Plectosporium blight of pumpkin and ranunculus caused by Plectosporium tabacinum

Based on inoculation experiments and morphological studies on the pathogenic isolates of Plectosporium spp., Microdochium blight (Hakuhan-byo in Japanese) of pumpkin (Cucurbita maxima Duch.) occurring in Japan was reconfirmed to be caused by Plectosporium tabacinum, and seedling blight (Kabugare-byo in Japanese) of ranunculus (Ranunculus asiaticus L.) was demonstrated to be caused by P. tabacinum. Both diseases are renamed Plectosporium blight in this article. Some isolates of the fungus appeared to have host specificity, whereas the others had either weak or no pathogenicity to pumpkin and ranunculus.     

Cutting rot of chrysanthemum (<Emphasis Type="Italic">Chrysanthemum morifolium</Emphasis>) caused by <Emphasis Type="Italic">Plectosporium tabacinum</Emphasis>

Cutting rot of chrysanthemum was found on cuttings of cv. Jimba No.2 in 2008. The cuttings were imported, then transplanted in Aichi Prefecture. Root development was not initiated in about 30% of the cuttings. The cut stem ends developed black discolouration and decay. When healthy cuttings were the fungus isolated from diseased cuttings, these cuttings developed the same disease symptoms. The characteristics and morphology of the fungal culture were identical to those of Plectosporium tabacinum. We propose that the new disease be named cutting rot of chrysanthemum.     

Gray mold of pearl lupine caused by <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

Severe blight of stems, leaves and pods caused by Botrytis cinerea was found on pearl lupine (Lupinus mutabilis), a legume crop, grown in Kagawa Prefecture, Japan, in March–June 1996–2002. This disease was named “gray mold of pearl lupine” as a new disease. One of the fungal isolates obtained in this study was deposited in Genebank, National Institute of Agrobiological Sciences as accession MAFF238557.     

Induction of systemic resistance to <Emphasis Type="Italic">Exobasidium vexans</Emphasis> in tea through SAR elicitors

The effect of two chemical elicitors (acibenzolar-S-methyl benzo-[1,2,3]- thiadiazole-7-carboxylic acid S-methyl ester [Boost 500SC]) and salicylic acid in inducing resistance in tea plants against blister blight disease caused by Exobasidium vexans Massee, was studied. Treatments with elicitors resulted in reduced severity of blister blight disease in nursery plants on challenge with the pathogen. There was a significant increase in the activities of defense enzymes like phenylalanine ammonia lyase, peroxidase and β-1,3-glucanase on elicitor treatments in tea leaves challenged with the pathogen than on unchallenged leaves. Acibenzolar-S-methyl (ASM) at 0.14% registered the lowest disease severity (25.2%), whereas treatments with salicylic acid were inferior. Under field conditions, the application of ASM at 0.14% resulted in disease protection of 25%. When ASM was applied in alternate rounds with a standard fungicide, the disease protection improved to 46.8%. The importance of incorporating ASM as a component in integrated disease management and also its importance in organic tea cultivation is discussed.     

Rhizoctonia Blight of Yacon Caused by Rhizoctonia solani AG-1 (IB)

Severe blight of stems and leaves caused by Rhizoctonia solani AG-1 (IB) was found on yacon (Smallanthus sonchifolius), a Compositae tuber crop, grown in Ehime Prefecture, Japan, from August to September 1996 and 1999. We named it “Rhizoctonia blight of yacon” as a new disease. Received 15 October 2001/ Accepted in revised form 25 November 2001     

Antifungal activities of hyoscyamine and scopolamine against two major rice pathogens: <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis> and <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

The antifungal activities of hyoscyamine and scopolamine, major alkaloids extracted from the desert plant Hyoscyamus muticus, against two rice pathogens, Magnaporthe oryzae and Rhizoctonia solani, were studied. The minimum inhibitory concentration of hyoscyamine that resulted in distinctive inhibition (MIC₅₀) was 1 μg/ml for both fungi. Exposure to hyoscyamine caused the leakage of electrolytes from the mycelia of both fungi. Hyoscyamine (>1 μg/ml) irreversibly delayed or inhibited conidial germination and appressorium formation in M. oryzae grown on polystyrene plates. Hyoscyamine effectively inhibited the attachment of conidia to the surface of rice (Oryza sativa) leaves and inhibited appressorium formation on the leaves. A high concentration of scopolamine (1000 μg/ml) also delayed or inhibited conidial germination in M. oryzae, but conidial germination was restored after washing the conidia with water. Antifungal activity of hyoscyamine was reduced by scopolamine. Magnaporthe oryzae infection was significantly suppressed (by >95%) in leaves of intact rice plants treated with hyoscyamine (10 μg/ml). Moreover, 10 μg hyoscyamine/ml significantly reduced the disease severity index for sheath blight to ≤0.2, when compared with the disease index of control plants (>7.0). Hyoscyamine (>20 μg/ml) completely inhibited sclerotial germination and development of R. solani by delaying the initiation, maturation, and melanization of the sclerotia. These results suggest that tropane alkaloids may be useful for controlling blast and sheath blight diseases of rice and for studying the mechanisms that regulate conidial germination in M. oryzae and sclerotial germination and development in R. solani.     

