D. B. Baird

Gene expression profiling of Naïve sheep genetically resistant and susceptible to gastrointestinal nematodes

BackgroundGastrointestinal nematodes constitute a major cause of morbidity and mortality in grazing ruminants. Individual animals or breeds, however, are known to differ in their resistance to infection. Gene expression profiling allows us to examine large numbers of transcripts simultaneously in order to identify those transcripts that contribute to an animals susceptibility or resistance.ResultsWith the goal of identifying genes with a differential pattern of expression between sheep genetically resistant and susceptible to gastrointestinal nematodes, a 20,000 spot ovine cDNA microarray was constructed. This array was used to interrogate the expression of 9,238 known genes in duodenum tissue of four resistant and four susceptible female lambs. Naïve animals were used in order to look at genes that were differentially expressed in the absence of infection with gastrointestinal nematodes. Forty one unique known genes were identified that were differentially expressed between the resistant and susceptible animals. Northern blotting of a selection of the genes confirmed differential expression. The differentially expressed genes had a variety of functions, although many genes relating to the stress response and response to stimulus were more highly expressed in the susceptible animals.ConclusionWe have constructed the first reported ovine microarray and used this array to examine gene expression in lambs genetically resistant and susceptible to gastrointestinal nematode infection. This study indicates that susceptible animals appear to be generating a hyper-sensitive immune response to non-nematode challenges. The gastrointestinal tract of susceptible animals is therefore under stress and compromised even in the absence of gastrointestinal nematodes. These factors may contribute to the genetic susceptibility of these animals.

Geographical origin of an introduced insect pest, Listronotus bonariensis (Kuschel), determined by RAPD analysis.

The Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae), is an important introduced pasture pest in New Zealand. In this study geographical populations of this species were analysed using polymerase chain reaction-based randomly amplified polymorphic DNA (RAPD), in an attempt to determine the geographical origin of the pest. Morphologically indistinguishable individuals were collected from nine South American, five New Zealand and one Australian populations. Ten primers were screened for usefulness, two of which revealed significant, scorable polymorphisms between these populations. The results indicated that the sampled New Zealand L. bonariensis populations originated from the east coast of South America.

Normalization of microarray data using a spatial mixed model analysis which includes splines

MOTIVATION Microarray experiments with thousands of genes on a slide and multiple slides used in any experimental set represent a large body of data with many sources of variation. The identification of such sources of variation within microarray experimental sets is critical for correct deciphering of desired gene expression differences. RESULTS We describe new methods for the normalization using spatial mixed models which include splines and analysis of two-colour spotted microarrays for within slide variation and for a series of slides. The model typically explains 45-85% of the variation on a slide with only approximately 1% of the total degrees of freedom. The results from our methods compare favourably with those from intensity dependent normalization loess methods where we accounted for twice as much uncontrolled and unwanted variation on the slides. We have also developed an index for each EST that combines the various measures of the differential response into a single value that researchers can use to rapidly assess the genes of interest.

Occurrence and impact of pasture mealybug (Balanococcus poae) and root aphid (Aploneura lentisci) on ryegrass (Lolium spp.) with and without infection by Neotyphodium fungal endophytes

Abstract Pasture mealybug (Balanococcuspoae) was found infesting two field trials evaluating the performance of selected strains of the endophyte Neotyphodium lolii in ryegrass (Lolium spp.) in Canterbury, New Zealand. Deterioration of endo‐phyte‐free plots relative to endophyte‐infected plots had been observed. In Trial A, pasture mealybug were sampled in plots of the perennial ryegrass cultivar ‘Grasslands Nui’, without endophyte (nil), or infected with the wild‐type endophyte, or the selected strains, AR1 and AR37. In Trial B, mealybug numbers on six ryegrass cultivars infected with AR1 or wild‐type were compared with those on the same cultivars without endophyte. In sampling these trials, the presence of a root aphid, Aploneura lentisci, was also noted. Populations of mealybug in both trials were similar on all endophyte‐infected treatments and significantly lower than populations on nil treatments. Neither AR1 nor wild‐type appeared to reduce root aphid numbers, while AR37 may have had some effect. The amount of dead grass was significantly greater in nil than in endophyte‐infected plots in Trial A, and yield of ryegrass was correlated with numbers of mealybug and root aphid present. Pasture productivity in nil treatments had recovered by spring, in the year of the outbreak. The presence of endophyte, strain of endophyte and cultivar were all significant factors affecting both total dry matter and green yield in Trial B. Pasture mealybug accounted for 55% of the variation in a decline in growth rate that occurred in this trial over the summer‐autumn periods between 2000 and 2001, particularly in the nil treatments. Two years after the outbreak there was 25% less ryegrass and persistently lower pasture yields in nil plots. We conclude that pasture mealybug are capable of inflicting severe damage to endophyte‐free ryegrass in Canterbury, particularly during dry summer‐autumn periods.

Uraba lugens (Lepidoptera: Nolidae) in New Zealand: Pheromone Trapping for Delimitation and Phenology

Abstract A synthetic sex pheromone trapping survey of the leaf skeletonizer Uraba lugens Walker (Lepidoptera: Nolidae) demonstrated the unexpectedly widespread distribution of the insect across >40,000 ha of urban Auckland, New Zealand. A survey of eucalyptus trees planted in parks and other public areas showed a significant spatial correlation between trap catch and breeding populations, validating the trap survey results. Traps in trees showing damage had four-fold higher catches than traps placed in undamaged or nonhost trees, and <1% of damaged trees with traps failed to catch adult moths. Damage by larval feeding was correlated with male trap catch in the previous generation, offering good prospects for a pest management decision support system, provided that an economic threshold is developed. Catches increased by 3.4-fold in the same georeferenced trapping grid between November and December 2003 and between March and April 2004 across two generations, over the summer. A vertical transect showed that catches increased with height up to the top trap at 13 m (60% of mean tree height). Options for managing the insect will need to overcome the high rate of increase, the rate of spread, and the vertical distribution of the insect on tall eucalyptus trees.

