Triticum durum Desf. a Further Host of Barley Mild Mosaic Virus (BaMMV)

After mechanical inoculation by rubbing off with infectious plant sap barley mild mosaic virus (BaMMV) was transmitted to 29 provenances and cultivars of Triticum durum Desf. var. africanum Körn. as well as to the Italian durum wheat cvs ‘Valforte’ and ‘Valnova’. The infected plants reacted partially with distinct mosaic symptoms. BaMMV was detected by ELISA and immunoelectron microscopy.     

THE EFFECT OF TEMPERATURE ON INFECTION WITH STRAINS OF CUCUMBER MOSAIC VIRUS

Cucumber mosaic virus strains differed in their ability to multiply in plants at 37° C. Some strains multiplied in inoculated leaves and produced systemic symptoms in plants at this temperature; plants systemically infected with one such strain remained infected after prolonged treatment at 37° C. Other strains did not appear to multiply in inoculated leaves at 37° C. and heat treatment was successful in freeing plants from infection with these. Tests with one strain of each type showed both to be rapidly inactivated in expressed sap at 37° C.
Strains of cucumber mosaic virus forming small necrotic local lesions in leaves of french bean var. Canadian Wonder, produced many fewer lesions in plants kept after inoculation at 25° C. for 24 hr. and then at 15° C. than in plants kept continuously at the lower temperature.     

Effects of barley yellow mosaic disease resistant gene rym1 on the infection by strains of Barley yellow mosaic virus and Barley mild mosaic virus

Although a Chinese landrace of barley, Mokusekko 3, is completely resistant to all strains of Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV), and is known to have at least two resistant genes, rym1 and rym5, only rym5 has been utilized for BaYMV resistant barley breeding in Japan. In order to clarify the effect of rym1 on BaYMV and BaMMV, and to utilize the gene for resistant barley breeding, the susceptibilities of only rym1 carrying breeding lines against BaYMV and BaMMV were investigated. In the assessment of resistance to BaYMV-I, 341 F(2) populations derived from a cross between the resistant line Y4 with only rym1 and the susceptible cv Haruna Nijo shows that the segregation loosely fits a 1R:3S ratio (0.05 > P > 0.01), suggesting that the resistance is controlled by a single recessive gene, rym1. Further, none of the F(3) lines derived from the nine resistant F(2) plants showed any disease symptoms in the field infected by BaYMV-I. The same nine F(3) lines showed almost the same agronomic characters in the field infected by BaYMV-III as those in the uninfected field, apart from the symptom of showing numerous mosaics. This result indicates that the gene rym1 has an acceptable level of resistance to BaYMV-III. In the assessment of resistance to BaYMV-II, BaMMV-Ka1 and -Na1, an artificial infection method was adopted and the susceptibilities to those viruses were investigated. Although the control varieties, Ko A and Haruna Nijo, were infected with all of them, the rym1 gene carrying BC(2)F(3) lines were completely resistant to all strains. In summary, rym1 is completely resistant to BaYMV-I, -II, BaMMV-Ka1 and -Na1, and has an acceptable level of resistance to BaYMV-III. This study concludes with a discussion of the reason why the important resistance gene rym1 was eliminated along with resistant cultivars during breeding for resistance to BaYMV.     

Responses of some Asian and European barley cultivars to UK and Chinese isolates of soil-borne barley mosaic viruses

In field plots at Yancheng, Jiangsu, China, a range of European and Asian barley cultivars was grown in soil from three sites in China infested with barley yellow mosaic virus (BaYMV). Most of the cultivars resistant to the common European strain of BaYMV were susceptible to the Chinese isolates but cv. Energy remained disease-free. Barley mild mosaic virus (BaMMV) was also detected in one of these soils but affected only one Chinese cultivar and not those susceptible to BaMMV in Europe. This is the first report of BaMMV in China. Inoculation experiments confirmed the different cultivar response to UK and Chinese isolates of BaYMV and showed that resistance was to the virus and not to the vector. A range of Chinese cultivars selected for resistance to BaYMV were also resistant to a UK isolate of BaMMV.     

Mechanical Transmission of Barley Mild Mosaic Virus (BaMMV) to Rye (Secale cereale L.)

