Leucaena leucocephala Nodules Formed by a Surface Polysaccharide Defective Mutant of Rhizobium sp. Strain TAL1145 Are Delayed in Bacteroid Development and Nitrogen Fixation. Nikhat Parveen. (1)Department of Plant Molecular Physiology, (2) Department of Microbiology, University of Hawaii, Honolulu 96822 U.S.A. David T. Webb (3), and Dulal Borthakur(1). (1) Department of Plant Molecular Physiology; (3)Department of Botany, University of Hawaii, Honolulu 96822 U.S.A. MPMI 9:364-372. Accepted 11 March 1996. 1996 The American Phytopathological Society.

A Tn5lacZ-insertion mutant of the Leucaena-nodulating Rhizobium sp. strain TAL1145 defective in exopolysaccharide (EPS) and lipopolysaccharide (LPS) synthesis was characterized. This mutant, NP84, formed pseudonodules on Phaseolm vulgaris and Gliricidia sepium that did not show invasion by bacteria. On Leucaena leucocephala it formed nodules that appeared Fix^- at 4 weeks but Fix⁺ at 8 weeks after inoculation. Microscopic examination of the sections of the L. leucocephala nodules formed by NP84 after 4 weeks of inoculation showed fewer infected cells than in nodules formed by TAL1145. Ultrastructural differences were observed in the cells infected by NP84 compared with those infected by TAL1145. When NP84 was coinoculated with TAL1145 on L. leucocephala, all nodules were occupied by TAL1145 although some nodules showed double occupancy with NP84. None of the nodules were found to be infected by NP84 alone. A 3.8-kb DNA fragment of TAL1145 was identified and cloned that complemented NP84 for EPS, LPS, and symbiotic defects