Transmissibility of Broad bean wilt virus 1 by aphids: influence of virus accumulation in plants,virus genotype and aphid species

Broad bean wilt virus 1 (BBWV‐1) is transmitted by several aphid species in a non‐persistent manner. Transmission efficiency by vectors is a key factor for understanding virus epidemiology and applying disease control measures based on limiting virus spread. We evaluated the transmission rates of two genetically divergent BBWV‐1 isolates (PV‐132 from USA and Ben from Spain) infecting broad bean (Vicia faba L.) by isofemale lines of nine aphid species from eight different genera collected in Spain. Our analyses showed that: (a) the virus concentration in the source plant was a key factor in BBWV‐1 transmissibility; (b) The Spanish isolate Ben was transmitted more efficiently than the American isolate PV‐132 by most aphid species, but this was only due to the higher accumulation of Ben in plants, as both isolates had similar transmissibility after adjusting virus concentration and (c) The transmission rate varied greatly between the different aphid species.     

蚕豆萎蔫病毒2号分离物侵染对蚕豆叶片光合活性和叶绿体超微结构的影响

研究了受蚕豆萎蔫病毒2号（Broad bean wilt virus 2,BBWV2）中国分离物B935和欧洲分离物PV131侵染的蚕豆（Vicica faba）叶片光合特性、叶绿素荧光诱导动力学参数和叶绿体超微结构变化。感病蚕豆叶绿素含量减少,叶绿素a／b比逐步降低;光合气体交换参数Pn值和Gs值降低,Ci值升高;叶绿素荧光诱导动力学参数Fv/Fm、FV＇/Fm＇、ΦPSII、qP值均有不同程度降低,NPQ值升高;光合器结构遭到不同程度的破坏,B935侵染后叶绿体发育不良,片层结构疏松,PVl31侵染后叶绿体肿胀变圆,片层结构疏松瓦解。与B935相比,PV131侵染对以上各参数的变化有更大影响,且对叶绿体的破坏更为严重。实验结果表明BBWV2不同分离物对光系统II（PSII）的抑制作用与光合器受损程度相关。     

Lamium mild mosaic virus: a virus distantly related to broad bean wilt

Lamium mild mosaic virus (LMMV) was compared with some strains of broad bean wilt virus (BBWV). It differed somewhat in host range from BBWV; serologically, it was only distantly related to four strains of BBWV, all belonging to serotype I, but no reaction was detected with serotype II. BBWV and LMMV were not serologically related to six comoviruses. Like BBWV, LMMV sedimented in three components and the two viruses were morphologically indistinguishable, but LMMV had more slowly migrating RNAs and coat proteins. No distinctive pathological changes were seen in LMMV infected cells. It is proposed that LMMV be considered a distinct virus from BBWV but included with it in a new group of plant viruses.     

Estimation of residual N effect of faba bean and pea on two succeeding cereals using15N methodology

A field experiment was conducted using¹⁵N methodology to study the effect of cultivation of faba bean (Vicia faba L.), pea (Pisum sativum L.) and barley (Hordeum vulgare L.) on the N status of soil and their residual N effect on two succeeding cereals (sorghum (Sorghum vulgare) followed by barley). Faba bean, pea and barley took up 29.6, 34.5 and 53.0 kg N ha^–1 from the soil, but returned to soil through roots only 11.3, 10.8 and 5.7 kg N ha^–1, respectively. Hence, removal of faba bean, pea and barley straw resulted in a N-balance of about –18, –24, and –47 kg ha^–1 respectively. A soil nitrogen conserving effect was observed following the cultivation of faba bean and pea compared to barley which was of the order of 23 and 18 kg N ha^–1, respectively. Cultivation of legumes resulted in a significantly higher A_N value of the soil compared to barley. However, the A_N of the soil following fallow was significantly higher than following legumes, implying that the cultivation of the legumes had depleted the soil less than barley but had not added to the soil N compared to the fallow. The beneficial effect of legume cropping also was reflected in the N yield and dry matter production of the succeeding crops. Cultivation of legumes led to a greater exploitation of soil N by the succeeding crops. Hence, appreciable yield increases observed in the succeeding crops following legumes compared to cereal were due to a N-conserving effect, carry-over of N from the legume residue and to greater uptake of soil N by the succeeding crops when previously cropped to legumes.     

