Isolation and characterization of bacteria from nodules of crotalar1a species in Tanzania and the assessment of the nitrogen fixing capacity of the symbiosis.

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University of Dar es Salaam
In this study, a field survey to assess the availability of Crotalaria species growing in the wild and in cultivation was conducted. Some agronomic aspects of 8 Crotalaria species, namely; Crotalaria ochroleuca, C. retusa, C. laburnoides, C. natalitia, C. kirkii, C. laburnifolia, C. polysperma, and C. incana were examined. Bacteria from nodules of C. ochroleuca, C. retusa, C. laburnoides and C. incana were isolated and authenticated. The isolates were characterised on the basis of cultural features, host range, growth rates, ability to grow on different sugars, sensitivity to antibiotics, and growth at different pH and temperature ranges. Also, a preliminary evaluation of nitrogen fixation in the 8 Crotalaria species was conducted in pots by using field soils K A survey in the field, and the herbarium collections at the University of Dar es Salaam showed a wide distribution of Crotalaria species in Tanzania, growing in the wild and in the farms as weeds. C. ochroleuca ("marejea" in Kiswahili) was found mainly under small scale cultivation. It is particularly very popular in the southern parts-of -Tanzania. C. ochroleuca seeds germinated well (1009s in 5 days) without treatment. Seeds of other species required treatment for better germination. C. ochroleuca, C. retusa, C. kirkii, and C. laburnoides took about two months to flowering, while C. natalitia and C. Iaburnifolia reached flowering stage within 5 to | months. Based on plant heights, C. ochroleuca signifi¬cantly grew faster (at 95% confidence limit) within a period of two months compared to the other species. All the bacterial isolates nodulated their respective plant hosts, as well as other Crotalaria species and Vigna (cowpea), but failed to infect members of other cross-inoculation groups. The isolates had long generation times (29 i 59 hours)! and increased the pH of the growth medium. These features are typical of Bradyrhizobium species. All isolates were Gram-negative short rods (2— 3um), with polar or sub- polar flagella, most of the isolates were able to grow between 20 - 37 °C, and 30 °C as optimum. All isolates grew well between pH 5.0 - 8.1, some failed at a low pH of 4.1 and high pH of 8.4, and none were growing at even lower pH 3.0. Except for three isolates which failed to grow in galactose, all other isolates were able to grow in monosaccharides tested. Remarkable differences were observed in the antibiotic sensitivity pattern, each isolate was somewhat unique. It can be deduced from the results that bacteria modulating Crotalaria species are heterogeneous in characteristics. Of the 8 Crotalaria species studied, 6 species showed high values of shoot and nodule dry weights, total nitrogen content of shoots, nitrogenase activity of the nodules, and nitrogen fixation at different growth stages. These parameters were positively correlated. At flowering stage, the nitrogenase activity of the nodules, and the amount of nitrogen fixed ranged from 0-112 nMo 1/p 1 ant/min. and 0-189 kgN/ha, respectively. The results showed that the performance of Crotalaria species can greatly be influenced by environmental parameters. Based on nitrogen fixation and other qualities of a good green manure, C. ochroleuca, C. laburnoides, C. retusa and C. kirkii are promising species and deserve more research. The results of this study indicate that the choice to use "marejea" (C. ochroleuca) by farmers is not a bad one. Hopefully, future experiments will support this pre1iminary conc1usion.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF QR92.N6T3M9 1990)
Bacillus (Bacteria), Nitrogen
Muruke, M S.H. (1990) , Isolation and characterization of bacteria from nodules of crotalarla species in Tanzania and the assessment of the nitrogen fixing capacity of the symbiosis., Master dissertation, University of Dar es Salaam. Dar es Salaam