mean scores over four dates in 2000 of 4·86 and 4·09, respectively, on a 1–9 scale of increasing resistance, and of 4·10 and 2·35 on one date in 2001. However, the magnitude of the effect depended on the R-gene and the year of the trial. Data from a progeny of cv. Stirling (with an R-gene and a high level of field resistance) were examined and the same effect of an R-gene found. Fewer of the R-gene-bearing group of clones were highly susceptible, and more were resistant. The most resistant clones always bore the R-gene. It is concluded that increased resistance is conferred by the defeated R-gene or linked genes for field resistance.     

Selection of virulence in Meloidogyne chitwoodi to resistance in the wild potato Solanum fendleri

The possibilities of selecting virulence from a virtually avirulent root-knot nematode population towards resistance in wild potato have been investigated. Single egg masses of Meloidogyne chitwoodi, which had occasionally been produced on roots of resistant Solanum fendleri gave rise to eight lines after one generation on tomato. Five lines were able to circumvent completely the resistance of S. fendleri 93-114-12 resulting in a susceptible response similar to that of the control potato cv Nicola. Subsequently, a resistance test with other resistant genotypes of S. fendleri, S. bulbocastanum, S. stoloniferum and S. hougasii revealed that the virulent lines were also able to break through the resistance in most other species, but clear differences were noticed between the virulent lines. The results suggest a simple inheritance of virulence in M. chitwoodi towards resistance in S. fendleri. However, more virulence factors are involved to explain the differences on the other Solanum species between the virulent lines. The implications of the ease to select virulence with respect to the practical use of resistance in potato breeding and growing are discussed.     

Infection of plant material derived from Solanum acaule with Clavibacter michiganensis ssp. sepedonicus: temperature as a determining factor in immunity of S. acaule to bacterial ring rot

The development of potato ( Solanum tuberosum ) cultivars immune (completely free of infective agents) to bacterial ring rot disease, caused by Clavibacter michiganensis ssp. sepedonicus , would be a significant step toward eradication of the disease. Earlier results suggested that the wild potato species Solanum acaule , acc. PI472655 (genotype 7-8), was immune to C. michiganensis ssp. sepedonicus . The goal of the present study was to investigate the possibility of transferring this desirable trait to cultivated potato through interspecific somatic hybridization. Eight different somatic hybrids between S. acaule and S. tuberosum , with three different genome ratios, were tested for susceptibility to infection in the glasshouse using two C. michiganensis ssp. sepedonicus strains. All the somatic hybrids expressed symptoms of ring rot and were susceptible to infection as determined by IFAS (indirect immunofluorescent antibody staining) tests. The genome compositions of the hybrids influenced bacterial titres. Most of the hybrids with a higher proportion of the S. acaule genome contained lower numbers of C. michiganensis ssp. sepedonicus cells than hybrids with lower proportions of the S. acaule genome. In growth chamber tests, temperature was found to be a determining factor in the expression of immunity in the tetraploid S . acaule 7-8 line. At 21°C, S . acaule 7-8 was immune to infection by C. michiganensis ssp. sepedonicus , but at 15°C, plants supported large populations of the pathogen. However, none of the S. acaule plants expressed disease symptoms. Thus, S. acaule exhibits temperature-dependent immunity to infection by C. michiganensis ssp. sepedonicus and should be considered tolerant rather than immune.     

Selection for imidacloprid resistance in silverleaf whiteflies from the Imperial Valley and development of a hydroponic bioassay for resistance monitoring

A field-collected population of the silverleaf whitefly, Bemisia argentifolii, was selected with the nicotinyl compound, imidacloprid, over 32 generations to determine if resistance would develop when maintained under continuous selection pressure in a greenhouse. Resistance was slow to increase at first with low to moderate levels of resistance (RR from 6- to 17-fold) in the first 15 generations of selection. Further selection steadily led to higher levels of resistance, with the greatest resistance ratio at 82-fold, the gradual rise suggesting the involvement of a polygenic system. At the end of the selection, slopes of probit regressions were substantially steeper than earlier, indicating increased homogeneity of imidacloprid resistance in this strain. A hydroponic bioassay featuring systemic uptake of imidacloprid through roots was developed to monitor the changes in resistance to imidacloprid in the selected whitefly strain and in seven field-collected strains from Imperial Valley, California. Six out of seven field-collected strains exhibited low LC₅₀ values (0·002 to 0·512 mg ml^-1) compared to the selected resistant strain, with one exception where the LC₅₀ was 0·926 mg ml^-1 (RR=15·0). Variation in responses to imidacloprid in the field strains suggest that this technique is sufficiently sensitive to detect differences in susceptibilities of whitefly populations. The imidacloprid-resistant strain showed no cross-resistance to endosulfan, chlorpyrifos or methomyl (RR ranging from 0·4- to 1·5-fold). A low level of cross-resistance was observed to bifenthrin in the IM-R strain at 7-fold. The success of selection for resistance to imidacloprid has serious implications for whitefly control programs that rely heavily on imidacloprid. ©1997 SCI     

