Partial Resistance of Bell Pepper to Cucumber Mosaic Virus Movement within Plants: Field Evaluation of its Efficiency in Southern France

The spread of cucumber mosaic virus (CMV) was followed during three years in field plots of bell pepper varieties Yolo Wonder (susceptible) and Milord and Vania (partially resistant to CMV movement within plants). During the three test years, CMV spread was delayed 4 to 6 weeks in var. Milord and in var. Vania as compared to var. Yolo Wonder. Final CMV incidence and the apparent infection rate, the latter calculated from Van der Plank logistic analyses, were lower in var. Milord and in var. Vania than in var. Yolo Wonder. The resistance of var. Milord and var. Vania, expressed as a delay of spread and a reduced CMV incidence over the past three years, provides practical disease control.     

Study of multiplication of cucumber mosaic virus in susceptible and resistant Capsicum annuuum lines

A previous survey on pepper lines (Capsicum annuum L.) indicated that a susceptible cultivar, Yolo Wonder, reacted to cucumber mosaic virus (CMV) by producing a systemic yellow mosaic. By contrast, CMV caused no symptoms on lines Perennial and Vania. The virus is recoverable from the uninoculated leaves of Perennial, while in Vania CMV is restricted to the inoculated leaves. To interpret these phenomena, a comparative study on CMV multiplication rates, yield, specific infectivity and relative proportion of RNAs was made in the inoculated leaves of the three pepper varieties. The rate of CMV multiplication, as estimated by the double antibody sandwich form of enzyme-linked immu-nosorbent assay, was lower in Perennial than in Vania or Yolo Wonder. The yield of virus purified from Perennial was very low when compared with Vania or Yolo Wonder. The specific infectivity of the virus extracted from Perennial was less than that from Vania or Yolo Wonder. These results suggest that Perennial is resistant to CMV multiplication, while restriction of the virus in inoculated leaves of Vania is not due to the inhibition of the virus replication. However, polyacrylamide gel electrophoresis revealed that the RNA profiles of CMV purified from the three pepper lines were similar.     

Developpement de Leveillula taurica en Fonction des Facteurs Climatiques et Sensibilité de Capsicum annuumà Differents Stades Végétatifs

Influence of environmental factors on the development of L. taurica on pepper genotypes To our knowledge, the effects of certain environmental factors, as well as those of host genotype on the development of Leveillula taurica on pepper have not been extensively investigated. To study effects of the above factors on the development of this parasite, two Capsicum genotypes (‘Yolo Wonder' and ‘line 815’) have been tested and compared under different light and relative humidity conditions. In vitro, optimal light intensity for spore germination was situated between 20 and 80 μE/m²/s, and for the growth of germ tubes it was 20 μE/m²/s. In vivo, under continous darkness during 20 days, the different organs of the hosts were only slightly affected. Under light conditions, during 20 days after inoculation, the highest infection level on leaves was observed at 20 μE/m²/s, (60 % of leaves) while with the cotyledons it was observed between 20–80 μE/m²/s. Effects of relative humidity on the development of this parasite were also studied on ‘Yolo Wonder’ and ‘line 815′. With relative humidity below 50 %, 60 % of ‘Yolo Wonder’ plants and 33 % of ‘line 815’ were infected. Under conditions of saturated relative humidity, the level of infection was the inverse, i. e. 13 and 55 %, respectively. Moreover, ‘Yolo Wonder’ plants were found more or less susceptible to infection with L. taurica during their different development stages. At the cotyledon stage all plants were infected. After this stage, up to flowering, susceptibility depended on the physiological age of the leaves. First leaves (older leaves) were not infected, while young ones near the apex became progressively susceptible.     

