An evaluation of the apxIVA based PCR-REA method for differentiation of Actinobacillus pleuropneumoniae

A restriction analysis of PCR (PCR-REA) amplified apxIVA gene has been suggested as an alternative method for serotyping of Actinobacillus pleuropneumoniae by Jaglic et al. [Jaglic, Z., Svastova, P., Rychlik, I., Nedbalcova, K., Kucerova, Z., Pavlik, I., Bartos, M., 2004. Differentiation of Actinobacillus pleuropneumoniae by PCR-REA based on sequence variability of the apxIVA gene and by ribotyping. Vet. Microbiol. 103, 63-69]. The current study investigated whether this alternative method could distinguish between the reference strains of serovars 13-15 and the value of the method when applied to 47 field isolates representing serovars 1-3, 5, 7-9, 12 and 15 as well as non-typable isolates. The reference strains of serovars 13 and 14 had the same sized product after the apxIVA PCR, while the product for serovar 15 was of different size compared to all the other serovar reference strains. The CfoI digest profiles of the reference serovars 13 and 14 strains were different from each other and from all other serovars. The HpaII digest profiles of these two serovars were very similar to each other, but both were distinctively different from the other serovar profiles. The CfoI digest profile of serovar 15 strain was very similar to the serovars 3 and 12 strains except for two faint extra bands for serovar 15. The HpaII digest profiles of serovars 12 and 15 reference strains were identical. The PCR-REA method correctly recognized the serovar of 21 of 43 field isolates. It was concluded that the method was a useful additional tool to support, but could not replace, conventional serotyping.

Cotton root systems and recovery of applied P and K fertilisers

With potential to accumulate substantial amounts of above-ground biomass, at maturity an irrigated cotton crop can have taken up more than 20 kg/ha phosphorus and often more than 200 kg/ha of potassium. Despite the size of plant accumulation of P and K, recovery of applied P and K fertilisers by the crop in our field experiment program has poor. Processing large amounts of mature cotton plant material to provide a representative sample for chemical analysis has not been without its challenges, but the questions regarding mechanism of where, how and when the plant is acquiring immobile nutrients remain. Dry matter measured early in the growing season (squaring, first white flower) have demonstrated a 50% increase in crop biomass to applied P (in particular), but it represents only 20% of the total P accumulation by the plant. By first open boll (and onwards), no response in dry matter or P concentration could be detected to P application. A glasshouse study indicated P recovery was greater (to FOB) where it was completely mixed through a profile as opposed to a banded application method suggesting cotton prefers a more diffuse distribution. The relative effects of root morphology, mycorrhizal fungi infection, seasonal growth patterns and how irrigation is applied are areas for future investigation on how, when and where cotton acquires immobile nutrients.

Highly heritable resistance to root-lesion nematode (Pratylenchus thornei) in Australian chickpea germplasm observed using an optimised glasshouse method and multi-environment trial analysis

Pratylenchus thornei is a root-lesion nematode (RLN) of economic significance in the grain growing regions of Australia. Chickpea (Cicer arietinum) is a significant legume crop grown throughout these regions, but previous testing found most cultivars were susceptible to P. thornei. Therefore, improved resistance to P. thornei is an important objective of the Australian chickpea breeding program. A glasshouse method was developed to assess resistance of chickpea lines to P. thornei, which requires relatively low labour and resource input, and hence is suited to routine adoption within a breeding program. Using this method, good differentiation of chickpea cultivars for P. thornei resistance was measured after 12 weeks. Nematode multiplication was higher for all genotypes than the unplanted control, but of the 47 cultivars and breeding lines tested, 17 exhibited partial resistance, allowing less than two fold multiplication. The relative differences in resistance identified using this method were highly heritable (0.69) and were validated against P. thornei data from seven field trials using a multi-environment trial analysis. Genetic correlations for cultivar resistance between the glasshouse and six of the field trials were high (>0.73). These results demonstrate that resistance to P. thornei in chickpea is highly heritable and can be effectively selected in a limited set of environments. The improved resistance found in a number of the newer chickpea cultivars tested shows that some advances have been made in the P. thornei resistance of Australian chickpea cultivars, and that further targeted breeding and selection should provide incremental improvements.