Nodulation competitiveness between contrasting phage phenotypes of pigeonpea rhizobial strains

Abstract

<span style="font-size:12.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:hi"="" lang="EN-IN">Competitiveness between (I) lysogenic <i>vs</i>. phage-indicator strains, (II) phage-resistant <i>vs</i> phage-sensitive strains, and (III) large plaque <i>vs</i>. small plaque developing strains was examined under laboratory and field conditions in order to study the involvement of these crucial phage sensitivity patterns in the competition for nodule occupancy of pigeonpea rhizobia. The phage-indicator strain (A039) exhibited higher competitiveness over the lysogenic strain (A025 Sm^r); the phage sensitive strain (IHP-195) over the phage resistant strain (IHP 195 Sm^rV^r); and the large plaque developing strain (A059) over the small plaque developing strain (IHP 195 Sm^r) in association with pigeonpea <i>cv</i>. bahar both under laboratory and field conditions. Dual inoculation of A025 Sm^r+ A039 and A059 + IHP 195 Sm^r (mixed in equal proportion just before treatment) improved the nodule occupancy by inoculant strains against native rhizobia and resulted into higher plant dry weight and yield as compared to their application as single inoculum. The phage-resitant mutant IHP 195 Sm^rV^rshowed reduced competitiveness against native rhizobia, compared to its parental strain . The dual inoculation of parental strain and phage-resistant mutant gave the same result as the inoculation of parental strain alone.</span>