Robustness of NIR calibrations for assessing fruit quality

Predictive models based on near infra-red spectroscopy for the assessment of fruit internal quality attributes must exhibit a degree of robustness across the parameters of variety, district and time to be of practical use in fruit grading. At the time this thesis was initiated, while there were a number of published reports on the development of near infra-red based calibration models for the assessment of internal quality attributes of intact fruit, there were no reports of the reliability ("robustness") of such models across time, cultivars or growing regions. As existing published reports varied in instrumentation employed, a re-analysis of existing data was not possible. An instrument platform, based on partial transmittance optics, a halogen light source and (Zeiss MMS 1) detector operating in the short wavelength near infra-red region was developed for use in the assessment of intact fruit. This platform was used to assess populations of macadamia kernels, melons and mandarin fruit for total soluble solids, dry matter and oil concentration. Calibration procedures were optimised and robustness assessed across growing areas, time of harvest, season and variety. In general, global modified partial least squares regression (MPLS) calibration models based on derivatised absorbance data were better than either multiple linear regression or `local' MPLS models in the prediction of independent validation populations . Robustness was most affected by growing season, relative to the growing district or variety . Various calibration updating procedures were evaluated in terms of calibration robustness. Random selection of samples from the validation population for addition to the calibration population was equivalent to or better than other methods of sample addition (methods based on the Mahalanobis distance of samples from either the centroid of the population or neighbourhood samples). In these exercises the global Mahalanobis distance (GH) was calculated using the scores and loadings from the calibration population on the independent validation population. In practice, it is recommended that model predictive performance be monitored in terms of predicted sample GH, with model updating using as few as 10 samples from the new population undertaken when the average GH value exceeds 1 .0 .

Fungal colonization of sago starch in Papua New Guinea

Sago starch is an important source of dietary carbohydrates in lowland Papua New Guinea. Over the past 30 years there have been sporadic reports of severe illness following consumption of sago starch. A common assumption is that fungal metabolites might be associated with the illness, leading to the need for a more thorough investigation of the mycoflora of sago starch. Sago starch was collected from areas of high sago consumption in Papua New Guinea for fungal analysis (69 samples). Storage methods and duration were recorded at the time of collection and pH on arrival at the laboratory. Yeasts were isolated from all samples except two, ranging from 1.2 × 103 to 8.3 × 107 cfu/g. Moulds were isolated from 65 of the 69 samples, ranging from 1.0 × 102 to 3.0 × 106 cfu/g. Of 44 samples tested for ergosterol content, 42 samples showed the presence of fungal biomass. Statistical analyses indicated that sago starch stored for greater than five weeks yielded significantly higher ergosterol content and higher numbers of moulds than sago stored for less than five weeks. The method of storage was also shown to influence mould numbers with storage in natural woven fibre containers returning significantly greater numbers than present in other storage methods tested. Potentially mycotoxigenic genera of moulds including Aspergillus and Penicillium were commonly isolated from sago starch, and as such storage factors that influence the growth of these and other filamentous fungi might contribute to the safety of traditional sago starch in PNG.

Resistance to insect growth regulator insecticides in populations of sheep lice as assessed by a moulting disruption assay

Low-volume, backline applications with the benzoylphenyl urea insecticides triflumuron and diflubenzuron represent in excess of 70% of treatments for the control of sheep lice, Bovicola ovis (Schrank) (Phthiraptera: Trichodectidae), in Australia. Reports of reduced effectiveness from 2003 and subsequent controlled treatment trials suggested the emergence of resistance to these compounds in B. ovis populations. A laboratory assay based on the measurement of moulting success in nymphs was developed and used to assess susceptibility to diflubenzuron and triflumuron in louse populations collected from sheep where a control failure had occurred. These tests confirmed the development of resistance to triflumuron and diflubenzuron in at least two instances, with estimated resistance ratios of 67-94X at LC50.

Co-evolution of wild rabbits (Oryctolagus cuniculus) and RHDV: resistance and virulence

Rabbit Haemorrhagic Disease Virus (RHDV) was introduced to Australia in 1995 for the control of wild rabbits. Initial outbreaks greatly reduced rabbit numbers and the virus has continued to control rabbits to varying degrees in different parts of Australia. However, recent field evidence suggests that the virus may be becoming less effective in those areas that have previously experienced repeated epizootics causing high mortality. There are also reports of rabbits returning to pre-1995 density levels, Virus and host can be expected to co-evolve. The host will develop resistance to the virus with the virus subsequently changing to overcome that resistance. It has been 12 years since the release of RHDV and it is an opportune time to examine where the dynamic currently stands between RHDV and rabbits. Laboratory challenge tests have indicated that resistance to RHDV has developed to different degrees in populations throughout Australia. In one population a low dose (1:25 dilution) of Czech strain RHDV failed to infect a single susceptible rabbit, yet infected a low to high (up to 73%) percentage across other populations tested. Different selection pressures are present in these populations and will be driving the level of resistance being seen. The mechanisms and genetics behind the development of resistance are also important as the on-going use of RHDV as a control tool in the management of rabbits relies on our understanding of factors influencing the efficacy of the virus. Understanding how resistance has developed may provide clues on how best to use the virus to circumvent these mechanisms. Similarly, it will help in managing populations that have yet to develop high levels of resistance.

