Springer Science and Business Media LLC

Helleborus net necrosis virus (HeNNV) in hellebores (Helleborus spp.) has been detected for the first time in Japan. Infected plants had black streaks on fresh leaves and black spots on sepals, which resembled the symptoms of black death disease. The morphology of the virus particles isolated from infected plants was comparable to that of carlaviruses. RT-PCR analysis showed that the entire HeNNV genomic sequence isolated in Japan shared 99% identity with that of HeNNV previously reported in the United States.

 Laboratory mutants of Cochliobolus heterostrophus resistant to iprodione were obtained after chemical mutageneses. All the mutants were able to grow on the medium amended with iprodione 100 μg/ml. They showed positive cross-resistance to procymidone and fludioxonil and were sensitive to high osmolarity. Crosses between the mutant and a wild-type strain revealed that the fungicide resistance and osmotic sensitivity traits were inherited by their offspring in a 1 : 1 mutant/wild type ratio, indicating that the mutant phenotypes in these strains were due to alteration at a single gene locus. Results from allelism tests indicated that three genes (Dic1, Dic2, Dic3) conferred the mutant phenotypes. Among them, Dic1 mutant strains were classified into three types on the basis of their phenotypes. The first type was moderately resistant to the fungicides and less sensitive to osmotic stress than the other Dic1 mutant strains. The second type showed moderate fungicide resistance, but growth was inhibited under lower osmotic stress (50 mM KCl). The other Dic1 mutant strains grew well on medium containing iprodione and fludioxonil even at a concentration of 100 μg/ml and were highly sensitive to osmotic stress. The Dic2 and Dic3 mutant strains had moderate resistance to the fungicides with low-level osmotic sensitivity. The Dic1 gene was epistatic to Dic2 and Dic3 for fungicide resistance and hypostatic to them for osmotic sensitivity. These results suggest that the osmoregulatory system is involved in fungicide resistance in laboratory mutants of C. heterostrophus.

Pseudomonas cichorii causes rot on lettuce leaves, distinct from the necrotic spots of infected eggplant leaves. On lettuce leaves, P. cichorii invades intercellular spaces through stomata and grows vigorously, causing rot on the leaves. Surprisingly, P. cichorii does not produce pectate lyase, the most important enzyme for degrading plant cell walls. Alternatively, infection with P. cichorii causes heterochromatin condensation and DNA laddering in lettuce cells, followed by induced cell death, which results in disease symptoms. Thus, apoptotic programmed cell death (PCD) is associated with the symptoms on lettuce leaves. Although PCD in P. cichorii-infected eggplant leaves is also associated with necrotic spots caused by the bacteria, there are differences in the responses of the two hosts. P. cichorii harbors the N-acetyltransferase family gene (pat) and the hrp genes (hrp) encoding a type III secretion system, adjacent to an aldehyde dehydrogenase gene (aldH). The virulence of P. cichorii is hrp-dependent in eggplant, but not in lettuce. Furthermore, hrp, pat and aldH are implicated in the diversity of P. cichorii virulence on susceptible Asteraceae species. The involvement of hrp, aldH and pat in bacterial virulence on the respective species has no relationship with the phylogeny of the plants species. When these results are considered together, P. cichorii has multiple virulence determinants. The involvement of not only hrp but also aldH and pat in P. cichorii virulence arose after species diversification of host plants. Host responses implicated in symptom development have been responsible for the development of virulence determinants of P. cichorii.

A correction to this paper has been published: https://doi.org/10.1007/s10327-021-01008-7

Species of Colletotrichum are common pathogens that cause loquat fruit rot in Nagasaki Prefecture, Japan. For clarifying the site of infection and the Colletotrichum species responsible for anthracnose in loquat trees, fungi were isolated from asymptomatic flowers and rotten fruits and identified to the species rank based on morphological and molecular phylogenetic analyses. Nineteen isolates from 148 rotten fruits were identified as C. fioriniae (12 isolates), C. nymphaeae (2 isolates), C. gloeosporioides s. s. (1 isolate), and four unidentified species of Colletotrichum. From 900 asymptomatic flowers, C. fioriniae (5 isolates), C. gloeosporioides s. s. (1 isolate), C. siamense (2 isolates), an unknown species (11 isolates) belonging to the C. acutatum species complex, and 2 were Colletotrichum spp. All isolates were pathogenic on wounded leaves and fruits. These results imply that C. fioriniae and C. gloeosporioides s. s. infect flowers and cause loquat fruit rot after maturation. However, the pathogenicity of the other species remains unclear as does the reason for the differences in the composition and proportions of fungal species in fruits and flowers. Eleven isolates obtained from asymptomatic flowers that also cause anthracnose disease in loquat were identified as a novel species of Colletotrichum, which was named C. nagasakiense sp. nov.

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.

Barley (Hordeum vulgare) mildew locus o (mlo) mutants exhibit strong resistance to penetration by the powdery mildew fungus Blumeria graminis f. sp. hordei. MLO, a seven-transmembrane protein localized at the plasma membrane is thought to be involved in intracellular calcium signaling. However, its molecular function and the mechanism by which mlo mutations confer resistance to penetration by the fungus remain poorly understood. A large number of mlo alleles with different amino acid substitutions at each intracellular loop have been found in various cultivars. However, it is difficult to analyze how each amino acid is involved in penetration resistance by comparing these cultivars because they differ substantially in their genetic background and in the presence or absence of resistance genes recognizing avirulence factors from the pathogen. In this study, we used a CRISPR/Cas9-mediated genetic modification system to generate mlo mutants in the transformable cultivar Golden Promise to enable complementation experiments with the aim of elucidating the molecular function of MLO. An mlo mutant with a thymine insertion in the second exon and penetration resistance to B. graminis f. sp. hordei was obtained. Susceptibility was restored in cells in which the MLO-mCherry gene was introduced using particle bombardment, indicating that this mlo mutant could be a useful genetic tool for complementation experiments using transgenes expressing a variety of mlo alleles.

The pesticides used to tackle potato pathogens, including bacteria, are environmentally damaging, so more sustainable treatments are needed. Because plant defense-related hormones such as methyl jasmonate and salicylic acid and the elicitor chitosan can stimulate plant defense systems, the effect of these compounds was tested by adding them to a watering solution 2 days before inoculating two S. tuberosum cultivars with either Pectobacterium carotovorum strain 5890 or P. atrosepticum strain 889. Growth and the production of several defense phenolic compounds were determined in treated and untreated plants, inoculated or not. P. carotovorum 5890 was more virulent than P. atrosepticum 5889 as reflected by higher levels of phenolic compounds in the plants. The defense-related hormone salicylic acid offered the most protection against the bacteria without interfering with plant growth. Because plants produce and accumulate secondary metabolites for protection against infection, higher production was accompanied by less pathogen damage and higher resistance.

 In 2001 virus-like symptoms of yellowing, interveinal chlorosis, leaf-rolling, and necrotic fleck were observed on greenhouse- and field-grown tomato plants (Lycopersicon esculentum Miller) in Gunma and Tochigi Prefectures, Japan. Characteristics of the causal agent, such as particle morphology, whitefly transmission, and symptomatology, are similar to those of Tomato infectious chlorosis virus (TICV) and Tomato chlorosis virus, species of the genus Crinivirus in the family Closteroviridae. Electrophoretic analysis of extracted double-stranded RNAs revealed two major species of approximately 7 kbp. Sequencing of reverse transcription-polymerase chain reaction products using the specific primers for heat shock protein 70 homolog and diverged coat protein genes of closteroviruses indicated that the virus was TICV.