Corymbia leaf oils,latitude, hybrids and herbivory: A test using common‐garden field trials

Foliar oils, particularly monoterpenes, can influence the susceptibility of plants to herbivory. In plants, including eucalypts, monoterpenes are often associated with plant defence. A recent analysis revealed an increase in foliar oil content with increasing latitudinal endemism, and we tested this pattern using three eucalypt taxa comprising a latitudinal replacement cline. We also examined the relative concentrations of two monoterpenes (α‐pinene and 1,8‐cineole), for which meta‐analyses also showed latitudinal variation, using hybrids of these three taxa with Corymbia torelliana. These, and pure C. torelliana, were then assessed in common‐garden field plots for the abundance and distribution of herbivory by four distinct herbivore taxa. Differing feeding strategies among these herbivores allowed us to test hypotheses regarding heritability of susceptibility and relationships to α‐pinene and 1,8‐cineole. We found no support for an increase in foliar oil content with increasing latitude, nor did our analysis support predictions for consistent variation in α‐pinene and 1,8‐cineole contents with latitude. However, herbivore species showed differential responses to different taxa and monoterpene contents. For example, eriophyid mites, the most monophagous of our censused herbivores, avoided the pure species, but fed on hybrid taxa, supporting hypotheses on hybrid susceptibility. The most polyphagous herbivore (leaf blister sawfly Phylacteophaga froggatti) showed no evidence of response to plant secondary metabolites, while the distribution and abundance patterns of Paropsis atomaria showed some relationship to monoterpene yields.     

Relationships between photosynthetic area and other growth attributes with grain yield in 6- and 2-row barley genotypes

Six-row and 2-row barley genotypes were grown as individually spaced plants in the field, and estimates of area of green tissue and other characters were obtained at ear emergence and maturity. Positive correlations (P<0.01) were found within both 6- and 2-row types between grain dry wt per main culm and grain number, mean date of ear emergence, area of green tissue above the flag-leaf node, and dry wt of the third leaf below the ear (F-2 leaf). This supports the hypothesis that the magnitude of assimilate supply prior to anthesis is a very important determinant of grain yield in barley, and the possible use of the F-2 leaf as a criterion for selection of genotypes with a large photosynthetic capacity and grain yield is discussed.