Lettuce Virus Research Articles

Citrus psorosis virus RNA 1 is of negative polarity and potentially encodes in its complementary strand a 24K protein of unknown function and 280K putative RNA dependent RNA polymerase

Citrus psorosis virus (CPsV), the type member of genus Ophiovirus, has three genomic RNAs. Complete sequencing of CPsV RNA 1 revealed a size of 8184 nucleotides and Northern blot hybridization with chain specific probes showed that its non-coding strand is preferentially encapsidated. The complementary strand of RNA 1 contains two open reading frames (ORFs) separated by a 109-nt intergenic region, one located near the 5′-end potentially encoding a 24K protein of unknown function, and another of 280K containing the core polymerase motifs characteristic of viral RNA-dependent RNA polymerases (RdRp). Comparison of the core RdRp motifs of negative-stranded RNA viruses, supports grouping CPsV, Ranunculus white mottle virus (RWMV) and Mirafiori lettuce virus (MiLV) within the same genus ( Ophiovirus), constituting a monophyletic group separated from all other negative-stranded RNA viruses. Furthermore, RNAs 1 of MiLV, CPsV and RWMV are similar in size and those of MiLV and CPsV also in genomic organization and sequence.

Occurrence of Mirafiori Lettuce Virus and Lettuce Big-vein Virus in Relation to Development of Big-vein Symptoms in Lettuce Crops

Big-vein disease (BV) of lettuce has been attributed to infection by Lettuce big-vein virus (LBVV), vectored by the soil fungus Olpidium brassicae. The finding of a second soil-borne virus in lettuce, Mirafiori lettuce virus (MiLV), led to a re-investigation of the role of LBVV in big-vein disease, with evidence emerging that both MiLV and LBVV are vectored by O. brassicae, and that MiLV, not LBVV, is the cause of BV (Lot et al. (2002), Phytopathology 92: 288–293). The two viruses have coat proteins of similar size but have different morphologies and are serologically unrelated. We tested individual lettuce plants in BV-prone fields and protected crops in France and Italy for the presence of the two viruses, using DAS-ELISA and antisera specific for each virus. Both MiLV and LBVV were found at high incidence, often together but sometimes separately. Symptoms were frequently found to be associated with MiLV alone or both viruses, but rarely LBVV alone. However, no absolute correlation emerged, because sometimes MiLV was present in the absence of symptoms, and vice versa. To clarify the situation, individual lettuce plants were examined over a period of time in two further surveys. In surveys of protected crops in France, plants with big-vein were always ELISA-positive for MiLV, or else symptomless plants positive for MiLV were later seen to develop big-vein symptoms. Presence or absence of LBVV appeared to have no effect on symptom development. In surveys of open fields in Italy, all combinations were found: presence of both viruses, apparent absence of both viruses, or presence of each one alone, in plants that developed BV. At the end of the observation period, nearly all plants had BV and contained both viruses.

Resistance to Lettuce Big-Vein Disease in Lettuce Cultivars

In a field where lettuce big-vein disease had occurred, the relationship between symptom expression and two viruses associated with the disease (Lettuce big-vein virus and Mirafiori lettuce virus) was investigated in a total of 60 lettuce cultivars (Lactuca saliva L.). Both viruses were detected in all lettuce cultivars. In the crisphead type, the degree of resistance to symptom expression was related to the stage at which the virus was detected, especially with Mirafiori lettuce virus. In the butterhead, cos, stem and red leaf types, both viruses were detected in the early growing stages, while few or no typical symptoms were observed at harvest.

A Mild Systemic Reaction to Lettuce Mosaic Virus in Lettuce: Inheritance and Interaction with an Allele for Resistance

In crosses of lettuce (Lactuca sativa L.) between parents producing a mild or susceptible reaction to lettuce mosaic virus, a single gene segregated. The heterozygote reacted in an intermediate manner. In crosses between mild-reacting and resistant parents, the mild reaction gene and the resistant gene segregated independently. The resistant and mild alleles together produced a new phenotype that is usually symptomless. The gene symbol proposed is Mi'Mi, where Mi' gives the mild phenotype. Breeding is in progress to combine the mild and resistant traits in new lettuce cultivars.

