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  • Author or Editor: Katrina G. Porter x
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Our objective was to develop a virucide-based method to eliminate cymbidium mosaic virus from infected dendrobium protocorm-like bodies during micropropagation. We tested two virucides—dithiouracil and ribavirin. The best treatments for recovery of virus-negative tissue and subsequent plant development were 0.1 mm ribavirin or 0.2 mm dithiouracil in liquid medium for 5 or 6 weeks followed by culture on solid medium with 0.1 mm ribavirin or 0.1 mm dithiouracil, respectively. Most propagules transferred to solid medium were virus-free at 17 weeks on ribavirin, with up to 100% free of virus after 32 to 38 weeks on ribavirin or dithiouracil. Virus loss among protocorm-like bodies cultured without virucides ranged from 0% to 37%. Most plants remained free of virus 2.5 years after chemotherapy and flowered normally.

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Several colchicine-induced amphidiploids of blackspot-resistant, wild diploid rose species were produced for interbreeding with tetraploid garden roses. Shoot-tip chromosome counts confirmed that 86-7 (Rosa wichuraiana Crep. × R. rugosa rubra Hort.) and 86-3 (R. laevigata Michx. × R. banksiae Aiton) are amphidiploids (2n = 4x = 28), and that 84-1000 (R. roxburghii Tratt. × R. laevigata Michx.) is a mixoploid with diploid (2n = 2x = 14) and hypotetraploid (2n = 4x-1 = 27) sectors. The measured volume of pollen grains and guard cells was higher in the tetraploids. Pollen stainability was higher in amphidiploids 86-3 and 86-7 than in mixoploid 84-1000. The amphidiploid 86-7 has greater pollen fertility as determined by crossing with a range of commercial tetraploid roses than 86-3 and 84-1000, but is less fertile than its parental diploid species. Leaflets of the amphidiploids are larger and more crinkled along the midrib than in their diploid parents. These three amphidiploids provide new additions to tetraploid rose germplasm.

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