The Influence of Temperature and Moisture on Seed Viability Period in Barley (Hordeum distichum L.)

Storage experiments were carried out on barley seed (Hordeumdistichum L.) lasting from 1 min to 926 days, including 52 hermeticstorage environments covering a range of temperatures from 3to 90 °C and 5·5 per cent to 24·6 per centmoisture content (f. wt basis). Over the entire range of conditionssurvival curves conformed to negative cumulative normal distributionsand, for any given measure of longevity, e.g. half-viabilityperiod, longevity was roughly proportional to the negative exponentof both temperature and moisture content. Although previouslyreported viability equations were adequate to describe theserelationships over restricted ranges of environments, over theextended range of conditions tested here it was shown that therelationship between log seed viability and temperature is infact slightly convex, whilst that between log seed viabilityand moisture content is slightly concave. An improved viabilityequation was applied which takes into account those curvaturesand, at the same time takes into account the initial viabilityof a seed lot which reflects pre-storage deterioration. Thefit was excellent and thus it is now possible to predict percentageviability of any lot of barley seed after any storage periodunder a very wide range of conditions. Hordeum distichum L., barley viability, seed longevity, seed storage, moisture content of barley seed, temperature, influence of seed viability     

Soil chemical properties as related to forest succession in a highland area in north-east Tasmania

The relationship between vegetational type and a number of soil chemical factors was examined in secondary successions from fire-maintained eucalypt/grass to climax rainforest communities growing on uniform granitic soil parent material. Canonical variates analysis, which utilized the following variables: pH; loss on ignition; total N, P, K, Ca, and Mg; cation exchange capacity and exchangeable Ca, K, and Mg; and potentially mineralizable N, revealed close overall similarity between surface soils of adjacent types, and significant differences among those of types distant from each other in the successional sequences. Exchangeable Ca, mineralizable N, total N. P, and Mg, and pH all differed significantly among soils of the vegetational types. However, the only identifiable gradients in soil properties that were detected within a successional sequence were in total and mineralizable N, which tended to increase, and pH, which generally tended to decrease with progression towards the climax vegetation. Nitrification was promoted by the presence of Acacia dealbata and apparently inhibited by the presence of Leptospermum lanigerum; it was more rapid in soils beneath late successional vegetation than in those from climax vegetation or early stages of succession, and was inhibited in soil from old (> 200 years) grassland. It was concluded that differences among soils in chemical composition and rates of mineralization of N were due to differences in species composition of the vegetational types that they carried for the time being.     

Further studies relating chlorogenic acid concentration in carrots to carrot fly damage

The effects of first generation carrot fly larval damage on chlorogenic acid concentration in carrots was investigated in a field experiment at Wellesbourne in 1985. In a separate experiment carrots grown in the absence of a resident population of carrot fly were also analysed for chlorogenic acid; these carrots maintained low concentrations of chlorogenic acid through the summer and autumn until low ground temperatures occurred from November to January. The relationship between chlorogenic acid concentration and damage by the first generation of carrot fly was described by a similar model to the one derived previously for late-generation damage but without the cultivar dependence. This may have been because first generation damage takes place in mid-summer when soil temperature is not sufficiently low for differential chlorogenic acid production by carrot cultivars. The model supports the hypothesis that carrot fly damage increases chlorogenic acid production which subsequently encourages further attack. The increase in acid production due to the low winter temperature may be the mechanism which, in turn, induced a differential cultivar response in carrots harvested during the winter.     

Further investigations of the host range of the carrot fly, Psila rosae (F.)

Techniques were developed for testing umbelliferous species against naturally-occurring populations of carrot fly in the field. The most efficient technique involved exposure of plants to either first or second generations of the insect in the field, followed by caging of infested plots and trapping of emerged flies in water in yellow water dishes. In a series of field experiments between 1981 and 1989 inclusive, a total of 132 umbelliferous species and sub-species were tested against carrot fly. Seventy-eight of these proved to be new hosts, 27 were confirmed as hosts and 27 failed to support any carrot flies. Six non-umbelliferous plant species failed to be colonised by carrot fly. Sources of variability in investigations of the host range of insects are discussed.     

Host-plant susceptibility to the carrot fly, Psila rosae. 2. Suitability of various host species for larval development

Several apiaceous and two asteraceous species were tested for their suitability to support larval development of the carrot fly. Plants grown in pots or transplanted from seed beds into pots, were inoculated with a specific number of eggs. Pupae and non-pupated larvae were collected 6–7 wk after inoculation. Both the number and weights of pupae produced varied widely among the species. Cultivated carrots Daucus carota sativus often gave rise to only moderate numbers of pupae, but these invariably attained the highest weights. Pimpinella major was the only apiaceous plant tested that did not yield any carrot flies. The two asteraceous plants Cichorium intybus and Tanacetum vulgare failed to support larval development. Total carrot fly biomass produced per plant was influenced by both the host species and the root weight. Emergence rates of adult flies were positively correlated with pupal weights. Small individuals tended to have a longer total developmental time from egg to adult fly.     

Equine Culicoides hypersensitivity in Florida: biting midges collected in light traps near horses

Twenty-three species of Culicoides were trapped near pruritic horses during a 2-year survey in Florida. Nearly 99% of the biting midges collected were represented by Culicoides insignis Lutz, C. edeni Wirth and Blandon, C. stellifer (Coquillett), C. niger Root and Hoffman, C. haematopotus Malloch and C. venustus Hoffman. The relative contribution to the total catch by each of these species varied among collection sites. Seasonally, different species attain their largest population sizes at different times. Association of species collected in light traps with the seasonality of lesion development on the horses suggests that more than one species must be involved in causing Culicoides hypersensitivity in horses from Florida. Nulliparous females were present in most months that females of the same species were active; in some cases, species were trapped in each month of the year, particularly at the more southerly sites. The species of biting midge most likely to be involved in Culicoides hypersensitivity in horses in Florida are C. insignis, C. stellifer and C. venustus based upon their mammalophilic behaviour and seasonality.