Changes in abundance and infectivity of powdery mildew conidia from cucumber plants treated systemically with lithium chloride

Systemic treatment of cucumber plants with lithium chloride reduced the numbers of conidia produced by colonies of powdery mildew, Sphaerotheca fuliginea , growing on leaves, and lowered the infectivity of conidia produced from those leaves when they were applied to leaves of untreated plants. Production of conidiophores was lower in both lithium-treated and calcium-deprived plants, and lithium slightly decreased the calcium content of leaves. When the lithium-containing growth medium was supplemented with phosphate, conidiophore production was still markedly reduced, although leaves had normal levels of calcium. Fungal development was not correlated with either the calcium or phosphorus content of leaves. It is concluded that, although severe calcium deficiency can inhibit fungal development, the inhibitory effects of lithium are not mediated through alterations in calcium or phosphorus uptake by host tissues.     

Partial characterization of a closterovirus associated with apple mealybug-transmitted little cherry disease in north america

ABSTRACT Little cherry disease (LChD) is a serious economic problem of sweet cherry production in western North America where apple mealybug is the principle vector. LChD is associated with a distinct species of double-stranded (ds) RNA. In this study, filamentous virus particles were purified from LChD-infected trees and shown to contain single-stranded RNA corresponding to the previously reported dsRNA isolated from infected trees. The virus particles were characterized and were similar to monopartite members of the genus Closterovirus. A portion of the genome was sequenced and found to be most closely related to the RNA-dependent RNA polymerase of Grapevine leafroll-associated virus-3, a mealybug-transmitted closterovirus. The characteristics of the mealybug-transmitted Little cherry virus in North America are very different from those of a closterovirus associated with a similar disease in Europe.