First report of leaf blight disease of <Emphasis Type="Italic">Gloriosa superba</Emphasis> L. caused by <Emphasis Type="Italic">Alternaria alternata</Emphasis> (Fr.) Keissler in India

Leaf blight disease was found on Gloriosa superba L. (Liliaceae), an endangered, herbaceous, perennial, climbing lily that produces colchicine, in West Bengal, India in 2004. Small brownish spots on leaves developed into concentric rings, which eventually darkened and coalesced to blight the entire leaf. The causal fungus was morphologically identified as Alternaria alternata (Fr.) Keissler. This is the first record of A. alternata on G. superba.     

Effect of SS-toxin,a metabolite of <Emphasis Type="Italic">Stemphylium solani</Emphasis>, on H<Superscript>+</Superscript>-ATPase activity and standard redox system in plasma membranes from seedlings leaves of garlic (<Emphasis Type="Italic">Allium sativum</Emphasis>)

Leaf blight of garlic (Allium sativum) is a severe disease in garlic-growing regions. SS-toxin is a newly described non-proteinaceous toxin produced by the phytopathogenic fungus, Stemphylium solani, the cause of garlic leaf blight. In this study, the effects of SS-toxin on the H⁺-ATPase activity and standard redox activity in the plasma membranes isolated by aqueous polymer two-phase partitioning from garlic seedling leaves were studied in vitro. The H⁺-ATPase activity, NADH oxidation rate and Fe(CN)₆³⁻ reduction rate of the plasma membranes isolated from susceptible and resistant cultivars were all inhibited in a dose-dependent manner. Our results suggest that, under in vitro conditions, the plasma membrane H⁺-ATPase and standard redox system can be both the cellular targets of SS-toxin.     

Disease severity,incidence and races of <Emphasis Type="Italic">Setosphaeria turcica</Emphasis> on sorghum in Uganda

In order to understand the underlaying causes of new severe turcicum leaf blight outbreaks in East Africa, a survey was undertaken in Uganda to examine the sorghum—Setosphaeria turcica interaction in terms of disease severity and incidence, the overall fungal population structure, and new resistant resources. Highest disease severities were recorded on caudatum accessions, whereas kafir genotypes were most resistant. The disease was more severe in the most humid farmlands compared to moderately dry agro-ecologies. In districts with wide adoption of the Epuripur variety a very high incidence (100%) of turcicum leaf blight was found. The two S. turcica mating type genes MAT1-1 and MAT1-2 assessed on fungal isolates deriving from both sorghum and maize diseased leaves were found in 20 of 23 districts sampled and in equal proportions. Upon cross inoculation on maize differential lines, four S. turcica isolates were identified as race 1, two as race 2, and one isolate corresponded to race 0 and race 3, respectively. The remaining 10 S. turcica isolates did not cause any disease symptoms on the maize lines assessed. Highly resistant accessions originating from a regional collection were found among the five sorghum races (kafir, guinea, caudatum, bicolor and durra), and are now implemented in new sorghum disease resistance programs.     

<Emphasis Type="Italic">Fusarium langsethiae</Emphasis> pathogenicity and aggressiveness towards oats and wheat in wounded and unwounded <Emphasis Type="Italic">in vitro</Emphasis> detached leaf assays

In vitro detached leaf assays involving artificial inoculation of wounded and unwounded oat and wheat leaves were used to investigate the potential pathogenicity and aggressiveness of F. langsethiae, which was linked recently to the production of type A trichothecenes, HT-2 and T-2 in cereals in Europe. In the first two experiments, two assays compared disease development by F. langsethiae with known fusarium head blight pathogen species each used as a composited inoculum (mixture of isolates) at 10°C and 20°C and found all fungal species to be pathogenic to oat and wheat leaves in the wounded leaf assay. In the unwounded leaf assay, F. langsethiae was not pathogenic to wheat leaves. Furthermore, there were highly significant differences in the aggressiveness of pathogens as measured by lesion length (P < 0.001). In the second two experiments, pathogenicity of individual F. langsethiae isolates previously used in the composite inoculum was investigated on three oat and three wheat varieties. The wounded leaf assay showed that all isolates were pathogenic to all oat and wheat varieties but only pathogenic towards oat varieties in the unwounded assay. Highly significant differences (P < 0.001) in lesion length were found between cereal varieties as well as between isolates in the wounded assay. Significant differences in lesion lengths (P = 0.014) were also observed between isolates in the unwounded assay. Results from the detached leaf assays suggest that F. langsethiae is a pathogen of wheat and oats and may have developed some host preference towards oats.     