Characterisation and serology of virus-like particles associated with faba bean necrotic yellows

A disease showing chlorosis, leaf rolling and stunting in Vicia faba and other legumes was observed in West Asia and North Africa during 1987–1988. The putative causal agent could not be transmitted mechanically, but could be transmitted by aphids, most efficiently by Acyrthosiphon pisum, in the persistent manner. Further studies revealed isometric virus-like particles (VLPs) closely associated with the disease, although their infectivity could not be demonstrated by membrane feeding. These particles, measuring c. 18 nm in diameter and containing a capsid protein of about 22 kDa and ssDNA of about 1 kb, are hereafter designated faba bean necrotic yellows virus (FBNYV). A high proportion of circular nucleic acid molecules of about 0.9 kb were visualised by electron microscopy. Hybridisation analysis of cloned viral DNA suggests that the circular genome is larger than 1 kb and consists of several components of similar size. An antiserum produced against FBNYV was used in ELISA, immunoelectron microscopy (IEM) and Western blot experiments for virus detection in aphids and field samples and for serological comparison with other viruses. Weak heterologous reactions between FBNYV and subterranean clover stunt virus (SCSV) were detected in IEM, but could not be confirmed in ELISA or Western blots. No serological relationship to banana bunchy top virus (BBTV) was detected. Using a direct tissue blot immunoassay (TBIA), FBNYV was detected in vascular tissue of infected faba bean leaves and stems.     

First Report of AG-A of Binucleate Rhizoctonia in China, Pathogenic to Soya Bean, Pea, Snap Bean and Pak Choy

Twenty binucleate Rhizoctonia (BNR) isolates were collected from roots of soya bean, pea, snap bean and pak choy with root rot symptoms in Yunnan Province, China. Chinese isolates anastomosed with the tester isolate of anastomosis group‐A (AG‐A; C‐517) with a high C2 fusion rate (>70%). Chinese isolates were pathogenic to soya bean, pea, snap bean and pak choy and had 97% similarity sequence of 5.8S rDNA‐internal transcribed spacer with AG‐A tester isolates SN‐2 and C‐662. When compared with other groups, AG‐Ba and AG‐Bb, Chinese isolates showed 77% sequence similarity. These results show that Chinese isolates belong to AG‐A of BNR. Growth rate, hyphal diameter, cultural characteristics and pathogenicity of the Chinese isolates differed significantly from the tester isolate of AG‐A. This is the first report on AG‐A in China.     

Arabis mosaic and Prunus necrotic ringspot viruses in hop (Humulus lupulus L.)

Purified virus preparations made from nettlehead-diseased hop plants, or from Chenopodium quinoa, to which the virus was transmitted by inoculation of sap, contained polyhedral virus particles of 30 mμ diameter which were identified serologically as arabis mosaic virus (AMV). There were serological differences between AMV isolates from hop and from strawberry, and also differences in host range and in symptoms caused in C. quinoa and C. amaranticolor. AMV was always associated with nettlehead disease. The nematode Xiphinema diversicaudatum occurred in small numbers in most hop gardens, but was numerous where nettlehead disease was spreading rapidly. Preparations from nettlehead-affected hops also contained a second virus, serologically related to Prunus necrotic ringspot virus (NRSV), in mild and virulent forms which infected the same range of test plants but showed some serological differences. Mild isolates did not protect C. quinoa plants against infection by virulent isolates. Hop seedlings inoculated with virulent isolates of NRSV developed symptoms indistinguishable from those of split leaf blotch disease. Latent infection with NRSV was prevalent in symptomless hop plants. Nettlehead disease is apparently associated with dual infection of AMV and virulent isolates of NRSV. An unnamed virus with rod-shaped particles 650 mμ long was common in hop and was transmitted by inoculation of sap to herbaceous plants. Cucumber mosaic virus was obtained from a single plant of Humulus scandens Merr.     

