The challenges of maintaining a collection of wild sunflower (Helianthus) species

Thirty-eight species of the genus Helianthus L. were evaluated for methods of sowing, cultivation, seed germination, length of the vegetative period, self-fertility, and seed production for traits important for genebank maintenance. Direct sowing gave poor results, while germination of seeds, growing plantlets in the greenhouse, and transplanting them to the field was more appropriate. Cultivation as a living collection in the field was found to be a convenient way to maintain perennial species because of their high self-sterility. Seed germination was very low, with an average of 26.3 % in the annual species. By removing the seed hull and coat (dehulling), it increased germination to 64.4 %. Seeds of most of the perennial species did not germinate, while the average germination with the use of dehulling was 23.9 %. The number of days to flowering in the annual species averaged 76 days, while in the perennial species it was much longer, averaging 121 days. For some species, photoperiod manipulation is recommended to get them to flower before first frost. Self-fertility in the majority of tested species was close to zero so that self-pollination is not a useful seed regeneration method. Sibbing in isolation cages proved to be most efficient method for seed production, but with mandatory pollen movement or the use of bees for pollination. Information about curation of wild sunflower genebanks should be useful for increasing efficiency in collection maintenance of Helianthus genetic resources which are increasingly being used for sunflower pre-breeding.