Determination of agronomic practices for the management of blight of chickpea caused by <Emphasis Type="Italic">Ascochyta rabiei</Emphasis> in Turkey: 1. Appropriate sowing date

In order to determine the most appropriate dates for planting chickpea in central Anatolia, Turkey, six cultivars were planted at three sites that differed in disease pressure. In two of the sites, disease pressure from Ascochyta rabiei was promoted by spreading infected chickpea debris on the soil surface at the time of planting and, at one of these, sprinkle irrigation was applied. In the third site, where conditions were dryer, no artificial inoculum was provided. Plants from seeds sown in early March had the most disease and in the sprinkle irrigated plots the disease severity ranged from 7.8 on the most susceptible cv. Canitez to 3.3 on the least susceptible Gokce as scored on the 1–9 scale where 1 = no disease and 9 represents a plant killed by the fungus. There was an inverse relationship between disease severity and yield, production from blight resistant cultivars of around 2,000 kg ha⁻¹ being more than twice that of susceptible ones. Delaying planting for 3–5 weeks reduced the severity of ascochyta blight but also reduced the yields in four of the six cultivars. In contrast, reduction in disease severity by delayed sowing resulted in yield increases for the susceptible cvs Canitez and Local, although yield level was not as much as those of the less susceptible cvs sown early. Delay of 6–9 weeks almost eliminated ascochyta blight but yields of all cultivars were seriously compromised by drought stress. In consequence, chickpea farmers are recommended to use resistant or tolerant cultivars and sow early in March. For less resistant cultivars, sowing in early April is recommended. Further delay is not recommended unless irrigation is provided and fungicide spraying is recommended where signs of infection are present under conditions conducive to the disease.     

Web Blight of Fan Columbine, <Emphasis Type="Italic">Aquilegia flabellata, </Emphasis>Caused by <Emphasis Type="Italic">Rhizoctonia solani </Emphasis>AG1-IB : A New Disease Record

A new disease, found on fan columbine in August of 1997, first appeared as necrotic spots on leaves and within a week caused wilting of all the leaves. Fungal mycelia bound aerial parts of the plants together, formed mats of mycelia and eventually killed the plants. The pathogen, isolated from the infected leaves and stalks, was identified as Rhizoctonia solani AG1-IB in respect to hyphal anastomosis and culture types. The common name of web blight is proposed for this new occurrence on fan columbine (Kumonosu-byo in Japanese). Received 24 November 1999/ Accepted in revised form 4 February 2000     

Anthracnose of <Emphasis Type="Italic">Polygonatum falcatum</Emphasis> caused by <Emphasis Type="Italic">Colletotrichum dematium</Emphasis>

Severe spotting, blight and drop of leaves caused by Colletotrichum dematium were found on potted plants of Polygonatum falcatum, a liliaceous ornamental, in open fields in Kagawa Prefecture, Japan, in May 2001. This new disease was named anthracnose of P. falcatum. Keisuke Tomioka, Jouji Moriwaki, Toyozo Sato contributed equally to this work. The fungal isolate and its nucleotide sequence data obtained in this study were deposited in Genebank, National Institute of Agrobiological Sciences and the DDBJ/EMBL/GenBank databases under accessions MAFF239500 and AB334523, respectively.     

A novel pathosystem to study the interactions between <Emphasis Type="Italic">Lotus japonicus</Emphasis> and <Emphasis Type="Italic">Fusarium solani</Emphasis>

A wilt disease of the model legume Lotus japonicus was observed in a greenhouse in Tokyo, Japan in May 2004. Roots of diseased plants were rotted and dark brown with lesions spreading to lower stems and leaves, resulting in rapid plant death. The causal agent was identified as Fusarium solani based on the morphology. Sequence analysis of rDNA supported the identification. Inoculation of roots of healthy plants with conidia reproduced characteristic disease symptoms, and F. solani was reisolated from lesions, satisfying Koch’s postulates. The isolate also caused chlorotic to necrotic lesions on leaves of healthy plants after wound-inoculation. Infection by F. solani of leaves of L. japonicus was confirmed histologically. Mycelia were observed in the intercellular spaces of parenchymatous tissues in the lesion area and the surrounding tissues. This is the first report of fungal disease on L. japonicus satisfying Koch’s postulates. We named it “Fusarium root rot of L. japonicus” as a new disease. The compatibility of L. japonicus and F. solani is expected to form a novel pathosystem for studying interactions between legumes and fungal pathogens. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB258993 and AB258994.     

