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QTL identified for seedling and adult plant crown rot resistance in four partially resistant hexaploid wheat sources. PCR-based markers identified for use in marker-assisted selection. Crown rot, caused by Fusarium pseudograminearum, is an important disease of wheat in many wheat-growing regions globally. Complete resistance to infection by F. pseudograminearum has not been observed in a wheat host, but germplasm with partial resistance to this pathogen has been identified. The partially resistant wheat hexaploid germplasm sources 2-49, Sunco, IRN497 and CPI133817 were investigated in both seedling and adult plant field trials to identify markers associated with the resistance which could be used in marker-assisted selection programs. Thirteen different quantitative trait loci (QTL) conditioning crown rot resistance were identified in the four different sources. Some QTL were only observed in seedling trials whereas others appeared to be adult plant specific. For example while the QTL on chromosomes 1AS, 1BS, and 4BS contributed by 2-49 and on 2BS contributed by Sunco were detected in both seedling and field trials, the QTL on 1DL present in 2-49 and the QTL on 3BL in IRN497 were only detected in seedling trials. Genetic correlations between field trials of the same population were strong, as were correlations between seedling trials of the same population. Low to moderate correlations were observed between seedling and field trials. Flanking markers, most of which are less than 10 cM apart, have now been identified for each of the regions associated with crown rot resistance.

Trials conducted in Queensland, Australia between 1997 and 2002 demonstrated that fungicides belonging to the triazole group were the most effective in minimising the severity of infection of sorghum by Claviceps africana, the causal agent of sorghum ergot. Triadimenol (as Bayfidan 250EC) at 0.125 kg a.i./ha was the most effective fungicide. A combination of the systemic activated resistance compound acibenzolar-S-methyl (as Bion 50WG) at 0.05 kg a.i./ha and mancozeb (as Penncozeb 750DF) at 1.5 kg a.i./ha has the potential to provide protection against the pathogen, should triazole-resistant isolates be detected. Timing and method of fungicide application are important. Our results suggest that the triazole fungicides have no systemic activity in sorghum panicles, necessitating the need for multiple applications from first anthesis to the end of flowering, whereas acibenzolar-S-methyl is most effective when applied 4 days before flowering. The flat fan nozzles tested in the trials provided higher levels of protection against C. africana and greater droplet deposition on panicles than the tested hollow cone nozzles. Application of triadimenol by a fixed wing aircraft was as efficacious as application through a tractor-mounted boom spray.

Sorghum ergot (Claviceps africana) has had a significant impact on seed production and breeders’ nurseries in Australia since it was first found in 1996. In this paper, 3 distinct key development stages of sorghum that are related to ergot infection were identified: flag leaf stage, pollen starch accumulation stage, and flowering period. Relationships between weather variables during these 3 stages and ergot severity as well as pollen viability were analysed using observed data from 2 field trials, a serial planting trial and a genotype trial, conducted at Gatton, Queensland. The duration of the flag leaf stage and of the flowering period was estimated from thermal time. An infection factor was introduced and calculated based on hourly temperature during the flowering period. This infection factor and the mean relative humidity at 0900 hours during the flowering period were the main factors influencing ergot infection. Mean daily minimum temperature during flag leaf stage also had a significant effect on ergot severity, although no significant relation was found between this mean daily minimum temperature and pollen viability. A linear regression model using the above 3 factors accounted for 94% of the environmentally caused variation in ergot severity observed in the genotype trial.