Taxonomic Appraisal of Nodulation in the Leguminosae of Pakistan

ABSTRACT: Rhizobia are gram negative bacteria that infect roots of leguminous plants and form root nodules. Legume-rhizobia symbioses are of practical importance in providing sustainable food supply and increased agricultural productivity. Existing lists published on the nodulating ability of Pakistani legumes were merged to compile a comprehensive list. The list contained 225 species distributed in 75 genera that were native to Pakistan. Legumes were arranged according to the recommendations of International Legume Database and Information Center (ILDIS) for legumes of south Asia. Out of 225 species examined, 28 belonged to Caesalpinioideae, 29 belonged to Mimosoideae and 168 belonged to Papilionoideae. The percentage of nodulation in Caesalpinioideae, Mimosoideae and Papilionoideae was 0%, 96%, 99% respectively. Conflicting reports on the nodulation status of some Caesalpiniod legumes have been discussed. Doubtful reports on nodulation may arise from inaccurate identification of root nodules. This is particularly due to the fact that structures like galls, tumors, knots, hypertrophies and mycorrhizae that grow on the roots bear superficial resemblance with nodules. It is interesting to note that major cases of doubtful nodulation reported in the past for Leguminosae concern Caesalpinioideae. The matter needs investigation at the molecular level. Present results confirm early findings that nodule formation is more commonly present than absent in Mimosoideae and Papilionoideae, the reverse is true for Caesalpinoideae.