GENETIC VARIATION, HERITABILITY AND EXPECTED GENETIC GAINS IN MILICIA EXCELSA (IROKO)

Abstract

Phytolyma lata resistivity of two provenances and of 61 clones of Milicia excelsa was determined in our central nursery at Mesewam, approximately 15 km south-east of Kumasi, Ghana. Assessment of Phytolyma resistivity was carried out using the conventional breeding methods of provenance trials and mass selection followed by vegetative propagation and clonal testing. The Cote d'lvoire provenance grew significantly faster than the Ghana provenance, suggesting that the Cote d'lvoire provenance is more tolerant to Phytolyma attack than the Ghana provenance. Selection of the Cote d'lvoire provenance resulted in 34% gain in height over the population mean. Also, substantial variabilities in number of galls and height growth were observed among individual clones. After one year of growth in the field, 24 clones were identified as being tolerant to the pest with a selection differential and a gain in height of 20.5 cm and 36.7% respectively. The results suggest that considerable variability with respect to Phytolyma resistivity exists within Milicia populations, and this can be exploited for large genetic gains.