Genetic diversity and relationships in mulberry (genus Morus) as revealed by RAPD and ISSR marker assays

Abstract

Background: The genus Morus, known as mulberry, is a dioecious and cross-pollinating plant that is the sole food for the domesticated silkworm, Bombyx mori. Traditional methods using morphological traits for classification are largely unsuccessful in establishing the diversity and relationships among different mulberry species because of environmental influence on traits of interest. As a more robust alternative, PCR based marker assays including RAPD and ISSR were employed to study the genetic diversity and interrelationships among twelve domesticated and three wild mulberry species.

Results: RAPD analysis using 19 random primers generated 128 discrete markers ranging from 500-3000 bp in size. One-hundred-nineteen of these were polymorphic (92%), with an average of 6.26 markers per primer. Among these were a few putative species-specific amplification products which could be useful for germplasm classification and introgression studies. The ISSR analysis employed six anchored primers, 4 of which generated 93 polymorphic markers with an average of 23.25 markers per primer. Cluster analysis of RAPD and ISSR data using the WINBOOT package to calculate the Dice coefficient resulted into two clusters, one comprising polyploid wild species and the other with domesticated (mostly diploid) species.

Conclusion: These results suggest that RAPD and ISSR markers are useful for mulberry genetic diversity analysis and germplasm characterization, and that putative species-specific markers may be obtained which can be converted to SCARs after further studies.

Figure 1

RAPD profiles of 15 mulberry species using a) OPY-13 and b) OPW-03 primers. M indicates λ-HindIII-EcoRI digest markers. Arrows indicate putative species-specific markers.

Figure 2

ISSR profile of 15 mulberry species using the primer (TG)₇. The size-range of the ISSR fragments in base-pairs is indicated.

Figure 3

Dendrogram derived from UPGMA cluster analysis using Dice coefficient of a) RAPD and b) ISSR based markers Numbers on the nodes indicate the number of times a particular branch was recorded per 100 bootstrap replications.