Host plant specificity in several species of generalist mite predators

1. Species in the genus Neoseiulus are considered to be generalist predators. with some species used in biological control programmes against phytophagous mites and insects. 2. A general survey of Neoseiulus species in inland Australia indicated that different species are associated with particular tree species. This pattern of host plant use was investigated for four Neoseiulus species (N. buxeus, N. cappari, N. brigarinus, N. eremitus) by means of a sampling programme through time and across space. 3. Each species of Neoseiulus was collected entirely or mostly from one species of tree: little or no overlap was detected despite the tree species growing in well-mixed stands. Host plant specificity thus appears to be strong in this genus. 4. Species in two other genera (Pholaseius and Australiseiulus), also considered to be predatory, showed a similar association with particular tree species. 5. The implications for the use of these predators in biological control are considerable. In particular, phytoseiid species with specific needs in terms of host plants may not be suitable for use as general purpose predators. Meeting the needs of phytoseiids through the modification of host plant attributes may be a step towards enhancing their efficacy as biological control agents.

Breeding for low input conditions and consequences for participatory plant breeding: Examples from tropical maize and wheat

Participatory plant breeding (PPB) has been suggested as an effective alternative to formal plant breeding (FPB) as a breeding strategy for achieving productivity gains under low input conditions. With genetic progress through PPB and FPB being determined by the same genetic variables, the likelihood of success of PPB approaches applied in low input target conditions was analyzed using two case studies from FPB that have resulted in significant productivity gains under low input conditions: (1) breeding tropical maize for low input conditions by CIMMYT, and (2) breeding of spring wheat for the highly variable low input rainfed farming systems in Australia. In both cases, genetic improvement was an outcome of long-term investment in a sustained research effort aimed at understanding the detail of the important environmental constraints to productivity and the plant requirements for improved adaptation to the identified constraints, followed up by the design and continued evaluation of efficient breeding strategies. The breeding strategies used differed between the two case studies but were consistent in their attention to the key determinants of response to selection: (1) ensuring adequate sources of genetic variation and high selection pressures for the important traits at all stages of the breeding program, (2) use of experimental procedures to achieve high levels of heritability in the breeding trials, and (3) testing strategies that achieved a high genetic correlation between performance of germplasm in the breeding trials and under on-farm conditions. The implications of the outcomes from these FPB case studies for realizing the positive motivations for adopting PPB strategies are discussed with particular reference for low input target environment conditions.

Can long-distance dispersal be inferred from the New Zealand plant fossil record?

New Zealand is generally thought to have been physically isolated from the rest of the world for over 60 million years. But physical isolation may not mean biotic isolation, at least on the time scale of millions of years. Are New Zealand's present complement of plants the direct descendants of what originally rafted from Gondwana? Or has there been total extinction of this initial flora with replacement through long-distance dispersal (a complete biotic turnover)? These are two possible extremes which have come under recent discussion. Can the fossil record be used to decide the relative importance of the two endpoints, or is it simply too incomplete and too dependent on factors of chance? This paper suggests two approaches to the problem-the use of statistics to apply levels of confidence to first appearances in the fossil record and the analysis of trends based on the entire palynorecord. Statistics can suggest that the first appearance of a taxon was after New Zealand broke away from Gondwana-as long as the first appearance in the record was not due to an increase in biomass from an initially rare state. Two observations can be drawn from the overall palynorecord that are independent of changes in biomass: (1) The first appearance of palynotaxa common to both Australia and New Zealand is decidedly non-random. Most taxa occur first in Australia. This suggests a bias in air or water transport from west to east. (2) The percentage of endemic palynospecies in New Zealand shows no simple correlation with the time New Zealand drifted into isolation. The conifer macrorecord also hints at complete turnover since the Cretaceous.

Differentiation of peanut seedborne potyviruses and curcumoviruses by RT-PCR

Seedborne peanut viruses pose important constraints to peanut production and safe movement of germ plasm. They also pose a risk of accidental introduction into previously disease-free regions. We have developed reverse transcription-polymerase chain reaction (RT-PCR) assays based on identical cycling parameters which identified peanut stripe, Peanut mottle, Peanut stunt, and Cucumber mosaic viruses through production of specific DNA fragments of 234 bp, 327 bp, 390 bp, and 133 bp, respectively. Assay sensitivity in the picogram range was achieved. The two potyviruses and two cucumoviruses could be differentiated using duplex RT-PCR assays. These assays should be useful for testing peanut leaves or seeds for virus identification in epidemiological studies, seed testing or in post-entry quarantine.

