High Frequency Somatic Embryo Formation in Cultures of Immature Embryos of Guineagrass, Panicum maximum JACQ

Somatic embryogenesis and plant regeneration were studied in 12 genotypes of the facultative apomictic species Panicum maximum Jacq. (Guineagrass). Embryogenic callus was initiated from immature embryos (0.5∼1.0mm long) on MS medium (MURASHIGE and SKOOG, 1962) supplemented with 10mg1-1 2, 4-dichlorophenoxyacetic acid (2, 4-D), 10% coconut water and solidified with 0.8% Agar. Initially various types of callus were obtained and embryogenic responses were found to be correlated with the genotypes investigated. Somatic embryos could be induced from all genotypes except one, but varieties "Petrie" and "Gatton" appeared to have the highest embryogenic capacity among the twelve genotypes. For somatic embryo germination and plant formation MS medium supplemented with GA3 and cytokinins was used. The best response was observed with 1.0mg1-1 GA3 and 1.0mg1-1 kinetin. The twelve genotypes analyzed can be classified into three groups by the frequency of somatic embryo formation and the degree of apomixis. The first group consists of highly apomictic genotypes with a high embryogenic capacity-"Petrle" and "Gatton" The second group is composed of highly apomictic types with lower tendency to form somatic embryos- "Natsuyutaka" N68/84-1-s 6, N68/84-1-s 7 N68/84-1-o 6, N68/84-1-o 8 and N68/96-8-o 10. The third group is formed by types displaying a lower tendency both in apomixis and formation of somatic embryos-S67, N68/84-1, N68/96-8, N68/96-8-o 1.