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Summer Death of French Bean: New Hosts of the Pathogen, Vector Relationship, and Evidence against Mycoplasmal Etiology. J. W. Bowyer, Senior Research Assistant, Department of Microbiology, Medical School, University of Queensland, Herston, Queensland, Australia 4006; J. G. Atherton, Reader, Department of Microbiology, Medical School, University of Queensland, Herston, Queensland, Australia 4006. Phytopathology 61:1451-1455. Accepted for publication 12 July 1971. DOI: 10.1094/Phyto-61-1451.

The French bean summer death (SD) causal agent was transmitted by the leafhopper Orosius argentatus to, and recovered from, Datura stramonium, Beta vulgaris var. vulgaris, B. vulgaris var. cicla, Callistephus chinensis, and five susceptible cultivars of French bean. The agent was also transmitted to, and recovered from, the SD-tolerant French bean cultivars Hawkesbury Wonder and Brown Beauty, but not Phaseolus aureus, P. lathyroides, or Solanum nigrum. Only D. stramonium, B. vulgaris var. vulgaris, and the susceptible bean cultivars showed disease symptoms; B. vulgaris var. cicla, C. chinensis, and the tolerant bean cultivars were symptomless carriers. The SD agent was transmitted from D. stramonium to D. stramonium and tomato (Lycopersicon esculentum ‘Grosse Lisse’), and from tomato to tomato and D. stramonium by grafting. The minimum latent period of the SD agent in adult leafhoppers was between 24 and 48 hr. Leafhopper infectivity persisted for at least 21 days after access to a diseased plant. Infectivity was not lost during molting of the final instar. Single leafhoppers transmitted both the legume little leaf agent (one of the probable mycoplasmalike agents) and the SD agent. Viruslike particles or microorganisms were not detected by electron microscopy in SD-diseased plants or infective leafhoppers. Treatment of SD-infected tomato with tetracycline hydrochloride (achromycin) had no apparent effect on graft or leafhopper transmission of the SD agent. These results are interpreted as evidence against possible mycoplasmal etiology of the disease. The causal agent is apparently similar to the beet curly top agent in several respects.

Additional keywords: Phaseolus vulgaris, beetroot, silver beet.