No description available.

No description available.

Infection of legume roots with Rhizobium species results in the development of a root nodule structure in which the bacteria form an intracellular symbiosis with the plant. It is reported here that the infection of soybean (Glycine max L.) roots with Rhizobium japonicum results in the synthesis by the plant of at least 18-20 polypeptides other than leghemoglobin during the development of root nodules. Identification of these "nodule-specific" host polypeptides (referred to as nodulins) was accomplished by two-dimensional gel analysis of the immunoprecipitates formed by a "nodule-specific" antiserum with in vitro translation products of root nodule polysomes that are free of bacteroidal contaminations. Nodulins account for 7-11% of the total ('35)S-methionine-labeled protein synthesized in the host cell cytoplasm, and the majority of them are of 12,000-20,000 molecular weight. These proteins are absent from the uninfected roots, bacteroids and free-living Rhizobium, and appear to be coded for by the plant genes that may be obligatory for the development of symbiosis in the legume root nodules. Analysis of nodulins in ineffective (unable to fix nitrogen) nodules developed due to Rhizobium strains SM5 and 61A24 showed that their synthesis is reduced and their expression differentially influenced by mutations in rhizobia. / Apart from the low molecular weight nodulins, a 35,000 MW polypeptide present in the nodule cytoplasm was also identified as "nodule-specific". This protein, referred to as nodulin-35, represents about 4% of the total cytoplasmic protein in root nodules, and its appearance is not affected by mutations in several nodulating strains of Rhizobium. Nodulin-35 was not detected in uninfected soybean, bacteroids or free-living Rhizobium, and it appears to be synthesized by the plant during the formation of root nodules. / Whereas the transformation of free-living Rhizobium into bacteroids is accompanied by substantial changes within the population of cytoplasmic proteins, the majority of plant polypeptides from nodules are also present in uninfected (non-nodulated) roots. Hence, to further identify and isolate the "nodule-specific" proteins, it was essential to develop several immunological procedures, including a preparative adsorption of antibodies with antigens, the multiple immunoreplica technique, and isolation of a single-copy mRNA by immunoprecipitation of the nascent peptide-polysome complex, which are described in this thesis. / In addition, two polypeptides of bacterial origin were found to be cross-reactive with the "nodule-specific" antiserum, suggesting that they are secreted into the host cell cytoplasm during symbiotic nitrogen fixation.

Cabbage root fly passes through three generations a year in the south of England. The first generation peaks in late April to early May having overwintered in diapause. Recently, populations have been discovered in which the emergence of first generation flies was protracted, lasting until mid-July. The project aimed to investigate the incidence of late emergence in Devon and to examine the ways in which late emergers differed from early emergers in their progress through diapause. A new emergence trap was developed and used in conjunction with yellow water traps to monitor the emergence of cabbage root fly populations at locations of contrasting agricultural practice. Late emergence was widespread in Devon, occurring later (up to September), and in a greater proportion of some populations than any previously reported. The phenomenon appears to be a response to the planting of brassicas in June, as flies emerging at the normal time may not be able to locate a host crop. Emergence in a substantial proportion of one population was delayed for a year. This has not been been previously reported in cabbage root fly and represents a 'sit and wait' strategy associated with short-lived habitats, occurring in patches often separated by considerable distances but which frequently reappear in approximately the same location. A gas chromatography technique was developed which is capable of individually monitoring the respiration rates of large numbers of pupae. The results suggested that the temperature optimum for diapause development may r1se in late emergers, possibly above the threshold for postdiapause development. There was considerable 1ntrapopulat1on variation in temperature responses. Overall, the results suggest that the level of variation in temperature response and emergence times between and within populations will require careful local investigation with continuous reassessment of selection pressures, for an accurate prediction of cabbage root fly emergence.

No description available.

No description available.

Woody plants are encroaching into a karst savanna on the Edwards Plateau in central Texas, but their impact on hydrology is unclear because of high variability in soil depth and uncertainties about shallow and deep root contributions to water uptake, and water dynamics in rocky soil. The overall objectives of this study are to quantify contributions of shallow and deep roots to water uptake, and to quantify the impact of rock on soil hydraulic properties and water storage. A study was conducted in a karst savanna with ~50% woody cover to monitor spatial and temporal variations in soil moisture and root water uptake with neutron probe and time-domain reflectometry measurements. Bulk density was measured using gamma densitometry. Measurements were made to a depth of 1.6 m in a 25 m  25 m grid (5 m node spacing). The results showed that rock created high spatial variability in water storage. Water storage capacity in the measurement grid ranged from 185 to 401 mm, and coupled with heterogeneous distribution of trees led to high spatial variability in root water uptake. Most of the water uptake came from the upper 1 m of the soil profile, but 10% came from below 1.6 m. This indicated that roots had access to water stored within the bedrock, possibly in soil pockets. Statistical analysis showed that spatial distribution of θ was significantly correlated with rock distribution in the profile. Laboratory evaporation measurements showed that Small volume fractions of rock can increase evaporation from soils by slowing upward movement of water, thereby maintaining capillary connectivity to the surface for a longer period of time. Two simulation models, van Genuchten (VG) and Durner, were compared with the data from evaporation experiments. Results showed that the Durner model was more appropriate than the VG model for describing water retention and hydraulic conductivity of rocky soils.