Identification of viruses isolated from plum trees affected by decline, line-pattern and ringspot diseases

Viruses obtained from plum trees infected with either decline, line-pattern or ringspot diseases were characterized and identified. All the viruses were serologically related to Prunus necrotic ringspot virus (NRSV); those from trees with decline or ringspot were serologically indistinguishable from cherry strains of NRSV but differed in pathogenicity, whereas the virus from trees with line pattern was closely related to apple mosaic virus. When returned from herbaceous hosts to Prunus, line-pattern and ringspot isolates reproduced symptoms characteristic of the diseased sources. One virus isolate from trees with decline diminished the vigour of young plum trees. Comparison with other investigations shows that at least two unrelated viruses cause plum line-pattern disease in America and Europe.     

Verticillium wilt of pea (Pisum sativum)

A wilt disease of garden pea (Pisum sativum) caused by Verticillium dahliae is described and the range of pathogenicity of the isolate investigated. It is pathogenic to potato, sweet pea, antirrhinum and broad bean and isolates of V. dahliae from potato, lucerne and sweet pea and V. albo-atrum from lucerne are pathogenic to pea. Since the most common disease symptoms, acropetal progression of chlorosis and necrosis of the leaves followed by premature defoliation are indistinguishable from natural senescence, it is probable that disease and senescence symptoms are confused in the field. The premature defoliation results in marked reduction in green leaf area, leaf dry weight and pod yield.     

Biological properties of necrotic and non-necrotic strains of bean yellow mosaic virus in cool season grain legumes

A collection of 51 bean yellow mosaic virus (BYMV) isolates was transmitted from infected Trifolium subterraneum (subterranean clover) to Lupinus angustifolius (narrow‐leafed lupin) by Myzus persicae (green peach aphid). Depending on isolate and L. angiistifolius genotype used, two distinct responses developed in L. angustifolius plants, either systemic necrosis and plant death or non‐necrotic reactions of varying severity. Ten isolates caused necrosis and plant death in cv. Danja. However, when nine of these were inoculated to breeding line 90L423‐07‐13, seven induced non‐necrotic reactions, while two caused necrosis and plant death. Thirty seven isolates always produced non‐necrotic reactions regardless of genotype of L. angustifolius inoculated. Non‐necrotic and necrotic isolates originally came both from lupins and other species, and the non‐necrotic isolates were no less efficiently transmitted by M. persicae than the necrotic ones. When one isolate of each type was inoculated together to T. subterraneum and nine months later this culture was used as an acquisition source for aphid transmission to L. angustifolius, only the necrotic type was detected. Previous infection of L. angustifolius plants with a non necrolic isolate prevented subsequent infection by a necrotic one. All necrotic and non‐necrotic isolates reacted with BYMV antiserum in ELISA but only two cross‐reacted with antiserum to clover yellow vein virus (CYVV). When selected necrotic and non‐necrotic isolates were inoculated to differential hosts, all behaved like BYMV and not CYVV. When three isolates of each type were transmitted to 11 other cool season grain legume species, except in Cicer arietinum (chickpea), there were no necrotic reactions, but symptom severity varied with the isolate and species inoculated. The two isolates that caused necrosis in C. arietinum did not do so in L. angustifolius. The six isolates from Vicia faba (faba bean) all caused non‐necrotic reactions in L. angustifolius cv. Danja and 90L423‐07‐13. These and two necrotic isolates readily infected five genotypes of V. faba always causing severe symptoms. However, three non‐necrotic isolates from L. angustifolius and a further necrotic isolate were poorly infectious on V. faba in which they generally induced mild symptoms. These results show that at least three strain groups of BYMV can be distinguished by their reactions in different L. angustifolius genotypes, one causing necrosis and death in cv. Danja and 90L423‐07‐13, one causing necrosis and death in Danja but not 90L423‐07‐13, and one causing non‐nccrotic reactions in both. These strain groups could not be distinguished when representative necrotic and non‐necrotic isolates were inoculated to other grain legume species. However, inoculation to V. faba distinguished two other BYMV strain groupings differing in severity of symptoms and ability to infect this species.     

