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Interactions of Bean Yellow Mosaic Virus and an Aphid Vector with Phytophthora Root Diseases in Arrowleaf Clover. R. G. Pratt, Research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Mississippi State University, Mississippi State 39762; M. M. Ellsbury(2), O. W. Barnett(3), and W. E. Knight(4). (2)(4)Research entomologist, and research agronomist, Departments of Plant Pathology and Weed Science, Entomology, and Agronomy, respectively Mississippi State University, Mississippi State 39762; (3)Professor, Department of Plant Pathology and Physiology, Clemson University, Clemson SC 29631. Phytopathology 72:1189-1192. Accepted for publication 30 December 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982.. DOI: 10.1094/Phyto-72-1189.

Arrowleaf clover was inoculated with bean yellow mosaic virus (BYMV), Phytophthora erythroseptica, and P. megasperma f. sp. trifolii individually and in dual virus-fungus combinations at 7 and 9 wk. Dual inoculations were accomplished simultaneously and sequentially. Severity of symptoms was evaluated by root disease scores, root volumes, and dry weights of foliage. Simultaneous dual inoculations, and prior inoculations with BYMV, greatly increased severity of symptoms as compared to those caused by the virus and Phytophthora species individually. These increases were often synergistic as determined by root disease scores. Subsequent inoculations of BYMV into plants infected with Phytophthora resulted in smaller increases in severity of symptoms. In alsike clover, a species tolerant to BYMV and resistant to the Phytophthora spp., dual inoculations with BYMV and P. megasperma f. sp. trifolii did not consistently give more severe symptoms than those caused by the pathogens individually. Plants of healthy and BYMV-infected arrowleaf clover were colonized more heavily by the pea aphid in the greenhouse than were plants infected by P. erythroseptica with or without BYMV. However, in assays repeated during three seasons in the field, no differences were observed in frequencies of natural infection by BYMV in healthy and Phytophthora-infected arrowleaf clover.

Additional keywords: Acyrthosiphon pisum, Phytophthora erythroseptica, Phytophthora megasperma f. sp. trifolii, Trifolium hybridum, and Trifolium vesiculosum.