2019 ASHS Annual Conference

The genus Begonia is one of the largest flowering plants. Over 1,900 Begonia species have been described with many more species undescribed. Several important horticultural groups of Begonia hybrids have been developed, including cane types, rhizomatous types, tuberous types, rex begonia, wax begonia, and B. x hiemalis. While Begonia species are found mostly in subtropical and tropical areas, some are native to temperate regions. Most of these temperate plants are from high altitudes in China, India, and surrounding countries, and have relatively limited distribution. One exception is B. grandis, which is probably the most cold-hardy species, with a distribution from northern China to Bangladesh to the west and Malaysia to the south. There has been a moderate interest to develop Begonia hybrids with cold-hardiness to extend the growing season or to even perennialize. There are mainly three problems with B. grandis for its use in breeding: compatibility with other species, availability of compatible species, and heritability of cold-hardiness. While most B. grandis hybrids do not display substantial cold-hardiness, one B. grandis hybrid, B. ‘Smooch,’ is purported to be a hybrid with a Taiwanese species (B. chitoensis) and cold-hardy to USDA Cold Hardiness Zone 6a, suggesting the possibility of developing fully cold-hardy Begonia hybrids. In the section Platycentrum, several species of unknown identities and hybrids such as B. ‘Benictochiba’ and B. ‘Silver Series™’ can survive in USDA Cold Hardiness Zone 7 or above. Species in the section Platycentrum and hybrids are notable for attractiveness of their foliage, which should be considered when developing hybrids. Thus, various combinations of crosses involving B. grandis have been made and germination rate has been recorded to investigate the compatibility of B. grandis with species in the section Platycentrum as well as others. To this date, seedlings of several crosses such as B. grandis ‘Heron’s Pirouette’ x B. ningmingensis var. bella, B. grandis ‘Sapporo’ x B. muliensis, and B. formosana x B. ‘Chandler’s Hardy,’ have been acquired.