Inheritance and Interactions of Necrotic, Mottled, and Resistant Reactions to Lettuce Mosaic Virus in Lettuce

Segregation data from crosses between necrotic and mottled lettuce (Lactuca sativa L.) parents showed that a single gene controls the difference in type of reaction to lettuce mosaic virus: necrosis is dominant to mottled. Segregation data from crosses between resistant and necrotic parents differed, depending on the necrotic parent. In crosses with the necrotic cultivar Prizehead, there were two independent genes, one controlling necrotic vs. mottled and the other resistant vs. susceptible. In a cross with the necrotic cultivar Maikonig, resistance was epistatic to necrotic, suggesting a second necrotic allele. Crosses among necrotic cultivars indicated a single gene for the necrotic reaction, with the possibility of more than one necrotic allele. Necrotic alleles identified are named Necrotic-1m and Necrotic-1p.

Transmission by Olpidium brassicae of Mirafiori lettuce virus and Lettuce big-vein virus, and Their Roles in Lettuce Big-Vein Etiology

ABSTRACT Big-vein disease occurs on lettuce worldwide in temperate conditions; the causal agent has been presumed to be Lettuce big-vein virus (LBVV), genus Varicosavirus, vectored by the soilborne fungus Olpidium brassicae. Recently, the role of LBVV in the etiology of big-vein disease has been questioned because a second soilborne virus, Mirafiori lettuce virus (MiLV), genus Ophiovirus, has been found frequently in big-vein-affected lettuce. LBVV and MiLV, detectable and distinguishable by enzyme-linked immunosorbent assay using specific antisera, were tested for their ability to be transmitted from lettuce to lettuce by mechanical inoculation of sap extracts, or by zoospores of O. brassicae, and to cause big-vein disease. Both viruses were mechanically transmissible from lettuce to herbaceous hosts and to lettuce, but very erratically. LBVV was transmitted by O. brassicae but lettuce infected with only this virus never showed symptoms. MiLV was transmitted in the same manner, and lettuce infected with this virus alone consistently developed big-vein symptoms regardless of the presence or absence of LBVV. With repeated mechanical transmission, isolates of both viruses appeared to lose the ability to be vectored, and MiLV appeared to lose the ability to cause big-vein symptoms. The recovery of MiLV (Mendocino isolate, from Cali-fornia) from stored O. brassicae resting spores puts the earliest directly demonstrable existence of MiLV at 1990.

The Use of Green Fluorescent Protein-Tagged Recombinant Viruses to TestLettuce mosaic virusResistance in Lettuce

ABSTRACT Seed certification and the use of cultivars containing one of two, probably allelic, recessive genes, mo1(1) and mo1(2), are the principal control methods for Lettuce mosaic virus (LMV) in lettuce. Although for a few LMV isolates, mo1(2) confers resistance with most isolates, the genes mo1(1) or mo1(2) confer a tolerance, and virus accumulation is readily detected in mo1-carrying plants. This phenotype complicates evaluation of the resistance status, in particular for mo1(1), for which there are no viral strains against which a true resistance is expressed. Two green fluorescent protein (GFP)-tagged viruses were constructed, derived from a non-resistance breaking isolate (LMV-0) and from a resistance-breaking isolate (LMV-E). An evaluation of 101 cultivars of known status was carried out with these recombinant viruses. Using the LMV-0-derived recombinant, identification of mo1-carrying cultivars was simple because, contrary to its wild-type parent, systemic movement of LMV-0-GFP was abolished in resistant plants. This assay detected four cases of misidentification of resistance status. In all these cases, further tests confirmed that the prior resistance status information was incorrect, so that a 100% correlation was observed between LMV-0-GFP behavior and the mo1 resistance status. Similarly, the LMV-E-derived recombinant allowed the identification of mo1(2) lettuce lines because its systemic movement was restricted in mo1(2) lines but not in susceptible or in mo1(1) lines. The tagged viruses were able to systemically invade another host, pea, irrespective of its resistance status against another member of the genus Potyvirus, Pea seed-borne mosaic virus. The use of these recombinant viruses could therefore greatly facilitate LMV resistance evaluation and speed up lettuce breeding programs.

An Ophiovirus isolated from lettuce with big-vein symptoms.