Yield losses from infestations of root maggots (Delia spp.) (Diptera: Anthomyiidae) can be severe in canola crops in central Alberta. Studies were undertaken in central Alberta, Canada to manipulate agronomic practices that have potential to affect crop yield, root maggot infestations, and the survival and abundance of Aleochara bilineata (Coleoptera: Staphylinidae), which is an important natural enemy of root maggots. I investigated tillage regime (conventional versus zero tillage), row spacing, and seeding rate to assess effects on Delia spp. and A. bilineata populations. In general I observed greater root maggot incidence and damage, and greater activity density of A. bilineata, in plots subjected to a conventional tillage regime than in a zero tillage regime. I found relatively greater parasitism of root maggot puparia by A. bilineata in plots subjected to a zero tillage regime than a conventional tillage regime. No consistent effects were observed on A. bilineata activity in relation to seeding rate and row spacing. In this study, there is no evidence to conclude that tillage regime had a significant effect on canola seed yield. Seed yields in relation to seeding rate and row spacing were variable. In the context of integrated pest management in canola cropping systems, I suggest that canola growers utilize zero tillage in conjunction with adopting the currently recommended seeding rates of between 5.6 to 9.0 kg per ha and row spacing of 30 cm because this can bring advantages in terms of improved management of root maggots and other important canola pests like flea beetles and weeds. / Plant Science

Two fungi that cause disease on onion in the Mid Murray region of South Australia were investigated. These were Fusarium oxysporum f. sp. cepae, the cause of damping off of seedlings, wilting in the field, and basal rot in storage, and Phoma terrestris, which causes pink root. The aim of the study was to investigate resistant or tolerant cultivars and crop rotations as possible management strategies for these diseases. Several Fusarium spp. were isolated from onion roots and bulbs in the field, onion bulbs in storage, soil, and onion seed. All isolates were tested for pathogenicity by various means, however, none caused disease and therefore could not be identified conclusively as F. oxysporum f. sp. cepae. As a result research on Fusarium was discontinued. Pink discolouration was detected on onion roots in commercial crops at Bowhill, South Australia, and isolation of P. terrestris from roots was attempted. Several published and novel methods were employed with variable success. Only one of the published methods yielded P. terrestris, but results were inconsistent. Two methods developed in this study permitted isolation of P. terrestris. In both cases, infested plant material was incubated on wheat straw agar (WSA), which turns pink in the presence of P. terrestris. One method involved soaking surface sterilised pink-pigmented wheat straw in solution, at approximately 24ºC for 2 days, and then spreading 1 ml of the resulting suspension on acidified potato dextrose agar (APDA) and incubating for a further 7 to 10 days. The second method involved dispensing warm sterile water into a plate of pink-pigmented WSA, agitating the plate, and spreading 1 ml aliquots onto APDA, and incubating for 7 to 10 days. One isolate of P. terrestris, shown to be pathogenic to onion was used in subsequent experiments. Several brown onion cultivars commonly grown in the Mid Murray region of South Australia, or marketed as tolerant to pink root, were examined for susceptibility to infection by P. terrestris. Seven cultivars were tested in vitro, and seedlings of eight cultivars were grown in a greenhouse for 4 months in soil naturally infested with P. terrestris. Selected cultivars were also evaluated in the field. Of the cultivars tested, none was significantly less susceptible to infection by P. terrestris than any other as indicated by pink pigment on WSA. Cereals such as wheat, oat and barley, as well as lucerne and canola, are grown in rotation with onion to provide ground cover, to minimise soil erosion and reduce inoculum of pathogens between onion crops. As the susceptibility of these rotation crops to P. terrestris was not known, several were tested in the field and in the greenhouse for their ability to act as hosts for P. terrestris. Likewise, the potential of weeds commonly found in onion fields to act as hosts of P. terrestris was investigated. Less P. terrestris was detected in the roots of plants of oat cultivars Marloo and Swan, as well as barley cultivars Galleon and Schooner than of most other crops tested and, thus, these cvs were considered less likely to act as hosts of P. terrestris. Weeds such as Brassica tournefortii, Portulaca oleracea and Oxalis pes-caprae collected from the field were infected by P. terrestris, whereas P. terrestris was not detected in the roots of Chenopodium album. In summary, new methods for isolation of P. terrestris were identified and may, with further development, aid in research on pink root. The onion cultivars tested in this study did not differ in susceptibility to pink root, but more cultivars should be tested. P. terrestris infected a range of other crops and weeds, and it is recommended that further work is conducted in this area to facilitate cultural management of onion crops to minimise build up of inoculum in the soil. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1473377 / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2009

Thesis (Ph. D. in Plant Pathology)--University of California, Davis, Jan. 1953. / Includes bibliographical references (leaves 65-69). Also available via the World Wide Web. (Restricted to UC campuses).