Genetic Variation Among and Within Uromyces Species Infecting Legumes

Genetic variation of 30 different Uromyces isolates collected on faba bean, lentil, common vetch, pea, chickpea, alfalfa, cowpea and lupin was studied. Random Amplified Polymorphic DNA markers were used showing clear differences among Uromyces species. Uromyces viciae-fabae isolates clustered according to the host, with a clear cluster including all U. viciae-fabae ex Vicia faba isolates. The U. viciae-fabae ex Lens culinaris isolate was the nearest to the cluster of U. viciae faba ex V. faba isolates, followed by U. pisi from Canada and U. viciae-fabae ex V. sativa . No association was found among molecular diversity and virulence or geographic origin within U. vicia-fabae ex V. faba isolates. Among the three U. pisi isolates considered, a great variability was observed and no grouping could be established. The most different isolate from the rest of species considered was U. striatus , followed by U. vignae . The two U. ciceris-arietini isolates clustered together and so did the two U. lupinicolus isolates.     

Properties of a host range and coat protein variant of broad bean true mosaic comovirus from Vicia faba

Unlike other described isolates of broad bean true mosaic comovirus (BBTMV), a variant, code name SB, infected some non-leguminous plant species and, in N. benthamiana, induced systemic mottling and puckering of the leaves. However, like other described BBTMV isolates, purified SB particle preparations contained isometric particles c. 28 nm in diameter that sedimented as two nucleoprotein components with S_{20, w} values of 90S and 109S; some preparations occasionally contained a component of c. 50S. Virus particles contained two ssRNA species which, when denatured in glyoxal, had estimated M_T values of 2.1 × 10⁶ and 1.3 × 10⁶ and co-electrophoresed with cowpea mosaic virus RNA-1 and RNA-2 respectively. Isolate SB was serologically indistinguishable from British and German isolates of BBTMV. However, SB virus particles contained a major polypeptide (L) of M_r between c. 31 000 and up to three minor ones (S) or M_r between c. 20 000 and 24 000. This contrasts with protein preparations from other BBTMV isolates that typically contain only two polypeptides of M_r c. 37 000 (L) and 21 000 (S). Following isopycnic centrifugation in CsCl, SB particles purified from pea separated into two major components with densities of 1.39 and 1.44 g cm^-3 and a minor component of estimated density 1.43 g cm^-3. In Cs₂SO₄, virus preparations separated into three major components with densities of 1.30, 1.32 and 1.36 g cm^-3 and a minor one of density 1.27 g cm^-3. In CsCl isopycnic gradients, SB particles purified from TV. benthamiana separated into two components with densities of 1.38 and 1.43 g cm^-3. During immuno-electrophoresis in agarose gels, freshly prepared virus and preparations stored for up to 4 days at 4°C contained a single component that migrated rapidly to the anode, whereas similar preparations of an English isolate of BBTMV migrated as a single component that moved only slowly toward the anode but which, within 48 h, contained an additional component with a migration rate similar to that of isolate SB. Isolate SB is therefore a host range variant of BBTMV which, in comparison with previously described isolates of BBTMV, has an increased negative charge of its particles prior to any appreciable degradation of its S protein, and S protein that is degraded less rapidly. These features probably account for the anomalies observed in isopycnic centrifugation.     

Integrated control of root rot and wilt disease of faba bean by soil amendment with suppressive compost in combination with seed coating with an antagonistic yeast

