How does stalk anatomy of sugarcane relate to fibre content and strength?

The dry matter content of the sugarcane stalk consists of soluble sugars and insoluble fibre. Although the fibre content of Saccharum officinarum is typically low, with the introgression of S. spontaneum a wider range of fibre characteristics can be identified in commercial cultivars. These characteristics, including fibre content and fibre strength, can have a profound impact on the millability of the cane. Recently, several high-yielding cultivars were developed with fibre- quality measurements outside the typical range and these were classified as ‘soft canes’. Fibre quality is classified using tests that were developed in the 1980s to measure three physical parameters: shear strength, impact resistance, and short-fibre content. These tests are costly and time consuming but provide a useful indicator of the effect of a clone on factory operation and performance. Biochemical analysis has shown that the main components of sugarcane fibre are cellulose (72%) and lignin (21%), which are derived from the plant cell walls. In the sugarcane stalk, the lignin is predominantly located in the thickened cell walls of the peripheral rind tissue, which provides structural support, and in the vascular bundles, which transport water and nutrients. The majority of the stalk consists of the sucrose-storage pith tissue, which has thinner cell walls with a relatively higher content of cellulose. Our study demonstrates that there are significant differences in stalk morphology traits among cultivars with different fibre- quality characteristics. SRA1 A , a soft cane cultivar, has significantly thinner rind and lower density of vascular bundles indicating a higher ratio of pith area to vascular bundle number. This contrasts with SRA5 A and Q208 A , both of which have significantly thicker rinds and higher density of vascular bundles. These stalk-anatomy traits are associated with differences in fibre characteristics and could potentially be used to develop a high-throughput screen for fibre quality in sugarcane. Key words Fibre quality, soft fibre, vascular bundles