The effects of the timing of inoculation (before or after flowering) of ‘Shiranekomugi’ (moderately resistant) and ‘Yukichikara’ (relatively susceptible) cultivars of Triticum aestivum with Fusarium graminearum on the disease severity and subsequent accumulation of deoxynivalenol (DON) in the grain were examined in fields in Miyagi Prefecture, Japan, for three years. “Flowering” was defined as the time when 40-50% of the spikelets in a head were flowering. A conidial suspension of the fungus was periodically sprayed onto the heads of two cultivars from first heading (12-17 days before the flowering) to 30 days after the flowering. Consequently, both cultivars had the highest disease severity and DON levels in the grains when inoculated at various times from 3 days before to the day of flowering in both cultivars, indicating that this is the most susceptible period for each cultivar. At other times of inoculation, however, the levels of disease severity and DON were not always consistent. DON levels were significantly higher in grains of cv. Yukichikara after inoculation during the period. These results suggested that the levels of disease severity and toxin accumulation in relation to the timing of inoculation depends on the cultivar; thus, elucidating these relations for each wheat cultivar is important for developing effective control strategies. A high correlation coefficient between the ratio of flowering spikelets in a head and the ratio of heads with at least one flowering spikelet was observed for each cultivar in the field. This correlation suggests that evaluating the ratio of the flowering heads is useful for estimating the ratio of flowering spikelets in each head, which indicates the time of flowering. The ratio of flowering heads in a field could then be used as an indicator for timing the application of control measures.
A virus, isolated from Ipomoea batatas in Oita Prefecture in Japan, infected I. nil, I. setosa and Chenopodium amaranticolor in a host range test of 16 species in 10 families. Symptoms on I. nil were distinct from those on plants infected with Sweet potato feathery mottle virus (SPFMV) severe strain (S), ordinary strain (O) and tokushima strain (T). Leaf extracts of infected I. nil lost infectivity after one day at 20°C and after dilution of 10−3-10−4. The thermal inactivation point was 50-60°C. The virus is filamentous, ca. 850 nm long, and transmitted by Myzus persicae. The coat protein (CP) of the virus is composed of 355 amino acids and has 93-99% homology at the amino acid level with the CP of Sweet potato virus G (SPVG). In a phylogenetic analysis based on the amino acid sequences of the CP, the virus grouped in the SPVG cluster with viruses isolated from sweet potato in the world. The SPVG isolate rarely caused slight skin discoloration on storage roots of I. batatas. The severity of disease on storage roots of I. batatas was greater after co-infection with SPFMV-S and SPVG than after infection with SPFMV-S alone. From all these results, the virus was identified as an isolate of SPVG (SPVG-Oita). This report is the first on the detection of SPVG in Japan.
In 2004, an unidentified disease causing chlorotic yellows on the leaves of melon (Cucumis melo) plants was found in Kumamoto Prefecture. A few flexuous filamentous structures (ca. 900 nm in length) were observed with transmission electron microscopy. RT-PCR and subsequent nested PCR amplified a DNA fragment, which had 75% and 73% similarities with a corresponding sequence for Cucurbit yellow stunting disorder virus and Beet pseudo-yellows virus, respectively. Both Bemisia tabaci Q-biotype and B. tabaci B-biotype (syn. B. argentifolii) acquired and transmitted the virus, and the infected melon plants developed the original symptoms of the disease. These results demonstrate that the virus is a new species in the genus Crinivirus (family Closteroviridae), and we propose the name Cucurbit chlorotic yellows virus.
A 2658-bp full-length cDNA encoding a lipoxygenase (AaLOX1) was identified from Baby kiwi (Actinidia arguta). The deduced amino acid sequence of the gene is about 70% identical to plant liopxygenases (LOXs) of strawberry, potato and cucumber. The amino acid sequence possesses a PLAT motif and several of the typical LOX motifs. AaLOX1 is predicted to be located in the cytoplasm. AaLOX1 is inducible, and the transcripts accumulate in leaves within 0.5 hr after either wounding or inoculation with a pathogen or nonpathogen.
Rhizoctonia solani AG-1 IB was isolated from seedlings of Dahurian patrinia (Patrinia scabiosaefolia) with damping-off, and pathogenicity of the fungus was confirmed. This report is the first of damping-off of Dahurian patrinia caused by R. solani in Japan.
Peduncle blight and leaf spot on smoke tree (Cotinus coggygria) and water-soaked lesions on stock (Matthiola incana) petal were observed in Yamagata Prefecture from 2005 to 2007. The causal fungus of these diseases was identified as Colletotrichum acutatum on the basis of morphological characteristics and rDNA-ITS sequence homology. This report adds C. acutatum as new pathogen of smoke tree anthracnose. Petal anthracnose was coined for the disease on stock because the symptoms were different from the anthracnoses reported previously.