For this study, 21 isolates of fungi belonging to Rhizoctonia and Fusarium genera were isolated from the diseased faba bean plants, obtained from the different localities in Assiut governorate, showing root rot and wilt symptoms. The isolates proved to be pathogenic on Masr 1 faba bean cultivar under greenhouse conditions. F. oxysporum isolates caused wilt disease; however, the isolates of R. solani and other Fusarium species caused root rot. The virulence of isolates on the tested faba bean cultivar was different. The highly pathogenic isolates of these fungi were employed in this study. The effect of soil amendment with Planta Rich and Rich Composts (CMs) alone or in combination with seed coating by the antagonistic yeast Pichia guilliermondi before sowing on the severity of Rhizoctonia and Fusarium root rot and Fusarium wilt of faba bean was tested under greenhouse and field conditions. The tested isolates of yeast proved to be highly antagonistic to the pathogen in vitro. The test rates of CMs were equivalent to 2, 7, 10 and 14 ton/feddan in the greenhouse and 7 and 10 t/feddan in the field conditions. Uncomposted soil was used as a control. The results showed that the tested CMs have a suppressive effect on the severity of root rot and wilt diseases of faba bean under greenhouse and field conditions. The application of CMs (Planta Rich and Rich) alone at the rates equivalent to 2, 7, 10 and 14 t/feddan in greenhouse and 7 and 10 t/feddan in the field conditions to the soil infested with the tested pathogens reduced percentage of the tested diseases compared with uncomposted soil. Combined CMs treatments with yeast seed treatment increased the suppressive effect of CMs on the disease severity.     

Transmission characteristics and some other properties of bean yellow vein-banding virus, and its association with pea enation

Bean yellow vein-banding virus (BYVBV) has been found occasionally in mixed infection with pea enation mosaic virus (PEMV) in spring-sown field beans (Vicia faba minor) in southern England. Glasshouse tests confirmed that, like PEMV, BYVBV is transmissible by manual inoculation and by aphids in the persistent manner. However, BYVBV can be transmitted by aphids only from plants that are also infected with a helper virus, usually PEMV. Thus after separation from PEMV by passage through Phaseolus vulgaris it was no longer aphid-transmissible. It became aphid-transmissible again only after re-mixing in plants with PEMV or with a substitute helper, bean leaf roll virus (BLRV). It was not transmitted by aphids that fed sequentially on plants singly infected with PEMV and BYVBV. Thus the interaction between BYVBV and PEMV (or BLRV) that enables BYVBV to be transmitted by aphids seems to occur only in doubly infected plants. However, it was not transmitted by aphids from plants doubly infected with BYVBV and broad bean wilt virus (BBWV). BYVBV and PEMV were transmitted more readily by Acyrthosiphon pisum than by Myzus persicae; neither virus was transmitted by Aphis fabae. Phenol extracts of BYVBV-infected leaves were more infective than phosphate buffer or bentonite-clarified extracts and were sometimes infective when diluted to 1/1000. The infectivity of BYVBV in phosphate buffer extracts of leaves singly infected with BYVBV, unlike that in extracts of leaves doubly infected with BYVBV and PEMV (or BLRV), was destroyed by treatment with organic solvents. BYVBV infected 11 of 28 plant species that were inoculated with phenol extracts; seven of the infected species were legumes. No transmission of BYVBV was detected through seed harvested from infected field bean plants. Isometric particles c. 30 nm in diameter were seen in extracts of plants doubly infected with BYVBV and PEMV but not in extracts of plants infected with BYVBV alone. Leaves of plants infected with BYVBV, alone or with PEMV, contained membrane-bound structures c. 50–90 nm in diameter associated with the tonoplast in cell vacuoles. These structures were not found in healthy leaves. BYVBV has several properties in common with other known aphid-borne viruses that are helper-dependent and transmitted in a persistent manner. Possibly, as suggested for some of them, aphid transmission of BYVBV depends on the coating of its nucleic acid with helper virus coat protein.     

Soil moisture and potassium affect the performance of symbiotic nitrogen fixation in faba bean and common bean

