柑桔裂皮病发生情况鉴定

 柑桔裂皮病(exocortis)是以枳、枳橙和檫檬作砧木的柑桔树的严重病害,它的病原是一种类病毒^[4]。有的毒系引起砧木部树皮纵向开裂或翘裂,植株矮化,树势衰退;有的毒系仅引起植株矮化。此病除了嫁接传播外,亦通过修枝剪等与韧皮部接触传播。病害的鉴定,以利用指示植物为主。敏感的指示植物是Etrog香橼的USDCS 60-13选系和亚利桑那861选系^[1、2]。此外,亚利桑那861-S-1选系更为敏感^[3]。它不仅适用于鉴定一般毒系,亦适用于鉴定弱毒系。防治措施以通过茎尖嫁接脱毒或鉴定选择无病母树繁殖无毒苗木为主,亦要注意防止通过工具等的田间传播。     

佛手采后致病青霉的分离鉴定

佛手(Citrusmedica var.sarcodactylis Swingle)又名九爪木、五指橘、佛手柑,为芸香科柑橘属常绿小乔木.主产于闽、粤、川、浙等省,其中浙江金华“金佛手”最为著名,被称为“果中之仙品,世上之奇卉”.其果形美观、色泽金黄、香味浓郁,具有药用价值高、贮藏期长的特点[1],是金华地区的传统特产之一.     

Long‐term survival of Acidovorax citrulli in citron melon (Citrullus lanatus var. citroides) seeds

Long‐term survival of Acidovorax citrulli in citron melon (Citrullus lanatus var. citroides) seeds was investigated. Citron melon seed lots infected with A. citrulli were generated in the field by inoculating either the pistils (stigma) or pericarps (ovary wall) of the female blossoms. Seventeen A. citrulli isolates from 14 different haplotypes belonging to two different groups (group I and II) were used for inoculation. After confirming that 100% of seed lots were infected, they were stored at 4°C and 50% RH for 7 years. After storage, the viability of A. citrulli cells from individual lots was determined by plating macerated seeds on semiselective medium as well as growing seeds for 14 days and scoring for bacterial fruit blotch symptoms. The type of A. citrulli isolate (group I or group II) used did not significantly influence bacterial survival. However, A. citrulli survival was significantly greater in seed lots generated via pistil inoculation (52·9 and 29·4%) than via pericarp inoculation (23·5 and 17·6%). Repetitive extragenic palindrome (rep)‐PCR on A. citrulli isolated from citron melon seed lots after storage displayed similar fingerprinting patterns to those of the reference strains originally used for blossom inoculation, indicating that cross‐contamination did not occur. The results indicate that A. citrulli may survive/overwinter in citron melon seeds for at least 7 years and bacterial survival in seed was influenced more by method of blossom inoculation than by the type of bacterial isolate.     

Citrus viroid II variants associated with ‘Gummy Bark’ disease

A viroid etiology for citrus gummy bark (CGB) disease of sweet orange is supported by the similarity of symptom expression to cachexia disease of mandarins and tangelos caused by the hop stunt viroid (HSVd) related citrus viroid II (CVd-II), as well as the detection of CVd-II variants in CGB infected Washington navel and Dörtyol sweet orange, a Turkish cultivar. A survey was made of 67 clones of CVd-II related variants recovered from severe CGB symptomatic and non-symptomatic trees of the same cultivars growing in close proximity. Only CVd-IIa, a non-cachexia inducing variant, was found in non-symptomatic Washington navel trees and no CVd-II variants were recovered from the Dörtyol control. CGB infected sources contained a number of CVd-II related variants with the predominant species detected closely related to CVd-IIc, a known cachexia inducing viroid. Biological activity of representactive variants from CGB sources was determined by transmission to citron (Citrus medica) as well as by bioassay on the indexing host for cachexia, Parson's Special mandarin (Citrus reticulata).     

Separation of citrus viroids by shoot-tip grafting in vitro

Arizona 861-S1 citron ( Citrus media L.) infected with a severe exocortis isolate containing four citrus viroids was used as source of tissue for shoot-tip grafting in vitro. Out of 51 attempts, 25 successful grafts were obtained. Only 16 plants survived transplanting and of these 12 were viroid-free. The viroid profile of the other four plants showed fewer viroids than the original field source. The significance of these results, as compared with previous reports on the recovery of viroid-free plants, is discussed. The results show the usefulness of shoot-tip grafting in vitro as a tool to recover single viroid isolates from complex field sources.     

