Nodulation competitiveness between contrasting phage phenotypes of pigeonpea rhizobial strains

Compe titi veness betwee n (I ) lysogeni c liS. phage-indicator strain s, (II ) phage-resistant liS phage-sens iti ve strain s, a nd (Ill ) large plaque liS. small plaque developing strain s was examined under labo rato ry a nd fi e ld conditions in o rd e r to study thc in volveme nt of these c ru c ial phage sensitivity patt e rn s in th e competiti o n for nodule occupancy of pigeonpea rhi zobia. The phage-indicato r strain (A039) exhibited hi g he r competitiveness over th e lysogeni c strain (A025 Sm'); th e phage sensitive stra in (l HP-1 95) over the phage resista nt strain (lHP 195 Sm'Y'); and th e large plaque developing strain (A059) over th e s ma ll plaque developin g strain (IHP 195 Sm') in association with pi geon pea cv. bahar bo th under la bo rat o ry a nd field conditions. Dual in ocul at ion of A025 Sm' + A039 a nd A059 + IHP 195 Sm' (mix ed in equa l proportion just be fo re treatm e nt ) improved th e nodul e occupancy by in ocul ant strain s against nati ve rhi zobia a nd result ed il1l o hi ghe r plal1l dry weight and y ie ld as compared to th eir application as s in g le in oculum. The phage-resi tant muta nt IHP 195 Sm'Y' showed reduced competiti ve ness against nati ve rhi zobia, compared to it s paren tal strain . The dual in oculation of parental strain a nd ph age-resista nt mutant gave the same result as th e in ocul ati o n of parel1lal strain a lo ne.