Cell Wall Polysaccharides of Near-Isogenic Lines of Melon (Cucumis melo L.) and Their Inbred Parentals Which Show Differential Flesh Firmness or Physiological Behavior

We characterized differences in cell wall material and polysaccharide structures, due to the quantitative trait loci associated with higher flesh firmness in a nonclimacteric near-isogcnic line (NIL) SC7-2, and with the climacteric behavior of the NIL SC3-5-1, using their nonclimacteric inbred parentals, Piel de Sapo (PS) and PI 161375 (SC). PS was firmer and had a higher ripening index and greater hemicellulosic content than SC, with its lower wall material yield, and uronic acid, neutral sugar, cellulose and free sugar content and higher pectic content. SC3-5-1 showed lower uronic acid values, a higher soluble solid content, and similar flesh firmness to PS. SC3-5-1 yielded mainly high molecular weight polysaccharides in the imidazole-soluble fraction than PS. SC7-2 showed greater flesh firmness, a higher neutral sugar (especially galactose and mannose) and uronic acid content, together with a larger cellulose and alpha-cellulose residue than PS. SC7-2 also contained more polysaccharides of low molecular weight in the first pectic fraction and shifted toward higher molecular weights in the main peak of the 4 M potassium-soluble fraction compared with PS.