Productivity of Acacia angustissima accessions at two sites in the subtropics
Low leaf biomass yields coupled with small land sizes are some of the major constraints faced by smallholder farmers that grow protein-rich fodder trees and shrubs. Given these challenges, availability of highly productive seed sources would be important to enable farmers to produce leaf fodder in sufficient quantities. 14 accessions of Acacia angustissima were evaluated for leaf, wood and total biomass production at two subtropical sites with uni-modal rainfall in Zimbabwe, with the objective of identifying high leaf biomass yielding accessions. There were up to fourfold difference in biomass yield between the accessions. Leaf dry matter yield ranged from 1.65 to 8.81 Mg ha-1 and 3.7 to 12.4 Mg ha-1 for wood biomass at the higher altitude site (1530 m a.s.l.) but were much lower at 1272 m a.s.l. where they ranged between 0.37 and 4.88 Mg ha-1 for leaf and 0.4 and 7.2 Mg ha-1 for wood. The most productive accessions for leaf biomass were 16231 and 18579 at the higher altitude site, while 18586 and 18501 had the highest yields at the lower altitude. Although no one accession was consistently high yielding across the two sites, the least productive accessions were consistently poor at both sites. The advantage of using selected superior accessions over the unselect bulk seed was up to 85%. These findings underscore the need to promote the use of only high yielding accessions rather than unselect bulk seed. This study identified new, more productive accessions of A. angustissima that potentially widens the genetic base of the germplasm assembled in Zimbabwe.
Key words: Leaf biomass, accession, accession × site interaction, Acacia angustissima.