LAUSR

In subtropical environments where sugarcane (Saccharum spp.) crops are frequently limited by the growth cycle duration, earliness in maturity is a key genotypic trait. Using the concept of source-sink relationships, we hypothesised that earliness is controlled by tillering dynamics (DT) which define sink strength early in the growth cycle. Five modern commercial sugarcane genotypes with similar sucrose yields and varying precocity were grown in the field during three years and their DT, sucrose accumulation (DS) and source-sink relationships over time were characterised. Canonical correlations and principal components analysis revealed that DT explained 68% of the total variance in DS. Early ripening genotypes exhibited lowest thermal time to the end of tiller mortality (θTf), lowest stalk survival and culm number, and greatest sugar content at θTf (Si). Rate and duration of the sucrose accumulation phase did not explain genotypic variation in final sugar content nor in earliness when considered in isolation without taking into account the Si effect. In this set of modern genotypes, final sucrose yield was most explained by stalk number variation. We conclude that dynamics of tillers appearance and senescence modified early source-sink relationships thus determining differential sucrose contents around θTf and precocity for maximal sugar accumulation. θTf, closely associated with the 14-leaf phenological stage, emerged as a candidate trait to screen for genotypic variation in ripening precocity, cycle length and yield.