Yield Performance and Bean Quality Traits of Cacao Propagated by Somatic Embryogenesis and Grafting

Twelve cacao (Theobroma cacao) clones propagated by grafting and rooted cuttings of somatic embryo-derived plants were grown on an Ultisol soil at Corozal, Puerto Rico and evaluated for six years under intensive management. Year, variety, the year x variety and propagation treatment x variety interactions showed significant effects for dry bean yield, number of pods produced, pod index, plant height and stem diameter.  Propagation treatments had a significant effect on dry bean yield and pod index but not on number of pods produced.  Average yield across varieties for both propagation treatments was 2,087.9 kg.ha^-1. yr^-1 of dry beans.  There was a highly significant variety effect.  ‘UF-668’ was the top yielder averaging 2,536.7 kg.ha^-1.yr^-1.yr^-1 of dry beans; however, this yield was not significantly different than the average yield of varieties TARS-30, TARS-1, TARS-13, TARS-14 and TARS-2 which averaged 2,427.0 kg.ha^-1.yr^-1.  Except for ‘UF-668’, the TARS varieties were released in 2009 as high-yielding selections.  Propagation treatments had a significant effect on dry bean yield.  Dry bean yield of varieties propagated by grafting was 7% higher (2,166.7 kg.ha^-1.yr^-1) than those propagated by somatic embryogenesis (2,009.2 kg.ha.yr^-1).  This yield difference could not be attributed to grafted plants being more vigorous nor by differences in root architecture.  The lowest pod index value in both propagation treatments was obtained for ‘UF-668’ however, pod index for this variety did not differ significantly from values for ‘TARS-2’ and  ‘TARS-23’ in grafted plants and from ‘TARS-2’,  ‘TARS-23’, and ‘TARS-1’ in plant propagated by somatic  embryogenesis.  With few exceptions, flavor characteristics were not significantly affected by propagation treatments.  Although there were significant differences between plant propagation treatments for some of the variables measured in this study, these were not of a magnitude that would preclude the use of somatic embryogenesis as a viable and reliable propagation system for cacao.