The bionomics of Listronotus bonariensis (Coleoptera: Curculionidae) in Canterbury, New Zealand

A study was conducted in 1990–1995 in Canterbury, New Zealand to describe the phenology and seasonal abundance of all stages of the Argentine stem weevil Listronotus bonariensis (Kuschel), a New Zealand pest of Gramineae. Of note were major fluctuations in the densities of all stages from one season to the next which were not explained directly in terms of the availability of Neotyphodium lolii -free ryegrass tillers. The overwintering mortality rates of L. bonariensis were found to be linear and remarkably similar between seasons and locations in the absence of pathogens. This study also showed that care must be taken in the use of existing data to analyse the impact of the recently introduced South American parasitoid wasp Microctonus hyperodae Loan as a biological control agent of L. bonariensis ; errors may exist because of earlier sampling biases. In spite of the confounding effects of seasonal variation in the L. bonariensis population, reduction in the size of the L. bonariensis first summer generation egg and larval peaks coincided with a build up of M. hyperodae .

Effect of sire breed on growth, carcass, and wool characteristics of lambs born to Merino ewes in New Zealand

Abstract Sire breed effects were studied in 1080 lambs born over three years to Merino ewes and 6–10 sires each of Merino, Poll Dorset, Border Leicester, Texel, Oxford Down, and Suffolk breeds. Ewes bearing crossbred lambs required more assistance at lambing than those with purebred Merino lambs. Poll Dorset cross lambs grew fastest and purebred Merinos slowest from tailing until they were 12 months old (P < 0.05). While purebred Merinos tended to have less carcass fat throughout the trial, differences between the other crossbreds changed with time. Texel and Poll Dorset cross carcasses generally had larger eye muscle size (P < 0.05) than other sire breeds. Carcasses were “blockier” for crossbreds, particularly Texel and Oxford Down, but weights of individual cuts were similar for all breeds. At 12 months of age, greasy fleece weights were heaviest (P < 0.05) in Border Leicester cross lambs (4.4 kg) and least in Suffolk crosses (3.1 kg). It is concluded that Merino cross lambs can produce 20‐kg carcasses by 9 months of age under improved pasture conditions. Local sire breeds were competitive with more recently imported sire breeds for meat production.

Safety zones for a Sclerotinia sclerotiorum-based mycoherbicide: Accounting for regional and yearly variation in climate

Abstract Variation in the width of ‘safety zones’ for sheep and dairy pasture treated with a Sclerotinia sclerotiorum (Lib.) de Bary-based mycoherbicide was quantified using 10 years of climate data from each of five regions in New Zealand. Acceptable and risk-averse zones were defined as the maximum distances in any direction from a treated pasture where ‘added:natural’ ratios of air-borne S. sclerotiorum spores are 1:1 and 1:10, respectively. The 10-year mean 1:1 safety zone had zero width for sheep pasture at all locations, and was at most, 50 m wide for dairy pasture. The width of the 10-year mean 1:10 zone varied regionally from 314 to 443 m for sheep and from 175 to 280 m for dairy pasture, and the 90th percentile 1:10 zones were up to 41% wider. Linear relationships between safety zone width and mean wind speed were evident and these could be used to derive region-specific safety zones.

Multitrophic interaction between the ryegrass Lolium perenne, its endophyte Neotyphodium lolii, the weevil pest Listronotus bonariensis, and its parasitoid Microctonus hyperodae

Abstract Field experiments in Canterbury, New Zealand, investigated four levels of interaction involving the clavicipitaceous endophytic fungi Neotyphodium lolii measured as ppm of the alkaloid peramine in bulked samples of Lolium perenne, the weevil pest Listronotus bonariensis, and its braconid parasitoid Microctonus hyperodae. Weevil numbers were unusually low and the expected inverse relationship between ground densities and peramine concentration was not observed. There was, however, a highly significant tritrophic interaction whereby percent parasitism was inversely related to ppm of peramine. Possible mechanisms for this interaction are discussed and it is suggested that it may have been the result of reduced feeding intensity of L. bonariensis that led to a corresponding reduction in opportunity for the parasitoid to attack.

Linear patterns of dispersal and build up of the introduced parasitoid Microctonus hyperodae (Hymenoptera : Braconidae) in Canterbury, New Zealand

The dispersal of Microctonus hyperodae Loan, an introduced parasitoid of the South American grassland pest Listronotus bonariensis Kuschel, was measured in Canterbury, New Zealand. Considering all directions, the mean annual dispersive increment was 1.9 ± 0.9 km year –1 as measured in the winters of 1993, 1994 and 1995. The parasitoid’s ground distribution suggested that its movement was biased towards the south-west indicating probable wind-borne dispersal. The overall relatively low rate of dispersal was thought to be related to the inhibitory effects of M. hyperodae parasitism on L. bonariensis flight. A generalized linear model fitted to percentage of L. bonariensis parasitized took a simple form, with a quadratic increase in weevil infection, that with time, gradually decreased. The build-up of parasitism at the release site was significantly greater than the rates at the other sites measured in this study ( P c . 140 km 2 .