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
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