Abstract:
Albizia lebbeck is a multipurpose, fast-growing tree species widely grown in the tropical region. It has been introduced to the Sudan before since the sixty of last century and was basically used as an ornamental or shade tree across the country landscape including roads, parks and dwellings. However, trees of Albizia lebbeck growing in Khartoum state show two distinct crown forms viz. round (RC) and irregular crown (IC). Because no information exists about the original sources of its introduction, especially the provenances or the genotypes, consequently it has been found difficult to say with certainty whether this variation in this very important characteristics is genetically controlled or due to environment x genotype interaction.
The present work is an attempt forward to study the genetic variation between the two crown ideotypes displayed by the tree populations grown within Khartoum state in the Sudan. In this connection, an investigation into the genetic variation was conducted using random amplified polymorphic DNA (RAPD) analysis. Using four RAPD primers a total of 40 polymorphic bands out of 43 were detected. The Shannon’s index and Nie’s genetic diversity were used to partition the variation. Nonetheless, comparisons showed high similarities between the two crown ideotypes viz. RC and IC.
In addition, a nursery experiment was conducted to study the early growth characteristic related to crown form. Seedlings showed significant differences between the two crown ideotypes for crown length, crown diameter, branch length, number of leaves and crown /stem ratio but not for stem length and number of branches characteristics.
To complete the picture a rooting of cutting experiment was undertaken using IBA at concentrations of 0.00, 400 and 800 ppm. Analysis of variance showed highly significant differences between the effects of the IBA concentrations for the number of roots produced but neither for the root length nor the shoot/root ratio characteristics. However, IBA at 400 ppm produced the biggest mean number of roots per stem cutting. Results were discussed on the basis of assumed genetic variation in crown form of Albizia lebbeck and the consequences of the possibility of the production of the desired form using juvenile seedlings phenotypic characteristics. Further more, the study explored the possibility of establishing a rooting of stem cutting protocol in an effort to standardize vegetative propagation technique for the species in Sudan in case it is needed to produce seedlings clonally.