CMV抑制PVYN CP基因沉默及其介导的抗病性

以前曾报道用RNA介导的抗病毒策略,获得了高度抗病的表达马铃薯Y病毒坏死株系外壳蛋白基因(PVY^N CP)的转基因烟草,并对T1、T2代转基因植株进行了遗传和抗病性分析。此次以T,代转基因植株为试验材料,在筛选高度抗病植株并证明其抗病性是基于转基因沉默的基础上,采用Northern杂交的方法,证明CMV侵染抑制了转基因植株中PVY^N CP基因的沉默,而且CMV对PVY^N CP基因沉默的抑制部位是发生在接种后的新生叶上,接种叶及其下部叶片中PVY^N CP基因沉默则未受到影响。采用ELISA方法对CMV PVY^N复合接种的转基因植株进行PVY^N检测,结果表明,接种叶及下部叶没有检测到PVY^N,植株叶片对PVY^N表现为抗病。而在CMV接种后植株新生叶中则检测出了高滴度的PVY^N,植株叶片对PVY^N表现为感病。该文报道了在表达PVY^N CP基因的RNA介导抗性转基因植株中,异源病毒侵染抑制了转基因的沉默,并导致转基因植株的抗病性丧失。     

Accelerated leaf senescence takes part in enhanced resistance in cucumber mosaic virus inoculated pepper leaves

Altered photosynthetic reactions in cucumber mosaic virus (CMV) inoculated leaves of virus resistant lines L113 and L57 and susceptible pepper (Capsicum annuum L.) plants cv. Albena grown in controlled environment and in the field were investigated. The CMV inoculated leaves of virus resistant lines developed different symptoms—necrotic local lesions on L113 and chlorotic spots on L57 while the same leaves of susceptible cv. Albena were symptomless. The changes in Photosystem II (PSII) and PSI electron transport were evaluated by chlorophyll fluorescence, and far-red (FR) light induced leaf absorbance A _810–860. CMV infection caused a decrease in maximal PSII quantum yield, F _v/F _m, in susceptible leaves. Increased non-photochemical fluorescence quenching in CMV-inoculated leaves of both resistant lines were observed. In CMV-inoculated leaves of all tested plants FR light induced P700 oxidation was decreased. In the present study, the viral-infected pepper plants grown in controlled environment to avoid the effects of abiotic factors were used as model system that allow us to investigate the differences in leaf senescence in CMV-inoculated leaves of susceptible and resistant pepper lines expressing different symptoms. Earlier leaf falls of inoculated leaves as a result of accelerated leaf senescence is important for building successful secondary virus resistance strategy following fast responses such as hypersensitive reaction.     

Screening for Barley Yellow Dwarf Luteovirus Resistance in Barley on the Basis of Virus Movement

The movement of barley yellow dwarf luteovirus (BYDV) was evaluated in susceptible and resistant barley and bread wheat genotypes. After leaf inoculation, the virus infected the root system and the growing point of susceptible earlier than resistant, barley genotypes. No difference in virus movement occurred in resistant and susceptible wheat genotypes. It was possible to reliably differentiate susceptible from resistant genotypes when root extracts of 41 barley genotypes were tested by DAS-ELISA 3 or 4 days after inoculation at the oneleaf stage. When barley plants inoculated at the two- or three-leaf stage were assayed by tissue-blot ELISA on nitrocellulose membrane, virus was detected in the phloem vessels of the growing points of the susceptible, but not of the resistant genotype, 4–6 days after inoculation. Our results thus suggest that screening for BYDV resistance in barley could be done quickly and cheaply especially when assays are made by the tissue-blot test.     

