Graduate Thesis Or Dissertation
 

Evaluation of Rubus seed characteristics: seed coat morphology, anatomy, germination requirements and dormancy breaking

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  • Rubus seed characteristics; seed coat morphology, anatomy, germination requirements and dormancy were studied in order to define protocols for breaking seed dormancy. Morphological analysis of the seed coat (testa) using scanning electron microscopy (SEM) included 56 seed accessions of 10 subgenera preserved in the collections of the US Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR), Corvallis, Oregon. Macromorphological characteristics differed among groups at the subgenus level. Rubus odoratus L. and R. parviflorus Nutt. (subg. Anoplobatus) had a unique hilar end hole and R. saxatilis had seed coat sculpturing inconsistent with its assigned subg. (Cyclactis) and appeared more in common with subg. Idaeobatus. These morphological characteristics of Rubus seed revealed by SEM provide additional information to identify infrageneric levels. Seed of 17 commercially important blackberry cultivars were examined with light and scanning electron microscopy to determine cultivar identity of blackberry fruit using seed coat characters. One key characteristic is the shape of the raphe: straight, concave or convex. Seed shape, color, size and seed-coat sculpturing further distinguish the cultivars. Scarification methods and effective germination requirements were determined for six species of wild Rubus seed. Fresh untreated R. caesius seed had 14.5% germination, but untreated seed of the other five species did not germinate. Most sulfuric acid scarified seed germinated by 6 months with a few more by 12 months. Sodium hypochlorite scarified seed germinated poorly at 6 months, but significantly improved by 12 months. This study indicates that Rubus species vary in their germination requirements with R. hoffmeisterianus exhibiting low dormancy and R. occidentalis very deep dormancy, while the others had moderate dormancy. The seed coat anatomy of R. hoffmeisterianus, R. occidentalis, and R. caesius that exhibited unique responses to germination treatments showed unique structures and cell composition. Especially unique were the sclereids; each had differing layers of exo-, meso-, and endotesta. The anatomical characteristics of each species shown in this study may provide useful information regarding anatomical differences of seed coat hardness and texture. The appendices contain additional SEM micrographs of the seed surface of a wide range of Rubus species.
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