Provenance and family variation in germination, early seedling growth, fruit composition and seed mass in Sclerocarya birrea (A. Rich.) Hochst. sub-species caffra (Sond.) Kokwaro (Anacardiaceae) : the Marula

Thesis (M.Sc.) -- University of Stellenbosch, 1998.

This thesis is an analysis of the variation between and within provenances of Sclerocarya birrea sub-species caffra (marula) with respect to the following parameters: germination and survival of seedlings, height and root collar diameter increment, germination of fresh seed, seed mass of dried fresh seed, total soluble solids (total sugars) content of fresh fruits, and the vitamin C content of fresh fruits and family heritabilities of fruit parameters and seed mass. These traits are considered to be of high economic importance in the ongoing domestication and improvement of indigenous fruit tree species like marula in the arid and semi-arid regions of Africa. The investigation consisted of two main studies: Study one: Germination and early seedling growth of provenances and families Study two: Fruit composition, seed mass, germination of fresh seed and heritability estimates Study one was carried out using a seed lot supplied by the Botswana National Tree Seed Centre and study two made use of a seedlot from Swaziland. Germination and early seedling growth followed a randomized complete block design with nested effects; there were three replicates, three provenances and twelve families. A nested sampling procedure was followed for fruit composition and seed mass; there were four areas, eight to ten families per area and fifty fruits per family. Germination of fresh seed assumed a randomised complete block design; there were five replications with thirty seven families each. • Significant differences in germination existed between provenances and between individual families, while there were no significant differences between families within provenances. Survival was 100% for all families except one. • Significant differences existed between provenances in both height and root collar diameter at five months and eight months. There were no significant differences in percent increment in both height and root collar diameter. No significant differences were observed between individual families for height at five and eight months and percent height increment. Significant differences were found between individual families in root collar diameter at five and eight months, but non-significant differences existed in percentage diameter increment. • There was a strong positive relationship between height and root collar diameter. • There was significant provenance and family variation in seed mass and vitamin C. Total soluble solids lacked provenance variation but had wide family variation. • There was no correlation between parameters except a significant correlation between rainfall intensity and total soluble solids content; the lower the rainfall the higher the soluble solids content and vise versa. • The most variable parameter (vitamin C) had the highest family heritability, however all the parameters had relatively high family heritabilities, of above 0.5. • No germination occurred in fresh seed and this was attributed to premature exposure of seed cells to optimum germination conditions. It was recommended that provenances and families over a wide range should be covered to capture more provenance and family variation in both early seedling growth and fruit quality studies. For germination only mature seed should be sown since fresh seeds have to over-winter to mature, otherwise they rot and there is no germination. The environmental parameters have to be studied in greater detail. For instance, instead of area average annual rainfall the real amount of rainfall that the particular tree or family gets per year should be considered. With respect to the results of fruit composition and seed mass a family study could be of remarkable importance in the identification of superior genotypes, making use of the wide family variation that exists.

Masters