Pythium rot of figmarigold (<Emphasis Type="Italic">Lampranthus spectabile</Emphasis>) caused by <Emphasis Type="Italic">Pythium aphanidermatum</Emphasis>

A new leaf rot disease was found on the leaves of figmarigold (Lampranthus spectabile). The causal organism, identified as Pythium aphanidermatum was found to cause the same symptoms after artificial inoculation and was then reisolated from the inoculated plants. We propose to name the disease Pythium rot of figmarigold.     

Epidemiology of root rot caused by <Emphasis Type="Italic">Leptosphaeria maculans</Emphasis> in <Emphasis Type="Italic">Brassica napus</Emphasis> crops

The infection of above-ground tissues of Brassica napus by Leptosphaeria maculans is well understood. However, root infection (root rot) under field conditions, the development of root rot over time and its relationship to other disease symptoms caused by L. maculans has not been described. A survey of B. napus crops was conducted in Australia to investigate the incidence and severity of root rot. Additionally, the pathway of root infection was examined in field experiments. Root rot was present in 95% of the 127 crops surveyed. The severity and incidence of root rot was significantly correlated with that of crown canker; however, the strength of this relationship was dependent on the season. Root rot symptoms appeared before flowering and increased in severity during flowering and at maturity, a pattern similar to crown canker suggesting that the infection of the root is an extension of the crown canker phase of the L. maculans lifecycle. All isolates of L. maculans tested in glasshouse experiments caused root rot and crown canker in B. napus and Brassica juncea. In the field, the main pathway of root infection is via invasion of cotyledons or leaves by airborne ascospores, rather than from inoculum in the soil. Root rot was present in crops in fields that had never been sown to B. napus previously, in plants grown in fumigated fields, and in glasshouse-grown plants inoculated in the hypocotyl with L. maculans.     

White root rot disease of the lacquer tree <Emphasis Type="Italic">Toxicodendron vernicifluum</Emphasis> caused by <Emphasis Type="Italic">Rosellinia necatrix</Emphasis>

In early August 2010, lacquer trees (Toxicodendron vernicifluum) severely damaged by a root rot disease were found on plantations in Iwate, Japan. The causal agent was a fungus identified as Rosellinia necatrix, based on morphology and the sequence of the ribosomal DNA internal transcribed spacer region. The fungus was clearly pathogenic on T. vernicifluum root plantings. This report is the first of white root rot on T. vernicifluum.     

Fusarium rot of hyacinth caused by <Emphasis Type="Italic">Gibberella zeae</Emphasis> (anamorph: <Emphasis Type="Italic">Fusarium</Emphasis><Emphasis Type="Italic"> graminearum</Emphasis>)

Severe rot of leaves, peduncles and flowers caused by Gibberella zeae (anamorph: Fusarium graminearum) was found on potted plants of hyacinth (Hyacinthus orientalis), a liliaceous ornamental, in greenhouses in Kagawa Prefecture, Japan, in January 2001. This disease was named “Fusarium rot of hyacinth” as a new disease because only the anamorph, F. graminearum, was identified on the diseased host plant. The authors contributed equally to this work. The fungal isolate and its nucleotide sequence data obtained in this study were deposited in the Genebank, National Institute of Agrobiological Sciences and the DDBJ/EMBL/GenBank databases under the accession numbers MAFF239499 and AB366161, respectively.     

Dumontinia root rot of liver leaf caused by <Emphasis Type="Italic">Dumontinia tuberosa</Emphasis>

Foliar wilt as well as crown and root rot with sclerotia formation has affected potted liver leaf (Hepatica nobilis var. japonica f. magna) in Ojiya, Niigata Prefecture, Japan, since 2006. Apothecia developed from the sclerotia on soil surface of pots with the diseased plants in March. A fungus forming the apothecia was identified as Dumontinia tuberosa (Sclerotiniaceae) based on its morphology and demonstrated to cause the disease. We coined the name “Dumontinia root rot (Dumontinia-negusare-byo in Japanese) of liver leaf” for the new disease.     

Pythium wilt of lettuce caused by <Emphasis Type="Italic">Pythium uncinulatum</Emphasis> in Japan

Pythium wilt of lettuce was found in two fields in Hyogo Prefecture, Japan in January 2007. On the basis of morphological characteristics and the rDNA-ITS sequences, the causal organism was identified as Pythium uncinulatum, unknown in Japan. A pot inoculation test demonstrated that P. uncinulatum was pathogenic to lettuce and garland chrysanthemum (both in Compositae), but no symptoms developed on nine species of vegetable plants from Amaranthaceae, Apiaceae, Brassicaceae, Cucurbitaceae, Liliaceae, or Solanaceae.     

