Improving the identification, handling and storage of “difficult” seeds ...

Table 5. Completed tests and proportion of fails for species from the combined list at the first three intervals (initial, 1 st
and 2 nd )
Test No of completed tests No of failed tests Proportion of failed tests
Initial 2624 952 36%
1 st retest (10 years) 1279 244 19%
2 nd retest (20 years) 538 46 9%
Total 4441 1242
A total of 1242 tests have failed (germination percentage of 75% or less). Failure to germinate
could indicate inappropriate testing conditions, the need to overcome dormancy (by seed coat
scarification or cold stratification for example), poor initial viability (immature seeds, post harvest
handling) or, in the case of re-tests, declining viability in storage (poor storage conditions, short
lived species, immature seeds that had not reached max. storage potential). As expected, the
proportion of failed tests declines after the initial stage, as germination protocols are established for
each particular species.
The number of initial tests required to obtain a satisfactory germination percentage of 75% or above
might be considered as an indication of how “difficult” a species is with respect to germination
requirements. The higher the number of initial tests, the more likely that there are dormancy issues
The average number of initial tests was calculated for each of the 292 species (Table 6).
Table 6. “Difficult” species from the combined list, requiring an average number of tests of 4 or more, to complete
initial stage
Family Genus Species Family Genus Species
VALERIANACEAE Valerianella locusta POACEAE Panicuma sp
UMBELLIFERAE Pimpinella sp POACEAE Panicum brizantha
AIZOACEAE Tetragonia tetragonioides POACEAE Panicum maximum
GENTIANACEAE Gentiana lutea POACEAE Digitaria eriantha
CANNABACEAE Humulus lupulus POACEAE Setaria sphacelata
COMPOSITAE Vernonia sp POACEAE Digitaria sp
CAPPARACEAE Cleome gynandra POACEAE Setaria incrassata
LABIATAE Teucrium polium POACEAE Phalaris arundinacea
MALVACEAE Hibiscus sabdariffa POACEAE Eragrostis curvula
LEGUMINOSAE- Ceratonia siliqua POACEAE Paspalum notatum
CAESALPINIOIDEAE
POACEAE Panicum sp
Of those species requiring an average of 4 or more tests to pass the initial test, Poaceae species
feature frequently. According to the Handbook of Seed Technology for Genebanks (Ellis et al,
1985), some species of Panicum show persistent dormancy and often require scarification of the
seed coat, the addition of Potassium nitrate to the germination medium.or lengthy after-ripening
periods to remove dormancy. Digitaria sp. also express extreme dormancy, overcome by afterripening.
The removal of covering structures in many species of Poaceae is an unreliable method of
breaking dormancy, and often causes damage to the seeds.
Relative longevity
The ITPGRFA Annexe 1 list was queried against relative longevity values, as defined by Walters et
al (2005) in a study of longevity of genebank-stored seeds. 48 species from the ITPGRFA list
featured in their study,. Most were found to be long-lived or with medium-term longevity (Table 7).
The three main families represented were Cruciferae, Gramineae and Leguminosae-Papilionoideae.
There appears to be no consistent pattern in relative longevity amongst genera within these three
families.