Optimized scarification protocols improve germination of diverse Rubus germplasm

Authors: WADA, SUGAE - Oregon State University; Reed, Barbara

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2011
Publication Date: 8/23/2011
Citation: Wada, S., Reed, B.M. 2011. Optimized scarification protocols improve germination of diverse Rubus germplasm. Scientia Horticulturae. 130:660-664.

Interpretive Summary: Seed collections of the wild relatives of cultivated blackberry and raspberry are maintained at the National Clonal Germplasm Repository, Corvallis, OR. These seeds can be stored dry and remain viable for many years; however germination is often poor or erratic due to a deep double dormancy. Information on wild species germination requirements is rarely available, and germination may be poor or slow, making it difficult for scientists to use them for breeding improved cultivars. In this study, seed attributes were delineated and germination tests were conducted on 8 diverse species from seed stored at -20°C for 1 to 23 years. Seed weight, seed coat thickness and hardness varied widely. Species with moderate or high germination all had soft or slightly-hard seed coats. Scarification of the seed coat with sulfuric acid or sodium hypochlorite was followed by germination treatments . The standard scarification protocols were not optimum for many species. Seed viability testing was useful for determining optimum scarification durations. Acid scarification followed by a germination treatment of potassium nitrate and gibberellic acid was highly effective for germinating most species. Two species had rapid germination due to an unusual seed coat structure that allowed water to easily enter the seed. Effective acid exposure can be established based on the amount of embryo damage seen with viability testing techniques. Some species with extremely-hard seed coats had little or no germination, and longer scarification times are suggested based on seed size, seed coat thickness and hardness and viability testing.

Technical Abstract: Seed collections of the wild relatives of cultivated blackberry and raspberry (Rubus species) are maintained at the National Clonal Germplasm Repository, Corvallis, OR. Seeds of Rubus species are orthodox and can be stored dry and remain viable for many years; however germination is often poor or erratic due to a deep double dormancy. Information on wild species germination requirements is rarely available, and germination may be poor or slow, making it difficult for scientists to use them for breeding improved cultivars. In this study, seed attributes were delineated and germination tests were conducted on 8 diverse Rubus species in 6 of the 12 Rubus subgenera from seed stored at -20°C for 1 to 23 years. Seed weight, seed coat thickness and hardness varied widely. Species with moderate or high germination all had soft or slightly-hard seed coats. Scarification with 98% H2SO4 or 14% NaOCl was followed by germination treatments of deionized water (DI), smoke gas or a combination of gibberellic acid (2.03mg/L GA3) and potassium nitrate (34 mg/L KNO3) during stratification. The standard scarification protocols were not optimum for many species. Tetrazolium testing was useful for determining optimum scarification durations. H2SO4 scarification followed by a germination treatment of KNO3 and GA3 was highly effective for the most species. Two species in subgenus Anoplobatus had a hilar-end hole that allowed rapid germination of unscarified seed. Effective scarification exposure can be established based on the amount of embryo damage seen with 2,3,5 triphenyl tetrazolium chloride (TZ) viability testing. Some species with extremely-hard seed coats had little or no germination, and longer scarification times are suggested based on seed size, seed coat thickness and hardness and viability testing.