Germination responses of Croton macrostachyus (Euphorbiaceae) to various physico-chemical pretreatment conditions

Abstract

Croton macrostachyus Hochst. ex Del. (Euphorbiaceae) is a multipurpose, deciduous, and medium sized tree of pantropic occurrence. Because the species has numerous useful qualities (e.g., establishment and growth in disturbed sites, drought tolerance, fast growth rate, copious litter/necromass production, suitability for agroforestry, and ability to attract avian frugivores), its speedy restoration has become increasingly critical. Germination studies were therefore conducted on seeds pooled from five widely located provenances with a view to supporting efforts geared toward the speedy propagation and restoration of this valuable tree species. Seed pretreatments were achieved using various dilution levels of plant-derived smoke–water (1:1, 1:10, 1:100 and 1:1000), as well as gibberellic acid (GA3) or potassium nitrate (KNO3) ranging in concentration from 0.1 to 100μmol. The control was to use distilled water for seed pretreatment. Seeds were germinated under either illuminated (ca 60μmolm−2s−1; cool-white fluorescent lamp) or non-illuminated conditions. Experiments on the impact of seed storage durations, as well as storage temperatures were also conducted. The study found that germination percentage (GP: ca 90%), and mean germination time (MGT: 14days) were significantly (P<0.001) better when seeds were pretreated with smoke–water and germinated under non-illuminated conditions, than when these were pretreated with various concentrations of GA3 or KNO3 (GP and MGT of ca 65% and 20days, respectively). Germination percentage (GP) and germination vigor (GV) declined with increasing storage-time for all storage temperatures, but GV's decline was faster for seeds stored at 22°C than for those stored at 5 and 15°C. On the other hand, mean germination time (MGT) increased significantly (P<0.01) with seed storage-time of up to 8months at 5, 15, and 22°C, but the increase was more marked for seeds stored at 22°C than for those stored at 5 and 15°C. From these investigations, it is concluded that germination of C. macrostachyus seeds through use of smoke–water is faster, cheaper, and technically less demanding, compared to that of either GA3 or KNO3. The study also concludes that C. macrostachyus is intermediate between orthodox and recalcitrant seeds, and that it is non-photoblastic.