The role of refuge areas in the phenology of Rhopalosiphum padi in low rainfall cropping areas of South Australia

Extensive surveys of possible aphid habitats in South Australia indicated that irrigated perennial grass pastures in the Mount Lofty Ranges and Lower Murray Valley were summer refuges for Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Large numbers of aphids build up in these pastures each year during autumn (April and May) with numbers peaking in May. The size of the May peak was related to the number of aphids surviving the summer. The proportions of alates were highest in May and August/September. Both peaks coincided with a photoperiod of between 11.2 and 11.5 h, and partial correlations suggested that aphid density, photoperiod and temperature were all significant determinants of alate production.     

The role of annual grasses in the phenology of Rhopalosiphum padi in the low rainfall belt of South Australia

Rhopalosiphum padi (L.) (Hemiptera: Aphididae) was the first species of cereal aphids to colonise annual grasses across the state each year. Numbers were higher in the Lower Murray Valley than in the Mount Lofty Ranges or Adelaide Plains. At all locations, numbers generally increased until grasses reached the boot stage after which they declined. Alatoid production commenced in late July in response to crowding, but thereafter plant age and photoperiod were more important determinants. Metopolophium dirhodum (Walker) (Hem-pitera: Aphididae) and Sitobion nr fragariae (Hemiptera: Aphididae) first appeared in annual grasses in late July.     

Development of sequence‐tagged microsatellites for the barley net blotch pathogen,Pyrenophora teres

A modified sequenced‐tagged microsatellite (STM) profiling procedure was used to develop 80 STMs for the barley net blotch pathogen, Pyrenophora teres. Of these, 60 STMs amplified 67 loci in one or both of the spot (P. teres f. maculata) and net (P. teres f. teres) forms of the pathogen. When screened on six field‐sampled isolates of each pathogen form, 25 STMs revealed 26 polymorphic loci, with an average of 3.2 ± 1.0 alleles and mean gene diversity of 0.59 ± 0.12.     

Development of sequence tagged microsatellites (STMs) for the barley scald pathogen Rhynchosporium secalis

A rapid and cost efficient technique was developed and used to generate 168 sequence tagged microsatellites (STMs) in the barley scald pathogen Rhynchosporium secalis. Sixty‐two STMs, amplifying 66 loci, revealed a high level of polymorphism among a diverse set of 16 Australian isolates. Each locus revealed two to nine alleles (average 4 ± 1.82), and a gene diversity measure of 0.54 was obtained. This technique not only halved the cost of marker development compared to traditional methods, but substantially reduced the cost of performing fluorescence‐based microsatellite assays. These STMs provide a powerful tool for genetic studies in R. secalis.     

ZOOGEOGRAPHY OF SOME TERRESTRIAL MICRO-ARTHROPODA IN ANTARCTICA

1. A review is presented of the information relating to the distribution of free-living terrestrial Cryptostigmata, Prostigmata and Collembola in the south polar region. 2. The Maritime zone, comprising the Antarctic Peninsula and its neighbouring islands, forms a less-clearly definable faunal province than does the Continental zone where generic and specific endemism is high. The Maritime distribution of the micro-arthropods forms no consistent pattern, although in the case of the two groups of mites a distinction can be made between a southern and a northern Maritime fauna. The boundary between these two elements appears to lie between the South Orkneys and the South Sandwich Islands. 3. As far as distribution in the Sub-Antarctic is concerned, all three groups of micro-arthropods show certain general similarities, although in each case particular features can also be distinguished. All three show relatively high specific endemism in the Sub-Antartcic, which sugge:ts that this zone is a faunal province distinct from that of the cold temperate zone to the north and other parts of the Antarctic to the south. It seems equally reasonable to recognize that this province can be subdivided into western and eastern parts, each with its own distinct group of species, although the extent to which this separation is expressed varies from group to group. In all three groups there is an element which is circum-Sub-Antarctic in distribution, but this element is more in evidence in the Collembola than in the mites. From the study of the distribution of endemic species in the Sub-Antarctic it is concluded that the fauna of the eastern part has been isolated from the south temperate zone fauna for longer than it has in the west. 4. In all three groups of micro-arthropods a relic element can be identified, the present distribution of which is consistent with the idea of a former continuous distribution extending across a southern land mass incorporating both the eastern and western parts of the continent, the islands on the Scotia Ridge, and the older Sub-Antarctic islands of South Georgia, Macquarie and, possibly, Kerguelen. In the Cryptostigmata in particular, this relic element, which is represented by members of the Podacaridae, is joined in the Sub-Antarctic and Maritime zones by a penetrant element which probably has invaded the south polar region from the north during the post-Pleistocene period. 5. An alternative hypothesis is also discussed, namely that present distribution patterns of micro-arthropods can be explained solely in terms of post-Pleistocene colonization. It is accepted that limited overseas dispersal could have occurred in recent times, indeed may still be occurring between, for example, the various volcanic islands in the eastern Sub-Antarctic, between the south temperate zone and the Sub-Antarctic, and between the latter and the Maritime zone. However, there is no evidence to suggest that any appreciable amount of long-range dispersal is occurring, on the scale required to support this hypothesis. In addition, there is no evidence that rates of speciation in the south polar region are rapid enough to produce the kind of evolutionary divergence which is implicit in the theory of post-Pleistocene colonization.     

Effect of High Temperature During Grain-filling on the Structure of Developing and Malted Barley Grains

High temperatures (up to 35 °C) were applied to plants ofmalting barley,Hordeum vulgareL. (‘Schooner’) fora period of 5 d during grain-filling. Heat treatment had a profoundeffect on the structure of the mature barley grain. There wasevidence of degradation of endosperm storage products in heat-treatedgrain. Starch granule development was reduced in sub-aleuronecells following heat treatment and alterations to starch granuledistribution and growth were observed in the endosperms of thesegrains. Endosperm cell wall and crushed cell layer (CCL) developmentwere sensitive to high temperatures, with the reduced thicknessof the CCL and generally patchy Calcofluor fluorescence of endospermcell walls indicative of partial hydrolysis of ß-glucans.Increased growth of the embryo took place in heat-treated grainscompared with control grains. Endosperm texture was generallymore friable in heat-treated grains than in control grains,and these grains overmodified during malting, with considerabledegradation of starch in the form of extensive pitting of A-typestarch granules. Evidence is presented for developmental andgermination events occurring simultaneously within the developinggrain.Copyright 1998 Annals of Botany Company Barley,Hordeum vulgareL., starch granules, crushed cell layer, scutellum, embryo, fluorescence microscopy, scanning electron microscopy, confocal microscopy, malting quality.