Growth and agarose characteristics of isomorphic gametophyte (male and female) and sporophyte of Gracilaria dura and their marker assisted selection

Abstract The characteristics of agarose and growth for three isomorphic life phases of G . dura with their bio-molecular marker assisted selection have been described in this study. The tetrasporophyte showed superior quality of agarose over gametophytes and recorded growth rate was highest for females. The genetic relatedness studied with ISSR markers showed quadratic line of correlation between these phases (R 2  = 1). Their genetic diversity determinants as percentage of polymorphic loci (PPL), average heterozygosity (He) and Shannon's Weaver index (I) were 55.55%, 0.5 ± 0.07 and 0.33 respectively. The cytological analysis for chromosome count revealed 8 chromosomes in haploid gametophytic thallus (N) and 16 for diploid tetrasporophyte (2N) together with genetic structure analysis confirmed to their sexual mating behaviour. Their marker assisted selection based on ISSR generated characteristic band of 430 bp specific to male, 860 bp for female and two bands of 800 and 1600 bp for tetrasporophytic thallus from primer ‘A’. Similarly ISSR primer ‘E’ also generated bands specific to male, female and tetrasporophytes while others gave bands specific to either of life phase. Interestingly, endogenic ABA content was significantly higher for haploid gametophytes (female more than male) than diploid tetrasporophyte while no significant difference was observed in IBA content. Thus the study described not only the features of three life phases of G . dura but also reliable biomarkers for differentiating such isomorphic life phases which could be beneficial for the selection of cultivar and in breeding programmes.