Drought tolerance and yield increase of soybean resulting from improved symbiotic N2 fixation

Drought is by far the most important environmental factor contributing to crop yield loss, especially in soybean [Glycine max (L.) Merr.] where symbiotic fixation of atmospheric nitrogen (N₂) is sensitive to even modest soil water deficits. Decline of N₂ fixation with soil drying causes yield reductions due to inadequate N for protein production, which is the critical seed product. In this paper, we present a combined physiological and breeding research effort to develop soybean lines that have diminished sensitivity of N₂ fixation to drought. A preliminary physiological screen was used to identify lines that potentially expressed N₂ fixation drought tolerance. One hundred progeny lines derived from a cross between Jackson, a cultivar proven to have N₂ fixation tolerance to drought, and KS4895, a high-yielding line, were tested in the screen. Seventeen lines were identified for subsequent yield trials in moderate- and low-yielding rainfed environments. Two lines, found to have higher yields than commercial checks in these environments were then tested in the greenhouse for their N₂ fixation activity in drying soil. Nitrogen fixation activity was found to persist at lower soil water contents than exhibited by the sensitive parent. These two soybean lines offer a genetic resource for increased yields under rainfed conditions as a result of decreased sensitivity of N₂ fixation to water deficit.     

Variation among New Zealand isolates of Sphaeropsis sapinea

Sphaeropsis sapinea is a pathogen of many coniferous species and causes significant losses to the plantation forestry industries of many countries. New Zealand isolates of S. sapinea were examined for colony and morphological characteristics, and pathogenicity to Pinus radiata seedlings. Considerable variation was observed in colony growth form and colour, and in the growth rates on four agar media. The conidial dimensions, carbon and nitrogen utilization, and pathogenicity also varied among the isolates. The variation observed was such that the isolates could not be placed within previously described distinct morphotypes and the present results concur with previous studies cautioning the use of morphological criteria alone to partition the species. These results contrast markedly with previous reports and seemingly indicate a change in the New Zealand S. sapinea population. This difference may reflect the re‐introduction or spread of additional isolates or a shift in the structure of the resident population.     

Application of high-resolution melt curve analysis for classification of infectious bronchitis viruses in field specimens

Objective A real-time polymerase chain reaction (PCR)/high-resolution melt (HRM) curve analysis protocol was developed in our laboratory to differentiate infectious bronchitis (IB) virus reference strains. In the current study, this method was used to detect and classify IB viruses in field submissions. Procedure Over an 11-month period samples from 40 cases of suspected IB virus were received and 17 submissions were positive for IB virus by polymerase chain reaction. HRM curve analysis classified each strain as subgroup 1, 2 or 3 strain (12 submissions) or a strain that was unable to be classified (5 submissions). The 3′ untranslated region (UTR) and partial S1 gene nucleotide sequences for the 17 IB virus strains were determined and their identity with those of the relative reference strains compared to confirm the classifications generated using the HRM curve analysis. Results Of the 12 IB field viruses classified as subgroup 1, 2, or 3 using HRM curve analysis, the 3′UTR and S1 gene nucleotide sequences had identities ≥99% with the respective subgroup reference strain. Analysis of the 3′ UTR and S1 gene nucleotide sequences for the five IB virus strains that could not be classified indicated that four belonged to one of the subgroups, and one was a potential recombinant strain (between strains from subgroups 2 and 3). A novel recombinant strain was also detected. Conclusion HRM curve analysis can rapidly assign the majority of IB viruses present in field submissions to known subgroups. Importantly, HRM curve analysis also identified variant genotypes that require further investigation.     

Presumed case of "stiff-horse syndrome" caused by decreased gamma-aminobutyric acid (GABA) production in an American Paint mare

Glutamic acid decarboxylase (GAD) converts glutamic acid into the inhibitory neurotransmitter γ-aminobutyric acid (GABA). Increased serum GAD (auto) antibody concentrations were found in a mare with increased postural musculature tone resulting in stiffness and recumbence. The mare was treated with dexamethasone which resulted in resolution of clinical signs and decreased GAD antibody concentrations.