Influence of Type and Age of Primary Somatic Embryo on Secondary and Cyclic Somatic Embryogenesis of Cassava (Manihot esculenta Crantz)

Abstract

This study investigated the influence of age of the cotyledons, cut from primary somatic embryos (PSE) developed from shoot meristems (SM) or immature leaf lobes (LL), on secondary somatic (SSE) and cyclic (CSE) embryogenesis of two cassava cultivars at the Central Biotech Laboratory, International Institute of Tropical Agriculture (IITA), Ibadan, between 2006 and 2010. A completely randomized design with three replicates was used for the study. Only PSE at the age of 4 weeks recorded significant (P<0.05) differences in SSE frequency and efficiency between the SM and LL sources. CSE production was highest using 0 to 4 weeks old SSE cotyledons, and significant (P<0.05) differences were only recorded between the SM and LL sources when the age of the SSE cotyledons was older than 6 weeks. The CSE frequencies from the SM source were significantly greater than that from the LL source when 8 and 10 week-old SSE cotyledons were used. The CSE frequencies from SM (81%, 82%) were still significantly higher than those from LL (41%, 40%)  at the 5th and 6th cycles respectively while the CSE efficiency only differed at the 4th cycle, with SM (7.1) being significantly more than from LL (5.2). These results also enrich the literature by specifying the age of somatic cotyledon suitable for further somatic embryogenic cycles; 0 to 8 weeks for SSE and 0 to 5 weeks for CSE, irrespective of the cultivar (TME 12 or Kibaha) or source (SM or LL). This study further concluded that cyclic embryos should be discarded after the 4th CSE cycle and fresh starting material should be used to restart the somatic embryogenic process.