Hybridization and in Vitro Regeneration of Immature Zygotic Embryos of Melia Volkensii for Accelerated Breeding

Abstract

Melia volkensii (Melia) is a hardwood East African tree species that can be harvested in 15 years. The tree has great potential in commercial plantations in the arid and semi-arid regions (ASALs) of Kenya due to its drought-tolerance and multi-purpose utility. A breeding program initiated for the species started with the establishment of 2 clonal seed orchards (CSOs) of 100 clones each in Kitui and Kibwezi. However, the clones exhibited notable differential seed productivity with implications on the progeny’s genetic diversity and the CSOs’ seed sufficiency. Melia’s known seed dormancy, long juvenile stage and difficulties in propagation further reduce the effective quantities of available planting stock and slow down the breeding program. Understanding flower characteristics potentially influencing hybridization among the clones and hence seed production can enhance early selection for seed yield and inform future CSO designs. Application of accelerated breeding methods can likewise shorten the breeding time for improved tree products. The objectives of this study were: i) to determine inflorescence morphometric characteristics influencing hybridization and seed yield in M. volkensii and ii) to determine the amenability of immature zygotic M. volkensii embryos to in vitro regeneration on basal media supplemented with varying levels of plant growth regulators (PGRs). Measurements were taken from 360 flowers and their respective inflorescences systematically selected from 5 high seed yielding and 5 low seed yielding clones in the Kibwezi CSO and the measurements evaluated against known seed productivity of the clones. Correlation analyses of the floral characteristics did not indicate a strong influence on seed productivity....