Purification and some properties of Papaya meleira virus, a novel virus infecting papayas in Brazil

'Meleira', or 'sticky disease', is currently the most damaging papaya disease in the mid-eastern Brazilian growing regions. Consistent disease transmission via latex injection, presence of similar isometric particles in the laticiferous vessels of diseased plants, and detection of double-stranded DNA in naturally and experimentally infected papaya trees suggest that a virus is the causal agent. Conclusive evidence for viral aetiology was previously lacking, mostly because every attempt to purify the putative virus from infected papayas had failed. Following the successful purification and partial characterization of the meleira virus, healthy papaya seedlings injected with purified virus particles later developed typical symptoms of the disease. Negatively stained, isometric, full and 'empty' purified virus particles measured 42 and 38 nm, respectively. The viral genome was a single dsRNA molecule of about 12 kbp. Several capsid proteins, ranging in size from 14·4 to 45 kDa, were consistently revealed by PAGE. Papaya meleira virus (PMeV) appears to represent a novel group of viruses, with no known similar counterpart among known plant-, vertebrate-, invertebrate- or prokaryote-infecting viruses.     

Infection process of <Emphasis Type="Italic">Pseudocercospora musae</Emphasis> on banana leaf

Yellow Sigatoka that is caused by Pseudocercospora musae is an important banana disease. The aim of this study was to elucidate the infection process of P. musae in banana leaves by scanning electron microscopy. Leaf samples were inoculated on the abaxial surface with P. musae and then analysed at 12, 24, 36, 48, 72, 96, 120, 144, and 168 h post inoculation (hpi) and at 36 and 50 days post inoculation (dpi). The conidia were found to be germinated between 24 and 36 hpi and penetrated through the stomata between 96 and 120 hpi, or more generally from 144 hpi. P. musae colonized the spongy parenchyma at 36 dpi and the palisade parenchyma at 50 dpi. Sporulation occurred at 50 dpi on the adaxial surface of leaves through the emergence of conidia on conidiophores through the stomata. Considering the importance of yellow Sigatoka in banana production, our results provide a better understanding of the life cycle of the fungus for treatment processes.     

The response to <Emphasis Type="Italic">Potato virus X</Emphasis> infection of tomato plants treated with ISR2000

Elsinoë fawcettii, a fungal pathogen causing scab disease in citrus, is one of the destructive diseases having an adverse role in the fresh fruit market. We observed the infection behaviour of E. fawcettii on young leaves of satsuma mandarin daily and described the time course of symptom development with a focus on morphological changes during disease progress. The E. fawcettii isolate 16–1, belonging to Florida Broad Host Range (FBHR), was infectious and generated typical symptoms on adaxial as well as abaxial surfaces of the leaf. Of the conidia inoculated and adhered, only a few were able to germinate and create typical symptoms. Conidia extended their germ tubes from 1 day post-inoculation where a few possessed globose appressorium-like structures (APL) at their tip. The APL were found on both surfaces while symptoms could be produced without them. Dark regions were induced 1–2 days post-inoculation (dpi) under fluorescent microscopic observation. Cuticle and mesophyll cells including epidermis in the infected dark region were degraded, resulting in cellular necrosis. The adjacent cells of the necrotic region were enlarged and gradually covered leaving a grooved shaped necrotic center and appeared as a first visible symptom 3 dpi. Hyphae were extended through the necrotic epidermis and colonized intra- and inter-cellularly in mesophyll tissue. Also lamellated cell-wall was observed as a boundary between infected and non-infected regions in the lesion after typical symptoms were formed. The lamellation in the cell simultaneously occurred forming a compaction of host cells and a semi-circular arc of lammellated cells was formed on the boundary of the infected and non-infected regions of the lesion.     