Experimental infection of Australian brushtail possums, Trichosurus vulpecula (Phalangeridae : Marsupialia), with Ross River and Barmah Forest viruses by use of a natural mosquito vector system

Brushtail possums, Trichosurus vulpecula Kerr, were experimentally infected with Ross River (RR) or Barmah Forest (BF) virus by Aedes vigilax (Skuse) mosquitoes. Eight of 10 animals exposed to RR virus developed neutralizing antibody, and 3 possums developed high viremia for < 48 hr after infection, sufficient to infect recipient mosquitoes. Two of 10 animals exposed to BF virus developed neutralizing antibody. Both infected possums maintained detectable neutralizing antibody to BF for at least 45 days after infection (log neutralization index > 2.0 at 45 days). Eight possums did not develop neutralizing antibody to BF despite exposure to infected mosquitoes. These results suggest that T. vulpecula may potentially act as a reservoir species for RR in urban areas. However, T. vulpecula infected with BF do not develop viremia sufficient to infect mosquitoes and are unlikely to be important hosts for BF.

The natural history of Hendra and Nipah viruses

Pteropid bats (flying foxes), species of which are the probable natural host of both Hendra and Nipah viruses, occur in overlapping populations from India to Australia. Ecological changes associated with land use and with animal husbandry practices appear most likely to be associated with the emergence of these two agents. (C) 2001 Editions scientifiques et medicales Elsevier SAS.

Mineral nutrition and plant morphogenesis

Plant morphogenesis in vitro can be achieved via two pathways, somatic embryogenesis or organogenesis. Relationships between the culture medium and explant leading to morphogenesis are complex and, despite extensive study, remain poorly understood. Primarily the composition and ratio of plant growth regulators are manipulated to optimize the, quality and numbers of embryos or organs initiated. However, many species and varieties do not respond to this classical approach and require further optimization by the variation of other chemical or physical factors. Mineral nutrients form a significant component of culture media but are often overlooked as possible morphogenic elicitors. The combination of minerals for a particular plant species and developmental pathway are usually determined by the empirical manipulation of one or a combination of existing published formulations. Often only one medium type is used for the duration of culture even though this formulation may not be optimal for the different stages of explant growth and development. Furthermore, mineral studies have often focused on growth rather than morphogenesis with very little known of the relationships between mineral uptake and morphogenesis. This article examines the present knowledge of the main effects that mineral nutrients have on plant morphogenesis in vitro. In particular, the dynamics of nitrogen, phosphorus, and calcium supply during development are discussed.

A general model for host plant selection in phytophagous insects

We develop a general theoretical framework for exploring the host plant selection behaviour of herbivorous insects. This model can be used to address a number of questions, including the evolution of specialists, generalists, preference hierarchies, and learning. We use our model to: (i) demonstrate the consequences of the extent to which the reproductive success of a foraging female is limited by the rate at which they find host plants (host limitation) or the number of eggs they carry (egg limitation); (ii) emphasize the different consequences of variation in behaviour before and after landing on (locating) a host (termed pre- and post-alighting, respectively); (iii) show that, in contrast to previous predictions, learning can be favoured in post-alighting behaviour-in particular, individuals can be selected to concentrate oviposition on an abundant low-quality host, whilst ignoring a rare higher-quality host; (iv) emphasize the importance of interactions between mechanisms in favouring specialization or learning. (C) 2002 Elsevier Science Ltd.

Constitutive expression of a phenylalanine ammonia-lyase gene from Stylosanthes humilis in transgenic tobacco leads to enhanced disease resistance but impaired plant growth

Transgenic tobacco plants expressing a phenylalanine ammonia-lyase cDNA (ShPAL), isolated from Stylosanthes humilis, under the control of the 35S promoter of the cauliflower mosaic virus were produced to test the effect of high level PAL expression on disease resistance. The transgenic plants showed up to eightfold PAL activity and were slowed in growth and flowering relative to non-transgenic controls which have segregated out the transgene. The expression of the ShPAL transgene and elevated PAL levels were correlated and stably inherited. In T-1 and T-2 tobacco plants with increased PAL activity, lesion expansion was significantly reduced by up to 55% on stems inoculated with the Oomycete pathogen Phytophthora parasitica pv. nicotianae, Lesion area was significantly reduced by up to 50% on leaves inoculated with the fungal pathogen Cercospora nicotianae. This study provides further evidence that PAL has a role in plant defence. (C) 2002 Elsevier Science Ltd. All rights reserved.

Molecular rates parallel diversification contrasts between carnivorous plant sister lineages

In the carnivorous plant family Lentibulariaceae, the bladderwort lineage (Utricularia and Genlisea) is substantially more species-rich and morphologically divergent than its sister lineage, the butterworts (Pinguicula). Bladderworts have a relaxed body plan that has permitted the evolution of terrestrial, epiphytic, and aquatic forms that capture prey in intricately designed suction bladders or corkscrew-shaped lobster-pot traps. In contrast, the flypaper-trapping butterworts maintain vegetative structures typical of angiosperms. We found that bladderwort genomes evolve significantly faster across seven loci (the trnL intron, the second trnL exon, the trnL-F intergenic spacer, the rps16 intron, rbcL, coxI, and 5.8S rDNA) representing all three genomic compartments. Generation time differences did not show a significant association. We relate these findings to the contested speciation rate hypothesis, which postulates a relationship between increased nucleotide substitution and increased cladogenesis. (C) 2002 The Willi Hennig Society.

