Diploid and haploid embryogenesis in Larixleptolepis, L. decidua, and their reciprocal hybrids

Abstract

Diploid and haploid embryogenesis was induced in two Larix species (L. decidua and L. leptolepis) and their reciprocal hybrids. Diploid embryogenic tissue was initiated in immature zygotic embryos isolated with the micropylar half of the megagametophyte left attached. These were placed either on modified LM or MSG medium supplemented with the growth regulators 2,4-D and 6-benzyladenine. MSG medium was solidified with either gellan gum or agar. There was no appreciable difference in response between the two. Haploid embryogenesis was induced in isolated megagametophytes placed on modified LM medium supplemented with 2,4-D and 6-benzyladenine. Diploid embryogenic tissue was subcultured on medium with growth regulators, but haploid embryogenic tissue grew well on medium without growth regulators. There were few morphological differences between the diploid and haploid embryogenic tissue. In all species and hybrids, haploid cultures contained more coenocytic long cells. Binucleate cells were most common, but tetranucleate and octanucleate cells were also present. Haploid cultures showed poorer organization than the diploid ones, with only a few cultures having well-developed embryoids. Haploid tissue originated from expanded cells of the megagametophyte. Diploid tissue originated from the suspensor region of the zygotic embryo; it proliferated from isolated clusters of meristematic cells in early embryoids. Diploid and haploid cultures differed not only from the outset, but also in the mature embryoids they produced.