Separation and interference of strains from a citrus tristeza virus isolate evidenced by biological activity and double-stranded RNA (dsRNA) analysis

Separation of strains of citrus tristeza virus (CTV), differentiated by their double-stranded RNA (dsRNA) profiles, was obtained by graft-inoculating citron plants from a Mexican lime that had been recently aphid- or graft-inoculated with a mild CTV isolate (T-385). Up to 24 sub-isolates with differing dsRNA profiles were obtained from the aphid-inoculated lime. Some of these sub-isolates induced stronger symptoms in several citrus species than the original T-385 isolate. One sub-isolate, T-385-33, was mild in Mexican lime, but induced stem pitting on sweet orange. Inoculation of this isolate on Mexican lime, sour orange and Eureka lemon induced mild or no symptoms when inoculum was taken from citron, but very severe symptoms when the inoculum was from sweet orange. Mexican lime and sweet orange plants co-inoculated with T-385-33 from sweet orange in combination with the other 23 sub-isolates showed mild symptoms. The results obtained suggest that there is natural cross-protection among sub-isolates in the original T-385 isolate.     

The response of plant species used in agriculture and horticulture to viroid infections

The reactions of the viroids causing cucumber pale fruit (CPFV), chrysanthemum stunt (CSV) and citrus exocortis (CEV) in different plant species and varieties used in agriculture and horticulture were studied. These viroids caused identical symptoms on tomato and potato. The reactions of chrysanthemum Mistletoe to CPFV or CSV were identical, but CEV-infected plants reacted quite differently. CPFV and CEV caused the same type of symptoms on cucumber plants but symptoms of CEV were always weaker.Ten of the tested horticultural crop species appeared to be susceptible to CPFV, of which eight produced symptoms. In the Netherlands, however, CPFV is only described as pathogen on cucumber plants grown in glasshouses. Ten species were susceptible to CSV of which three produced symptoms. In the Netherlands CSV only occurs in chrysanthemum. Nine of the tested crops proved to be susceptible to CEV and seven were sensitive to this viroid which occurs in citric crops of (sub)tropical climate zones.Our results show that the viroids studies form potential pathogens for other crops than cucumber and chrysanthemum which are now affected by two of them.Samenvatting Het viroïde dat de bleke-vruchtenziekte bij komkommer veroorzaakt (CPFV), chrysanthemum stunt viroïde (CSV) en citrus exocortis viroïde (CEV) produceren symptomen op tomaat en aardappel, die niet van elkaar zijn te onderscheiden. De reactie van chrysant Mistletoe op CPFV of CSV is identiek, maar na infectie met CEV reageren de planten volkomen anders. Komkommers ontwikkelen dezelfde symptomen na een besmetting met CPFV en CEV, hoewel laatstgenoemd agens altijd een zwakker ziektebeeld oproept.Tomaat, aardappel, aubergine, chrysant, komkommer, augurk, meloen enBenincasa bleken gevoelig te zijn en paprika en petunia vatbaar voor CPFV, terwijl in Nederland alleen van komkommergewassen bekend is, dat ze aangetast worden door dit pathogeen.Tomaat, aardappel en chrysant waren ook gevoelig voor CSV, vatbaar voor dit viroïde waren paprika, petunia,Nicandra, andijvie, komkommer, augurk enBenincasa cerifera. In ons land kennen we stunt alleen in de chrysantenteelt. Negen gewassen bleken vatbaar te zijn voor CEV, en zeven waren gevoelig voor dit viroïde, dat alleen in (sub)tropische klimaatzones voorkomt.Vierentwintig cultuurgewassen bleken onvatbaar te zijn voor alle drie viroïden. De resultaten van dit onderzoek wijzen er op dat CPFV, CSV en CEV nauw verwant zijn, maar niet identiek.     

