Twelve polymorphic microsatellite loci from the Asian citrus psyllid,Diaphorina citri Kuwayama,the vector for citrus greening disease,huanglongbing

Twelve polymorphic microsatellite markers were developed from microsatellite‐enriched DNA libraries and mined from an expressed sequence tags library of Diaphorina citri, the vector of the citrus greening disease (huanglongbing). Analysis of 288 individuals from Florida, Texas, and Brazil showed that allelic diversity ranged from three to eight alleles per locus and observed and expected heterozygosities ranged from 0.014 to 0.569 and from 0.052 to 0.653, respectively. These variable microsatellite loci can provide means for assessing overall genetic variation and migration patterns for this agriculturally important pest species. This information can be used to aid in developing successful management strategies.     

Diversity and salt tolerance of native Acacia rhizobia isolated from saline and non‐saline soils

Re‐establishing native vegetation in stressed soils is of considerable importance in many parts of the world, leading to significant interest in using plant–soil symbiont interactions to increase the cost‐effectiveness of large‐scale restoration. However, effective use of soil microbes in revegetation requires knowledge of how microbe communities vary along environmental stress gradients, as well as how such variation relates to symbiont effectiveness. In Australia, shrubby legumes dominate many ecosystems where dryland salinity is a major issue, and improving plant establishment in saline soils is a priority of regional management agencies. In this study, strains of rhizobial bacteria were isolated from a range of Acacia spp. growing in saline and non‐saline soils. Replicates of each strain were grown under several salinity levels in liquid culture and characterized for growth and salt tolerance. Genetic characterization of rhizobia showed considerable variation among strains, with salt tolerance and growth generally higher in rhizobial populations derived from more saline soils. These strains showed markedly different genetic profiles and generic affiliations to those from more temperate soils, suggesting community differentiation in relation to salt stress. The identification of novel genomic species from saline soils suggests that the diversity of rhizobia associated with Australian Acacia spp. is significantly greater than previously described. Overall, the ability of some symbiotically effective strains to tolerate high salinity is promising with regard to improving host plant re‐establishment in these soils.     

Effect of nitrogen on interactions between ryegrass mosaic virus (RMV) and Lolium species in mixed swards

The effect of rate of nitrogen applied to three Lolium perenne-based field swards on the development of RMV symptoms and on the impact of the virus on the growth and composition of the swards was examined over two growing seasons. Glasshouse experiments investigated the competition between Lolium spp. in relation to RMV infection and rate of nitrogen. In general, there was a higher incidence of RMV symptoms at the higher rates of nitrogen but the relationship was not consistent in all experiments. RMV infection only significantly reduced the cumulative total yield of the sward that contained the very susceptible Lolium multiflorum cv. Barverdi and was treated with the higher rate of nitrogen. However, yield losses were consistently greater at the higher rates of nitrogen. RMV altered the relative yields of sward components and the effect was greatest after an extended period of severe frost at the end of 1995. There is evidence that the frost severely restricted the yield of RMV-infected L. multiflorum tillers in 1996. Where RMV reduced the yield of susceptible species, there was significant compensatory growth by less susceptible companion species, i.e. L. perenne and Phleum pratense, but the compensation was generally incomplete, resulting in reduced yields for virus-infected swards. RMV had no significant effect on the overall quality of the three field swards but for cv. Barverdi grown in the glasshouse it significantly reduced the percentage organic matter and water soluble carbohydrate, and D value. The reductions were greater at the higher rates of nitrogen.     

Evaluation of reference genes for real‐time PCR quantification of gene expression in the Australian sheep blowfly,Lucilia cuprina

The Australian sheep blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae), is an important pest of sheep in Australia and other parts of the world. However, the paucity of information on many fundamental molecular aspects of this species limits the ability to exploit functional genomics techniques for the discovery of new drug targets for its control. The present study aimed to facilitate gene expression studies in this species by identifying the most suitable reference genes for normalization of mRNA expression data. Quantitative real‐time polymerase chain reaction (PCR) was performed with 11 genes across RNA samples from eggs, L1, L3, pupae and adult life stages, and two normalization programs, Normfinder and geNorm, were then applied to the data. The results showed an ideal set of genes (18S rRNA, 28S rRNA, GST1, β‐tubulin and RPLPO) for data normalization across all life stages. The most suitable reference genes for studies within specific life stages were also identified. GAPDH was shown to be a poor reference gene. The reference gene recommendations in this study will be of use to laboratories investigating gene expression in L. cuprina and related blowfly species     

Chill-induced wilting and hydraulic recovery in mung bean plants

• 1 The hydraulic conductance of roots of chilling-sensitive mung bean plants is reduced markedly at low temperatures. When roots are chilled suddenly under high irradiance, or when plants with roots chilled in the dark are exposed to a natural dawn, the stomata remain open for several hours. During this period the plants may wilt severely if the evaporative demand is sufficiently large. Under lower evaporative demand and less severe wilting, the plants may subsequently rehydrate.
• 2 Following root chilling there is a rapid (> 30 min) initial change in root conductivity (3. 2- fold).
• 3 Within hours the hydraulic conductivity of the pathway from stem xylem to leaf tissue decreases dramatically.
• 4 Within 1 d, the hydraulic conductivity of the roots decreases further (4. 5-fold).
• 5 Over 5 d these large resistances disappear and conductivity recovers to a value greater than at the start of chilling. This response and stomatal closure allow the plant to rehydrate to a condition similar to that of controls.
• 6 There is no simple relation between this hydraulic recovery and the accumulation of abscisic acid in the roots.

     

Chilling Sensitivity in Plants: Do the Activation Energies of Growth Processes Show an Abrupt Change at a Critical Temperature?

The rates of increase in dry weight, leaf area, and length ofhypocotyl plus radicle of mung bean (Vigna radiata L.) and morningglory (Pharbitis nil Chois) all show marked responses to decreasingtemperature, although when drawn as Arrhenius plots these responsesresemble smooth curves rather than sets of intersecting straightlines. Chilling sensitivity was shown to be dependent on temperature,light intensity, and the previous history of the plant. It isargued on theoretical grounds that changes in membrane lipidmobility would not be expected to cause abrupt changes in theslope of such Arrhenius plots at either the enzyme or wholeplant level.     

Cloning,recombinant expression and inhibitor profiles of dihydrofolate reductase from the Australian sheep blow fly,Lucilia cuprina

While dihydrofolate reductase (DHFR) is an important drug target in mammals, bacteria and protozoa, no inhibitors of this enzyme have been developed as commercial insecticides. We therefore examined the potential of this enzyme as a drug target in an important ectoparasite of livestock, the Australian sheep blow fly, Lucilia cuprina (Diptera: Calliphoridae) (Wiedemann). The non‐specific DHFR inhibitors aminopterin and methotrexate significantly inhibited the growth of L. cuprina larvae, with IC₅₀ values at µg levels. Trimethoprim and pyrimethamine were 5–30‐fold less active. Relative IC₅₀ values for the inhibition of recombinant L. cuprina DHFR by various inhibitors were in accordance with their relative effects on larval growth. The active‐site amino acid residues of L. cuprina DHFR differed by between 34% and 50% when compared with two mammalian species, as well as two bacteria and two protozoa. There were significant charge and size differences in specific residues between the blow fly and human DHFR enzymes, notably the L. cuprina Asn21, Lys31 and Lys63 residues. This study provides bioassay evidence to highlight the potential of blow fly DHFR as an insecticide target, and describes differences in active site residues between blow flies and other organisms which could be exploited in the design of blow fly control chemicals.