Alternative hosts and seed transmissibility of soybean blotchy mosaic virus

Soybean blotchy mosaic virus (SbBMV) is an important virus of soybean in the warmer regions of South Africa. The presence of the virus is associated with blotchy mosaic symptoms on soybean leaves and significant annual yield losses. The virus is a member of the genus Cytorhabdovirus and persists between soybean growing seasons. In this study, multiple specimens of indigenous tree species, other crops and herbaceous weeds surrounding soybean fields with high disease incidences of SbBMV were tested for the presence of SbBMV by RT-PCR in order to determine whether the presence of alternative hosts facilitates the seasonal carry-over of the virus. Commercial soybean cultivars commonly grown in the region were also evaluated for seed transmissibility of the virus. A total of 487 accessions representing 27 different species were screened and one accession each of Flaveria bidentis, Lamium amplexicaule and Gymnosporia buxifolia tested positive for the presence of SbBMV and may serve as possible alternative hosts of SbBMV, allowing over-wintering of the virus when soybean is absent. Symptoms associated with SbBMV infection were not present in any of the 2, 829 seedlings collected from naturally infected SbBMV plants, and none of the 21 seedlings showing various abnormalities and tested by RT-PCR were positive. SbBMV does not appear to be seed transmissible in soybean at an incidence above that which numbers screened would have detected the virus. It was concluded that the presence of alternative plant hosts, functioning as viral reservoirs during the soybean off-season might allow for the re-emergence of the disease early in the soybean production season each year. Future work will investigate the role of Peragallia caboverdensis, the leafhopper vector of SbBMV, and specifically the possible propagative transmission of the virus in the persistence of the disease.     

<Emphasis Type="Italic">Alternaria alternata</Emphasis>: A new seed-transmitted disease of coriander in South Africa

This is the first report of Alternaria leaf spot disease on coriander (Coriandrum sativum L.) in South Africa. Using the agar plate method, Alternaria alternata was isolated from coriander seed lots together with four other fungal genera, which included Aspergillus, Fusarium, Penicillium and Rhizopus. Standard seed germination tests of coriander seed lots infected with seed-borne mycoflora showed a positive correlation with the number of diseased seedlings (r?=?0.239, p?<?0.01). Pathogenicity tests demonstrated that this seed-borne A. alternata was pathogenic on coriander and symptoms on leaves first appeared as small, dark brown to black, circular lesions (<5 mm diam.) that enlarged and coalesced to form dark brown blotches as time progressed. Leaf spot disease was most severe (64%) on wounded leaves inoculated with A. alternata. Re-isolation of A. alternata from diseased coriander plants satisfied the Koch’s postulates, thus confirming it as the causal agent of Alternaria leaf spot disease. Parsimony analysis based on rpb2 (GenBank Accession No. KT895947), gapdh (KT895949) and tef-1α (KT895945) sequences confirmed identity of the Alternaria isolate, which grouped within the A. alternata clade. Alternaria alternata was shown to be transmitted from infected coriander seed to the developing plants.     

Intercellular invasion of rice roots at the seedling stage by the rice false smut pathogen, <Emphasis Type="Italic">Villosiclava virens</Emphasis>

False smut is a serious disease affecting rice production worldwide. Initial infection of rice seedlings by Villosiclava virens was clarified using axenically cultured chlamydospores to inoculate rice roots. Chlamydospores were found on rice roots at 1 day post inoculation (dpi), and were germinating at 1–4 dpi. At 4 dpi, the infection germ tube had invaded the intercellular space between epidermal rice root cells. Between 5 and 11 dpi, branching and fusion-like structures were observed that may contribute to the establishment of the hyphal network on the root surface.     

Impact of primary infection site of <Emphasis Type="Italic">Fusarium</Emphasis> species on head blight development in wheat ears evaluated by IR-thermography

The effect of the primary infection site by Fusarium graminearum and F. culmorum within wheat ears on Fusarium head blight (FHB) was investigated under controlled conditions. FHB development was assessed visually and thermographically following inoculation by: (i) spraying ears, or injecting inoculum into spikelets on (ii) tip, (iii) centre and (iv) base of the ears, separately. Fusarium infection significantly increased the temperature span within ears 6 days post inoculation (dpi), especially infections starting at the ear tip. The temperature difference between air and ear was negatively correlated to FHB severity and enabled disease detection even 29 dpi. F. culmorum caused significant higher disease severity neither reflected in the frequency of infected kernels nor in thousand kernel weight (TKW). Spray inoculations had the strongest effect on TKW, whereas tip inoculations had no effect. Centre and base inoculations had intermediate effects on TKW, although FHB levels did not differ with the same trend among inoculation scenarios. The overall low correlations among FHB severity, infected kernels and TKW are explained by the pathogen spread within ears – downwards more than upwards – and the effect on yield formation which is lower for infections of the upper parts of ears. An exponential model showed high goodness of fit for gradients of infected kernels within ears (R ²  ≥ 70) except tip infection with F. culmorum. This study confirmed that FHB is a function of the primary infection site within ears. Thermography was useful to differentiate among infection scenarios and may be applied in breeding for FHB resistance.     

