The eight Rubus species from the NCGR collection are classified
in six subgenera and were from samples collected from worldwide
geographical regions and stored for 1–23 years at −20
◦
C(Table 1).
Seeds for these species arrived at NCGR through various routes,
and the maturity of the seed, handling after collection and any prior
storage information are often not well documented. The only study
of Rubus seed longevity in cold storage was by Clark and Moore
(1993) who studied open-pollinated blackberry (Rubus spp.) seeds
after 22–26 years of cold storage at 4–5
◦
C. They reported germi-nation ranging from 0 to 84% with 3 h sulfuric acid scarification. As
seeds age, both viability and germination inhibiting substances may
diminish. Since scarification techniques are not well defined, this
can also impact germination. It is difficult to draw conclusions on
the effectiveness of germination tests for some of the stored species
in our study because there were no initial germination tests and the
conditions of collection and handling before cold storage at NCGR
are often not known. As a whole, the best treatment for a wide range
of species was scarification with H
2
SO
4
and germination in the
presence of GA
3
+ KNO
3
(Table 3). This treatment produced >36%
germination for 6 of 8 species and was as good as, or better than,all other treatments ( Table 3). Species with thin, soft seed coats
appear to lose viability sooner than those with thicker, harder seed
coats and this should be studied further to determine safe storage
for these species.