AbstractThe nodulation and nitrogen-fixing resources of legumes from 54 counties (or towns) of Guangdong Province were investigated, and the corresponding rhizobia were isolated and collected. The investigation on nodulation and rhizobial collection for leguminous crops was representative of Guangdong because a widespread area was investigated within the province (from 110°54′ to 117°11′E and from 21°04′to 24°52′N). However, the investigation for wild leguminous plants was not complete due to their scattered distribution in the field and the restricted time. In total, 484 nodule samples were collected, belonging to 78 species and 37 genera, of which those of Crotalaria micans , Phyllodium elegans and Podorcarpium leptopus have not been previously reported. All of the nodule samples were collected from the natural nodulation legumes without inoculation with rhizobia, and two-thirds of the nodulated legumes originated from or are distributed in China, such as Albizia turgida , Archidendron (Pithecellobium) clypearia, Erythrophleum fordii, Ormosia glaberrima, Desmodium reticulatum, Phyllodium elegans , Podorcarpium leptopus , Millettia dielsiana, Mucuna birdwoodiana, and Kummerowia striata . The species Mimosa sepiaria, Crotalaria pallida, Sesbania cannabina, Acacia confuse, Acacia auriculiformis (all perennial legumes), Glycine max, Arachis hypogaea, Vigna rabiata, Vigna unguiculata subsp. sesquipedalis, and Vigna unguiculata subsp. cylindrica (all annual leguminous crops) were widely distributed in Guangdong Province. Their nodules were round, ellipse or coralloid in shape and pink or yellow in color, with sizes ranging from 1 to 10 mm in length. The nitrogenase activity of 24 species was determined using acetylene reduction method, and it ranged from 1 to 10 μmol C₂H₄·g^-1 fresh nodule·h^-1 . High nitrogenase activities were found among leguminous crops in the nodule sample of Glycine soja (21.29 ～ 46.76 μmol C₂H₄·g^-1 fresh nodule·h^-1) and among wild legumes in Codariocalyx gyroides (38.93 μmol C₂H₄·g^-1 fresh nodule·h^-1) of wild legumes. Among the 410 rhizobial strains isolated from the nodule samples, 58.4% colonies appeared within seven days and 41.6% after the 8th day. Of the 312 strains reinoculated to their corresponding host legumes, the nodulation rate was 96.3% for the leguminous crops and 86.9% for the wild legumes. Our investigation showed that all the 20 species of leguminous crops which had been recorded in the Flora of Guangzhou were nodulation and nitrogen-fixing.