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.     

First report of blueberry red ringspot disease caused by <Emphasis Type="Italic">Blueberry</Emphasis><Emphasis Type="Italic">red</Emphasis><Emphasis Type="Italic">ringspot</Emphasis><Emphasis Type="Italic">virus</Emphasis> in Japan

Virus-like symptoms—red ringspots on stems and leaves, circular blotches or pale spots on fruit—were found on commercial highbush blueberry (Vaccinium corymbosum) cultivars Blueray, Weymouth, Duke and Sierra in Japan. In PCR testing, single DNA fragments were amplified from total nucleic acid samples of the diseased blueberry bushes using primers specific to Blueberry red ringspot virus (BRRV). Sequencing analysis of the amplified products revealed 95.7–97.7% nucleotide sequence identity with the BRRV genome. This paper is the first report of blueberry red ringspot disease caused by BRRV in Japan. The nucleotide sequence data reported in this paper are available in the GenBank/EMBL/DDBJ database as accessions AB469884 to AB469893 for BRRV isolates from Japan.     

Resistance assessment and biochemical responses of sugar beet lines against <Emphasis Type="Italic"> Pythium aphanidermatum,</Emphasis> causing root rot

Wood-staining fungi, moulds and decay fungi colonize freshly cut wood. Of these, only ophiostomatoid fungi are considered major agents of sapstain on logs and freshly sawn lumber because they can cause permanent staining and discoloration. Sapstain in pine pallets significantly reduces their market value and use in the food industry. The aim of this study was to identify the sapstaining fungi that colonize Scots pine wood used in pallet production. In addition, we evaluated the growth and stain intensity of six isolates of ophiostomatoid fungi on freshly cut Scots pine billets. Fungi were isolated from samples of Scots pine and identified based on morphology and DNA sequence comparisons for three gene regions (ITS, β-tubulin, TEF-1α). A total of 1259 isolates representing 31 fungal species were obtained from the pine samples in Poland during July and September. The isolates represented different ecological and taxonomical groups and belonged to the categories of staining fungi, decay fungi and surface moulds. The most frequently isolated fungi were ophiostomatoid fungi (14 species including an unknown Leptographium sp. and Ophiostoma sp.) and moulds (mainly Trichoderma and Mucor spp.). Of the ophiostomatoid species, Ophiostoma floccosum, O. piceae, O. piliferum and Endoconidiophora pinicola were the predominant species. The results of pine billet inoculation showed that among the six fungal species tested, E. pinicola exhibited the fastest growth in all three directions on the billets. Ophiostoma minus and O. piliferum displayed moderate growth rates in pine billets, while O. floccosum, O. piceae, and Leptographium lundbergii grew very slowly, especially in the tangential and radial directions. The information provided in this paper will help develop more effective control strategies for sapstain prevention in Scots pine.     

Choanephora rot of floral tops of <Emphasis Type="Italic">Hyoscyamus muticus</Emphasis> caused by <Emphasis Type="Italic">Choanephora cucurbitarum</Emphasis>

Floral rot of Egyptian henbane (Hyoscyamus muticus L.) was found on potted plants in a greenhouse in Yamaguchi city, Japan, in the late summer of 2008 and 2009. The symptoms were identical to those of rots caused by Choanephora species. The pathogen was isolated and identified as C. cucurbitarum (Berkeley and Ravenel) Thaxter. This new disease was named Choanephora rot (Kougai-kabi-byo) of Egyptian henbane.     

First report of Choanephora rot of ice plant (<Emphasis Type="Italic">Mesembryanthemum crystallinum</Emphasis>) caused by <Emphasis Type="Italic">Choanephora cucurbitarum</Emphasis> in Japan

In summer 2007, leaf and stem rot of ice plants was found in a hydroponic greenhouse in Japan. The causal agent was a fungus identified as Choanephora cucurbitarum (Berkeley & Ravenel) Thaxter, based on pathogenicity, morphology, mating tests, and sequence analysis of the ribosomal DNA ITS region.     

