Germination of Cola anomala (K. Shum.) Shott and Endl seeds: effects of provenance, substrate and dehydration

Abstract

As a step in the process of Cola anomala domestication, investigations were undertaken on germination requirements and desiccation tolerance of its seeds. Three seed provenances (Bamenda, Bayangam and Dschang), three substrates (forest top soil, river sand and a mixture of forest top soil and river sand) and two photoperiods (12 hours/day and, continuous darkness) were investigated for their effects on seed germination. To evaluate their desiccation tolerance, fresh seeds were dried at room temperature for 16 days during which seed moisture content, seed germination percentage and electrical conductivity of seed leachate were monitored at two-day intervals. Results showed that germination percentages were significantly (P < 0.05) higher both on forest top soil alone (86.04 ± 4.8%), and on a mixture of forest top soil and river sand (83.56 ± 4.5%), than on river sand alone (69.96 ± 4.7%). Seeds from Bamenda showed a higher germination percentage (91.4 ± 4.7%) than those from either Bayangam (77.36 ± 4.7%) or Dschang (70.8 ± 4.8%). The desiccation tolerance test revealed that as response to drying, the mean germination percentage was first slightly reduced as moisture was lost, then declined considerably at moisture content below 50.28%. Total germination failure was observed when seed moisture reached 32.24%. Electrical conductivity of seed leachate exhibited a strong correlation with loss of viability as well as with desiccation. It is concluded that there is a provenance-related variation in C. anomala seed germination. The best substrate for germination is forest top soil supplemented or not with river sand in a 1/1 (v/v) ratio. C. anomala seeds are desiccation-sensitive and their storage behaviour is recalcitrant.

Keywords: Desiccation tolerance, critical moisture, lethal moisture, electrical conductivity, electrolyte leakage, storage behaviour.