Rapid in vitro microindexing of viroids in citrus

A new laboratory technique combining shoot-tip grafting in vitro and biological indexing on indicator plants was explored for the detection of citrus exocortis and related viroids. Τhree in vitro laboratory methods were used and compared with the classical biological method. With the classical in vivo method, diagnosis is based on the expression of symptoms on indicators 11–14 weeks after inoculation. In contrast, with the first in vitro method, microindexing in vitro of citron seedlings by graft inoculation, diagnosis was possible 12 days after inoculation; with the second method, microindexing in vitro of citron cuttings by graft inoculation, 20 days after inoculation; and with the third method, microindexing in vitro of citron cuttings by injection inoculation, 40 days after inoculation. Inoculated Etrog citron plantlets grown in vitro and tested by RT-PCR showed the same viroid content as the source plants. Of the three in vitro viroid indexing methods, microindexing on cuttings by grafting was easier and more reliable than microindexing either on seedlings or on cuttings by injection.     

Host range and symptomatology of a graft-transmissible pathogen causing bud union crease of citrus on trifoliate rootstocks

A graft-transmissible pathogen causing bud union crease of Nagami kumquat SRA–153 on Troyer citrange was characterized for host range and symptomatology. Buds of Marsh grapefruit, Nules clementine, Eureka lemon and Pineapple sweet orange preinoculated with kumquat SRA–153 were propagated on citrange rootstocks. Some plants of Nules clementine and Eureka lemon had developed bud union crease six months after propagation, whereas all Marsh grapefruit and Pineapple sweet orange plants still showed normal bud union after one year. On indexing these preinoculated species, Nules clementine and Eureka lemon caused vein clearing in Pineapple sweet orange and Dweet tangor, chlorotic blotching in Dweet tangor and stem pitting in Etrog citron, whereas Marsh grapefruit and Pineapple sweet orange caused only chlorotic blotching in Dweet tangor and stem pitting in Etrog citron. Following shoot-tip grafting in vitro of kumquat SRA–153, kumquats 38–1 and 497–2 obtained from it caused chlorotic blotching in Dweet tangor and stem pitting in Etrog citron, but not vein clearing in Pineapple sweet orange and Dweet tangor or bud union crease when propagated on citrange. These results suggest the presence of at least two pathogens or pathogen strains in kumquat SRA–153 and the elimination of one of them after shoot-tip grafting in vitro or inoculation on Marsh grapefruit or Pineapple sweet orange. They also indicate that the pathogens in kumquat SRA–153 can be detected by indexing on Dweet tangor or Etrog citron.     

A combined indexing and budwood propagation method for citrus

Several budwood-transmitted citrus diseases, including citrus tristeza virus, citrus psorosis, citrus impietratura and a range of citrus viroids, were tested both visually and biochemically on a combined indicator (CInd) plant consisting of an Alemow (Citrus macrophylla) rootstock grafted with Etrog citron (C.medica) and Sour orange (C.aurantium) or Sweet orange (C.sinensis) buds. Indexing on CInd plants is economical for limited testing space; an additional advantage is that, by collecting budwood directly from the CInd plants, the risk of diagnostic failure due to uneven pathogen distribution in the budwood source tree is considerably reduced.     

Citrus leprosis virus: properties, diagnosis, agro-ecology and phytosanitary importance

Citrus leprosis disease, caused by citrus leprosis virus (CiLV), had severe effects on sweet oranges in Florida (US) until the 1920s, after which it became rare. In South America, it appeared in the 1930s, first in Argentina and then in Brazil, where it is now widespread and very dangerous. It has also been reported in Paraguay, Peru, Uruguay and Venezuela. CiLV is transmitted by three species of Brevipalpus , mainly Brevipalpus phoenicis. The virus mainly attacks sweet orange, but also citrange, citron, Cleopatra mandarin, grapefruit, lemon, mandarin, sour orange and tangor. CiLV is a non-enveloped rhabdovirus characterized by bacilliform particles measuring 120–130 × 50–55 nm, present in mesophyll and vascular parenchyma within cisternae of the endoplasm reticulum. Viroplasm structures are present in the infected cells. CiLV has been partially purified and its dsRNA as been investigated. It is mechanical transmissible to 13 test plant species belonging to the genera Atriplex, Beta and Chenopodium (Chenopodiaceae), Gomphrena (Amaranthaceae) , and Tetragonia (Tetragoniaceae). Using some of these herbaceous test plants, grown at a suitable temperature, it is possible to diagnose CiLV in 3–4 days. CiLV is covered by lists and requirements in phytosanitary regulations, but the information given is often misleading. For phytosanitary purposes, it is important to consider the following main points: (a) both CiLV and its vectors need to be considered; (b) sweet orange fruits can be infected even more than propagation material; and (c) CiLV does not infect susceptible citrus systemically, or any of its known hosts.     