Identification of a major gene (Mex-1) from Coffea canephora conferring resistance to Meloidogyne exigua in Coffea arabica

Among the most damaging root-knot nematode species, Meloidogyne exigua is especially common in Latin America and constitutes a major agronomic constraint in all major coffee-growing ( Coffea arabica ) areas. Growing nematode-resistant coffee represents the most promising option for control of the pest. The present study aimed to determine the mode of inheritance of the M. exigua resistance transferred into C. arabica from a related species, Coffea canephora , and to identify associated molecular markers. Segregation data analysis of F ₂ progeny derived from a cross between the resistant introgression line T5296 and the susceptible accession Et6 showed that the resistance to M. exigua is controlled by a simply inherited major gene (designated the Mex -1 locus). The gall index distribution exhibited by the F ₂ individuals suggested incomplete dominant expression. Fourteen AFLP markers were found associated with the resistance to M. exigua and a localized genetic map of the chromosome segment carrying Mex -1 was constructed. Furthermore, the association of the identified AFLP markers with Mex -1 was confirmed by analysis of a set of genotypes involving 28 introgression Arabica lines either resistant or susceptible to M. exigua in field conditions. These results represent an important starting point to enhance backcross breeding programmes and to perform an early selection of resistant seedlings.     

Expression of resistance to the root-knot nematodes,Meloidogyne hapla andM. fallax,in wildSolanum spp. under field conditions

In 1995 two fields in the Netherlands, naturally infested withMeloidogyne hapla (Wageningen) andM. fallax (Baexem), were used to evaluate resistant and susceptibleSolanum genotypes under natural conditions. In April, genotypes were planted in circular microplots. Soil samples were taken and analyzed for the occurrence of second-stage juveniles every six weeks. From August onwards, large differences between resistant and susceptible genotypes in numbers of juveniles were found in the soil. For all resistant wildSolanum genotypes the level of infection in soil at the end of the growing season in October was equal to or lower than at the beginning. Glasshouse experiments were performed with the same genotypes and nematode populations (i.e. originally derived from these fields) and the results were comparable with the observations from the field. It is concluded that resistance, as selected in glasshouse trials, corresponds well with resistant behaviour in the field and that it is worthwhile to transfer the resistance from theseSolanum sources to commercial potato cultivars for successful control of root-knot nematodes.     

Epidemiological importance of Solanum sisymbriifolium, S. nigrum and S. dulcamara as alternative hosts for Phytophthora infestans

Lesions of Phytophthora infestans were found on woody nightshade ( Solanum dulcamara ), black nightshade ( S. nigrum ) and S. sisymbriifolium during a nationwide late blight survey in the Netherlands in 1999 and 2000. Pathogenicity and spore production of P. infestans isolates collected from potato ( S. tuberosum ), S. nigrum , S. dulcamara and S. sisymbriifolium were determined on several host plant species, and oospore formation in naturally infected and inoculated foliage of hosts was quantified. The present population of P. infestans in the Netherlands is pathogenic on S. nigrum , S. dulcamara and S. sisymbriifolium . Oospores were produced in leaves of S. nigrum , S. dulcamara and S. sisymbriifolium following infection with A1 and A2 isolates. Therefore these plant species should be regarded as alternative hosts for the late blight pathogen. In the case of S. nigrum and S. dulcamara infection was a relatively rare event, suggesting that diseased plants do not significantly contribute to the overall late blight disease pressure present in potato-production areas. Oospore production in ageing S. nigrum and S. dulcamara plants in autumn, however, may generate a considerable source of (auto) infections in following years. Considerable numbers of sporangia and oospores were produced on S. sisymbriifolium following infection with P. infestans . Additional field infection data are needed to evaluate the epidemiological consequences of a commercial introduction of S. sisymbriifolium as a potato cyst nematode trap crop.     