The effect of salicylic and jasmonic acids on tomato physiology and tolerance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> (CMV)

Cucumber mosaic virus (CMV) is one of the most important plant viruses responsible for sharp reductions in the production of many cultivated plants. Activities of antioxidant enzymes, photosynthetic capacity, proline and total soluble carbohydrates (TSC) content were measured in the leaves of tomato (Solanum lycopercicum cv. Falat) plants treated with phytohormones (salicylic and jasmonic acids and their combination) and inoculated with CMV at 0, 1, 2, 4, 6, 8, and 15 days after the treatments. Based on the results, catalase (CAT) activity decreased in the healthy and infected plants, but peroxidase (POD) activity increased in the CMV-infected plants signifying that POD is more active in H₂O₂ scavenging in tomato. Because the hormone treatments inhibited the reduction in the enzyme activity, it may be considered as a controlling method against CMV. Superoxide dismutase (SOD) activity was lower in the control until 6 days post inoculation (dpi), but increased after 8 dpi. The infected plants and the hormone-treated plants showed an increased SOD activity from 0 to 15 dpi. Phenylalanine ammonia lyase (PAL) activity also increased in all the treatments over the time period (0-15 dpi). Net photosynthesis (NP) rate and chlorophyll content decreased under the virus infection and hormone treatment, whereas control plants had the highest NP and chlorophyll content. Proline accumulation occurred in the infected and hormone- treated plants, but TSC content decreased in comparison to the control. Reduction of TSC content was not significant in the hormone and virus- treated plants. Expression of CMV coat protein gene (CMV-CP) was decreased by approximately 34% in SA+JA+CMV treatment in comparison to the CMV-infected plants. In conclusion, CMV had harmful effect on physiological traits of tomato plants, but hormone application induced resistance. This resistance may be accomplished through the combination of both hormone-related signaling pathways which likely established a strong resistance network together.     

Transgene-mediated resistance to <Emphasis Type="Italic">Papaya ringspot virus</Emphasis>: challenges and solutions

Global papaya production is severely affected by papaya ringspot disease caused by Papaya ringspot virus (PRSV). Management of this potyvirus is challenging, due to 1) its non-persistent transmission by numerous aphid species and 2) the diversity of PRSV strains that exists within a country or between different geographical regions. Papaya cultivars with transgenic resistance have reduced the impact of the disease. There are no effective alternatives to transgenic resistance available in areas where disease pressure is high. In Hawaii, transgenic papayas such as “SunUp” and “Rainbow” have remained resistant to PRSV more than two decades saving the commercial papaya industry. Following the success in Hawaii, researchers from other countries have focused on developing PRSV-resistant transgenic papaya. These transgenic cultivars often demonstrated an initial transitory resistance that was ultimately overcome by the virus. For other cases, resistance was inconsistent. That is, some transgenic lines were resistant while others were not. Transgenic cultivars are now losing PRSV-resistance for various reasons in China and Taiwan. In this review, we present an update on work with transgenic papaya with resistance to PRSV. The focus is on factors affecting transgenic resistance in papaya and our attempt to explain why the Hawaiian scenario of complete and durable resistance has not been replicated in other regions. The utilization of more recent technologies to the development of virus resistance in papaya is also discussed.     

Temperature and plant age drive downy mildew disease epidemics on oilseed <Emphasis Type="Italic">Brassica napus</Emphasis> and <Emphasis Type="Italic">B. juncea</Emphasis>

