Committee approved the overall collation and analysis of the data from individual universities (approval 016190S). Each university gained approval from their institution's HREC to provide the deidentified data.
An investigation of the chemical basis for rice allelopathy to the rice weed arrowhead (Sagittaria montevidensis) was undertaken using GC/MS and GC/MS/MS techniques. Twenty-five compounds were isolated and identified from the root exudates of both allelopathic and non-allelopathic rice varieties. Phenolics, phenylalkanoic acids, and indoles were among the chemical classes identified. Two indoles previously unreported in rice were detected in the exudates, 5-hydroxy-2-indolecarboxylic acid and 5-hydroxyindole-3-acetic acid. Several other compounds identified in this study have not previously been reported in rice root exudates, namely mercaptoacetic acid, 4-hydroxyphenylacetic acid, and 4-vinylphenol. The levels of 15 compounds present in the exudates were quantified using GC/MS/MS. Six of the seven most abundant compounds were phenolic acids. Significant differences exist between the allelopathic and non-allelopathic cultivars in their production of three of these six compounds. Greater amounts of trans-ferulic acid, p-hydroxybenzoic acid, and caffeic acid were detected in the exudates of allelopathic cultivars. The seventh compound, abietic acid, was significantly higher in the non-allelopathic cultivars.
In previous studies, 15 putative allelopathic compounds detected in rice root exudates were quantified by GC/MS/MS. In this study, multiple regression analysis on these compounds determined that five selected phenolics, namely caffeic, p-hydroxybenzoic, vanillic, syringic, and p-coumaric acids, from rice exudates were best correlated with the observed allelopathic effect on arrowhead (Sagittaria montevidensis) root growth. Despite this positive association, determination of the phenolic acid dose-response curve established that the amount quantified in the exudates was much lower than the required threshold concentration for arrowhead inhibition. A similar dose-response curve resulted from a combination of all 15 quantified compounds. Significant differences between the amounts of trans-ferulic acid, abietic acid, and an indole also existed between allelopathic and non-allelopathic rice cultivars. The potential roles of these three compounds in rice allelopathy were examined by chemoassay. Overall, neither the addition of trans-ferulic acid nor 5-hydroxyindole-3-acetic acid to the phenolic mix significantly contributed to phytotoxicity, although at higher concentrations, trans-ferulic acid appeared to act antagonistically to the phytotoxic effects of the phenolic mix. The addition of abietic acid also decreased the inhibitory effect of the phenolic mix. These studies indicate that the compounds quantified are not directly responsible for the observed allelopathic response. It is possible that the amount of phenolic acids may be indirectly related to the chemicals finally responsible for the observed allelopathic effect.
Objective To examine associations between extended medical graduates’ rural clinical school (RCS) experience and geographic origins with practising in rural communities five and eight years after graduation. Design, participants Cohort study of 2011 domestic medical graduates from ten Australian medical schools with rural clinical or regional medical schools. Main outcome measures Practice location types eight years after graduation (2019/2020) as recorded by the Australian Health Practitioner Regulation Agency, classified as rural or metropolitan according to the 2015 Modified Monash Model; changes in practice location type between postgraduate years 5 (2016/2017) and 8 (2019/2020). Results Data were available for 1321 graduates from ten universities; 696 were women (52.7%), 259 had rural backgrounds (19.6%), and 413 had extended RCS experience (31.3%). Eight years after graduation, rural origin graduates with extended RCS experience were more likely than metropolitan origin graduates without this experience to practise in regional (relative risk [RR], 3.6; 95% CI, 1.8–7.1) or rural communities (RR, 4.8; 95% CI, 3.1–7.5). Concordance of location type five and eight years after graduation was 92.6% for metropolitan practice (84 of 1136 graduates had moved to regional/rural practice, 7.4%), 26% for regional practice (56 of 95 had moved to metropolitan practice, 59%), and 73% for rural practice (20 of 100 had moved to metropolitan practice, 20%). Metropolitan origin graduates with extended RCS experience were more likely than those without it to remain in rural practice (RR, 2.0; 95% CI, 1.3–2.9) or to move to rural practice (RR, 1.9; 95% CI, 1.2–3.1). Conclusion The distribution of graduates by practice location type was similar five and eight years after graduation. Recruitment to and retention in rural practice were higher among graduates with extended RCS experience. Our findings reinforce the importance of longitudinal rural and regional training pathways, and the role of RCSs, regional training hubs, and the rural generalist training program in coordinating these initiatives.
In a previous study, lavender (Lavandula spp.) was found to be highly phytotoxic towards annual ryegrass (Lolium rigidum, ARG), a major weed of winter wheat crops in Australia. This research aimed to further explore this relationship and determine the chemical(s) responsible for the observed effect. In bioassay, it was determined that the stem and leaf extract of L. x intermedia cv. Grosso ranked highest and had the potential to reduce significantly the root growth of several plant species. An extract concentration of 10% almost completely inhibited ARG root growth. When the extract was tested for stability, there was no loss in phytotoxicity after the 256 day trial. Via bioassay-guided fractionation and chromatographic techniques, it was determined that the sub-fraction consisting of coumarin and 7-methoxycoumarin was most phytotoxic towards ARG. Chemoassays of 18 structural analogues of coumarin showed that coumarin itself was the most phytotoxic and largely responsible for the observed phytotoxicity of the extract. Soil trials were conducted using pure coumarin and the lavender extract, and in both instances, shoot length and weight were significantly reduced by post-emergence application at all concentrations evaluated.
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