Introduction

The necrotrophic fungus Pyrenophora tritici-repentis (Died.)

Drechs.However, to our knowledge, the in planta production of cate-

narin by parasitic fungi has not been demonstrated.Moreover, in order to

clarify the possible ecological and physiological roles of catenarin

produced by P. tritici-repentis, the phytotoxic and antimicrobial

activities of the pigment were assessed, respectively, on wheat and

a wide range of microorganisms associated with the pathogen

during its saprophytic and parasitic phases of growthIn some wheat production

areas, tan spot often occurs as part of a leaf-spotting complex on

wheat, in conjunction with Phaeosphaeria nodorum (E. Mu?ller)

Hedjaroude (anamorph: Stagonospora nodorum (Berk.) Castellani

and E.G. Germano), Mycosphaerella graminicola (Fuckel) J. Schro?t.The latter condition is also associated with other fungal and

bacterial pathogens, including Alternaria alternata (Fr.:Fr.) Keissl.,

Fusarium spp., Aspergillus spp., Cladosporium spp., and Pseudomonas

syringae pv. atrofaciens (McCulloch) Young et al. [11].It was previously hypothesized that the reddish discoloration of

wheat kernels associated with red smudge results from the secre-

tion and accumulation of catenarin [14], an anthraquinone pro-

duced by some isolates of P. tritici-repentis [14], as well as other

fungi [15-19] and some plants [20].In the absence of

a suitable host, P. tritici-repentis can survive saprophytically on

wheat debris on the soil surface, and the incidence of tan spot has

increased in recent years with the adoption of conservation tillage

practices that retain crop residues [4,5].The bioactivity of catenarin also suggests that in

addition to inhibiting the growth of microorganisms associated

with P. tritici-repentis during its saprophytic phase [14], the pig-

ment suppresses parasites accompanying the tan spot pathogen as

part of the wheat leaf-spotting complex.Evidence that

the pigment is produced in wheat kernels infected by P. tritici-

repentis would support the hypothesis [14] that catenarin causes

the red smudge symptom, and would also allow for a better as-

sessment of the impact of this pathogen on seed health, processing

characteristics, and food safety.On susceptible

host genotypes, P. tritici-repentis differentially induces combina-

tions of tan necrosis and/or extensive chlorosis.in

Cohn (anamorph: Septoria tritici Roberge in Desmaz.), and

Cochliobolus sativus (Ito and Kuribayashi) Drechs.