Virulence assessment of Australian Pyrenophora tritici-repentis isolates

The virulence of 57 Australian isolates of Pyrenophora tritici-repentis (Ptr), a necrotrophic fungal pathogen responsible for the major wheat disease tan spot, was assessed through plant infection assays. Isolates collected from the northern, southern, and western wheat-cropping regions of Australia were evaluated against 16 Australian bread wheat cultivars under controlled growth conditions. Following infection, the wheat panel displayed varying disease symptoms ranging from tiny necrotic specks to spreading chlorotic and necrotic lesions. Analysis of variance indicated that the wheat cultivar exhibited a greater effect on the disease response, explaining 62.7% of the variation, in comparison to the isolate (10.4%). The interaction between the cultivar and the isolate was statistically significant and was attributed to 9.8% of the total variation. All Ptr isolates examined were able to cause disease, but did not display a clear distinction in virulence on the wheat panel investigated, instead showing subtle differences in aggressiveness. Based on the disease responses, there was no obvious pattern between isolate aggressiveness and cropping region. Some cultivars, such as Hydra, exhibited an effective level of resistance in relation to the panel of isolates tested. All 57 Ptr isolates were found to possess the ToxA effector gene and lack the ToxB effector gene. The gene expression level of ToxA was up-regulated at 3 days postinfection in both ToxA-sensitive and -insensitive cultivars, independent of ToxA–Tsn1 recognition.     

Evaluating the importance of the tan spot ToxA–Tsn1 interaction in Australian wheat varieties

The necrotrophic fungal pathogen Pyrenophora tritici‐repentis (Ptr) causes the major wheat disease tan spot, and produces multiple necrotrophic effectors that contribute to virulence. The proteinaceous effector ToxA induces necrosis in wheat genotypes possessing the Tsn1 gene, although the importance of the ToxA–Tsn1 interaction itself in varietal disease development has not been well studied. Here, 40 Australian spring wheat varieties were assessed for ToxA sensitivity and disease response to a race 1 wildtype Ptr isolate and ToxA‐deleted strain at both seedling and tillering growth stages. ToxA sensitivity was generally associated with disease susceptibility, but did not always predict spreading necrotic symptoms. Whilst the majority of Tsn1 varieties exhibited lower disease scores following toxa mutant infection, several exhibited no distinct differences between wildtype and toxa symptoms. This implies that ToxA is not the major determinant in tan spot disease development in some host backgrounds and indicates the presence of additional effectors. Unexpectedly, several tsn1 varieties exhibited a reduction in disease severity following toxa mutant inoculation, which may suggest an indirect role for ToxA in pathogen fitness. Additionally, increased chlorosis was observed following toxa mutant infection in three varieties, and further work is required to determine whether this is likely to be due to ToxA epistasis of ToxC symptoms. Taken together, these observations demonstrate that Ptr interacts with the host in a complex and intricate manner, leading to a variety of disease reactions that are dependent or independent of the ToxA–Tsn1 interaction.     

Soil compaction under timber harvesting machinery: a preliminary report on the role of brash mats in its prevention

Abstract. Forest soil sustainability and future crop productivity is at risk if mechanised harvesting operations cause soil damage. In UK upland forestry, soil protection is usually provided by placing harvesting residues (brash) over areas where machinery traffic is required. In this study, various thicknesses of brash mat were tested for their ability to reduce compaction of a surface water gley soil at Kielder Forest, Northumberland. Changes in penetration resistance and dry soil bulk density were studied after passes by forest harvesting and timber extraction machinery running on the brash. The study shows that normal harvesting operations caused some soil compaction. However, the brash mat system was shown as important in protecting the soil. Soil under brash mats experienced some compaction to at least 45 cm depth. The thickest brash mat, composed of residues from 10 rows of trees, was unable to prevent compaction completely. Nevertheless, the protective role of the brash mat system was clearly confirmed when compared to timber extraction over bare soil. The point at which compaction has a detrimental effect on the establishment and stability of future tree rotations remains uncertain.     

The effect of dietary cooked potato flake on performance of broilers and on litter quality

1. Broiler chicks, reared on litter, were given diets containing either 40% maize, 40% cooked potato flake, or 20% of each, in crumb form ad libitum from 1 to 21 d and 21 to 63 d in five dietary treatments.

2. Birds receiving the diet with 40% cooked potato flake grew more slowly than birds receiving the other diets during both periods but their food consumption was the same.

3. Including cooked potato flake in diets decreased the dry matter of the litter: with 40% in the diet the litter dry matter was decreased to 26% in 49 d at a stocking rate of 11 birds/m².

4. If the litter was kept dry, 20% of cooked potato flake was found to be an acceptable inclusion rate for broiler diets.