SOME GENETIC OBSERVATIONS ON THE MONOPLOID BREEDING OF LAMINARIA JAPONICA

The present paper describes some experiments carried out in our laboratory in the recent several years. The main results are as follows: (1) By using individual gametophytes of the sea weed, new breeds of Laminaria japonica might be obtained. Similar principles of anther culture were applied to the breeding of this brown alga. Many of the sporophytes developed from single female gametophytes were quite normal in shape. They grew and matured in the sea in due time, some of them being larger than the control. (2) Although the ordinary sporophytes of Laminaria japonica are asexual, all parthenosporophytes grew to be female sporophytes. These produced zoospores which all germinated and grew into female gametophytes. The genetic basis of the female sex was thus seen to he different from that of the male and the sporophytes could be artificially separated into male rind female. The monoploid cells could be transformed into diploid ones by using colchicine or by natural doubling of chromosomes in the process of growth and development. (3) Although the life span of the gametophytes of Laminaria japonica is usually very short, some of them could be made to live a very long life and carry on vegetative growth to form calli, each of which contained millions of cells. Thus a single gametophyte could be torn up to become many gametophytes with the same genetic content. The result was the formation of cloncs of gametophytes. The clones could maintain the original sex and remained vigorous. The cells of the clones could give rise to sporophytes under suitable conditions without fertilization. Parthenogenesis of the female gametophytes and apogamy of the male gametophytes usually took place at the terminal cells, though other cells could do so as well.