Tracking an invader to its origins: the invasion case history of Crupina vulgaris

Summary Based on its Mediterranean origins and close relationship with other highly invasive Asteraceae species, Crupina vulgaris was declared a Federal Noxious Weed shortly after its discovery in Idaho in 1968. Twenty-two years later, surveys revealed over 25 500 ha infested with five separate populations in four states. Despite this expansion, no-one knew how this unlikely invader with its large seed was moving long distances or how it had escaped detection entering the country. The objectives of this study were to characterize the invasion history by estimating when, how, from where and how many times Crupina vulgaris was introduced in North America. Methods included molecular markers (random amplification of polymorphic DNA), distribution maps and historical sleuthing. Molecular markers linked all five North American populations with the Iberian Peninsula, with at least three colonization events. Distribution maps limited the area to northern Spain, where C. vulgaris occurs outside the range of Crupina crupinastrum . Site histories indicated four, perhaps five, successful introductions from northern Spain, associated with Basque sheepherders. Two remote sites (Lake Chelan, WA, and Modoc County, CA) had direct links with northern Spain from the 1950s into the 1970s. It appeared that the other introductions also occurred decades before the discovery dates. Detailed knowledge of individual invasion case histories is relevant for preventing future weed introductions and as a framework for future ecological investigations, such as effects of selection pressures during immigration or niche relationships in native and introduced habitats.     

Indexing of Citrus Viroids by Imprint Hybridisation

A method based on the hybridisation of tissue imprints was developed for routine indexing of citrus viroids. For maximum sensitivity and reliability, the inoculation of Citrus medica (Etrog citron) as a viroid amplification host is required. Hybridisation against Digoxigenin-labelled RNA- or DNA-probes followed by detection of viroid-probe hybrids using anti-DIG-alkaline phosphate conjugate and the chemiluminescence substrate CSPD was suitable for the detection of all citrus viroids with the same sensitivity as other available methods. The overall process is extremely simple and allows quick analysis of large numbers of samples by easily trained personnel and minimum equipment.     

Biological diversity of citrus tristeza virus (CTV) isolates in Spain

A survey of citrus tristeza virus (CTV) isolates was carried out in most citrus-growing areas in Spain. Twenty-two isolates were selected by geographical origin, cultivar of source tree, and symptoms observed on the host or in preliminary tests, and were biologically characterized.
A wide range of variation in transmissibility by aphids and symptom intensity on nine different indicator species or scion-rootstock combinations was observed among CTV isolates. Mexican lime. Citrus macrophylla , and to a lesser extent citron were the most useful hosts for characterizing these isolates, and leaf symptoms and stem pitting were the most discriminating traits. Positive correlation was observed between symptoms induced on Mexican lime and C. macrophylla , but not between the symptoms induced on these indicators under greenhouse conditions and the homologous symptoms on plants grown in the screenhouse. Some of the traits studied enabled us to establish relatively well-defined groups of isolates, but in most cases a continuous range of variation was obtained and no clear group could be defined.     

Genetics of soybean-Heterodera glycines system

Genetics of resistance to soybean cyst nematode (SCN), Heterodera glycines Ichinohe is very complex. Crosses involving PI 437654, which is resistant to all races of cyst nematodes with other sources of resistance (Peking, PI 88788, and PI 90763) indicated that resistance to race 3 was controlled by four genes, two of which were dominant resistance genes and the other two were recessive resistance genes. For race 5, a four gene model with two recessive and two dominant resistance genes in epistasis has been proposed. For race 14, the results suggested a three gene model with one dominant and two recessive alleles. Several other plant introductions have been isolated which have different genes conditioning resistance. Most of the currently grown soybean varieties derived resistance from Peking and/or PI 88788. Resistance to SCN in these soybean varieties has broken down because of the emergence of several new races and populations of SCN. The use of PI 437654 or Hartwig and other plant introductions with different genes for resistance will broaden genetic diversity and stabilize yield.     

