Wheat cultivar susceptibility to Gaeumannomyces graminis var. tritici and influence on Pseudomonas fluorescence numbers in the rhizosphere

Yields from wheat (Triticum aestivum L.) cultivars grown in natural soils and soils inoculated with Gaeumannomyces graminis var. tritici (Ggt), the fungus causing take-all, were obtained in separate second-year wheat fields over three successive growing seasons in Canterbury, New Zealand. Cultivars ‘Empress’, ‘Oakley’, ‘Phoenix’ and ‘Sage’ were compared with the standard, ‘Wakanui’, over three seasons, ‘Conquest’, ‘Consort’, ‘Einstein’ and ‘Starfire’ over three seasons, and ‘Raffles’, ‘Savannah’ and ‘Torch’ in one season. Root take-all severity averaged 44 % in Ggt-inoculated soils compared with 20 % in natural soils. Adding Ggt inoculum to soil at sowing decreased mean grain yields for all cultivars by 0.78 t ha−1 (9.5 %). ‘Starfire’ had the greatest yield (9.36 t ha−1) and ‘Consort’ the least (6.51 t ha−1) compared to ‘Wakanui’ at 8.24 t/ha. No cultivar exhibited resistance to take-all, but the variation in tolerance provided growers with management options. ‘Empress’, ‘Starfire’ and ‘Raffles’ produced high yields in soils initially containing large amounts of Ggt inoculum, and would be suitable as second year wheat crops where the risk of take-all is high. Soils sown with ‘Starfire’, ‘Oakley’ or ‘Sage’ resulted in the least build-up of inoculum after harvest, so these cultivars would be suitable as first-year wheat and less likely to induce Ggt inoculum in soil for subsequent wheat crops. The numbers of Pseudomonas fluorescens on wheat roots appeared not to be associated with any cultivar. Only in the first growing season were high numbers of these bacteria associated with high Ggt inoculum, which is a prelude to take-all decline.