Provenance variation in Khaya species for growth and resistance to shoot borer Hypsipyla robusta

Abstract

Khaya anthotheca and Khaya ivorensis (trade name African mahogany) of the family Meliaceae are among the most valuable tropical timber tree species of Africa. Continued supply of these timber species is threatened by over exploitation from natural forest and the difficulties in the establishment of mahogany plantations due to attack of shoot borer Hypsipyla robusta Moore. Hypsipyla attack destroys the growing shoots, causes forking, retards growth and reduces the economic value of the timber. In this study, provenance and within provenance evaluation for pest resistance and growth were studied. The results showed no significant ( P > 0.05) variation in growth among provenances of K. anthotheca and K. ivorensis. Significant variations ( P < 0.05) were however observed in growth parementers among progenies of both species. The growth (total height and diameter) of the highest-ranking progenies of the two species were twice those of the lowest-ranking progenies. K. anthotheca had a high heritability ( h 2 = 0.74) for height growth compared to that of K. ivorensis ( h 2 = 0.51) suggesting an inherent degree of higher genetic control in height growth for K. anthotheca than K. ivorensis. The degree of apical dominance and height growth were found to be the most important factors for selection for pest resistance. Backward selection based on the performance of the progenies identified nine and six mother trees of K. anthotheca and K. ivorensis respectively for conservation as seed trees. The results are discussed in relation with productivity in plantations, conservation of genetic resources of mahoganies and the potential of family and or individual selection for quick and high genetic gains.