APPLICATION OF RAPD MARKERS IN AN EXAMINATION OF HETEROSIS IN GELIDIUM-VAGUM (RHODOPHYTA)

Four morphologically indistinguishable isolates Of monoecious Gelidium vagum Okamura were crossed reciprocally to obtain hybrids for a study on heterosis in this alga. Approximately 50% outcrossing was achieved by adding a small fragment of the designated female parent to a much larger quantity of designated male thallus in the crossing dish. Hybri ds in the mixed population of isomorphic hybrid and inbred sporelings were identified by the presence of male-specific random amplified poly morphic DNA markers. Growth performance of hybrid tetrasporophytes was compared to that of their gametophytic parents and with inbred tetras porophytes at near-optimum and sub-optimum temperature and density. In general, the hybrids showed growth superiority over inbred lines, par ticularly under sub-optimum conditions. In these experiments, the hybr id plants from cross 129 x 130 exhibited a 9.5-130% higher growth rate as compared to the mid-value of the related inbred tetrasporophytes, strongly suggesting the presence of heterosis.