Age-related Resistance in Bell Pepper to Cucumber mosaic virus

We demonstrated the occurrence of mature plant resistance in Capsicum annuum‘Early Calwonder’ to Cucumber mosaic virus (CMV) under greenhouse conditions. When Early Calwonder plants were sown at 10 day intervals and transplanted to 10‐cm square pots, three distinct plant sizes were identified that were designated small, medium and large. Trials conducted during each season showed that CMV accumulated in inoculated leaves of all plants of each size category. All small plants (with the exception of the winter trial) developed a systemic infection that included accumulation of CMV in uninoculated leaves and severe systemic symptoms. Medium plants had a range of responses that included no systemic infection to detection of CMV in uninoculated leaves with the systemically infected plants being either symptomless or expressing only mild symptoms. None of the large plants contained detectable amounts of CMV in uninoculated leaves or developed symptoms. When plants were challenged by inoculation of leaves positioned at different locations along the stem or different numbers of leaves were inoculated, large plants continued to accumulate CMV in inoculated leaves but no systemic infection was observed. When systemic infection of large plants did occur, e.g. when CMV‐infected pepper was used as a source of inoculum, virus accumulation in uninoculated leaves was relatively low and plants remained symptomless. A time‐course study of CMV accumulation in inoculated leaves revealed no difference between small and large plants. Analyses to examine movement of CMV into the petiole of inoculated leaves and throughout the stem showed a range in the extent of infection. While all large plants contained CMV in inoculated leaves, some had no detectable amounts of virus beyond the leaf blade, whereas others contained virus throughout the length of the stem but with limited accumulation relative to controls.     

A natural recessive resistance gene against potato virus Y in pepper corresponds to the eukaryotic initiation factor 4E (eIF4E)

We show here that the pvr2 locus in pepper, conferring recessive resistance against strains of potato virus Y (PVY), corresponds to a eukaryotic initiation factor 4E (eIF4E) gene. RFLP analysis on the PVY-susceptible and resistant pepper cultivars, using an eIF4E cDNA from tobacco as probe, revealed perfect map co-segregation between a polymorphism in the eIF4E gene and the pvr2 alleles, pvr2(1) (resistant to PVY-0) and pvr2(2) (resistant to PVY-0 and 1). The cloned pepper eIF4E cDNA encoded a 228 amino acid polypeptide with 70-86% nucleotide sequence identity with other plant eIF4Es. The sequences of eIF4E protein from two PVY-susceptible cultivars were identical and differed from the eIF4E sequences of the two PVY-resistant cultivars Yolo Y (YY) (pvr2(1)) and FloridaVR2 (F) (pvr2(2)) at two amino acids, a mutation common to both resistant genotypes and a second mutation specific to each. Complementation experiments were used to show that the eIF4E gene corresponds to pvr2. Thus, potato virus X-mediated transient expression of eIF4E from susceptible cultivar Yolo Wonder (YW) in the resistant genotype YY resulted in loss of resistance to subsequent PVY-0 inoculation and transient expression of eIF4E from YY (resistant to PVY-0; susceptible to PVY-1) rendered genotype F susceptible to PVY-1. Several lines of evidence indicate that interaction between the potyvirus genome-linked protein (VPg) and eIF4E are important for virus infectivity, suggesting that the recessive resistance could be due to incompatibility between the VPg and eIF4E in the resistant genotype.     

Infective behaviour and aphid-transmissibility of Italian isolates of potato virus Y in tobacco and peppers

When mechanically inoculated to susceptible tobacco (Nicotiana tabacum L.) cultivars, nine isolates of PVY from Umbria (Central Italy) and two from Southern Latium gave rise to rapid systemic infection which developed within 6–8 days after inoculation. Systemic spread of the same isolates was slower, or much slower, in infected pepper (Capsicum annuum L.) cultivars, 8–14 days for Southern Latium isolates and 20 - 35 days for Umbrian ones. Aphid (Myzus persicae)-moculation of pepper and tobacco plants with two of the Umbrian and one of the Southern Latium isolates confirmed the results from sap-transmission and showed that fewer inoculated pepper plants become infected, especially with Umbrian isolates. In agreement with the data on systemic spread, aphid-acquisition trials indicated that tobacco plants became efficient PVY sources for vectors 6–8 days after inoculation with either group of isolates. Peppers became efficient acquisition hosts 8–15 days after inoculation with Southern Latium isolates but not until 22–45 days after inoculation with Umbrian ones. Southern Latium isolates induced more severe symptoms in pepper cultivars than Umbrian isolates did. One of the Southern Latium isolates was able to systemically infect the resistant pepper cv. Yolo Y, which was never infected by the Umbrian isolates. The Umbrian isolates tested seem to be better adapted to tobacco than peppers, while Southern Latium ones are well adapted to both.     