Big-vein is a widespread and damaging disease of lettuce, transmitted through soil by the chytrid fungus Olpidium brassicae, and generally supposed to be caused by Lettuce big-vein virus (LBVV; genus Varicosavirus). This virus is reported to have rigid rod-shaped particles, a divided double-stranded RNA genome, and one capsid protein of 48 kD, but has not been isolated or rigorously shown to cause the disease. We provide evidence that a totally different virus, here named Mirafiori lettuce virus (MiLV), is also very frequently associated with lettuce showing big-vein symptoms. MiLV was mechanically transmissible from lettuce to Chenopodium quinoa and to several other herbaceous test plants. The virus was partially purified, and an antiserum prepared, which did not react with LBVV particles in decoration tests. As reported for LBVV, MiLV was labile, soil-transmitted and had a single capsid protein of 48 kD, but the particles morphologically resembled those of ophioviruses, and like these, MiLV had a genome of three RNA segments approximately 8.5, 1.9 and 1.7 kb in size. MiLV preparations reacted strongly in Western blots and in ISEM with antiserum to Tulip mild mottle mosaic virus, an ophiovirus from Japan also apparently Olpidium-transmitted. They reacted weakly but clearly in Western blots with antiserum to Ranunculus white mottle virus, another ophiovirus. When lettuce seedlings were mechanically inoculated with crude or partially purified extracts from MiLV-infected test plants, many became systemically infected with MiLV and some developed big-vein symptoms. Such plants did not react in ELISA using an LBVV antiserum or an antiserum to tobacco stunt virus, and varicosavirus-like particles were never seen in them in the EM after negative staining. We conclude that MiLV is a hitherto undescribed virus assignable to the genus Ophiovirus. The cause or causes of lettuce big-vein disease and the properties of LBVV may need to be re-evaluated in light of our results.

Rotavirus and Hepatitis A virus in market lettuce ( Latuca sativa) in Costa Rica

We assessed the presence of rotavirus and Hepatitis A virus in lettuce bought in farmer markets from San José, Costa Rica, during months of low (April–June) and high (December–January) incidence of diarrhea associated with rotavirus, respectively. Lettuce samples were pooled and evaluated for rotavirus by enzyme-linked immunosorbent assay (ELISA) and for Hepatitis A virus by radioimmunoassay, polymerase chain reaction (PCR) and electron microscope. Three sample pools, collected during the period of high prevalence of diarrhea, were positive for rotavirus by ELISA and in one of them rotavirions were visualized by electron microscopy. Two samples pools collected during the same period were positive for Hepatitis A virus as shown by PCR. In almost all the pools fecal coliform bacteria were detected by cultivation and bacteriophages were visualized by electron microscopy.

Seasonal Cropping Pattern Effects on Abundance of Bemisia tabaci (Homoptera: Aleyrodidae) and Incidence of Lettuce Infectious Yellows Virus

The sweetpotato whitefly, Bemisia tabaci (Gennadius), was trapped throughout the southern desert agricultural region of California during two consecutive growing seasons. Trap data revealed changes in whitefly population densities that provide insight into the epidemiology of lettuce infectious yellows virus (LIYV) in fall melon and lettuce. Whitefly abundance increased rapidly from July to September in cotton. During that period, there were significant correlations between number of cotton fields in a region and number of whiteflies trapped in that region. Beginning in August and September, whitefly densities increased in melon, and the proportion of viruliferous whiteflies increased in cotton and melon. After the defoliation of cotton was initiated in September, whiteflies migrated to melons, which not only served as their host but also as a reservoir for LIYV. In October and November high numbers of viruliferous whiteflies were found in melon and lettuce. As melons were harvested and the fields dried, viruliferous whiteflies migrated to newly emerged lettuce.

Effects of some biotic and abiotic factors on symptom expression of lettuce big-vein virus in lettuce (Lactuca sativa)

SummaryA nutrient film technique (NFT) system was developed to infect lettuce plants with an isolate of Olpidium brassicae carrying lettuce big-vein virus (LBVV) and to examine the effect of some biotic and abiotic factors on symptom expression of the virus. The NFT system had the advantage of removing any effects due to variation in moisture and allowed continuous and natural infection of test plants. The developmental stage of lettuce plants (5 true leaves) and duration of exposure to inoculum (4 wk) in the NFT system that induced most severe symptoms were determined. Within the temperature range previously reported to favour symptom expression of LBVV (14–18°C), significant differences in symptom severity were detected. Despite previous reports that low temperatures favour symptom expression, the most severe symptoms were induced in the shortest time at 18°C. Compared with diurnal temperature regimes of 10°C night and 18°C day, plants kept at constant 18°C developed more severe symptoms more rapidly. S...

Identification of Resistance to Tomato Spotted Wilt Virus in Lettuce

Identification of Resistance to Tomato Spotted Wilt Virus in Lettuce

Genetics of resistance to beet western yellows virus in lettuce

Resistance to beet western yellows virus (BWYV) in the lettuce cultivars Burse 17 and Crystal Heart was controlled by a single recessive gene designated bwy. ELISA tests showed that resistant plants were not immune to infection by BWYV, and may develop some mild symptoms. However, the concentration of virus found in resistant plants was less than in susceptible ones. The cultivar Crystal Heart is being used as a source of resistance for breeding BWYV‐resistant crisp lettuce (iceberg) cultivars.

