SEED SIZE POLYMORPHISM IN KHAYA SENEGALENSIS (DESR.) A. JUSS.: IMPLICATIONS FOR SEED PROPAGATION

Abstract

Seed size variation has implications for the success of seedling establishment, but the underlying mechanisms are yet to be fully explored in many species, including Khaya senegalensis. Moreover, seed size is measured in different ways (for example, mass or length), but the extent to which these different ways of measurement differ in predicting seedling growth parameters is unknown. In this study, how well seed mass and seed length predict seed food reserves was tested. Then, pot experiments were conducted to determine which of the two measures of seed size was a better predictor of seedling size and root biomass allocation. Also, effects of seed size variation and its relation to sowing depth on seedling parameters were investigated. Results showed that both seed mass and seed length significantly predicted the amount of seed food reserves, but seed mass explained a greater percentage of the variability in seed reserves than seed length (64.1% versus 19.3%) and as a result, seed mass also better predicted seedling size. However, both seed mass and seed length poorly predicted root length and root biomass allocation. Also, it was found that at all the tested sowing depths in this study, larger seeds produced larger and taller seedlings, but a combination of large seeds with 0 cm sowing depth yielded the largest and tallest seedlings. Root length decreased with sowing depth, regardless of seed size. Root mass fraction of seedlings from small seeds decreased with sowing depth, while those from large seeds were unaffected. It is recommended that to produce larger seedlings with a greater allocation to root biomass, large seeds in combination with superficial sowing depth should be used when nursing K. senegalensis seeds.