Studies were undertaken on the effects of temperature (14/10 °C and 22/17 °C day/night) and plant age (15, 23, 31 and 40 day-old-plants) on the severity of downy mildew (Hyaloperonospora parasitica) on oilseed Brassica cultivars (temperature: Brassica juncea Montara, B. napus Atomic, ATR-Hyden, Hyola 432, Hyola 450 TT, Thunder TT; plant age: B. juncea Dune, B. napus Surpass 402 and Hyola 450 TT). For temperature studies, there were significant (P?<?0.001) effects of temperature, cultivar, and cultivar x temperature interaction. On cotyledons of susceptible cultivars (B. napus Hyola 450 TT and Thunder TT), plants were symptomatic at 22/17 °C by 48 h post inoculation (hpi) and with abundant sporulation evident by 72 hpi, and with all cotyledons of B. napus Thunder TT collapsed by 7 days post inoculation (dpi). However, at 14/10 °C, there were no symptoms on the same cultivars until 5 dpi, and sporulation only observed at 7 dpi. Percent disease index values (DI%) at 22/17 °C of B. juncea Montara and B. napus ATR-Hyden, Hyola 432, Atomic, Hyola 450 TT and Thunder TT were 4.5, 49.0, 51.4, 65.8, 86.3 and 96.0, respectively, with all except B. juncea Montara having significantly lower (P?<?0.001) disease at 14/10 °C with DI% values of 2.8, 30.4, 27.9, 31.1, 44.4 and 76.4, respectively. For plant age studies, there were significant (P?<?0.001) effects of plant age, cultivar, and cultivar x plant age interaction. DI% was significantly higher at 15 compared to 40 day-old-plants (dop) across all cultivars. B. juncea Dune showed greatest resistance, particularly on 40 dop, with DI% values of 25.8, 24.6, 22.9 and 7.5, for 15, 23, 31 and 40 dop, respectively. B. napus Surpass 402 showed high susceptibility on cotyledons of 15 dop but moderate resistance on leaves of other ages, with DI% values of 59.0, 31.2, 27.1 and 26.2 for 15, 23, 31 and 40 dop, respectively. B. napus Hyola 450 TT showed very high susceptibility at the cotyledon stage on 15 dop, but some resistance on 23 dop and more so on 31 and 40 dop, with DI% values of 84.0, 41.2, 35.4 and 32.9 for 15, 23, 31 and 40 dop, respectively. Together, these findings explain for the first time why development of downy mildew epidemics on susceptible cultivars occurs early in the growing season when warmer seasonal temperatures in autumn coincide with presence of seedlings; in contrast to later in the growing season on less susceptible older plants coinciding with cooler and less favourable winter temperatures. Increasing maximum and minimum temperatures associated with climate change have likely fostered the increased severity of downy mildew over the past 15 years.     

Endophytes of <Emphasis Type="Italic">Lippia citriodora</Emphasis> (Syn. <Emphasis Type="Italic">Aloysia triphylla</Emphasis>) enhance its growth and antioxidant activity

Sweet pepper (Capsicum annuum) is a popular crop worldwide and an asymptomatic host of the begomovirus (Geminiviridae) Tomato yellow leaf curl virus (TYLCV). A previous study showed that TYLCV could be transmitted by the seeds of tomato plants, but this phenomenon has not been confirmed in other plants. In 2015, four different cultivars of sweet pepper (‘Super Yellow,’ ‘Super Red,’ ‘Sunnyez’ and ‘Cupra’) known to be susceptible to TYLCV were agro-inoculated with a TYLCV infectious clone. Three months after inoculation, the leaves of the ‘Super Yellow’ cultivar showed 80% (8/10) susceptibility and the other three sweet pepper cultivars showed 30 to 50% susceptibilities. All of the ‘Super Yellow’ seed bunches (five seeds per bunch) from plants whose leaves were confirmed to be TYLCV-infected were also TYLCV-infected (8/8). The seeds of other cultivars showed 20 to 40% susceptibilities. Virus transmission rates were also verified with 10 bunches of seedlings for each cultivar (five seedlings per pool). Eight bunches of ‘Super Yellow’ seedlings (8/10) were confirmed to be TYLCV-infected and one to three bunches of each of the other cultivar seedlings were also infected. Viral replication in TYLCV-infected seeds and seedlings was confirmed via strand-specific amplification using virion-sense- and complementary-sense-specific primer sets. This is the first report of TYLCV seed transmission in sweet pepper plants and among non-tomato plants. Because sweet pepper is an asymptomatic host of TYLCV, seeds infected with TYLCV could act as a silent invader of tomatoes and other crops.     

Ralstonia solanacearum preferential colonization in the shoot apical meristem explains its pathogenicity pattern in tomato seedlings

Ralstonia solanacearum causes a lethal bacterial wilt disease in many plants by colonizing the vascular tissues of the hosts. Upon inoculation of tomato seedlings through either leaf or root, the wilting symptoms occur first at the apical region and then proceed downward along the shoot. The systemic order of the disease initiation and progression in the host, independent of the site of pathogen inoculation, is yet to be investigated. To understand the disease progression more clearly, we have carried out a systematic study of the pathogen localization by GUS staining of inoculated tomato seedlings, at 24-hour intervals from 0 days post-inoculation (dpi) to 5 dpi. In both inoculation methods, pathogen colonization was observed at 1 dpi at the apical meristem as well as the cotyledon leaves, where the disease initiates. As the disease progressed, colonization by the pathogen towards the lower region of the shoot was observed. Disease consistency and pathogenicity magnitude were observed to be higher using the leaf inoculation method than the root inoculation method. Several R. solanacearum transposon-induced mutants that were reduced in virulence by root inoculation but virulent by leaf inoculation were obtained. Using GUS staining, it was observed that these mutants were unable to localize in the shoot region when inoculated in the root. Our study indicates that the apical meristem and the cotyledon leaves are the first regions to be colonized in inoculated tomato seedlings, which might explain the disease initiation from this region.     

