Death of the root cortex of winter wheat in field conditions; effects of break crops and possible implications for the take-all fungus and its biological control agent, Phialophora radicicola var. graminicola

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Abstract
SUMMARY: Nuclear staining with acridine orange was used to study death of the root cortex of winter wheat grown after grass and non-graminaceous break crops in a field trial site in 1978. The top 5·4 cm of first seminal root axes had several anucleate cortical cell layers by late-February, and nearly five dead cell layers (of a maximum six) by mid-April. One of the next pair of roots to emerge (designated ‘2’) showed similar cortical death, but one of the subsequent pair (designated ‘4“)showed substantially less death at these times.Significantly more root cortex death was seen in first to third wheat crops after 1 or 2 years of grass than after swedes-potatoes, and in one replicate block compared with the other in the trial. But there was no significant difference in cortical death between first, second, third and 16th successive wheat crops.Root cortex death could not be attributed to infection by Gaeumannomyces graminis, Phialophora radicicola var. graminicola or the nematode Rotylenchus robustus. But its implications for root–infecting parasites are considered and, in particular, the enhanced cortical death in some crops compared with others may help to explain the reported differences in infection of wheat by P. radicicola var. graminicola, a biological control agent of take-all.