The influence of growth stage of different cereal species on host susceptibility to Gaeumannomyces graminis var. tritici and on Pseudomonas populations in the rhizosphere

Abstract

The dynamics of infection by Gaeumannomyces graminis var. tritici (Ggt), the soil-borne fungus causing the disease take-all, in wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.) and triticale (x Triticosecale Wittmack) was investigated at different growth stages of the cereal hosts. In the field, Ggt spreads along rows of plants from the inoculum sources. At harvest, Ggt DNA was detected up to 60 cm away from inoculum sources in all species except rye, although most of the take-all lesions occurred in roots less than 30 cm away in all species, with rye being the least affected. The greatest populations of fluorescent Pseudomonas sp-species were extracted from the rhizosphere of cereal roots sampled near the points of Ggt inoculation; were found prior to the booting growth stage in triticale and rye; and were not related to the concentration of Ggt in the roots. In pots in a glasshouse experiment, Ggt colonised seedling wheat roots to a concentration of 103 ng DNA/mg dried roots and caused 14 % take-all severity in roots during plant development. In rye, seedling roots contained Ggt DNA at 15 ng/mg dried root, which decreased to negligible concentrations until heading, then increased rapidly to 280 ng DNA/mg dried root at kernel development. Take-all root severity in rye increased from 1 to 50 % over that period. In a second glasshouse experiment, inoculation of roots of host plants at various growth stages with actively growing hyphae of Ggt showed that the pathogen was able to overcome resistance in rye plants after an establishment phase.