Expression of Resistance to CMV Migration in Pepper Seedlings

Previous studies have shown that the partially resistant genotypes of pepper ( Capsicum annuum L.), 'Milord' and 'Vania' are able to localize CMV infection in some shoots of the plants when inoculated at an adult stage. We have observed that the virus migration is restricted to the inoculated cotyledons when young seedlings of these genotypes are inoculated with the Fulton CMV/N strain. In the same conditions, susceptible genotypes become systematically infected. We have shown that the levelof resistance expression depends on the plant development stage, the environmental conditions and the inoculum concentration. The most favourable conditions to discriminate resistance to CMV migration at an early stage of plant development have been defined.     

Susceptibility of some Lycopersicon species and varieties to cucumber mosaic virus (CMV) and tobacco mosaic virus (TMV)

Susceptibility of 33 Lycopersicon species and varieties to Tobacco mosaic virus (TMV) and Cucumber mosaic virus (CMV) were studied. Plants were mechanically inoculated with the C/U1 strain of TMV and U/246 strain of CMV. Virus infection was checked by symptomatology, DAS ELISA and back inoculation (biotest). All the studied Lycopersicon species and varieties were susceptible to TMV-C/U1. L. esculentum Mill. convar. infiniens Lehm. var. flammatum Lehm., L. esculentum Mill. convar. fruticosum Lehm. var. speciosum Lehm. and L. esculentum Mill. convar. infiniens Lehm. var. validum Bail. showed extreme resistance to CMV-U/246. The other 30 species and varieties were susceptible to CMV-U/246. New compatible and incompatible host-virus relations have been reported. The extreme resistant Lycopersicon varieties could be used as resistance sources in tomato breeding.     

番木瓜抗病突变体阻碍环斑病毒体内运转

应用RT－PCR一步法检测了PRSV Ys株系在感病番木瓜及其抗病突变体植株体内的运转动态,结果表明：在感病植株中,接种后48hr接种叶的未接种部位可检出病毒,第4天部分接种叶柄可检出病毒,第6天植株各部位均能检出病毒;而在抗病植株中,接种后可以而且仅能在接种部位检出病毒;因而认为抗病突变体能够阻碍病毒从接种部位运出及（或）向未接种部位运入。     

Differentiation Among Bean Leafroll Virus Susceptible and Resistant Lentil and Faba Bean Genotypes on the Basis of Virus Movement and Multiplication

Systemic movement of Bean leafroll virus (BLRV) in susceptible and resistant lentil and faba bean genotypes was studied using plants grown in a plastic house. All the plants studied were inoculated with BLRV by viruliferous pea aphids (Acyrthosiphon pisum). Five plants/genotype of lentil and faba bean were harvested, respectively, at 3, 6, 9, 12 and 18 days and 1, 2, 3, 4 and 5 weeks after inoculation. Each plant was split into growing point, stem, stem base and root, and each was tested using tissue blot immunoassays (TBIA). Virus concentration in each section was estimated using a 0–3 score and a relative TBIA value was estimated accordingly for each genotype. In susceptible lentil genotypes (ILL 8063 and ILL 2581), BLRV was present in low concentrations in the growing point 3 days after inoculation and in high concentrations in all parts of the plant after 6 days. By contrast, the virus was not detected in the highly resistant genotype (ILL 74) until 18 days after inoculation. In the faba bean genotypes studied, BLRV was detected in high concentrations in all parts of the highly susceptible genotype (Fiord) 1 week after inoculation but only after 3 weeks in resistant genotypes (e.g. BPL 5274), but was not detected in the highly resistant genotypes (BPL 5278 and BPL 5279) 5 weeks after inoculation. The replication and systemic movement of BLRV was thus slower in resistant genotypes than in susceptible genotypes. Moreover, the use of TBIA scores clearly and easily differentiated resistant and susceptible genotypes. Our results suggest that BLRV movement and multiplication can be useful criteria when differentiating resistant from susceptible genotypes. In addition, undertaking the preliminary screening in a plastic house requires less space than direct planting in the field.     

