Ecological Studies on Lentil, Rhizobia; Competition and Persistence in Some Tropical Soils a Thesis Submitted to the Graduate Division of the University of Hawaii in Partial Fulfillment of the Requirements for the Degree of Master of Science in Microbiology

Thirty-one strains of Rhizobium leguminosarum were screened for their ability to fix nitrogen (effectiveness) on lentils (Lens esculenta). Fluorescent antibodies prepared against four of the most effective strains (NZP 5400, Hawaii 5-0, Nitragin 128A12, and Nitragin 128C53) and one other effective strain, Nitragin 175P1, were strain specific. NZP 5400, Hawaii 5-0, and Nitragin 128A12 were selected for competition studies. Rhizobia in lentil nodules were identified by immunofluorescence. In two separate growth chamber studies all possible combinations of the three strains were used to inoculate lentil seedlings grown in sterile vermiculite. In the first study which involved a commercial lentil cultivar, the following results were obtained: Hawaii 5-0 and NZP 5400 were equally competitive against one another and onethird of the nodules contained both strains; Nitragin 128A12 was a poor competitor against either of the other two strains and the incidence of double infection was much lower. The second growth chamber study involved three lentil cultivars (Benewah, Chilean, and Tekoa). Results of two strain competition were: NZP 5400 was superior to Nitragin 128A12 on all three cultivars and only 6% of the nodules were doublyinfected; NZP 5400 was slightly superior to Hawaii 5-0 on the Chilean cultivar, but the two were equally competitive on the other two cultivars and one-third of the nodules were doubly-infected; Nitragin 128Al2 dominated Hawaii 5-0 on both Benewah and Tekoa and the two were equally competitive on Chilean with one-third of the nodules being doubly-infected. In three strain competition NZP 5400 was superior to the other two strains on Tekoa and Chilean but all three strains were equally competitive on Benewah. The two most competitive strains from the first study, NZP 5400 and Hawaii 5-0, were further tested in the field in a Hawaiian inceptisol (Ustic Humitropept, pH 6.1). Commercial lentil seeds were pelleted with equal numbers of both strains. The two strains were equally competitive against one another and both were dominant against the native ineffective strains of lentil rhizobia which were present in low numbers. One-third of the nodules contained both of the introduced strains. One year later, uninoculated lentil seeds were planted in these same field plots to assess the persistence of these two strains. Both strains persisted over this period, but the Hawaiian isolate, Hawaii 5-0, was present in a higher proportion (51%) of the nodules. Only 24% of the nodules contained both strains. The competitiveness of all three strains was tested in another field experiment in a Hawaiian oxisol (Tropeptic Eutrustox, pH 5.8). Commercial lentil seeds were pelleted with equal numbers of all three strains and competition was assessed at low, medium, and high levels of phosphorus. Early (10 days) and late (8 weeks) sampling of nodules yielded the following results: Hawaii 5-0 was superior to the other two strains at the low phosphorus level; Hawaii 5-0 and Nitragin 128A12 were equally competitive at the medium phosphorus level; all three strains were approximately equal in competitiveness at the high phosphorus level. The incidence of double-infection varied from 0% to 26% depending on the phosphorus level and the sampling time.