Differences in sugarcane stool branching within Saccharum spontaneum genotypes and compared to Saccharum officinarum and commercial varieties

Commercial sugarcane varieties are hybrids between Saccharum officinarum, known for its high sucrose content but poor ratooning growth, and Saccharum spontaneum, known for its low sucrose but greater propensity to produce tillers and better disease resistance. While only 20% of the Saccharum hybrid genome originates from S. spontaneum, the genes underlying the ability to produce more tillers over successive harvests have historically been associated with this species. In order to assess the variation in stool branching and tiller recruitment, 10 genotypes were assessed, including four S. spontaneum, two S. officinarum, two recent S. spontaneum introgressed lines and 2 commercial hybrids. Differences in branching were observed amongst the S. spontaneum genotypes; while all were classified as sympodial rhizome types lacking a terminal bud, there were differences in the degree of branching and the lengths of the underground internodes, with some classified as sprawling (with seven levels of branching) and others as clumping (with four to five levels of branching) depending on the stem nodes. In contrast, the S. officinarum genotypes had limited branching, expanding to only three levels. The S. hybrids and S. spontaneum backcrosses had greater similarity to the clumping S. spontaneum genotypes than to the S. officinarum genotypes. Principal component analysis separated the genotypes of sprawling S. spontaneums, clumping S. spontaneum, hybrids/introgressed lines and S. officinarum. The variation in stool branching may be used to select S. spontaneum parents that would yield better ratooning abilities in their hybrids with S. officinarum, without the 'weediness' associated with sprawling rhizomes, for commercial sugarcane production.