Yield losses in grain sorghum due to rust infection

Although rust (caused by Puccinia purpurea) is a common disease in Australian grain sorghum crops, particularly late in the growing season (April onwards), its potential to reduce yield has not been quantified. Field trials were conducted in Queensland between 2003 and 2005 to evaluate the effect of sorghum rust on grain yield of two susceptible sorghum hybrids (Tx610 and Pride). Rust was managed from 28-35 days after sowing until physiological maturity by applying oxycarboxin (1 kg active ingredient/ 100 L of water/ha) every 10 days. When data were combined for the hybrids, yield losses ranged from 13.1% in 2005 to 3.2% in 2003 but differences in yield the between sprayed and unsprayed treatments were statistically significant (P≥0.05) only in 2005. Final area under the disease progress curve (AUDPC) values reflected the yield losses in each year. The higher yield loss in 2005 can be attributed primarily to the early development of the rust epidemic and the higher inoculum levels in spreader plots at the time of planting of the trials

Optimal environmental conditions for the infection and development of Puccinia purpurea on sorghum

Although rust can reduce grain yields of late-planted sorghum crops in Queensland, little research has been conducted on environmental parameters affecting infection and development. The effects of temperature, leaf wetness period, plant growth stage, urediniospore concentration and darkness period on the development of rust (Puccinia purpurea) on the inbred Sorghum bicolor line IS8525 were evaluated separately by artificial inoculation of plants under controlled conditions. Rust developed between 16 and 28 °C, with the optimum temperature being 20 °C. Disease severity (pustules cm−2) increased as the length of leaf wetness increased from 4 to 24 h. Infection occurred when plants were exposed to full light, full darkness and varying periods of darkness for the first 24 h after inoculation; 16 h of darkness resulted in the highest rust severity. Plants of IS8525 and of the more resistant line IS12539 inoculated 21–49 days after sowing developed higher levels of rust than others inoculated at, or close to, flowering (63 days after sowing). Rust severity also increased with increasing urediniospore concentrations, but leaf death occurred on young plants inoculated with the highest concentration (50 mg 100 mL water−1). The findings of this study have been used to develop an inoculation technique to detect putative pathotypes of P. purpurea in Australia

Quantitative proteomics to study the response of potato to contrasting fertilisation regimes

There is concern over the sustainability and environmental impact of mineral fertilisers and crop protection inputs used in intensive arable crop production systems. However, replacing mineral with organic fertilisers (animal and green manures) and restricting the use of chemosynthetic crop protection may significantly reduce crop yields. The effects of (a) replacing mineral with composted cattle manure fertiliser input and (b) omitting pesticide-based crop protection on potato (Solanum tuberosum) tuber yield, leaf and tuber mineral nutrient content and leaf protein profiles were investigated. Switching to organic fertiliser had a greater effect on yield and protein profiles than the omission of chemosynthetic crop protection. Leaf N and P composition were significant drivers of protein expression, particularly proteins involved in photosynthesis such as the large subunit of RuBisCO, RuBisCO activase and the photosystem I reaction centre, which were at higher abundances in potato leaves grown under mineral fertiliser regimes. Proteins known to be induced in response to stress, such as dehydroascorbate reductase and Glutathione S-transferases, were also shown to be up-regulated under mineral fertilisation, possibly associated with higher Cd composition, whereas two proteins known to be involved in biotic stress (1,3-β-d-glucan glucanohydrolase; putative Kunitz-type tuber invertase inhibitor) were more abundant under compost fertilisation. Results showed that switching from mineral to organic fertilisers led to reduced N availability, a significant change in leaf protein expression and lower tuber yield. In contrast, omission of chemosynthetic crop protection inputs had limited effects on protein expression and no significant effect on tuber yield. This study provides information on the effects of changes in nutrient supply on protein expression patterns. It is a prerequisite for the development of functional molecular markers for a directed strategy to inform breeding programmes to improve potato nutrient use efficiency