Antagonistic effects of biofilm-forming bacterial strains co-inoculated with blood disease pathogenic strain, <Emphasis Type="Italic">Ralstonia syzygii</Emphasis> subspecies <Emphasis Type="Italic">celebesensis</Emphasis> in banana plants

A blood disease pathogenic strain, Ralstonia syzygii subspecies celebesensis was used to study the possible association of biofilm-forming bacteria with the development and severity of blood disease in banana plants. Therefore, the objective of this study was to determine the effects of mono-culture and co-culture inoculation of isolated biofilm-forming bacteria with the blood disease pathogen in banana pseudostems in glasshouse conditions. Putative biofilm-forming bacteria were isolated from an infected banana plant and were further identified using 16SrRNA sequencing. Four isolates, identified as Enterobacter hormaechei, Enterobacter cloacae, Kosakonia radicincitans and Klebsiella pneumoniae, were inoculated as a mono- and co-culture with R. syzygii subsp. celebesensis into 2 months old banana plants. The observation after the 8 weeks of post inoculation showed that plants which were co-inoculated with the pathogen and K. radicincitans, a biofilm-forming bacterium, were the most susceptible towards the infection. In contrast, plants under two treatments (which were co-inoculated with the pathogen and E. cloacae and the pathogen with E. hormaechei) were less susceptible towards the infection. This study revealed the antagonistic effects of two biofilm-forming strains which reduced the severity of infection caused by the pathogenic agent. Scanning electron micrographs of the cross section of plant rhizomes indicated the dissimilarity of adhesion and host colonization conditions of the pathogen in each infected plant from different treatments.     

Infection of <Emphasis Type="Italic">Sorghum bicolor</Emphasis>, selected grass species and <Emphasis Type="Italic">Zea mays</Emphasis> by G<Emphasis Type="Italic">loeocercospora sorghi</Emphasis>, causal pathogen of zonate leaf spot

Zonate leaf spot (Gloeocercospora sorghi) is a common disease in Sorghum bicolor producing areas of the U.S., but little is known about its biology, virulence and severity on S. bicolor, Zea mays, and related crop grassweeds. Greenhouse studies were conducted to determine and compare the virulence and severity of G. sorghi on 10 commercially available sorghum hybrids, four Z. mays hybrids and selected grassweed species including Sorghum bicolor (grain sorghum and shattercane biotypes) and Sorghum halepense (Johnsongrass), two of the most problematic arable weeds. Plants from the respective species were inoculated with a local G. sorghi isolate and maintained in a dew-chamber at 24 °C for 24 h and then incubated under greenhouse conditions for 4 weeks. Plants were observed for lesion expression and rated using a modified Horsfall-Barrett scale (0–10). The first symptoms of infection were visible within 24 h following inoculation on shattercane and S. bicolor hybrids. Symptoms consisted of small, non-diagnostic purple lesions on the leaves. Results showed that S. bicolor, S. halepense and shattercane were susceptible to G. sorghi. All other species tested in this study were not infected. More particularly, disease severity, increased from a rating of 3 to 10 on sorghum and from 2 to 7 on S. halepense between 2 and 23 days after inoculation, respectively. However, disease severity on shattercane increased rapidly from 3.5 to 10 between 2 and 8 days after inoculation, respectively. Among the sorghum hybrids tested, FFR-322 appeared to be the most resistant to G. sorghi while Pioneer 83G66 appeared to be the most susceptible. Z. mays hybrids were not infected by the fungus used in this study. G. sorghi could be used effectively to manage shattercane and S. halepense infestations occurring in Z. mays and S. bicolor fields consisting of specific G. sorghi-resistant hybrids.     

