Effects of root-infecting fungi on wheat transport processes and growth

Abstract

Aurtobasidium bolleyi and Gaeumannomyces graminis damaged transport processes and decreased shoot growth of sand-grown wheat plants only if they colonized the stele and disrupted the phloem of most roots. One week after planting in sand infested by A. bolleyi the phloem of most roots was disrupted and no 14C-labelled assimilates were detected in them. K uptake, shoot water content and shoot growth were decreased. However, plants rapidly recovered because A. bollayi did not penetrate beyond the epidermis of new roots. G. graminis disrupted the phloem of some roots within the first week, but shoot growth was unaffected. During the next 4 weeks the phloem of most roots was disrupted and K uptake, shoot water content and shoot growth were severely decreased. Uptake of Ca and Mg was affected less. Phialophora radicicola, Pythium scleroteichum and Wojnomicia graminis did not penetrate root steles and did not affect transport processes or shoot growth. When wheat was planted in sand infested by Cochliobolus sativus or Fusarium culmorum, K uptake, shoot water content and shoot growth were decreased after 1 week although root steles were not colonized until 3 or 4 weeks later. Tests for phytotoxins revealed the presence of inhibitory substances in culture filtrates of C. sativus, but not F. culmorum.