Potassium (K) is reported to improve plant's resistance against environmental stress. A frequently experienced stress for plants in the tropics is water shortage. It is not known if sufficient K supply would help plants to partially overcome the effects of water stress, especially that of symbiotic nitrogen fixation which is often rather low in the tropics when compared to that of temperate regions. Thus, the impact of three levels of fertilizer potassium (0.1, 0.8 and 3.0 mM K) on symbiotic nitrogen fixation was evaluated with two legumes under high (field capacity to 25% depletion) and low (less than 50% of field capacity) water regimes. Plants were grown in single pots in silica sand under controlled conditions with 1.5 mM N (¹⁵N enriched NH₄NO₃). The species were faba bean (Vicia faba L.), a temperate, amide producing legume and common bean (Phaseolus vulgaris L.), a tropical, ureide producing species. In both species, 0.1 mM K was insufficient for nodulation at both moisture regimes, although plant growth was observed. The supply of 0.8 or 3.0 mM K allowed nodulation and subsequent nitrogen fixation which appeared to be adequate for respective plant growth. High potassium supply had a positive effect on nitrogen fixation, on shoot and root growth and on water potential in both water regimes. Where nodulation occurred, variations caused by either K or water supply had no consequences on the percentage of nitrogen derived from the symbiosis. The present data indicate that K can apparently alleviate water shortage to a certain extent. Moreover it is shown that the symbiotic system in both faba bean and common bean is less tolerant to limiting K supply than plants themselves. However, as long as nodulation occurs, N assimilation from the symbiotic source is not selectively affected by K as opposed to N assimilation from fertilizer.     

High temperature effects on photosynthesis and water relations of grain legumes

Effects of high temperature on photosynthesis, and its interaction with water relations in common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), faba bean (Vicia faba), and five cultivars of field pea (Pisum sativum) were investigated. Responses of all species were compared at 20/15, 30/15, or 30/25 °C day/night, and cowpea and pea were compared at 20/15 and 30/25 °C under well-watered and limited-water conditions. Response of pea to 20/15 and 30/25 °C during flowering was ascertained, and sensitivity of the photosystem of pea and faba bean to 40 °C was determined.High temperature decreased chlorophyll variable fluorescence (F_v), a measure of injury to photosynthesis, in all species except cowpea, which was highly tolerant. Leaf chlorophyll and most measures of growth were favored by high day temperature but not by high night temperature, and photosynthetic rates were enhanced by high temperatures that increased leaf chlorophyll and nitrogen (N) contents. High temperature diminished growth less than water deficiency and increased water use of all three species but only lowered the water potential in faba bean. Water deficiency generally decreased growth, water use, and water potential more at 30/25 °C than at 20/15 °C. Stress from high temperature during flowering of pea decreased all components of yield at maturity, particularly at nodes that flowered latest. Whole-chain photosynthetic activity in thylakoids of pea, faba bean, and wheat (Triticum aestivum) were equally sensitive to high temperature, suggesting that Photosystem Il was the most labile component. The results show that high temperature affects photosynthesis, growth, and water relations of grain legumes, and sensitivity to the stress differs among species and genotypes.     

Rapid detection and serotyping of prunus necrotic ringspot virus in perennial crops by enzyme-linked immunosorbent assay

Strains of prunus necrotic ringspot virus (NRSV) in hop and plum cultivars were rapidly and conveniently detected and serotyped by enzyme-linked immunosorbent assay. Antisera produced against the G isolate of NRSV from cherry and the Paradise isolate of apple mosaic virus (ApMV) from apple were used concurrently to ensure detection of all serotypes and to differentiate between them. Both NRSV and ApMV serotypes occurred in plum either as single or mixed infections. By contrast, the NRSV serotype was not found in hop, which contained either ApMV or a serotype intermediate between NRSV and ApMV.     

Nitrogen Fixation of Faba Bean (Vicia faba L.) Interacting with a Non-legume in Two Contrasting Intercropping Systems