Pathogenicity of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> and <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> against <Emphasis Type="Italic">Galleria mellonella</Emphasis>

The greater wax moth Galleria mellonella L. (Lepidoptera: Pyralidae) is occasionally found in beehives and is a major pest of stored wax. Entomopathogenic fungi have recently received attention as possible biocontrol elements for certain insect pests. In this study, 90 isolates of Beauveria bassiana and 15 isolates of Metarhizium anisopliae were screened for proteases and lipases production. The results showed significant variations in the enzymatic action between the isolates. In the bioassay, the selected isolates evinced high virulence against the 4th instar of the G. mellonella larvae. The isolates BbaAUMC3076, BbaAUMC3263 and ManAUMC3085 realized 100% mortality at concentrations of 5.5 × 10⁶ conidia ml⁻¹, 5.86 × 10⁵ conidia ml⁻¹, and 4.8 × 10⁶ conidia ml⁻¹, respectively. Strong enzymatic activities in vitro did not necessarily indicate high virulence against the tested insect pest. The cuticle of the infected larvae became dark and black-spotted, indicating direct attack of fungus on the defense system of the insects. The LC₅₀ values were 1.43 × 10³, 1.04 × 10⁵ and 5.06 × 10⁴ for Bba3263AUMC, Bba3076AUMC and Man3085AUMC, respectively, and their slopes were determined by computerized probit analysis program as 0.738 ± 0.008, 0.635 ± 0.007 and 1.120 ± 0.024, respectively.     

Potential of <Emphasis Type="Italic">Trichoderma</Emphasis> spp. and <Emphasis Type="Italic">Talaromyces flavus</Emphasis> for biological control of potato stem rot caused by <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis>

Sixteen isolates belonging to 11 species of Trichoderma (T. asperellum, T. ceramicum, T. andinensis, T. orientalis, T. atroviride, T. viridescens, T. brevicompactum, T. harzianum, T. virens, T. koningii and T. koningiopsis) were evaluated for biological control of potato (Solanum tuberosum) stem rot caused by Sclerotinia sclerotiorum. In dual culture tests, all antagonists significantly reduced sclerotia formation, and were able to inhibit radial growth of the pathogen. Growth inhibition by production of volatile and non-volatile inhibitors was also measured in in vitro tests. In screening the most efficient species of Trichoderma, establishment of mycelium on sclerotia and sclerotia lysis were also considered as important biocontrol qualities. Excluding T. asperellum, T. brevicompactum, T. andinensis and T. harzianum, all tested Trichoderma species were able to lyse sclerotia. The sclerotia-destroying species of Trichoderma and one isolate of Talaromyces flavus were tested in greenhouse tests and during 2 years of field experimentation during the 2007 and 2008 cropping seasons. After one aerial application of spore suspension in greenhouse trials, T. koningii, T. virens, T. ceramicum and T. viridescens were the most effective bio-agents and reduced significantly disease severity, and the least biocontrol efficacy was observed in T. flavus. Under field conditions and after five soil and foliar applications of spore suspension, all tested antagonists reduced significantly disease incidence. T. viridescens followed by T. ceramicum showed the best results. T. flavus and T. orientalis were less effective than other tested antagonists in both field trials.     

Visualization of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> cells during biocontrol of bacterial wilt disease in tomato with <Emphasis Type="Italic">Pythium oligandrum</Emphasis>

The biocontrol agent Pythium oligandrum (PO) can suppress bacterial wilt caused by Ralstonia solanacearum (RS) in tomato. To understand the primary biocontrol mechanisms of bacterial wilt by PO, we pretreated tomato plants with sterile distilled water or preinoculated them with PO, followed by inoculation with RS, then observed PO and RS in fixed sections of tomato tissues using a confocal laser-scanning microscope and fluorescence labeling until 14 days after the inoculation with RS. Horizontal and vertical movement of RS bacteria was frequently observed in the xylem vessels of roots and stems of tomato plants (cv. Micro-Tom) that had not been inoculated with PO. In plants that were preinoculated with PO, the movement of RS was suppressed, and bacteria appeared to be restricted to the pit of vessels, a reaction similar to that observed in resistant rootstocks. PO colonization was mainly observed at the surfaces of taproots, the junctions between taproots and lateral roots, and the middle sections of the lateral roots. PO was not observed near wound sites or root tips where RS tended to colonize. However, RS colonization was significantly repressed at these sites in PO preinoculated plants. These observations suggest that the induction of plant defense reactions is the main mechanism for the control of tomato bacterial wilt by PO, not direct competition for infection sites.     