Location of lettuce mosaic virus in mature lettuce seed tissues by immunogold cytochemistry.

Lettuce mosaic potyvirus (LMV) antigen was readily detected with imnunogold labelling in thin sections of the cells of the cotyledons, radicle, hypocotyl and endosperm of lettuce seed. This is the first report of the detection of LMV in the endosperm of lettuce seed.

Studies on resistance to beet western yellows virus in lettuce (Lactuca sativa) and the occurrence of field sources of the virus

An effective method based on glasshouse and field procedures was developed for screening commercial cultivars and other lettuce types for resistance to beet western yellows virus (BWYV). Field experiments in 1985, 1986 and 1987 showed that lettuce cultivars varied in their reaction to BWYV, but no high levels of resistance were identified in the main commercial types. Crisp types generally showed milder symptoms than butterhead or cos types, but individual butterhead cultivars were identified with resistance equal to the best crisp types. The highest levels of resistance were identified in Batavian type cultivars and extreme resistance or possible immunity was found in Lactuca perennis and L. muralis. BWYV caused yield reductions in some cultivars as high as 63% and reduced maturation by up to 38%, in others. There was no correlation between chlorotic leaf symptom severity and yield reduction.BWYV was isolated from a range of weed and non‐lettuce host species growing near affected lettuce crops. Isolates of BWYV obtained from infected lettuce and brassicas appeared to be similar. They infected sugar beet with difficulty but caused no symptoms, and could only be detected by ELISA serology.

Resistance to Tomato Spotted Wilt Virus in Lettuce

Abstract Tomato Spotted Wilt Virus (TSWV), a thrips-transmitted virus disease, has become a limiting factor in lettuce (Lactuca sativa L.) production throughout Hawaii and several other areas of the world. In this study, two partially resistant lettuce cultivars, Tinto and PI 342517 (‘Ancora’), were crossed with the susceptible check cultivar Green Mignonette and to each other. Results of resistance tests of the F1 and F2 plants suggest that ‘Tinto’ and PI 342517 have the same genes for resistance and that this resistance is partially dominant.

Incidence of Broad Bean Wilt Virus in Lettuce in New York State and Sources of Resistance

Abstract A 6-year (1975-1980) survey established that broad bean wilt virus (BBWV) was second only to cucumber mosaic virus (CMV) in causing destructive diseases in leading lettuce cultivars grown in New York State. Conversely, the widespread usage of certified seed had drastically reduced the occurrence of lettuce mosaic virus (LMV). Screening for resistance revealed that a number of accessions of Lactuca sativa and a few of L. virosa were tolerant to BBWV. Tolerant plants, although infected with the virus, remained symptomless or responded with a mild and often transient chlorotic mottle.

New plant disease records in New Zealand: Arabis mosaic virus in celery, lettuce, and Chinese cabbage; tomato spotted wilt virus in celery

Abstract New hosts in New Zealand are reported for arabis mosaic (ArMV) and tomato spotted wilt (TSWV) viruses. Celery and lettuce crops in the Heathcote Valley, Christchurch were found infected with ArMV, and some celery plants were also infected by TSWV. ArMV infection foci within the crops corresponded to sites previously planted with apricot trees|the nematode vector Xiphinema diversicaudatum (Micol.) occurred in soil under infected plants. ArMV was also found in Chinese cabbage near Pukekohe.

Reflective Mulches and Foliar Sprays for Suppression of Aphid-borne Viruses in Lettuce

Field tests indicated that reflective mulches repelled alate aphids and reduced incidence of cucumber mosaic virus (CMV) in late-planted lettuce but did not adequately suppress wingless aphids. Acephate, pirimicarb, demeton, and to a lesser extent, parathion, controlled apterous aphids but did not significantly reduce virus transmission. Oil sprays (2.5%) did not reduce CMV incidence or suppress aphid populations. Yellow pan water traps showed that peak aphid flights occurred in August and Myzus persicae (Sulzer) was the predominating vector on the lettuce. CMV and trace amounts of broad bean wilt virus and lettuce mosaic virus were detected in infected lettuce by using either differential symptoms produced on the host range indicator, visualization of virus particles in an electron microscope, or serology.

Cucumber mosaic virus in lettuce

Abstract Cucumber mosaic virus causes a severe disease in lettuce, symptoms consisting of yellowing, necrosis, and stunting. The virus has been isolated from lettuce crops at Christchurch, Otaki, Palmerston North, Feilding, and Mangere.