A field experiment was carried out to quantify biological nitrogen fixation (BNF) using the ¹⁵N isotope natural abundance method in maize (Zea mays L.)/faba bean (Vicia faba L.) and wheat (Triticum aestivum L.)/faba bean intercropping systems. Faba bean was yielding more in the maize/faba bean intercropping, but not in the wheat/faba bean intercropping. Biomass, grain yield and N acquisition of faba bean were significantly increased when intercropped with maize, and decreased significantly with wheat, irrespective of N-fertilizer application, indicating that the legume could gain or lose productivity in an intercropping situation. There was yield advantage of maize/faba bean intercropping, but no in wheat/faba bean intercropping. The grain yield of the faba bean intercropped with maize was greater than that of faba bean monoculture due to increases of the stems per plant and the pods per stem of faba bean. N fertilization inhibited N fixation of faba bean in maize/faba bean and wheat/faba bean intercropping and faba bean monoculture. The responses of different cropping systems to N-fertilizer application, however, were not identical, with competitive intercropping (wheat/faba bean) being more sensitive than facilitative intercropping (maize/faba bean). Intercropping increased the percentage of N derived from air (%Ndfa) of the wheat/faba bean system, but not that of the maize/faba bean system when no N fertilizer was applied. When receiving 120 kg N/ha, however, intercropping did not significantly increase %Ndfa either in the wheat/faba bean system or in the maize/faba bean system in comparison with faba bean in monoculture. The amount of shoot N derived from air (Ndfa), however, increased significantly when intercropped with maize, irrespective of N-fertilizer application. Ndfa decreased when intercropped with wheat, albeit not significantly at 120 kg N/ha. Ndfa was correlated more closely with dry matter yield, grain yield and competitive ratio, than with %Ndfa. This indicates that that total dry matter yield (sink strength), not %Ndfa, was more critical for the legume to increase Ndfa. The results suggested that N fixation could be improved by yield maximization in an intercropping system.     

Properties of spinach yellow mottle, a distinctive strain of tobacco rattle virus

A virus (isolate SYM) obtained from spinach plants in England with a severe yellow mottle disease induced symptoms resembling those of tobacco rattle virus (TRV) in several indicator species but caused systemic necrosis in Chenopodium amaranticolor and C. quinoa. It was transmitted to bait plants grown in soil containing the nematode Trichodorus primitivus. Purified virus preparations contained rod-shaped particles that were predominantly of four modal lengths: 188 nm (L particles), 101 nm (S particles), 57 nm and 48 nm (together called VS particles), containing RNA with mol. wts of 2.4, 1.5, 0.7 and 0.6 million, respectively. L particles (s°₂₀= 300 S) and S particles (230 S) greatly outnumbered VS particles (c. 150 S). All particles contained a single polypeptide species with estimated mol wt of 24 700, slightly larger than those previously reported for tobraviruses. Purified L particles were infective but both L and S particles were needed to induce the production of virus nucleoprotein particles. VS particles were not infective and apparently had no qualitative or quantitative effect on infection by L or by L plus S particles. S particles carried determinants for serological specificity and ability to invade C. amaranticolor systemically. Isolate SYM produced pseudo-recombinants with isolate PRN of TRV. Also, isolates CAM, OR and PRN of TRV, and isolate SYM, were found to be distantly related by three kinds of serological test. No relationship was detected between these isolates and pea early-browning virus in gel-diffusion precipitin tests or electron microscope serological tests, but a distant relationship between isolate SYM and pea early-browning virus was found by micro-precipitin tests. Isolate SYM therefore has closer affinities with TRV than with pea early-browning virus and is considered to be a distinctive strain of TRV.     

Clone banks of the mung bean, pea and spinach chloroplast genomes

All but one of the PstI restriction fragments from mung bean, pea, and spinach chloroplast DNAs have been stably cloned into pBR322. Large fragments (15-54 kb) were cloned at low efficiencies which decreased with increasing fragment length. However, plasmids containing fragments above 25-30 kb were too unstable to be useful. In particular, pBR322 derivatives containing the largest mung bean and spinach fragments (34 kb and 54 kb, respectively) are extremely unstable and rapidly delete parts of the plasmid sequence. The PstI fragments of mung bean chloroplast DNA which cover the 34-kb PstI fragment have been cloned into pACYC177. After a search of several thousand recombinants we were unable to recover a clone containing a 12.2-kb pea chloroplast PstI fragment and suggest that some property of its sequence may be inimical to the cloning process. The identity of the cloned fragments to native chloroplast DNA restriction fragments is demonstrated by restriction analysis and the ability to construct detailed restriction maps of the mung bean and pea chloroplast genomes.