VIEW ARTICLE

Interactions of Pseudomonas marginalis var. alfalfae, Erwinia amylovora var. alfalfae and an Unidentified Bacterium (WB-3) with Certain Root Pathogens of Alfalfa. P. A. Shinde, Graduate Student, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; F. L. Lukezic, Associate Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 64:1169-1173. Accepted for publication 5 April 1974. DOI: 10.1094/Phyto-64-1169.

Interactions between Pseudomonas marginalis var. alfalfae, Erwinia amylovora var. alfalfae and an unidentified bacterium (WB-3) from alfalfa roots and three root pathogens of alfalfa were studied. The P. marginalis var. alfalfae and Corynebacterium insidiosum combination resulted in a reduction in top symptoms in cultivars DuPuits and Buffalo compared to top symptoms produced by C. insidiosum alone. A possible antagonistic relation between the two bacteria occurred. A similar reduction in top symptoms occurred in DuPuits, when P. marginalis var. alfalfae was combined with Fusarium oxysporum f. sp. medicaginis. However, an increase in top symptoms with the P. marginalis var. alfalfae and F. oxysporum combination in Buffalo suggests that the host has an important role in this interaction. The F. tricinctum and P. marginalis var. alfalfae combination produced a synergistic effect, which resulted in a significant increase in top symptoms in both cultivars. In both cultivars, the E. amylovora var. alfalfae and C. insidiosum combination resulted in a reduction in top symptoms when compared to C. insidiosum alone. A similar reduction in top symptoms occurred in Buffalo when E. amylovora var. alfalfae was present in combination with F. tricinctum. However, the same combination in DuPuits resulted in a significant increase in top symptoms. The unidentified bacterium (WB-3) in combination with F. oxysporum produced a synergistic effect in both cultivars. A similar effect was observed in Buffalo, but not in DuPuits, when the bacterium was present in combination with F. tricinctum. The results obtained in this study indicate that these bacteria as well as the hosts do have a definite role in the development of alfalfa diseases caused by F. oxysporum and F. tricinctum but not by C. insidiosum under the conditions of these tests.