土耳其斯坦叶螨对杀螨剂的抗性选育及解毒酶活力变化

为探索土耳其斯坦叶螨的抗药性及其生化机理,在室内对敏感系土耳其斯坦叶螨分别用螺螨酯、甲氰菊酯和阿维菌素逐代处理,选育出抗性种群。结果表明,选育至15代,土耳其斯坦叶螨对螺螨酯、甲氰菊酯和阿维菌素的抗性指数分别达到268.63、37.98和112.68倍。分别测定敏感品系(SS)、抗螺螨酯(RS)、抗甲氰菊酯(RF)、抗阿维菌素(RA)品系的解毒酶活性显示,3种不同抗性品系相对SS品系的羧酸酯酶(CarE)、谷胱甘肽S-转移酶(GSTs)和多功能氧化酶(MFO)的比活力均有不同程度的提高,差异均达到显著水平(P0.05)。其中,RF品系的MFO比活力上升最快,是SS品系的12.7倍;RA品系的MFO比活力次之,是SS品系的5.76倍;RS品系的3种解毒酶比活力均增长较慢,其中CarE比活力上升最慢,是SS品系的1.31倍。由此表明,CarE、GSTs、MFO的活性增大可促进土耳其斯坦叶螨对3种杀虫剂的抗性形成;螺螨酯的抗性增强可能与CarE关系甚微;MFO活性的增加可能与甲氰菊酯抗性升高密切相关;GSTs、MFO的活性升高可能是土耳其斯坦叶螨对阿维菌素产生抗性的主要原因。     

The use of plastic bags as closed containers in screening for resistance to potato cyst nematode (Globodera rostochiensis and G. pallida)1

The use of a plastic bag as a closed container to screen for resistance in potatoes to potato cyst nematode in a controlled environment is described. Procedures to standardize the material tested and the inoculum used are outlined and the advantages of the system are discussed.     

甘薯根腐病抗病性室内鉴定方法的研究

将PDA 平面培养的甘薯根腐病菌研磨成浆,按一定比例加入蛭石中,接菌最适浓度为每200 g蛭石加1/ 2 培养皿菌浆,随后栽入薯苗,在25 ℃下培养25 ～30 d 后检查。以薯苗叶片枯黄程度及根部黑根死根多少划分病级,以病级平均数确定品种抗性,同时对抗感品种接种根腐病菌后过氧化物酶活性进行测定。试验证明,上述方法可以简便、快速、准确地测定品种对根腐病的抗性,同时也证明过氧化物酶活性作为量化分级标准的可行性。     

甘薯根腐病抗病性室内鉴定方法的研究

将PDA 平面培养的甘薯根腐病菌研磨成浆,按一定比例加入蛭石中,接菌最适浓度为每200 g蛭石加1/ 2 培养皿菌浆,随后栽入薯苗,在25 ℃下培养25 ～30 d 后检查。以薯苗叶片枯黄程度及根部黑根死根多少划分病级,以病级平均数确定品种抗性,同时对抗感品种接种根腐病菌后过氧化物酶活性进行测定。试验证明,上述方法可以简便、快速、准确地测定品种对根腐病的抗性,同时也证明过氧化物酶活性作为量化分级标准的可行性。     

甜菜夜蛾对氯虫苯甲酰胺抗性种群选育及鱼尼丁受体基因表达特征

为明确甜菜夜蛾Spodoptera exigua对氯虫苯甲酰胺的抗性发展及抗性种群中鱼尼丁受体(ryanodine receptor,RyR)基因的表达量变化,室内采用饲料混毒法进行甜菜夜蛾对氯虫苯甲酰胺的抗性选育,荧光定量PCR技术研究了抗性和敏感种群之间RyR基因mRNA表达量的差异。结果表明,室内选育31代后获得一个抗性倍数为105.60倍的甜菜夜蛾抗性种群,其mRNA表达量在甜菜夜蛾不同发育阶段及抗性种群和敏感种群之间均存在差异,以表达量最低的卵期作为对照,抗性种群中1龄幼虫表达量最高,是卵期的154.58倍;其次是雄性成虫,其表达量是卵期的101.51倍;2~5龄幼虫分别是卵期的59.56、35.35、72.99和19.84倍。抗性种群中1、2和4龄幼虫mRNA表达量分别是敏感种群的5.99、2.79和2.14倍,其余阶段低于敏感种群。表明甜菜夜蛾对氯虫苯甲酰胺的抗药性可能主要表现在幼虫阶段,RyR基因的表达量变化与氯虫苯甲酰胺诱导有关。     

Inheritance of resistance to angular leaf spot (Pseudomonas syringae pv. lachrymans) in cucumber and identification of molecular markers linked to resistance

Angular leaf spot is a common disease of cucumber ( Cucumis sativus ) caused by Pseudomonas syringae pv. lachrymans . Genetics of resistance to this disease was investigated using two sets of parameters: (i) disease severity, i.e. the number and size of necrotic and chlorotic lesions on the infected leaves, and (ii) presence or absence of a chlorotic halo around the necrotic spots on the infected leaves. Disease severity appears to be controlled by multiple genes and the heritability of the resistance was estimated to be 53%. The presence or absence of the chlorotic halo was determined to be governed by a single gene, with the presence of the halo (the susceptible phenotype) being a dominant character. A RAPD marker linked to the gene conferring the chlorotic halo was identified. Genetic distance between this marker, OP-AO07, a polymorphic 420 bp amplicon in the DNA of the susceptible plants, and the locus encoding the chlorotic halo was estimated to be 13 cM.