Optimized scarification protocols improve germination of diverse Rubus germplasm

Seed collections of the wild relatives of cultivated blackberry and raspberry (Rubus species) are maintained at the National Clonal Germplasm Repository, Corvallis, OR. 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. Eight diverse Rubus species in 6 of the 12 Rubus subgenera from seed stored at −20 °C for 1–23 years were studied. Seed weight, seed-coat thickness and hardness varied widely. Scarification with sulfuric acid (98% H₂SO₄) or sodium hypochlorite (14% NaOCl) was followed by germination treatments of deionized water (DI), smoke gas or a combination of gibberellic acid (2.03 mg/L GA₃) and potassium nitrate (34 mg/L KNO₃) during stratification. The commonly used scarification protocols were not effective for many species; but effective scarification exposure was established based on the amount of embryo damage seen with 2,3,5 triphenyl tetrazolium chloride (TZ) viability testing. H₂SO₄ scarification followed by a treatment with KNO₃ and GA₃ during stratification was highly effective for the most species. Two species in subgenus Anoplobatus had a hilar-end hole that allowed rapid germination of unscarified seed. 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.