Leaf curl syndrome of pigeonpea (Cajanus cajan (L.) Millsp.) is a systemic response to effective nodulation by the Rhizobium strain IC3342 uri icon

abstract

  • Rhizobium str. IC3342 is an unusual bacterium that causes a leaf curl syndrome in pigeonpea. Growth characteristics, plasmid profile, conserved nif and nod gene sequences and nodulation host range of this strain resemble that of the fast-growing Rhizobium str. ANU240 (NGR234). Leaf curl occurred only in hosts effectively nodulated. A plasmid-cured, non-nodulating derivative failed to induce leaf curl symptoms. The str. IC3342 competed poorly with fast- and slow-growing root-nodule bacteria, but the observed nodule occupancy of 10% was enough to produce leaf curl symptoms. Suppression of nodule development by added inorganic nitrogen also prevented symptom expression. Approach grafting of a healthy pigonpea plant with leaf curl symptoms resulted in the development of leaf curl symptoms on the growing shoots of the healthy plant within 8 days of graft union. Further symptom expression ceased after graft separation. Feeding xylem sap from the leaf curled plant to a healthy plant induced the initial symptom of the syndrome, bending of the growing leaf tip. It is concluded that leaf curl induction is a systemic response for which effective nodulation is an apparent prerequisite

publication date

  • 1991
  • 1991