Virus Diseases of Lentil - ARS英文书籍资料.doc

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1、Part 2D Page 1Diseases Caused by VirusesVirus Diseases OverviewViruses are obligate, acellular agents that reproduce inside living cells, spread between tissues, and frequently cause diseases in plants. They are a significant production constraint in chickpea and lentil. Virus diseases are often mis

2、diagnosed as physiological, toxicological, or nutritional disorders because symptoms are similar and no pathogen is visible, except under an electron microscope.In chickpea and lentil, many types of viruses are involved with genomes comprised of either single-stranded RNA or single-stranded DNA. Vir

3、uses that naturally infect chickpea include at least 25 species and 14 candidates (isolates that are potentially species) in 16 genera and 9 families. Viruses that infect lentil include at least 15 species and 3 candidates in 12 genera and 6 families.Entry of viruses into chickpea and lentil crops (

4、primary infection) is by vectors or infected seed. Spread from plant to plant within crops (secondary infection) is by vectors, predominantly aphids (Hemiptera: Aphididae). The pea aphid (Acyrthosiphon pisum Harris), cowpea aphid (Aphis craccivora Koch), green peach aphid (Myzus persicae Sulzer), an

5、d bean aphid (Aphis fabae Scopoli) are particularly important. For chickpea, leafhoppers are vectors for important viruses of genus Mastrevirus and also phytoplasmas, and thrips are vectors of less important viruses of genus Tospovirus and genus Ilarvirus.An understanding of dissemination mechanisms

6、 and reservoir hosts is important in developing strategies for virus control. Viruses infecting chickpea and lentil are different in terms of dissemination, even though the same virus species, aphid species, and reservoir hosts are involved. Chickpeas are colonized poorly or not at all by aphids. Th

7、ere are few apterae (wingless aphids) that walk from plant to plant unless colonizable weeds are present, Infection is by migrant alatae (winged aphids) that fly that alight on individual chickpea plants and then fly on to others, producing a scattered field distribution that is characteristic for v

8、irus diseases in chickpea (Fig. 1). Plants with symptoms are solitary or have only one or a few symptomatic Part 2D Page 2plants adjacent. Viruses acquired from hosts other than chickpea are generally most damaging although secondary spread from chickpea has been shown to occur for one virus species

9、 (Cucumber mosaic virus). Consequently, control strategies that aim to reduce buildup of aphids, establishment of early infection foci, or spread from these foci have limited benefit for chickpea. Examples are use of virus-free seed, seed-applied insecticide, and early aphicide sprays. In contrast,

10、these same strategies are commonly benefical for lentil, which is colonized extensively by legume-feeding aphids that can walk as apterae to adjacent plants or fly as alatae to other areas of crops. Secondary spread in lentil is evident from patches of many infected plants (Fig. 2). Heavy aphid popu

11、lations within lentil fields are often evidenced by numerous molt cases under the plants at the soil surface (Fig. 3).Losses in both chickpea and lentil can be minimized by optimizing cultural practices. Sowing time, seeding rate, and fertilizer should aim to give vigorous growth and early canopy cl

12、osure. Broadleaf weeds in and around crops should be controlled, as they can be sources of virus. Poorly-established, weedy crops are most vulnerable to damaging infestations (Fig. 4). Retention of standing stubble can deter flying aphids. Sources of resistance to specific virus species have been id

13、entified in lentil but are not widely available in commercial cultivars. Chickpeas exhibiting low incidence of infection (tolremicity) for a range of viruses have been identified in California, USA and Australia, and released as cultivars.The descriptions and illustrations that follow should be a us

14、eful for distinguishing diseases caused by viruses from those caused by other agents. However, the different virus species cannot be distinguished reliably by symptoms in chickpea and lentil and infection by mixtures of species is common. Identification of viruses by serological and nucleic acid-bas

15、ed techniques is important for making informed decisions on disease management strategies.Selected ReferencesBosque-Perez, N. A., and Buddenhagen, I. W. 1990. Studies on epidemiology of virus disease of chickpea in California. Plant Dis. 74:372-378.Part 2D Page 3Bos, L., Hampton, R. O., and Makkouk,

16、 K. M. 1988. Viruses and virus diseases of pea, lentil, faba bean, and chickpea. Pages 591-615 in: World crops: cool season food legumes. R. J. Summerfield, ed. Kluwer Academic Publishers, The Netherlands.Eastop, V. F. 1983. The biology of the principal aphid virus vectors. in: Plant virus epidemiol

17、ogy. The spread and control of insect-borne viruses, R. T. Plumb and J. M. Thresh, eds. Blackwell Scientific Publications, Oxford, UK.Klein, R. E., Larsen, R. C., and Kaiser, W. J. 1991. Virus epidemic of grain legumes in eastern Washington. Plant Dis. 75: 1186.Kumar, P. L., Kumari, S. M. G., and Wa

