Studies on the Developmentof Rhizobium Inoculum Using Moss as Carrier for Bambara Groundnut, Vigha Subterranea (L) Verdc.
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Date
1991-10
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University of Ghana
Abstract
Research was carried out to develop an effective inoculum carrier of the nodule bacterium, Rhizobium sp., for the inoculation of seeds of bambara groundnut [Vigna subterranea (L.) Verde, comb. nov. = Voandzeia subterranea (L.) Thouars] from a local material. Five outof 16 strains of Rhizobium sp. isolated from soils of legume farms at eight localities within a radius of 180 km from Legon were used in experiments to test the efficiency of the carrier that was developed. Plants infected by these five strains grew well, had high dry weights and high nitrogen contentof the shoots and formed many large nodules.
A good Rhizobium carrier was developed from the moss, Brachymenium sp. Harvested thalli were sun- dried for 10 days and decomposed for 15 days. When stored at room temperature, the Rhizobium- population of inoculated moss compostof 50 per cent moisture content rose to a maximum of 4.00 x 1011 cells per gram of compost after 10 weeks. The population remained stationary thereafter till the end of the 14th week without showing any signs of autolysis. Sterile compost inoculated and stored at room temperature for two weeks when the Rhizobium population rose to approximately 1 x 1011 cells per gram of compost was used to inoculate the seeds in the various experiments. Ex-Ada and Ex-Tamale varieties of bambara groundnut inoculated with the five strains of Rhizobium sp. all nodulated. Plants of Ex-Ada variety developed best at low light intensity (1100 - 2200 lux at 9.00 am, 4030 - 6200 lux at noon and 1600 - 1900 lux at 3.00 pm). Medium light intensity (1400 - 2800 lux at 9.00 am, 6400 - 9100 lux at noon and 2900 - 3500 lux at 3.00) was less favourable and high light intensity (5300 – 6200 lux at 9.00 am, 8800- 10000 lux at noon and 4600 - 6400 lux at 3.00 pm) was least favourable. After 30 days, the respective mean dry weights of the plants at the low, medium and high light intensities were 1.62 - 2.91g, 1.33 - 1.82g and 0.91 – l.41g; and the respective mean number of nodules per plant was 54 - 78, 42 - 51 and 16 - 21. Plants of E x - Tamale variety watered once in two days showed the best growth. Those watered once in four days showed moderate growth, and growth of plants watered once in six days was greatly reduced. After 30 days, the respective mean dry weights of plants watered once in two, four and six days were 1.00 - 1.68g, 0.64 - 0.94g and 0.48 - 0.76g, and the respective mean number of nodules per plant was 43 - 56, 16 - 25 and 8 - 11. In both tests, conditions of light and moisture which encouraged higher nodulation also induced the formation of larger nodules. It was concluded that compostof Brachymenium sp. is a good Rhizobium carrier and can be used for routine inoculation of bambara groundnut seeds. To derive the maximum benefit from the inoculation, it is desirable to identify the best strain of Rhizobium sp. for each variety of bambara groundnut.