Limited-scale field trial confirmed differences in growth and agarose characteristics in life-cycle stages of industrially important marine red alga Gracilaria dura (Gracilariales, Rhodophyta)

Abstract

The red alga Gracilaria dura is economically important due to its high-quality agarose. Previous studies with wild populations reported the existence of specific differences in functional traits as well as agar characteristics among life cycle stages. In farmed populations, such differences can be exploited for commercial gains. For that, the variation among stages still needs to be well established under farming scenarios. Here, we compared the life cycle stages of G. dura regarding morphological and anatomical structures, growth performance under preliminary field trials, characteristics of agarose of cultivated biomass with biochemical (NMR) and molecular profiling (SCoT). The male gametophyte was found to have a significantly higher growth rate of 6.23 ± 0.59% day−1 than the tetrasporophyte (5.10 ± 0.14% day−1) and cystocarpic female gametophyte (2.67 ± 0.32% day−1). A maximum agarose yield of 28.6 ± 1.53% was obtained from the tetrasporophyte, significantly higher than 27.4 ± 0.60% in cystocarpic female gametophyte and 25.2 ± 0.36% in male gametophyte. The gel strength of agarose from male gametophytes was 2384 ± 124.13 g cm−2, which was significantly higher than the 1900 ± 50 g cm−2 and 2122 ± 124.03 g cm−2 recorded from tetrasporophytes and cystocarpic female gametophytes, respectively. A metabolomic study by NMR spectroscopy showed critical differences in alanine, lactate and isethionic acid among stages. The genetic correlation studied with the SCoT marker showed an average polymorphism of 47.02%. The average heterozygosity and Shannon-Wiener index were 0.63 and 1.06 respectively. This study of characterising and differentiating isomorphic life phases of G. dura by a decisive biomarker could be a valuable reference point to select an appropriate cultivar for commercial farming and breeding programmes.