Distribution of lateral root primordia in root tips of Musa

The distribution of lateral root primordia in the root tips of four Musa landraces (Grande Naine, Pisang Berlin, Ngok Egome and Yangambi Km5) grown in the field has been investigated to evaluate the range of genetic variation of lateral root initiation. In banana (Musa sp.), lateral roots are initiated in the root tip, 0.6-4 mm behind the root/cap junction and arise in several protoxylem-based longitudinal rows or 'ranks'. Significant differences were observed among landraces for the position of the most distal primordium, however the longitudinal spacing between successive primordia along the ranks was similar for all landraces. All ranks were involved in lateral root initiation. The number of ranks also showed significant variations among landraces and was proportional to the stelar diameter. Hence the density of lateral roots (roots cm(-1)) was affected by stelar diameter variations. Finally, root elongation in the root tip was landrace-specific and not necessarily exponential, unlike suggested in previous studies. It is concluded that lateral root initiation in Musa is not involved in the genetic variations of root architecture in the field. A dissection of root architecture into components which may account for these variations is proposed in relation to the improvement of root system architecture. (C) 1999 Annals of Botany Company