The life cycle of <Emphasis Type="Italic">Stemphylium vesicarium</Emphasis>, the causal agent of Welsh onion leaf blight

Symptoms of Welsh onion leaf blight, caused by Stemphylium vesicarium, are divided into two types, i.e., brown oval lesions and yellow mottle lesions. Yellow mottle lesions exert considerable economic damage on Welsh onion in northern Japan. In this study, we investigated the life cycle of the pathogen in terms of seasonal fluctuation of spore dispersal and its relationship with development of disease, formation period of pseudothecia and overwintering of the pathogen based on field surveys, spore trapping and fungal isolation. Conidia were trapped throughout the cropping season except before mid June, when no ascospores were trapped. Brown oval lesions, which contained a large number of conidia, usually occurred in July followed by yellow mottle lesions with an increasing number of conidia trapped. These observations suggest that conidia released from brown oval lesions play an important role as a secondary inoculum source of the disease, leading to the development of yellow mottle lesions. Pseudothecia on leaves were first observed at the end of the cropping season or immediately after harvest (late October). The pathogen overwintered in the form of pseudothecia produced on leaves with or without symptoms. Ascospores failed to be trap in the field during the interval between before and beginning of the cropping season in April–May. However, pot experiments demonstrated that ascospores were released from leaf debris in November and rapidly increased in number after snow melt. From this circumstantial evidence, we hypothesize that ascospores are the primary inoculum source of Welsh onion leaf blight.     

Note: Evaluation of antibacterial activity of essential oil of<Emphasis Type="Italic">Rosa damascena</Emphasis> on<Emphasis Type="Italic">Erwinia amylovora</Emphasis>

Significant antibacterial activity was observed in the essential oil (E.O.) ofRosa damascena Mill. and the Minimum Bactericidal Concentration (MBC) of the E.O. was determined as 1386.5 μg ml⁻¹ forErwinia amylovora, the causal agent of fire blight disease. Ooze formation on immature pears and lesion formation in artificially inoculated shoots were completely (100%) prevented by the essential oil ofR. damascena (1500 μg ml⁻¹), essential oil ofThymbra spicata var.spicata (500 μg ml⁻¹) and streptomycin (100 μg ml⁻¹). Copper oxychloride plus maneb significantly reduced ooze formation and lesion formation, but the control was less than that obtained with the essential oils or streptomycin. The essential oil ofR. damascena may be a useful natural bactericide for the control of the fire blight pathogen,E. amylovora. http://www.phytoparasitica.org posting July 14, 2004.     

Genetic resistance to bacterial blight disease in Persian walnut

Bacterial blight disease of Persian walnut (Juglans regia, L.), caused by Xanthomonas arboricola pv. juglandis (Xaj), leads to significant nut losses in northern, central and western areas of Iran. To identify the natural sources of resistance to disease in the endemic walnut genotypes of Iran, sixteen walnut genotypes, collected from different areas of Hamedan province, were inoculated with Xaj in a randomized complete block design with five replicates for each genotype. Two-year old genotypes were gently sprayed with a suspension of bacteria adjusted to approximately 2 × 10⁹ cfu ml⁻¹ of distilled water in May. Infected leaves were rated for disease 28 and 42 days after inoculation, using a 0 to 5 severity scale, based on the number, size and distribution of lesions on the leaves. Data analyses showed that there were variations among genotypes in response to pathogen. Upon inoculation by bacterial suspension genotype 94 showed the highest resistance to both disease incidence and its progress after 4–6 weeks of infection. Genotype 65 showed high susceptibility to disease and genotype 69 showed high susceptibilities both to disease incidence and its progress after 4–6 weeks of infection.     