18、liyar, F. 2008. Virus diseases of chickpea. Pages 213-234 in: Characterization, diagnosis Genus Potyvirius) was previously known as bean virus 2 and Phaseolus virus 2. It was discovered in common bean (Phaseolus vulgaris L.) in 1925 and was the first virus reported to cause disease in chickpea in 19

19、56. Many different isolates of the virus occur in several important crops throughout the world. It causes significant losses in lentil, common bean, and faba bean, but is generally of minor importance in chickpea.SymptomsLentil. Symptoms on lentil include chlorosis, mild mosaic or mottling, and stun

20、ting. Leaves are often twisted or curled with necrosis along margins as the effects of the virus infection progress. Flowering and pod formation are reduced and consequently little seed is produced.Chickpea. Chickpea is susceptible to BYMV, but has a much lower incidence of natural infection than le

21、ntil. However, when infected, both Kabuli and Desi type chickpeas develop apical necrosis (Figs. 1 and 2), reddening of leaf margins, plant stunting and premature senescence. Plants that are infected early but do not die may develop leaves that are filiform (having very narrow leaflets) and sometime

22、s distorted.Causal AgentBYMV is a flexuous rod-shaped virion 750 nm in length containing single-stranded RNA and a coat protein with 282 amino acids. The genome is monopartite with 10,000 nucleotides. BYMV is serologically related to Clover yellow vein virus (ClYVV) which also infects many legume sp

23、ecies. The coat protein of BYMV is 68-76% identical at the amino acid level with the coat protein of ClYVV. BYMV is more distantly related to the legume-infecting potyviruses Bean common mosaic virus, Bean common mosaic necrosis virus, Pea seed-borne mosaic virus and Soybean mosaic virus. In chickpe

24、a, a number of Potyvirus isolates have been described that are similar biologically to BYMV. These include Chickpea yellow mosaic virus and Chickpea bushy dwarf virus which are distinct serologically from BYMV, and Chickpea distortion mosaic virus and Chickpea filiform virus which are related serolo

25、gically to, and may be a strains of Part 2D Page 9BYMV. These appear to be of only minor or localized importance, along with the recognized potyvirus species Lettuce mosaic virus and Turnip mosaic virus (Fig. 2) that have also been reported in chickpea.Disease Cycle and EpidemiologyBYMV has a broad

26、host range of over 200 plant species, predominantly legumes. The virus is acquired from infected weed and perennial plant sources by more than 20 aphid species and transmitted in a non-persistent manner. The most common aphids associated with transmission of BYMV to legume crops are Acyrthosiphon pi

27、sum, Macrosiphum euphorbiae (Thomas), Myzus persicae, Aphis gossypii (Glover) and Aphis fabae, but other species including cereal aphids may be important if present in high numbers. Common sources for the virus in the field include clover (Trifolium spp. and Melilotus albus), vetch (Lathyrus spp.),

28、and alfalfa (Medicago sativa). Consistent with other potyviruses, BYMV is mechanically transmissible. Faba bean (Vicia faba) and pea (Pisum sativum) are common pulse crops that are generally susceptible to BYMV and are also suitable hosts for colonization by aphids, thus providing a ready source of

29、inoculum. A significant reduction in yield can occur in lentil fields when the incidence of BYMV is high.ManagementBYMV is transmitted by seed at levels of up to 1% in lentil but is not reported to be seed-borne in chickpea. Use of lentil seed certified to be free of BYMV will aid in reduction of th

30、e virus within the crop. Maintaining low levels of the virus in surrounding crops and weed hosts can be difficult because of the wide host range of BYMV but spread of the virus can be managed by eliminating local weed hosts. As with other non-persistently transmitted viruses, application of insectic

31、ides to control spread of the virus by aphids is ineffective except where the vector has built up large populations in lentils. No resistance has been identified in chickpea and only a few sources of tolerance have been identified in lentil. Lentil accession ILL7163 has been reported in Australia to

32、 be resistant to BYMV. Selected ReferencesPart 2D Page 10Cheng, Y., and Jones, R. A. C. 2000. Biological properties of necrotic and non-necrotic strains of bean yellow mosaic virus in cool season grain legumes. Ann. App. Biol. 136:215-227.Kaiser, W. J., and Danesh, D. 1971. Etiology of virus-induced

33、 wilt of Cicer arietinum. Phytopathology 61:453-457.Larsen, R. C., Kaiser, W. J., Wyatt, S. D., Buxton-Druffel, K. L., and Berger, P. H. 2003. Characterization of a new potyvirus naturally infecting chickpea. Plant Dis. 87:1366-1371.Makkouk, K. M., Kumari, S. G., and Al-Daoud, R. 1992. Survey of vir

34、uses affecting lentil (Lens culinaris Med.) in Syria. Phytopathol. Mediterr. 31:188-190. Mali, V. R., Polajiwar, B., Nirmal, D. D., and Patil, F. S. 1988. Purification and properties of a virus causing distortion mosaic of chickpea. Indian Phytopath. 41:336-343.McKirdy, S. J., Jones, R. A. C., Latha

