Production and Identification of Colchicine-derived Tetraploid Vaccinium darrowii and Its Use in Breeding

Abstract

In Vaccinium L., most tetraploid hybrids between tetraploid cultivated highbush blueberry (V. corymbosum L.) and diploid darrow's evergreen blueberry (V. darrowii Camp) have been produced by exploiting V. darrowii's tendency to produce 2n gametes and a strong triploid block, which greatly reduces the number of triploid hybrids produced. Colchicine-derived tetraploids offer an alternative method of producing V. darrowii plants that will easily cross with tetraploid Vaccinium species. V. darrowii (2n = 2x = 24) seeds were imbibed in 0.2% aqueous colchicine solution for 24 h. The seeds were germinated and seedlings whose morphology suggested colchicine effects were selected at various stages of development. No macromorphological changes were consistently associated with chromosome doubling. However, stomatal guard cells and pollen size increased substantially as a result of chromosome doubling. Several types of plants were identified after colchicine treatment: 1) plants with a doubled LI (epidermal tissues) and LII (internal tissues) plant layers; 2) periclinal chimeras with a doubled LI layer and a normal LII; and 3) periclinal chimeras with a doubled LII layer and a normal LI. Of ≈4000 seedlings that emerged from colchicine-treated seeds, 200 were selected for further examination based on leaf and stem morphology. Of the 200, five appeared to be tetraploid in LI, LII, or both layers based on stomatal guard cell size and pollen size. Crosses between colchicine-derived V. darrowii (4x) plants and southern highbush blueberry (V. corymbosum) cultivars (4x) were successful compared with 4x–2x and 2x–4x crosses using diploid V. darrowii and tetraploid southern highbush blueberry. Stomatal guard cells and pollen screening of the colchicine-treated plants were used as indicators of doubled V. darrowii plants and periclinal chimeras. The results from the crosses between colchicine-treated V. darrowii plants and tetraploid highbush blueberry cultivars confirmed the information obtained by stomata and pollen screening.