Comparison of Resistance to Cotton Leaf Curl Disease (Multan/Burewala) in Gossypium hirsutum L. Varieties and Breeding Lines

Twenty‐four cotton varieties and advance breeding lines were evaluated for their resistance to cotton leaf curl disease (CLCuD; Multan/Burewala) under natural field and in glasshouse conditions for two consecutive years. Resistance was based on symptom expression and disease severity index. All the cotton genotypes exposed to the vector whitefly in the field and artificially infected by grafting manifested a high level of resistance against CLCuD (Multan) with the exception of genotype NIAB‐999 that was moderately resistant. All the test varieties/breeding lines were highly susceptible to CLCuD (Burewala) both in the field and the glasshouse. However, substantial differences were noted between genotypes for disease index under field conditions. Graft inoculation studies showed that all genotypes inoculated with CLCuD (Burewala) developed disease within 9–13 days whereas those graft‐inoculated with CLCuD (Multan) developed symptoms from 15 to 22 days after grafting. Severe reduction occurred in plant morphology, fibre and yield parameters of cotton variety NIAB‐111 following inoculation with CLCuD (Burewala) as compared with CLCuD (Multan).     

cmv1 is a gate for Cucumber mosaic virus transport from bundle sheath cells to phloem in melon

Cucumber mosaic virus (CMV) has the broadest host range among plant viruses, causing enormous losses in agriculture. In melon, strains of subgroup II are unable to establish a systemic infection in the near‐isogenic line SC12‐1‐99, which carries the recessive resistance gene cmv1 from the accession PI 161375, cultivar ‘Songwhan Charmi’. Strains of subgroup I overcome cmv1 resistance in a manner dependent on the movement protein. We characterized the resistance conferred by cmv1 and established that CMV‐LS (subgroup II) can move from cell to cell up to the veins in the inoculated leaf, but cannot enter the phloem. Immunogold labelling at transmission electron microscopy level showed that CMV‐LS remains restricted to the bundle sheath (BS) cells in the resistant line, and does not invade vascular parenchyma or intermediary cells, whereas, in the susceptible line ‘Piel de Sapo’ (PS), the virus invades all vein cell types. These observations indicate that the resistant allele of cmv1 restricts systemic infection in a virus strain‐ and cell type‐specific manner by acting as an important gatekeeper for virus progression from BS cells to phloem cells. Graft inoculation experiments showed that CMV‐LS cannot move from the infected PS stock into the resistant cmv1 scion, thus suggesting an additional role for cmv1 related to CMV transport within or exit from the phloem. The characterization of this new form of recessive resistance, based on a restriction of virus systemic movement, opens up the possibility to design alternative approaches for breeding strategies in melon.     

Peroxidase and chitinase isoenzyme activities during root infection of Chinese cabbage with Plasmodiophora brassicae

Roots of two Chinese cabbage (Brassica campestris L. ssp. pekinensis) varieties, one tolerant and one susceptible, were inoculated with Plasmodiophora brassicae in liquid medium and in soil. Chitinase and peroxidase activities were determined in roots and shoots 1–21 days after inoculation with resting spores of Plasmodiophora and the enzyme activities compared with healthy tissue of the same age. In infected roots of the susceptible variety ‘Granat’ chitinase activity was higher than in the control 10 days after inoculation with spores. In the tolerant variety ‘Parkin’ we detected an increase in chitinase activity at the same time, which was about twice that of ‘Granat’. Chitinase activity in ‘Granat’ was also enhanced on day 13, 14 and 17 after inoculation, whereas chitinase activity in ‘Parkin’ was lower in the infected roots than in the controls during that period. In the shoots no correlation between chitinase activity and infection in the two varieties was observed. Chitinase from Chinese cabbage was further characterized and showed a pH optimum at pH 4.5–5.5 and a temperature optimum at 35–45°C. After isoelectric focusing 7 isoenzymes were discovered, but there were almost no differences between infected and healthy root extracts. Two isoenzymes with pI 8.7 and 8.8 showed cross-reactivity with an antiserum against bean chitinases. The molecular mass of these isoenzymes was determined as 33 kDa. Total peroxidase activity was generally higher in root tissue of both varieties than in the shoots. Peroxidase activity was increased most prominently in infected ‘Granat’ roots on day 13 after inoculation and of both varieties on day 17 compared to the controls. In clubbed tissue of ‘Granat’ a specific peroxidase isoenzyme appeared the first time 21 days after inoculation and was most prominent 28–30 days after inoculation. This isoenzyme had a molecular mass of ca 24 kDa and a pI of ca 8.8. With respect to our results the strategy of the Plasmodiophorales for plant attack is discussed.     