TaqMan PCR assay for detection and quantification of <Emphasis Type="Italic">Stagonosporopsis tanaceti</Emphasis> in pyrethrum seed and seedlings

Pyrethrum seed has an important role in the transmission of Stagonosporopsis tanaceti, the cause of ray blight disease of pyrethrum. A TaqMan probe based polymerase chain reaction (PCR) assay was developed to quantify the level of S. tanaceti inocula in pyrethrum seed and seedlings. Primer pair (St_qF3, St_qR2) was designed based on the intergenic spacer (IGS) region of S. tanaceti, which produced a 125 bp amplicon specific to S. tanaceti. TaqMan PCR assay using St_qF3, St_qR2 and a probe St_qP was highly specific against the genomic DNA of S. tanaceti, but did not amplify DNA of 14 related Stagonosporopsis species or other foliar pathogens of pyrethrum. The sensitivity limit of this assay was measured using the cycle threshold (C_t) value which ranged from 17.59 for 10 nanograms (ng) to 36.34 for 100 femtograms (fg) genomic DNA of S. tanaceti. There was a significant negative correlation (r = ?0.999, P < 0.001) between the C_t value and the percent of S. tanaceti infected seed. In addition, this TaqMan PCR assay detected latent infection within seedlings. This assay could be applied to test commercial seed and seedlings before deciding on the appropriate management practices.     

<Emphasis Type="Italic">Aphelenchoides gorganensis</Emphasis> n. sp. (Nematoda: Aphelenchoididae)<Emphasis Type="Italic">,</Emphasis> a new species from Iran

Phytophthora capsici infection of chili pepper seedlings can cause substantial losses due to damping-off and collar rot diseases. Chemical control is no longer effective due to reported resistance development, on top of the related environmental concerns and the consumer demands for reduced use of fungicides. Biological control is a sustainable option, with several agents having been reported to be effective against this pathogen. This research focused on optimizing the application of strain THSW13 of Trichoderma hamatum and a bacterial isolate BJ10–86 with the objectives of improving chili pepper seed germination, reduce damping-off disease incidence, and improve the growth of the seedlings. Bacterial isolate BJ10–86 was subjected to molecular identification and found to be Pseudomonas aeruginosa. Chili pepper seeds treated with the biocontrol agents, individually or in combination, were seeded into commercial nursery media that had been pre-inoculated with P. capsici zoospores. Over a period of 35 days the chili pepper seed treatments significantly (P = 0.008) reduced the disease incidence of seedlings damping-off. Combined application of T. hamatum and P. aeruginosa was the best biocontrol treatment with an area under disease curve of only 36.61 units compared to 92.87 units for the control treatment. Similar results were observed in vitro where T. hamatum and P. aeruginosa synergistically inhibited P. capsici growth by 73.2 %. The inhibition activity of this treatment was similar to mefenoxam treatment, which implies that it is an effective and sustainable alternative for chili pepper seed treatment. The biocontrol seed treatment had no effect on seed germination and seedling growth.     

Symptom development,in planta distribution,and transmission of <Emphasis Type="Italic">Impatiens necrotic spot virus</Emphasis> in gentian: evidence for survival in roots and winter buds

Impatiens necrotic spot virus (INSV) causes serious damage to gentian (Gentiana spp.). Symptom development, in planta distribution, and transmission of INSV were studied after mechanical inoculation of gentian plants and propagation of shoot cuttings from infected stock plants. When young gentian plants at the 2nd-leaf stage were inoculated with INSV, plants developed systemic symptoms that were restricted to a few upper leaves. However, older plants at the 6th-leaf stage did not develop systemic symptoms. After plant inoculation, INSV was detected using DAS-ELISA in symptomatic upper leaves, and rootlets and winter buds, but not in asymptomatic leaves. When asymptomatic shoot cuttings from infected stock plants were vegetatively propagated in a thrips-free glasshouse, 44.4% of those obtained from the apical shoot and 20.6% of those obtained from the middle section of the plant developed systemic symptoms. These results indicated that when gentian plants were infected with INSV, the virus was preferentially transported from the infected leaves to the root and winter buds. However, even asymptomatic shoot cuttings may develop systemic symptoms when obtained from infected stock plants. Therefore, vegetative propagation from infected stock plants can be a source of INSV infection.     

First report of leaf spot on lettuce caused by <Emphasis Type="Italic">Curvularia aeria</Emphasis>

In 2017, leaf spots were found on lettuce growing in fields in Songkhla Province, southern Thailand. The fungus isolated from the spot lesions on the leaves was identified as Curvularia aeria (Bat., J.A.Lima and C.T.Vasconc.) Tsuda based on morphological characteristics and DNA sequences of the ITS region of the rRNA gene. After a conidial suspension of the isolate was sprayed on lettuce seedlings, the leaf spots developed on lettuce seedlings, and the fungus was reisolated; leaves of plants inoculated with water did not develop spots. This is the first report of C. aeria causing leaf spot on lettuce.