Border Patrol: Epicuticular Leaf Wax Mediates Resistance of Azalea Genotypes (Rhododendron spp.) to Azalea Lace Bug [Stephanitis pyrioides (Scott)]

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  • 1 University of Georgia, Horticulture, Griffin, GA, 30223

Azalea lace bug (ALB) is a significant pest on azalea, with feeding injury causing speckling and discoloration on affected leaves. Feeding damage also results in a reduction of stomatal gas exchange and leaf chlorophyll content, postulated to diminish growth and flowering rates.

In azalea, specific lipid components of the plant cuticle have been implicated in ALB resistance of R. canescens. In this study, epicuticular leaf wax was extracted from the leaves of four azalea genotypes, divided into two groups: a resistant group including R. periclymenoides and `Fourth of July' and a susceptible group including R. austrinum and `My Mary'. Leaf wax was extracted and resuspended in solution for application to all entries in a full diallel manner, including controls of solution only and no treatment. Each genotype–solution treatment included 10 replications. The leaf wax solution was applied to each replication (leaf) by painting the solution on one side of the midrib, yet on both abaxial and adaxial surfaces. Two leaves attached to a stem and four female adult ALB were placed in separate 32-mL sealed cups. Experimental conditions were 24 °C and 12-hour daylength for 96 h, at which time the number of live adults, frass spots, and eggs were counted. Data revealed that application of leaf wax solution had an impact on the level of frass and egg deposition by ALB in both resistant and susceptible genotypes. The effect was most pronounced when a solution of resistant genotypes was placed on susceptible genotypes, as the application resulted in lower numbers of frass spots and eggs compared to the nil control. However, an increase in frass and eggs was observed when extract of susceptible genotypes was applied to resistant genotypes.

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