Time-course analysis of the phenols in cucumber mosaic virus-resistant, -tolerant and -susceptible tomato genotypes

In this study, changes in quantity and quality of phenolic compounds were compared in cucumber mosaic virus (CMV)-inoculated and -un-inoculated plants of nine resistant, tolerant, susceptible and highly susceptible genotypes at three different time intervals. Total phenolic contents and the number of phenolic compounds were generally increased in CMV-inoculated plants. Maximum per cent increase in total phenolic contents over un-inoculated controls was observed as 77.55% in resistant genotype TMS-1, 84.17% in tolerant genotype L06238 and 82.88% in resistant genotype L02223 after 10, 20 and 30 days of inoculation, respectively. Thin layer chromatography of inoculated and un-inoculated plants indicates that in most of the tested genotypes, the number of phenolic compounds varied from cultivar to cultivar and within the same cultivar, depending upon the status of plants and growth stages. However, the trend of increase in quantity and quality of phenolic compounds in the tested units was not constant to draw a meaningful conclusion.     

Physiology of Rice Tungro Virus Disease: Increased Cytokinin Activity in Tungro-Infected Rice Cultivars

Tungro virus infection decreased the chlorophyll content in the susceptible rice (Oryza sativa) cultivar ‘Taichung Native 1’, while it increased the pigment in the less-susceptible cultivar ‘IR 20’ during the later stages of infection. The virus was recovered from the infected susceptibile cultivar as early as 3 days after inoculation. Relatively low amounts of virus were recovered from the less-susceptible cultivar between 12 and 30 days after inoculation. The senescence of detached leaves of virus-infected less-susceptible cultivar incubated in water in darkness was considerably delayed compared to healthy leaves. The cytokinin activity in the extracts from inoculated less-susceptible cultivar was 69% higher than in the extracts from the healthy plants.     

Assimilatverteilung in Sommergerstensorten mit unterschiedlicher Resistenz gegenüber dem Echten Mehltau (Erysiphe graminis f. sp. hordei)

Distribution of assimilates in cultivars of spring barley with different resistance against powdery mildew (Erysiphe graminis f. sp. hordei) Transport and distribution of radioactive labelled assimilates in spring barley cultivars with different degrees of resistance to powdery mildew were studied after ¹⁴CO₂-treatment of single leaves. Plants of the cultivars ‘Amsel’ (susceptible), ‘Asse’ (adult plant resistant), and ‘Rupee’ (resistant) were analyzed at the vegetative growth stage (5. leaf unfolded) and the generative growth stage (anthesis). At the vegetative growth stage the assimilate export from the mildew inoculated 5. leaf of ‘Amsel’ and ‘Rupee’ is decreased; in ‘Asse’, there is no considerable change of assimilate distribution due to infection. At the generative growth stage the assimilate export from the infected flag leaf of ‘Amsel’ is reduced when the fungus, is sporulating. In the cultivar ‘Asse’ the assimilates are bound at the infection site until the seventh day after inoculation, then the transport of assimilates to the ear is increased. In ‘Rupee’ mildew inoculation causes an enhanced assimilate transport to the ear. The changes in assimilate distribution due to mildew inoculation are discussed with respect to the different types of host-parasite-interactions and the source-sink-activities in the different cultivars.