The variability in lateral root development and branching in a number of strains of exotic cottons was determined in three separate studies. In the first study, seeds of each strain were germinated in 17.4 x 16.4 cm polyethylene growth pouches in a constant temperature incubator in the dark. Nutrient solution was added to each pouch and the seed kept moist by a filter paper insert in each pouch. Measurements of the tap root length, lateral root length, and numbers of lateral roots were made daily for a period of seven days. The vascular bundle arrangement of the tap roots of each strain were also determined at the end of the seven-day period. In the second study, selected strains were grown in the greenhouse in 5.00cm diameter x 150cm long acrylic tubes filled with a sandy loam soil. The soil was washed from a number of tubes at selected intervals and the branching intensity of the root systems determined. Thirdly, a number of the strains were also grown in the field where plants were excavated at the end of the season and the development of lateral roots in the top 30cm of the soil profile determined.

There were significant differences in the number and length of lateral roots in the seven-day old seedlings between the strains that were evaluated. Total lateral root lengths ranged from 41.0cm (T110) to 2.3cm (T488) while the number of lateral roots ranged from 86 (T110) to 4.4 (T488). The branching intensity (No. laterals per cm tap root) ranged from 4.50 (T25) to 0.66 (T488). The branching intensity of the seedlings in the pouches was related both to the elongation rate and the vascular arrangement of the tap root with those strains having the highest tap root elongation rate and the lowest number of vascular bundles having, in general, the lowest branching intensity. There was also some agreement between those strains that were highly branched in the growth pouches relative to their branching intensity in the field experiments. There was, however, a significant interaction between the two environments possible due to differences in plant age effects since the experiments in the acrylic tubes in the greenhouse showed the branching intensity to change as the plants grew older. The differences in lateral root development and branching intensities observed could have a significant impact on the development of rooting depth and rooting density which, in turn, could impact the availability of water and nutrients to plants at different stages of growth.