Abstract
Genetic diversity is fundamentally important in crop improvement and provides plants with the capacity to meet the demands of changing environments. This work was carried out to assess the diversity and the extent of genetic relatedness among a number of assembled cassava (Manihot esculenta Crantz) accessions. We conducted a microsatellite marker analysis of 89 cassava accessions collected from Ghanaian and exotic sources. These accessions were assayed using 35 simple sequence repeat (SSR) markers. A total of 167 alleles were detected from 35 polymorphic markers with an average of 4.77 alleles per locus. High allelic frequency was detected across the accessions, ranging from 0.32 to 0.99 with an average of 0.62 per marker. Observed heterozygosity ranged from 0.03 - 0.97 across the accessions. Polymorphism information content (PIC) ranged from 0.03 to 0.78 with a mean of 0.45, indicating high level of polymorphism across the accessions. Comparatively, higher number of alleles, gene diversity and observed heterozygosity were detected among the local accessions compared with the exotic accessions indicating rich genetic diversity among them. Population structure analysis based on STRUCTURE identified two subpopulations and a large number of admixtures. Cluster analysis based on the neighbour joining algorithim further separated the collection into seven sub-groupings irrespective of geographical origin. This indicates the possible sharing of common genomic regions occurring across the accessions. High allelic frequency differences and levels of heterozygosity were observed among the germplasm. These findings indicated significant genetic variability in the germplasm to warrant selection.
Highlights
Cassava (Manihot esculenta Crantz) is an important staple crop, widely cultivated and consumed in Sub-Saharan Africa
Assessment of diversity at the molecular level can detect variations and/or markers linked to certain genomic regions, which is very reliable due to little or no environmental influence compared to phenotypic markers [50]
The results of the current study reveal moderate to high levels of polymorphism across the 89 cassava accessions analysed, as was found for the genus Manihot at large [51]
Summary
Cassava (Manihot esculenta Crantz) is an important staple crop, widely cultivated and consumed in Sub-Saharan Africa. Average yields at farm level are low (8t haÀ1) [5], compared with a potential yield of 90 t/ha under good agronomic management [2]. This could be due to the use of low yielding varieties that are susceptible to pests and diseases, as well as high sensitivity to harsh environmental conditions [6]. There is the need to develop new improved varieties that are adapted to these environments
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