After mechanical spraygun inoculation barley mild mosaic virus (BaMMV) was detected in barley cv. ‘Gerbel’ (control) as well as in rye cv. ‘Somro’, but not in wheat cv. ‘Kanzler’ and oat cv. ‘Alfred’. ELISA values of infected barley and rye were similar. Furthermore, infected rye plants developed symptoms typical for barley yellow mosaic virus infection.     

THE PROPERTIES OF TOMATO ASPERMY VIRUS AND ITS RELATIONSHIP WITH CUCUMBER MOSAIC VIRUS*

Chrysanthemum plants infected with tomato aspermy virus (TAV) produce severely distorted and discoloured flowers but show only slight leaf mottle.
TAV infected twenty-five of forty-five species (belonging to seventeen genera) tested and was transmitted by the aphid species Aulacorthum solarti, Macrosiphoniella sanborni and Myzus persicae .
Sap from infected tobacco leaves lost infectivity when diluted more than 1 in 10,000, when heated for 10 min. at above 65°C. and when stored for more than 42 hr. at 16–18°C.
Partial protection was obtained between TAV and two strains of cucumber mosaic virus. Evidence was obtained that this was true protection between related viruses and serological tests confirmed the view that TAV is a strain of cucumber mosaic virus. Evidence was obtained that this was true protection between related viruses and serological tests confirmed the view that TAV is a strain of cucumber mosaic virus.     

Purification and properties of blackberry chlorotic ringspot, a new virus species in subgroup 1 of the genus Ilarvirus found naturally infecting blackberry in the UK

A mechanically transmissible virus was isolated from Bedford Giant blackberry plants showing chlorotic mottling and ringspot symptoms growing in Scotland. It infected several herbaceous test plants, many of them symptomlessly. This virus was also transmitted to several Rubus species and cultivars by graft inoculation with scions from the field‐infected Bedford Giant plant. Most grafted plants were infected symptomlessly, but Himalaya Giant blackberry and the hybrid berry Tayberry developed symptoms similar to those in the infected Bedford Giant plant. In the sap of infected Chenopodium quinoa, the virus lost infectivity when diluted 10^?4 but not 10^?3, after 6 h and 48 h when kept at 20°C and 4°C, respectively, but was infective for more than 8 days when kept at ?15°C. Preparations of purified virus from infected C. quinoa or spinach sedimented as three major nucleoprotein components and consisted of quasi‐isometric particles that varied in size from 24 to 32 nm in diameter and that were not penetrated by negative stain. Such virus particle preparations contained a major polypeptide of ca 28 kDa and three single‐stranded RNA species of estimated size 3.2, 2.8 and 2.1 kb. The complete sequence of the largest RNA (RNA 1, 3478 nt) and the partial sequence of the other RNAs (1863 and 2102 nt long, respectively) were determined and compared with sequences in databases. These findings, together with the biological and biochemical properties of this virus, indicate that it should be regarded as a distinct species in subgroup 1 of the genus Ilarvirus even though it was serologically unrelated to existing members of this subgroup. The virus showed a very distant serological relationship with prune dwarf virus (PDV) but differed significantly from it in the amino acid sequence of its coat protein, experimental host range and symptomatology and was unrelated to PDV at the molecular level. The virus, tentatively named blackberry chlorotic ringspot virus, is therefore a newly described virus and the first ilarvirus found naturally infecting Rubus in the UK.     

Identification of Barley mild mosaic virus Isolates in Germany Breaking rym5 Resistance*

In winter and early spring 2004 unequivocal mosaic symptoms were detected for the first time in Germany on six plants of the barley cv. ‘Tokyo’ carrying the resistance gene rym5. By serological and electron microscopic investigations Barley mild mosaic virus (BaMMV) was identified in all plants and could be re‐transmitted to cv. ‘Tokyo’ as well as to additional cultivars carrying rym5. In contrast to this, genotypes carrying the resistance genes rym1 + rym5, Rym2, rym4, rym7, rym9, rym11, rym12, rym13, Rym14^Hb, rym15 or Rym16^Hb turned out to be resistant. Furthermore, the BaMMV isolates were not transmissible to different dicotyledonous species. Sequence analyses in the VPg coding region of RNA1 revealed differences to the known sequence of the original BaMMV isolate (BaMMV‐ASL1, AJ 242725) and also of a French pathotype (BaMMV‐Sil, AJ 544267, AJ 544268) which is also able to overcome the resistance mediated by rym5. At least in one location a spread of the area infested by this new strain was observed in 2004/2005 and 2005/2006.