Toxicity of propamocarb to the late blight fungus on potato

Propamocarb (Previcur-N; propyl-[3-dimethylamino-propyl] carbamate-monohydrochloride) was testedin vivo against 32 field isolates ofPhytophthora infestans from six countries. Fungicide dosages required to achieve 90% control of the blight ranged between 676 and 1530 ppm a.i. in potted potato (cv. ‘Alpha’) plants and between 1135 and 2648 ppm in potato tuber slices. Isolates from Israel were less sensitive to the fungicide than isolates from Europe or North America. Toxicity of propamocarb was not related to resistance or sensitivity to phenylamide fungicides (e.g. metalaxyl). Nevertheless, most metalaxyl-resistant isolates from Israel were less sensitive to propamocarb than most metalaxyl-sensitive isolates from this country. Monocyclic epidemics conducted with the 20 Israeli isolates in the field showed that 1081–2012 ppm of the fungicide was required to achieve 90% control of the disease. Laboratory experiments revealed that the fungicide was poorly active against sporangial germination and had a limited curative efficacy. It exhibited a translaminar translocation in leaves but a poor acropetal or basipetal systemicity from foliage. Propamocarb + mancozeb mixtures (1:1, v/w) were synergistically effective in controlling the blight. Growers in Israel use tank mixtures of propamocarb (Dynone) and mancozeb to combat late blight in potato fields where phenylamide-resistant isolates ofP. infestans are prevalent.     

Suppression of <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> by antifungal substances produced by the mycoparasite <Emphasis Type="Italic">Coniothyrium minitans</Emphasis>

A study was conducted to investigate production of antifungal substances (AFS) by Coniothyrium minitans (Cm), a mycoparasite of Sclerotinia sclerotiorum (Ss), in modified Czapek-Dox (MCD) broth and potato dextrose broth (PDB), and effects of AFS of Cm on mycelial growth and germination of sclerotia and ascospores of Ss and incidence of leaf blight of oilseed rape caused by Ss. Results showed that mycelial growth of Ss was reduced by 41.6 and 84.5% on 3 day-old cultures grown on potato dextrose agar (PDA) amended with 10% (v v⁻¹) of cultural filtrates of Cm grown in MCD (MCD_cm) after incubation for 6 and 15 days, respectively, and by 2.7 and 15.7% on PDA amended with 10% (v v⁻¹) of cultural filtrates of Cm grown in PDB for 6 and 15 days, respectively. In addition to retardation of mycelial growth, morphological abnormality of Ss such as hyphal swellings and cytoplasm granulation were also observed in colonies grown on PDA amended with cultural filtrates of MCD_cm. Sclerotia of Ss soaked in the filtrates of MCD_cm for 24 h remained viable, but their ability to undergo myceliogenic germination on PDA was delayed, compared to sclerotia treated with MCD. Germination of ascospores of Ss was unaffected on PDA amended with 10% of the filtrates of MCD_cm. However, germ tubes of Ss were shortened and deformed by the formation of hyphal swellings in the treatment of MCD_cm. Treatment of leaves of oilseed rape with cultural filtrates of MCD_cm reduced incidence of leaf blight caused by Ss, compared to the controls (water or MCD). This study suggests that AFS produced by Cm plays an important role in the suppression of mycelial growth and germ-tube development of ascospores of Ss and that there is potential for using AFS of Cm to control leaf blight of oilseed rape caused by ascospores of Ss.     

Leaf position,leaf age and plant age affect the expression of downy mildew resistance in <Emphasis Type="Italic">Brassica oleracea</Emphasis>

Downy mildew caused by the oomycete Hyaloperonospora parasitica (formerly Peronospora parasitica) is a worldwide foliar disease of Brassica vegetables, which may cause seedling loss in the nurseries and damage to adult plants in the field. Disease symptoms start from the lower leaves and progress upwards. Three experiments were conducted under controlled environment conditions, using inoculated leaf discs, to determine the influence of leaf position, plant age, and leaf age on the expression of resistance to downy mildew in various Brassica oleracea genotypes. The upper leaves were more resistant than the lower leaves when 7–19 week-old plants of broccoli and Tronchuda cabbage were tested. Broccoli lines ‘PCB21.32’ and ‘OL87123-2’ were fully susceptible at the cotyledon stage, showed a clear resistance increase from lower to upper leaves at 6 weeks and ‘PCB21.32’ was fully resistant 16 weeks after sowing. Immature leaves were more resistant than adjacent fully expanded mature leaves. Susceptibility increased with leaf age when the same leaf was tested at two to 4-week intervals. Leaf age and upper-leaf position on the stem had opposite effects on disease score, since younger leaves collected from lower positions and older leaves collected from upper positions tended to score similarly in compatible interactions. The progression of downy mildew from the base of the plant upwards on B. oleracea in the field could be due to differences in leaf resistance in addition to environmental variation. To maximise the expression of a compatible reaction in adult plants lower leaves of Brassica plants that are at least 12 weeks-old should be used.