Epidemiology of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">syringae</Emphasis> on tomato

Leaf spot of tomato, incited by Pseudomonas syringae pv. syringae, has been reported recently in Italy on grafted and non-grafted tomato plants (scion Cuore di Bue, rootstock Solanum lycopersicum x Solanum hirsutum cv. Beaufort). In some greenhouses, more than 80% of plants were affected, with a marked reduction in yield. This work was undertaken in order to understand the effect of the number of hours of incubation at high relative humidity (r.h.) and temperature as well as the effect of the presence of wounds at infection time on the development of leaf spot. A difference in sensitivity to leaf spot was observed in the various cultivars tested, in terms of severity of P. syringae pv. syringae, with “Cuore di Bue” being the most susceptible of these cultivars. The development of leaf spot is mostly favored by the presence of wounds, at temperatures between 15 and 20°C. The severity of the disease is lower at 10 and 25°C and very low at 30°C. Under the most favorable temperature conditions, the presence of wounds is sufficient to allow the development of the pathogen immediately upon incubation at high r.h. The effect of wounds and the relatively low requirement of hours of incubation at high r.h. suggest the need for careful management and handling of plants when temperatures range between 15 and 25°C, and particularly within 15 and 20°C. All operations carried out, particularly at transplant and immediately after, should avoid the creation of wounds.     

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.     

First report of phytophthora rot on <Emphasis Type="Italic">Wasabia japonica</Emphasis> caused by <Emphasis Type="Italic">Phytophthora drechsleri</Emphasis> in Japan

In September 2014, Phytophthora rot on wasabi plants [Wasabia japonica (Miq.) Matsum.] was found for the first time in the city of Okutama, Tokyo, Japan. A Phytophthora sp. strain was constantly isolated from brown stem bases and rhizomes of infected plants. The same symptoms as those observed in the field were produced in vitro through inoculation of test plants with the isolated Phytophthora sp. The fungus was identified as Phytophthora drechsleri based on morphological and DNA sequence comparison. Phytophthora rot, “eki-byo” in Japanese, is proposed for this disease common name.     

Functional analysis of the melanin biosynthesis genes <Emphasis Type="Italic">ALM1</Emphasis> and <Emphasis Type="Italic">BRM2</Emphasis>-<Emphasis Type="Italic">1</Emphasis> in the tomato pathotype of <Emphasis Type="Italic">Alternaria alternata</Emphasis>

The tomato pathotype of Alternaria alternata (A. arborescens) produces the dark brown to black pigment melanin, which accumulates in the cell walls of hyphae and conidia. Melanin has been implicated as a pathogenicity factor in some phytopathogenic fungi. Here, two genes of the tomato pathotype for melanin biosynthesis, ALM1 and BRM2-1, which encode a polyketide synthetase and a 1,3,8-trihydroxynaphthalene (THN) reductase, respectively, have been cloned and disrupted in the pathogen. The gene-disrupted mutants, alm1 and brm2-1, had albino and brown phenotypes, respectively. The wild-type and the mutants caused the same necrotic lesions on the leaves after inoculation with spores. These results suggest that melanin is unlikely to play a direct role in pathogenicity in the tomato pathotype A. alternata. Scanning electron microscopy revealed that the conidia of both mutants have much smoother surfaces in comparison to the wild-type. The conidia of those mutants were more sensitive to UV light than those of the wild-type, demonstrating that melanin confers UV tolerance.     

Nonhost resistance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> against <Emphasis Type="Italic">Colletotrichum</Emphasis> species

Arabidopsis thaliana exhibits a durable resistance called nonhost resistance against nonadapted fungal pathogens. A. thaliana activates preinvasive resistance and terminates entry attempts by nonadapted fungi belonging to the genus Colletotrichum, which cause anthracnose disease in many plants. In the interaction between A. thaliana and nonadapted C. tropicale, the preinvasive resistance involves the PENETRATION 2-related antifungal secondary metabolite pathway and the ENHANCED DISEASE RESISTANCE 1-dependent antifungal peptide pathway. The development of invasive hyphae by C. tropicale owing to the reduction of preinvasive resistance then triggers the blockage of further hyphal expansion via the activation of the second layer of resistance, i.e., postinvasive resistance, which guarantees the robustness of the nonhost resistance of A. thaliana against Colletotrichum pathogens. Both the tryptophan-derived metabolic pathway and glutathione synthesis play critical roles in the postinvasive resistance against C. tropicale, although the molecular mechanism of postinvasive resistance remains to be elucidated. In this review, we describe the current understanding of the molecular background of the Arabidopsis nonhost resistance against Colletotrichum fungi and discuss perspectives for future research on this durable resistance.