Genetic Diversity Assessment of Sorghum [Sorghum bicolor (L.) Moench] and Pearl Millet (Pennisetum glaucum L.) Landraces Collected from Zimbabwe’s Communal Areas, based on Microsatellites and Isozymes.
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Landraces of sorghum [Sorghum bicolor (L.) Moench] and pearl millet (Pennisetum glaucum L.) are grown throughout Zimbabwe and frequently given names describing important traits they possess or their origin. Little is known about the consistency of the relationships between names and genetic identity, and thereby the usefulness of names is developing strategies for germplam conservation and use. This study analysed genetic diversity of 52 sorghum and 47 pearl millet landraces from two districts of Zimbabwe, Nyanga North and Tshlotsho, using isozyme and microsatellite techniques. Six enzymes: alcohol dehydrogenase (ADH), peroxidase (POD), α-esterase (α-EST), β-glucosidase (β-GLU), acid phosphatase (ACID-P) and malate dehydrogenase (MDH), were tested by isoelectric focusing (IEF) and histochemical staining of polyacrylamide gels. Microsatellite analysis was done using polyacrylamide gels stained with ethidium bromide. Genetic similarities (simple matching coefficients) were calculated and dendrograms were used to compare relationships based on indigenous local names and the origin of the accessions. Out of seven sorghum microsatellite primers tested, 20 polymorphic bands were scored with the number of bands ranging from two to five per genotype. The dendrogram revealed that the genotypes could be grouped into seven clusters at 62 per cent similarity level. Some genotypes clustered by indigenous local names into Musoswe (1355, 1441 and 1460), Sorghum (1459 and 1480), Shodhani (1450 and 1430) and Ipwa (1346 and 1496). Other groups identifiable by their villages of origin included Renzva (1459 and 1480), Kamunhukamwe (1430 and 1450), Siyazama (1572, 1592, 1593,1557 and 1555), Samakande (1343 and 1345) and Mangezi (1401 and 1412). Some genotypes from Nyanga North were closely related to those from Tsholotsho. These included genotypes 1483 (Nyamuwaya-waya) and 1487 (Sorghum) from Nyanga North which were 100 per cent similar to 1523 (Isigobane) and 1537 (Tsweta khaki) respectively from Tsholotsho district. Based on the markers used, seven of the 15 accessions collected from Tsholotsho were judged to be duplicates of material also found in Nyanga North. At 68 per cent similarity level, all the 47 pearl millet genotypes grouped into four clusters. There was a strong association between microsatellite data and indigenous local names in some genotypes. Groups identifiable by local names included Halale (1596 and 1571), Tsholotshobearded (1644 and 1643), Mudhambure (1408, 1382, 1418, 1435 and 1396), Isigumu (1570 and 1581), Isifumbata (1564 and 1650) and Nyagushe (1386 and 1375). Some landraces clustered by villages into Sizanani (1544, 1562 and 1548), Phakamani (1644 and 1643), Siyazama (1579 and 1624), Renzva (1462 and 1466), Mangezi (1408, 1382, 1418, 1386 and 1396) and Kamunhukamwe (1440 and 1443). There were some pearl millet genotypes that clustered with those from a different village and district altogether. Genotypes 1466 (Mudhambure) and 1447 (Nyagushe) from Nyanga North which were 100 per cent similar to 1570 (Isigumu) and 1524 (PMV-3) respectively, from Tsholotsho. Despite being simple and rapid, isozyme analysis could not distinguish between genotypes in both crops. Only ACID-P and POD produced visible and well-resolved bands in sorghum and pearl millet respectively. The rest of the enzymes had either no, too low or over activity henece not conclussive. Microsatellite markers showed that even when local names were similar, the genotypes those names represented were rarely similar genetically. The results of this study indicate that farmer-given names are neither the best guide to the presence of diversity nor a good unit of sampling. This underscores the need for further studies on the best sampling method.