Callus induction and plant regeneration from broccoli (Brassica oleracea var. italica) for transformation

We evaluated the efficiency of callus induction and plantlet regeneration from hypocotyl explants of broccoli (Brassica oleracea var. italica). The cultivars were ‘Marathon’, ‘Greenbelt’, and ‘Shogun’. Transformation success was not affected by the presence of tobacco feeder-cell layers on the culture media. The frequency of shoot regeneration was greater from 10-d-old hypocotyls than from 14-d-old hypocotyls. Both ‘Marathon’ and ‘Greenbelt’ had higher potentials for tissue regeneration than did ‘Shogun’. We found that for transformation selection, the optimum concentration was either 50 mg/L kanamycin or 100 mg/L genetkin.

Equine respiratory viruses in foals in New Zealand

AIMS: To identify the respiratory viruses that are present among foals in New Zealand and to establish the age at which foals first become infected with these viruses. METHODS: Foals were recruited to the study in October/ November 1995 at the age of 1 month (Group A) or in March/ April 1996 at the age of 4-6 months (Groups B and C). Nasal swabs and blood samples were collected at monthly intervals. Nasal swabs and peripheral blood leucocytes (PBL) harvested from heparinised blood samples were used for virus isolation; serum harvested from whole-blood samples was used for serological testing for the presence of antibodies against equine herpesvirus (EHV)-1 or -4, equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3). Twelve foals were sampled until December 1996; the remaining 19 foals were lost from the study at various times prior to this date. RESULTS: The only viruses isolated were EHV 2 and EHV 5. EHV 2 was isolated from 155/157 PBL samples collected during the period of study and from 40/172 nasal swabs collected from 18 foals. All isolations from nasal swabs, except one, were made over a period of 2-4 months from January to April (Group A), March to April (Group B) or May, to July (Group C). EHV 5 was isolated from either PBL, nasal swabs, or both, from 15 foals on 32 occasions. All foals were positive for antibodies to EHV 1 or EHV 4, as tested by serum neutralisation (SN), on at least one sampling occasion and all but one were positive for EHV 1 antibodies measured by enzyme-linked immunosorbent assay (ELISA) on at least one sampling occasion. Recent EHV 1 infection was evident at least once during the period of study in 18/23 (78%) foals for which at least two samples were collected. SN antibodies to ERBV were evident in 19/23 (83%) foals on at least one sampling occasion and 15/23 foals showed evidence of seroconversion to ERBV Antibodies to ERAV were only detected in serum samples collected from foals in Group A and probably represented maternally-derived antibodies. Haemagglutination inhibition (HI) antibody titres greater than or equal to 1:10 to EAdV-1 were evident in 21/23 (91%) foals on at least one sampling occasion and 16/23 foals showed serological evidence of recent EAdV-1 infection. None of the 67 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. There was no clear association between infection with any of the viruses isolated or tested for and the presence of overt clinical signs of respiratory disease. CONCLUSIONS: There was serological and/or virological evidence that EHV-1, EHV-2, EHV-5, EAdV-1 and ERBV infections were present among foals in New Zealand. EHV-2 infection was first detected in foals as young as 3 months of age. The isolation of EHV-2 from nasal swabs preceded serological evidence of infection with other respiratory viruses, suggesting that EHV-2 may predispose foals to other viral infections.

Viruses associated with outbreaks of equine respiratory disease in New Zealand

AIM: To identify viruses associated with respiratory disease in young horses in New Zealand. METHODS: Nasal swabs and blood samples were collected from 45 foals or horses from five separate outbreaks of respiratory disease that occurred in New Zealand in 1996, and from 37 yearlings at the time of the annual yearling sales in January that same year. Virus isolation from nasal swabs and peripheral blood leukocytes (PBL) was undertaken and serum samples were tested for antibodies against equine herpesviruses (EHV-1, EHV-2, EHV-4 and EHV-5), equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3). RESULTS: Viruses were isolated from 24/94 (26%) nasal swab samples and from 77/80 (96%) PBL samples collected from both healthy horses and horses showing clinical signs of respiratory disease. All isolates were identified as EHV-2, EHV-4, EHV-5 or untyped EHV Of the horses and foals tested, 59/82 (72%) were positive for EHV-1 and/or EHV-4 serum neutralising (SN) antibody on at least one sampling occasion, 52/82 (63%) for EHV-1-specific antibody tested by enzyme-linked immunosorbent assay (ELISA), 10/80 (13%) for ERAV SN antibody, 60/80 (75%) for ERBV SN antibody, and 42/80 (53%) for haemagglutination inhibition (HI) antibody to EAdV-1. None of the 64 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. Evidence of infection with all viruses tested was detected in both healthy horses and in horses showing clinical signs of respiratory disease. Recent EHV 2 infection was associated with the development of signs of respiratory disease among yearlings [relative risk (RR) = 2.67, 95% CI = 1.59-4.47, p = 0.0171]. CONCLUSIONS: Of the equine respiratory viruses detected in horses in New Zealand during this study, EHV 2 was most likely to be associated with respiratory disease. However, factors other than viral infection are probably important in the development of clinical signs of disease.