In the commercial sugarcane crop, which is asexually propagated, development of the root system is initiated soon after planting a portion of stem (sett) with atleast one lateral bud.
The first roots formed are sett roots, which emerge from a band of root primordia above the leaf scar on the nodes of the sett.Sett roots can emerge within 24 hours of planting, although differences in the time required for root emergence occur among varieties. Sett roots are fine and highly branched roots, which sustain the growing plant in the first weeks after germination.
Shoot roots are second type of root, which emerge from the base of the new shoot 5-7 days after planting .The shoot roots are thicker and fleshier than sett roots and develop in to the main root system of the plant. Sett roots continue to grow for a period of 6-15 days after planting, mostly senescing and disappearing by 60-90 days as the shoot root system develops and takes over supply of water and nutrients to the growing shoot. By the age of 3 months, sett roots comprise less than 2% of root dry mass.
Sett roots initially have an elongation rate of a few mm/day, reaching 20 mm/day within a few days of germination under favourable conditions. Shoot roots grow more rapidly, with maximum rates of elongation of up to 80 mm/day observed, though only for short periods. Mean growth rates for shoot roots over 10 days were 40 mm/day in sandy soils and 28 mm/day in heavy clay.
Mean rates of root penetration, or the rate of descent of the root system, of 20-30 mm/day were also reported. Root penetration in another trial was 20 mm/day down to a depth of 1.6 m for rainfed crops, but slowed in irrigated crops to 17 mm/day in the first 1.0 m and 6 mm/day between 1.0 and 1.6 m.
Genotypic variation in sugarcane root systems is well documented and those producing many tillers normally produce many roots because each new tiller is a source of shoot roots. Likewise cultivars with more horizontal (weak gravitropic) root penetration are more resistant to lodging than those with strongly gravitropic root system.
A longitudinal section of a root tip consists mainly of four parts: the root cap, the growing point, the region of elongation, and the region of root hairs. The root cap protects the tender tissues of the growing point as the root pushes through the soil. The growing point consists mainly of an apical meristem, where cell division takes place.
In the region of elongation, the cells increase in size and diameter until they reach their ultimate size. The region of root hairs is characterized by epidermal cells forming outgrowths (hairs), which dramatically increases the root-absorbing surface.