Location: National Clonal Germplasm RepositoryTitle: Standardizing germination protocols for diverse raspberry and blackberry species) Author
Submitted to: Scientia Horticulturae
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/2011
Publication Date: 10/2/2011
Citation: Wada, S., Reed, B.M. 2011. Standardizing germination protocols for diverse raspberry and blackberry species. Scientia Horticulturae. 132:42-49. Interpretive Summary: Most blackberry and raspberry seeds are difficult to germinate because of a deep dormancy. This study was designed to define the seed characteristics and the germination requirements for diverse blackberry and raspberry species. Seeds collected from ripe fruit of field-grown plants of 17 species were immediately germinated without drying or acid treatment. Seed coat thickness and hardness varied greatly in the 17 species. Only four species had at least 50% germination of immediately-germinated, seed; the others had little or no germination, indicating dormancy. Dry seed of six of the species were scarified with concentrated acid or sodium hypochlorite followed by germination on blotters with four chemical treatments. Germination after acid scarification was significantly better than sodium hydroxide for four of the six species. Seeds of all six species germinated with the growth regulator giberellic acid and potassium nitrate or with a smoke gas solution . Optimal scarification duration depended on seed coat thickness and hardness. Seeds with very hard, thick seed coats may require longer scarification than is generally used. Acid scarification should be used to reduce the seed coat and the optimal acid exposure can be determined through seed viability testing.
Technical Abstract: Most Rubus species exhibit delayed or poor germination because of a deep double dormancy. The objective of this study was to improve Rubus seed germination protocols by defining the seed characteristics of diverse Rubus species and determining scarification and germination requirements. Seeds of field-grown plants of 17 Rubus species were germinated without drying or scarification. Only four species had = 50% germination of immediately-germinated, non-scarified seed, indicating dormancy. Seed-coat thickness and hardness varied greatly in the 17 species. Seed-coat thickness was better correlated with seed size (R= 0.82) than was hardness (R=0.71). Dry seed of six of the species were scarified with concentrated sulfuric acid (98% H2SO4) or sodium hypochlorite (14% NaOCl) followed by germination treatments of deionized water (DI), smoke gas solution, gibberellic acid (2.03 mg/L GA3) with potassium nitrate (34 mg/L KNO3) or GA3 alone. Germination after H2SO4 scarification was significantly better than NaOCl for four of the six species. Seed-coat thickness and hardness affected optimal scarification duration. Rubus seeds with very hard, thick seed coats may require longer scarification than is generally used. H2SO4 scarification should be used to reduce the seed coat and the optimal exposure should be determined through viability testing with 2,3,5 triphenyl tetrazolium chloride (TZ) rather than seed size or subgenus. Rubus seed germination was significantly increased for most species by treatment with GA3+KNO3 or smoke gas solution at the beginning of the warm stratification period.