35、m, L. J., and Coutts, B. A. 2000. Bean yellow mosaic potyvirus infection of alternative annual pasture, forage, and cool season crop legumes: susceptibility, sensitivity, and seed transmission. Aust. J. Agric. Res. 51:325-345.Schwinghamer, M. W., Thomas, J. E., Parry, J. N., Schilg, M. A., and Dann,

36、 E. K. 2007. First record of natural infection of chickpea by Turnip mosaic virus. Australasian Plant Disease Notes 2:41-43.Shukla, D. D., Ward, C. W., and Brunt, A. A. 1994. The Potyviridae. CAB International, Wallingford, UK.Snyder, W. C., Paulus, A. O., and Gold, A. H. 1956. Virus yellows of garb

37、anzo bean. Phytopathology 46:27.(Prepared by R.C. Larsen and M.W. Schwinghamer)Part 2D Page 11Fig. 1. Shoot tip necrosis in chickpea caused by early infection with Bean yellow mosaic virus (BYMV). (Courtesy R. C. Larsen)Fig. 2. Shoot tip necrosis in seedling chickpea caused by early infection with a

38、 chickpea isolate of Turnip mosaic virus (TuMV), a Potyvirus species related to Bean yellow mosaic virus (BYMV). (Courtesy M. W. Schwinghamer)Part 2D Page 12Cucumber mosaic virusCucumber mosaic virus (CMV) was first described in 1916 and has a large host range that includes over 1000 plant species i

39、n 85 families. It can cause severe losses in lentil during seasons of high aphid populations when infection incidences exceed 50%, but rarely causes significant damage in commercial chickpea crops. SymptomsLentil. Symptoms in lentil include a general chlorosis of the plant, leaf malformation and stu

40、nting (See Fig. 2 in Virus Diseases Introduction), often followed by premature death (Fig. 1). Leaflets may show a mild mosaic or reddening of leaf margins. A reduction in pod number or filling of pods generally occurs resulting in yield loss.Chickpea. For many CMV isolates and chickpea genotypes, s

41、ymptoms are more distinctive than for other virus species in chickpea. The most distinctive feature is internode reduction (Fig. 2), shoot proliferation, and slight stem kinking that can be described as bushy stunting (Fig. 3). Leaflets show pale chlorosis, reduction in size, and sometimes narrowing

42、 and pale mosaic (Fig. 4). Reddening may also occur on leaf margins of Desi chickpea lines. Chickpea seedlings may show necrosis of shoot tips. Plants sometimes die prematurely, but mortality is generally less than for other viruses and small groups of infected plants may persist after surrounding u

43、ninfected ones mature due to less use of soil moisture. Even when plants survive, seed yield is reduced greatly through failure of seed set.Causal AgentCMV is a member of the Family Bromoviridae, Genus Cucumovirus. It has a tripartite genome encapsidated in isometric particles ca. 29 nm in diameter

44、that contain RNA-1 (3389 nucleotides), RNA-2 (3035 nucleotides), or RNA-3 (2197 nucleotides). A sub-genomic RNA-4 is also encapsidated in the particles that contain RNA-3. The coat protein consists of 218 amino acids with a molecular weight of 24.2 kDa. The species has been divided into distinct ser

45、ogroups called subgroups I and II, with the latter comprising 70% of isolates. Phylogenetic analyses have shown that subgroup I can be divided into subgroups IA and IB both of which are distantly related to isolates belonging to subgroup II. CMV is distantly related to other Cucumovirus species Pean

46、ut stunt virus and Tomato aspermy virus.Part 2D Page 13EpidemiologyCMV can survive from year to year in many weed species, or in green vegetation and crops in temperate areas. Perennial legumes such as clover and alfalfa are ready sources of inoculum and many of these hosts may remain symptomless. T

47、he virus is transmitted in a non-persistent manner by many different aphid species. A number of these species including cereal aphids may be important in the case of lentil, but Acyrthosiphon pisum (pea aphid), where present, is likely to be the most important for chickpea. Aphids can acquire the vi

48、rus within a few seconds and transmission can occur in an equally short time period. Infectiveness is lost after brief probing but can be retained for hours by alate aphids if they do not probe. CMV is seed transmitted in lentil and chickpea, forage legumes, and in may weed species. Transmission by

49、seed is erratic in lentil and chickpea but can average 0.1% to 1%, occasionally reaching 2% or higher within seed lots. In chickpea, infected seed does not appear to lead to major losses in commercial crops but major losses have been demonstrated in experimental plots. There is more secondary spread in lentil than in chickpea, and consequently lentil seed infected with CMV can lead to major losses in commercial crops.ManagementCMV in lentil can be controlled by planting certified virus-free seed in localities where other sources of infection