Screening of chrysanthemum cultivars with resistance to chrysanthemum stunt viroid.

摘要

Cultivars resistant to chrysanthemum stunt viroid (CSVd) are desirable for stable production of chrysanthemum (Chrysanthemum x 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.