Jo-Ann Bentz

Leaf Element Content and Utilization of Maple and Elm as Hosts by the Potato Leafhopper (Homoptera: Cicadellidae)

Abstract Feeding injury and performance of the potato leafhopper, Empoasca fabae (Harris), was measured on two red maple clones (Acer rubrum L.), a Freeman maple cultivar (A. × freemanii E. Murray), two elm cultivars (Ulmus spp.), and an American elm clonal selection (U. americana L.), and was related to the leaf content of important nutritional elements. Significantly more eggs were laid and more nymphs became adults on American and Patriot elms than on the other clones. Although the mean number of eggs laid was not significantly different among the maple clones, nymphal survivorship was significantly higher on red maple 56026 than on the other maple clones. Although the number of eggs laid was linearly related to foliar nitrogen and phosphorus, survival of nymphs to adulthood was linearly related to foliar nitrogen. Significantly more leafhoppers from the wild population were collected from American elm, followed by Patriot elm and red maple 56026. Although none of the elms showed any evidence of feeding injury, the maple trees varied from tolerant (i.e., ‘Indian Summer’) to susceptible (i.e., red maple 56026). Leafhoppers may need to increase feeding on red maple 56026 as a compensatory response to the limited nutritional quality of this clone. Because the sex ratio of the wild population was close to 1:1, and consistent across clones, it appears that differences in the behavior of the potato leafhopper among clones were not a function of gender bias associated with each species. Resistance against the potato leafhopper among maples and elms is influenced, in part, by the nutritional content of the leaves. Yet, feeding injury is not a good indicator of host resistance against the potato leafhopper.

Maturity and temperature stratification affect the germination of Styrax japonicus seeds

Summary The effect of seed maturity, warm (18°C) or cold (5.5°C) temperature, and gibberellic acid (GA3) on Styrax japonicus seed germination was investigated. Morphological changes during fruit development were observed using magnetic resonance imaging (MRI) and to correlate changes in germination behaviour with time. Internal structures of fruits were identified using MRI, which showed tissues that contained water with different mobility in early growth stages. In the pericarp, the seed coat, and the endosperm of fruits harvested 17 weeks after anthesis, spin-lattice relaxation time T1 decreased with maturation of the fruits. This finding indicated the termination of the physiological role of the pericarp due to a loss of free water, and of water that existed in bound form in the endosperm and the cotyledons as seeds became dry. Magnetic resonance images of Styrax japonicus ‘Pink Chime’ fruits harvested 11 weeks after anthesis showed the formation of cotyledons and endosperm. Fruits were fully developed when harvested 13–15 weeks after anthesis. S. japonicus fruits harvested 12 weeks (1999) and 16 weeks (2000) after anthesis were fully developed and matured, and responded to germination-promoting treatments. To ensure good germination, or higher than 80%, seeds should be harvested 12–16 weeks after anthesis, and should be treated with one month of warm stratification (WS) followed by two months of cold stratification (CS). The maximum percent germination was 98%, after two months of WS followed by three months of CS, which is significantly higher than the percentage previously reported.