Macrocystis is an important marine resource in Chile, with severe problems of over-exploitation. Our study describes genetic materials and techniques for a further improvement of laboratory-based mariculture. For a systematic hybridization program we have selected one pair (cultivar) of gametophytes with favorable somatic and reproductive characteristics from each of seven localities in southern Chile. Sporophytes from all 49 crosses were grown for 10 weeks to seedling size. We report here that sporophytes from sympatric parents (intra-cultivar matings) grow to different length, depending on the locality and, importantly, that sporophytes from several inter-cultivar crossings show superior growth, suggesting heterosis with symmetric or asymmetric reciprocity. The genetic materials and techniques described here, together with our newly developed standardized seedling production protocols now available, constitute a significant step towards domestication of Macrocystis in analogy to terrestrial agriculture.