Symbiotic properties of sinorhizobia isolated from Acacia and Prosopis nodules in Sudan and Senegal

The host specificity, infection process and effectiveness of nodules produc ed by several African sinorhizobial strains on different Acacia and Prosopi s species (Leguminosae, Mimosoideae) were studied. Sinorhizobium arboris st rain HAMBI 1552(T), S. kostiense strains HAMBI 1489(T) and HAMBI 1493, S. s aheli strain HAMBI 1496 and S. terangae bv. acaciae strain ORS 1058 induced nitrogen fixing nodules on seedlings of the following African or Latin Ame rican species (marked with *): A. angustissima*, A. mellifera, A. nilotica, A. oerfota (synonym A. nubica), A. senegal, A. seyal, A. sieberiana, A. to rtilis subsp. raddiana, P. chilensis, P. cineraria, P. juliflora and P. pal lida*. All strains increased plant yield significantly compared with uninoc ulated seedlings watered with nitrogen-free medium, but none appeared to be superior. The sinorhizobial strains were unable to effectively nodulate Se sbania rostrata (Papilionoideae). All roots had hairs, but particularly in the case of Acacia spp. they were often sparse. After inoculation root hairs were deformed and, in general, i nfection in Acacia spp. occurred through short root hairs and in Prosopis s pp. through longer ones. After entry, the rhizobia filled infection pockets in the root hair, which later expanded into sac-like structures. When infe ction threads occurred, they usually started from sac-like structures. Elon gation and ramification of the nodules indicated that Acacia spp. and Proso pis spp. have indeterminate nodules. A persistent apical meristem, which is the characteristic feature of the indeterminate nodule type, was much clea rer in Prosopis spp. than in Acacia spp. Sinorhizobial strains formed tumou r-like structures with undifferentiated cell tissue on the Australian acaci a A. holosericea and ineffective, nodule-like structures on the African P. africana.