CHARACTERIZATION OF A COWPEA (VIGNA-UNGUICULATA) RHIZOBIOPHAGE AND ITS EFFECT ON COWPEA NODULATION AND GROWTH

A cowpea rhizobiophage (JRW 3 phage) from Jamaican soil was isolated and characterized. The phage has a polyhedral head and a non-contractile tail; maximum adsorption of the phage to the host occurred after 5 min. A one-step growth experiment revealed that the latent period, rise period and burst size of JRW 3 phage were 12 h, 16 h, and 28 plaque-forming units/cell, respectively. The JRW 3 phage was highly sensitive to heat, but survived well between pH 5 and 8. The phage was stable in EDTA, though completely inactivated in sodium citrate. Host range analysis showed that 7 of the 40 Rhizobium and Bradyrhizobium strains tested were sensitive to phage infection. The phage significantly reduced nodule numbers and shoot dry weight of cowpea plants when inoculated with rhizobia in combination with the phage.