Characterisation of citrus rootstock germplasm introduced as seeds to Australia from the People's Republic of China

Seeds were collected from a range of citrus rootstock types in China and sent to Australia for evaluation. Before evaluation proceeded, however, the seeds and their seedlings were characterised for uniformity and trueness-to-type. The seeds were cultured in vitro and/or germinated in sand beds to assess whether or not they were mono- or polyembryonic. Seedlings were then rogued on the basis of vigour and morphology before isozyme profiles were developed from leaf extracts to assess seedling uniformity within introductions. Isozyme profiles were also compared to those of the source trees, as well as hybrids generated between some of them in China, to assess and verify trueness-to-type. The degree of variability between the seedlings propagated from the imported seeds and their source trees in China differed between accessions, which highlighted some of the issues that need to be considered when importing citrus germplasm as seeds. Regardless of whether the seedlings could be shown to be identical to their source tree in China, three uniform seedlings of polyembryonic types were established in arboreta as Australian source trees to provide propagules for evaluation and possibly commercial use.