The resistance of Solanum okadae Hawkes & Hjert. (PI 458367), Solanum oplocense Hawkes (PI 473368), and Solanum tarijense Hawkes (PI 414150) to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Chrysomelidae: Chrysomelini), was studied. In replicated field trials all three accessions showed a high level of resistance to the beetle. No significant genetic variability between genotypes of the same species was found. Results from host acceptance behavior experiments, suitability for larval development tests, foliage consumption tests, and adult survival and oviposition tests supported the hypothesis that the mode of resistance differs between the three wild Solanum species. Solanum okadae and S. oplocense affected host acceptance and consumption. Because the beetle reacted differently to these two species it was hypothesized that the antifeedant chemical(s) differed in nature or quantity. S. tarijense contrasted with the other two species by affecting mostly adult colonization and oviposition.
Three methods were used to study genotype‐environment (GE) interactions of potato (Solanum tuberosum L.) yield. They were chosen to represent single (stability variance σ1 of Shukla, 1972), two (genotypic stability parameters α, λ of Tai, 1971), and three (genotypic components v1, v2 and v3 of Tai, 1975) parameters of measurement of genotypic contributions to the GE interactions. Data of marketable yield (W) and three yield components: number of stems/plot (X), number of tubers/stem (Y), and mean tuber weight (Z) of 30 genotypes were collected from nine trials in New Brunswick. Significant differences were found for σ2, α, and λ among the genotypes. The estimates of σ2 were highly correlated to those of λ. Both parameters showed a curvilinear relationship with v1 and v2 suggesting low σ2 and λ values were due to moderate genotypic responses to the environmental components (r1 and r2) supporting X and Y. The linear response parameter α showed close association with v3 which measured the genotypic response to the environmental component (r3) supporting Z. The estimates of v3 showed a moderately positive correlation with the mean marketable yield (W) and were larger than those of v1 and v2 for most genotypes. The estimates of r3 were larger and more variable than those of r1 and r2 over the environments. It is thus concluded that difficulty would be encountered locating high yielding genotypes without sensitive responses to the variation of r3.
A method of investigating genotype-environment interactions of field crops is presented. Based on the concept that yield components are determined sequentially at different stages in the ontology of plants and the hypothesis that the environmental resources can be separated into independent groups with each contributing to the development of a component trait, a causal relationship between environmental resources, component traits and yield is established (Fig. 1). The GE interaction effect is then represented by three multiplicative terms which are composed of three genotypic and three environmental components. These components are estimated using the method of path coefficient analysis based on the postulated causal relationship. Data of marketable yield and yield components of seven potato cultivars collected from two series of trials are examined by the proposed method.
SummaryAlate green peach aphids, Myzus persicae (Sulzer), tested in a flight chamber during their maiden flight period displayed behaviours ranging from repeated trivial flights to settling on the plants. The interaction of alate vector density and PVY n spread was dichotomous, virus spread was significantly related to vector density in some trials but virus spread was nil or limited and not significantly dependent on vector density in others. The green peach aphid colony used in these experiments provided a mixture of active and highly active alate populations. Results suggest that inactive and active vectors came from the active and highly active alate populations, respectively. Therefore, winged aphids within a species cannot alI be attributed the same vector efficiency unless known to originate from the same population. At a 15% inoculum level the intercept for the regression model for the spread of PVY n was 5.03% indicating that there is a significant probability of propagation at aphid densities as low as one. However, over the range of aphid densities tested, the rate of spread per aphid was low, 0.08%, suggesting that reinfection of newly infected plants or movement interference between aphid vectors rapidly became important factors negatively affecting virus spread. Although these results cannot be directly transferred to field conditions they provide confirmation that low M.persicae numbers can transmit unacceptable levels of mosaic and that low inoculum levels are required to decrease the risk of transmission by the small aphid numbers which cannot be realistically controlled.
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