Molecular Evidence of Distinct Introductions of the European Race of Gremmeniella abietina into North America

ABSTRACT The presence of the European (EU) race of Gremmeniella abietina var. abietina, the causal agent of Scleroderris canker of conifers, was first reported in North America in 1975 in the northeastern United States and subsequently in southern Quebec and Newfoundland during the late 1970s, where it quickly became established. We analyzed DNA profiles in samples from a historic collection of G. abietina var. abietina that included some of the first isolates of the EU race reported in the United States to test hypotheses concerning the G. abietina var. abietina epidemic in North America. Genetic diversity was partitioned by an analysis of molecular variance with haplotype frequencies and distances. Genetic differentiation was high between populations in continental North America and Newfoundland (between region differentiation, Phi(ct) = 0.665, P < 0.001). This result was not consistent with the hypothesis of a single introduction of the pathogen into the northeastern United States followed by secondary spread into northeastern Canada. In contrast, small levels of genetic differentiation were observed among continental North American populations (Phi(ct) = 0.047, P = 0.079), suggesting gene flow among these populations. A single haplotype of G. abietina var. abietina dominated the continental populations (80% of the isolates) but was absent from Newfoundland and Europe. Five haplotypes were found in the New-foundland population, all of which were either absent or very rare on the continent. Populations from continental North America clustered together and were distinct from a second cluster composed of European and Newfoundland populations. A phylogenetic analysis of the haplotypes indicated that some of the rare haplotypes may have derived from somatic mutations, whereas others probably occurred as the result of new introductions. The results are consistent with a scenario of distinct primary introductions of this pathogen into Newfoundland and continental eastern North America followed by secondary asexual propagation.     

Population structure of Solanum carolinense along the Takano River in Kyoto, Japan as determined by amplified fragment length polymorphism analysis

Areas infested with Solanum carolinense, an introduced perennial weed, have increased quickly in Japan. The genetic structure of a S. carolinense population along the Takano River in Kyoto, Japan was investigated using amplified fragment length polymorphism (AFLP) analysis to reveal how introductions and local spread have contributed to the development of this population. Along a terrace beside the river and an adjacent roadside, we defined a cluster of above‐ground shoots in the population as a subpopulation and 60 subpopulations were identified. Seventeen of these were selected and 165 shoots were analyzed by AFLP analysis using three primer pairs. The AFLP profiles revealed 69 genotypes and the presence of several clones, i.e. genotypes that were present in more than one individual. In total, 19 clones, comprising 2–34 identical genotypes, could be identified in the population. Each of these clones, except one, was allocated within each of the subpopulations. Clustering of the subpopulations was supported by high bootstrap values in all cases. Therefore, introductions from distant regions have mainly contributed to the development of this population, and local spread by seed or vegetative reproduction has rarely been important. The most likely introduction route of S. carolinense to this population was via planting associated with construction works.     

Population structure and mating system of Ascochyta rabiei in Tunisia: evidence for the recent introduction of mating type 2

The population structure of Ascochyta rabiei (teleomorph: Didymella rabiei ) in Tunisia was estimated among five populations sampled from the main chickpea growing regions using simple sequence repeat markers (SSR) and a mating type ( MAT ) marker. Mating type 2 isolates ( MAT1-2 ) had reduced genetic and genotypic diversity relative to mating type 1 isolates ( MAT1-1 ). This result, coupled with previous observations of lower overall frequency and restricted geographical distribution of MAT1-2 in Tunisia, and recent (2001) observation of the sexual stage, support the hypothesis of a recent introduction of MAT1-2 . Despite the presence of both mating types in Nabeul, Kef and Jendouba, the hypothesis of random mating was rejected in these locations with multilocus gametic disequilibrium tests. Highly significant genetic differentiation ( θ  = 0·32, G _ST = 0·28, P  < 0·001) was detected among populations and genetic distance and cluster analyses based on pooled allele frequencies revealed that populations from Nabeul and Kef were distinct from those in Beja, Bizerte and Jendouba. More than 70% of total gene diversity ( H _T = 0·55) detected was attributable to variation within populations compared to 28% among populations. This result, coupled with the occurrence of private alleles in each population, suggests that gene flow is currently limited among populations, even those separated by short geographic distances. The presence of two main genetic clusters was confirmed using Bayesian model-based population structure analyses of multilocus genotypes (MLGs) without regard to geographic origin of samples. The presence of MAT1-2 isolates in both clusters suggests at least two independent introductions of MAT1-2 into Tunisia that are likely to be the result of importation and planting of infected chickpea seeds.