Cultivars resistant to chrysanthemum stunt viroid (CSVd) are desirable for stable production of chrysanthemum (Chrysanthemum × morifolium Ramat.). We previously reported that CSVd was absent not only from shoot apical meristems (SAMs) but also from leaf primordia (LP) of resistant plants following CSVd inoculation. Using this characteristic as a phenotypic marker, we could identify several resistant cultivars in this study. CSVd was inoculated directly into the SAMs of 85 commercial cultivars by attaching SAMs to infected root tips in vitro, and the cultivars were tested for the presence of CSVd in newly expanded leaves. Of the 85 cultivars, 20 resistant candidates could be identified. These plants were classified into two types according to their CSVd infection characteristics: a CSVd-uninfected or slow titer-increasing type and a CSVd-disappearance type. Scions of four of the 20 candidate cultivars were grafted to CSVd-infected rootstocks for evaluation of the CSVd titer in newly expanded leaves. Although CSVd was detected at high titer in two candidate cultivars over the two-month testing period, 'Sei no Issei' and 'Mari Kazaguruma', other two candidate cultivars, proved to be resistant cultivars. In 'Sei no Issei', CSVd was detected temporarily after grafting, but titers decreased in the newly expanded leaves, while CSVd was not detected in a shoot tip of an infected plant and only at trace levels in a young leaf. 'Mari Kazaguruma' also proved to be a resistant cultivar with a slow titer increase. The different types of CSVd resistance in chrysanthemum cultivars will contribute to CSVd-resistant breeding. With some modifications, the in vitro screening method established here will be available for broadening the diversity of genetic resources resistant to CSVd.
Vitis coignetiae samples were collected from several locations in the northern area of Japan, and virome analysis using a high-throughput sequencing technique was performed. The data indicated that some of the collected samples were in mixed infections by various RNA viruses. Among these viruses, three were identified as newly recognized species with support of sequence identity and phylogenetic analysis. The viruses have been provisionally named the Vitis varicosavirus, Vitis emaravirus, and Vitis crypticvirus, and were assigned to the genus Varicosavirus, Emaravirus, and Deltapartitivirus, respectively.
Tomato yellow leaf curl virus (TYLCV) infections result in decreased tomato growth and reduced yields, and the production is almost entirely lost if plants are infected during early growth. 'Kyo-temari' is the commercial name for the parthenocarpic tomato 'MPK-1', which has been vegetatively propagated and distributed to local farmers in Kyoto City for commercial cultivation. During the winter of 2013, the typical yellow leaf curl symptoms of TYLCV were observed in 10 parthenocarpic tomato cultivars, including 'MPK-1', maintained as mother stock for vegetative propagation at Kyoto University. When microtissue direct polymerase chain reaction was conducted, a begomovirus-specific amplicon was detected in the plants with yellow leaf curl symptoms. Sequencing and phylogenetic analysis clarified that a TYLCV-Mild isolate was infecting the parthenocarpic tomatoes. Because signals of TYLCV were not detected in the shoot apical meristems (SAMs) of TYLCV-infected 'MPK-1' by in situ hybridization, elimination of TYLCV was conducted by regenerating plants from leaf primordia (LP)-free SAMs of parthenocarpic tomato cultivars. By combining the LP-free SAM culture and in vitro grafting, TYLCV-free plants were obtained in approximately three months. The technique developed in this study will contribute to the efficient elimination of TYLCV from vegetatively propagated parthenocarpic tomatoes.
In April 2023, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. The phylum was expanded by one new family, 14 new genera, and 140 new species. Two genera and 538 species were renamed. One species was moved, and four were abolished. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.
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