why diploid population is preferred over haploid for farming? Does it have any genetic advantage?

The dominance of diploids is difficult to explain: farmers most often do not know the difference between haploids and diploids, so if they selected for diploids, they did it unconciously. While diploids grow slightly faster than haploids in the laboratory, females grew twice as large and 15% faster than diploids, and haploid males grew as large and as fast as the maximum obtained by diploids in natural populations. We still lack evidence from comparative studies in farms. While heterosis could theoretically explain the dominance of heterozygous diploids, no evidence of heterosis was found in farms so far.

Great question Alan! Difficult to answer. There are so many things we still do not understand.
Certainly, the low genetic diversity is one big issue. We want to further test the efefcts of clonal diversity in farms'productivity and resilience to epiphytism. While selective breeding might produce some high profile strains, this will further reduce genetic diversity in farms, unless new strategies are explored to promote diversity, its turnover (i.e. replacement after producing seasons), and its evolution towards locally adapted strains (i.e. production based on strains adapted to the local environmental conditions instead of using outplanted strains from different regions/environments). In this context, we are wondering if it would be good and safe to bring natural strains from New Zeland to introduce new genetic diversity. An idea that has some risks, but could support breeding programs based on a progressive introgression (not to be cultivated directly).

Thank you.
I am discovering many aspects of eucheumatoid cultivation thanks to this workshop. And indeed, we have very similar concerns and challenges. I am really interested in establishing collaborations, maybe for a joint Safe Seaweed Coalition grant to explore and test some common ideas.