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.

摘要：根瘤菌（Rhizobia）是一类革兰氏阴性菌（Gram-negative bacteria），可侵染豆科植物根系并形成根瘤。豆科-根瘤菌共生体系在保障可持续粮食供应与提升农业生产力方面具有重要实践价值。现有已发表的巴基斯坦豆科植物结瘤能力相关列表经整合，形成一份全面的汇总列表。该列表涵盖75个属的225个巴基斯坦本土豆科物种，其分类遵循国际豆科数据库与信息中心（International Legume Database and Information Center, ILDIS）针对南亚豆科植物的分类规范。在所检测的225个物种中，28个隶属于云实亚科（Caesalpinioideae），29个隶属于含羞草亚科（Mimosoideae），168个隶属于蝶形花亚科（Papilionoideae）。上述三个亚科的结瘤率分别为0%、96%与99%。本文探讨了部分云实亚科豆科植物结瘤状态的相关争议报道。关于结瘤情况的存疑报道，可能源于根瘤鉴定的不准确——这主要是因为生长于根系的虫瘿、肿瘤、根结、肥大结构与菌根（mycorrhizae）等结构，在外观上与根瘤存在相似性。值得注意的是，过往文献中报道的豆科植物结瘤存疑案例，主要集中于云实亚科。该问题仍需从分子层面开展进一步研究。本研究结果验证了早期结论：含羞草亚科与蝶形花亚科更易形成根瘤，而云实亚科则恰好相反。