Vermiculite improves early development and survival of low chill stone-fruit embryos rescued in vitro

There are many reports of efficient embryo germination and the method has been optimized to suit subtropical low chill genotypes. However the subsequent growth, vigor, and ability of germinated embryos to develop and survive acclimatization is rarely reported. Many germinated embryos do not survive acclimatization, develop slowly, or fail to develop normally. Methods to improve plant development from in vitro embryo cultures are needed to improve the number of plants that survive to be useful in breeding programs. This paper describes an improved method of embryo rescue that significantly increases embryo shoot and root development that leads to increased plant survival. Four treatments: Woody Plant Media (WPM) solidified with agar, vermiculite with liquid WPM, vermiculite with WPM plus agar, and conventional stratification, were evaluated for embryo growth and subsequent plantlet development and survival for two low-chill peach and one low-chill nectarine cultivar. Highly significant improvements were found for shoot and root development of seedlings germinated in vermiculite based media compared to embryos germinated in conventional agar-based media. Vermiculite with WPM and agar improved plantlet growth subsequent to in vitro culture and significantly increased survival of germinated embryos resulting in more plants reaching the field.

Analysis of Daphnane Orthoesters in Poisonous Australian Pimelea Species by Liquid Chromatography-Tandem Mass Spectrometry.

Cattle grazing in arid rangelands of Australia suffer periodic extensive and serious poisoning by the plant species Pimelea trichostachya, P. simplex, and P. elongata. Pimelea poisoning (also known as St. George disease and Marree disease) has been attributed to the presence of the diterpenoid orthoester simplexin in these species. However, literature relating to previous studies is complicated by taxonomic revisions, and the presence of simplexin has not previously been verified in all currently recognized taxa capable of inducing pimelea poisoning syndrome, with no previous chemical studies of P. trichostachya (as currently classified) or P. simplex subsp. continua. We report here the isolation of simplexin from P. trichostachya and the development of a liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method to measure simplexin concentrations in pimelea plant material. Simplexin was quantified by positive-ion atmospheric pressure chemical ionization (APCI) LC-MS/MS with selected reaction monitoring (SRM) of the m/z 533.3 > 253.3 transition. LC-MS/MS analysis of the four poisonous taxa P. trichostachya, P. elongata, P. simplex subsp. continua, and P. simplex subsp. simplex showed similar profiles with simplexin as the major diterpenoid ester component in all four taxa accompanied by varying amounts of related orthoesters. Similar analyses of P. decora, P. haematostachya, and P. microcephala also demonstrated the presence of simplexin in these species but at far lower concentrations, consistent with the limited reports of stock poisoning associated with these species. The less common, shrubby species P. penicillaris contained simplexin at up to 55 mg/kg dry weight and would be expected to cause poisoning if animals consumed sufficient plant material.

Origin of leaf rust adult plant resistance gene Rph20 in barley

Rph20 is the only reported, simply inherited gene conferring moderate to high levels of adult plant resistance (APR) to leaf rust (Puccinia hordei Otth) in barley (Hordeum vulgare L.). Key parental genotypes were examined to determine the origin of Rph20 in two-rowed barley. The Dutch cultivar 'Vada' (released in the 1950s) and parents, 'Hordeum laevigatum' and 'Gull' ('Gold'), along with the related cultivar 'Emir' (a derivative of 'Delta'), were assessed for APR to P. hordei in a disease screening nursery. The marker bPb-0837-PCR, co-located with Rph20 on the short arm of chromosome 5H (5HS), was used to screen genotypes for the resistance allele, Rph20.ai. Results from phenotypic assessment and DNA analysis confirmed that Rph20 originated from the landrace 'H. laevigatum' (i.e., Hordeum vulgare subsp. vulgare). Tracing back this gene through the pedigrees of two-rowed barley cultivars, indicated that Rph20 has contributed APR to P. hordei for more than 60 years. Although there have been no reports of an Rph20-virulent pathotype, the search for alternative sources of APR should continue to avoid widespread reliance upon a single resistance factor.

Infection of mungbean seed by Macrophomina phaseolina is more likely to result from localized pod infection than from systemic plant infection

The ubiquitous fungal pathogen Macrophomina phaseolina is best known as causing charcoal rot and premature death when host plants are subject to post-flowering stress. Overseas reports of M.phaseolina causing a rapid rot during the sprouting of Australian mungbean seed resulted in an investigation of the possible modes of infection of seed. Isolations from serial portions of 10 mungbean plants naturally infected with the pathogen revealed that on most plants there were discrete portions of infected tissue separated by apparently healthy tissue. The results from these studies, together with molecular analysis of isolates collected from infected tissue on two of the plants, suggested that aerial infection of aboveground parts by different isolates is common. Inoculations of roots and aboveground parts of mungbean plants at nine temperaturexsoil moisture incubation combinations and of detached green pods strongly supported the concept that seed infection results from infection of pods by microsclerotia, rather than from hyphae growing systemically through the plant after root or stem infection. This proposal is reinforced by anecdotal evidence that high levels of seed infection are common when rainfall occurs during pod fill, and by the isolation of M.phaseolina from soil peds collected on pods of mungbean plants in the field. However, other experiments showed that when inoculum was placed within 130mm of a green developing pod and a herbicide containing paraquat and diquat was sprayed on the inoculated plants, M.phaseolina was capable of some systemic growth from vegetative tissue into the pods and seeds.

Isolation of multiple novel paramyxoviruses from pteropid bat urine

Bats have been found to harbor a number of new emerging viruses with zoonotic potential and there has been a great deal of interest in identifying novel bat pathogens to determine risk to human and animal health. Many groups have identified novel viruses in bats by detection of viral nucleic acid, however virus isolation is still a challenge and there are few reports of viral isolates from bats. In recent years, our group has developed optimized procedures for virus isolation from bat urine, including the use of primary bat cells. In previous reports we have described the isolation of Hendra virus, Menangle virus and Cedar virus, in Queensland, Australia. Here, we report the isolation of four additional novel bat paramyxoviruses from urine collected from beneath pteropid bat (flying fox) colonies in Queensland and New South Wales during 2009-2011.