A compromised Mlo pathway affects the response of barley to the necrotrophic fungus Bipolaris sorokiniana (Teleomorph : Cochliobolus sativus) and itstoxins
J. Kumar et al., A compromised Mlo pathway affects the response of barley to the necrotrophic fungus Bipolaris sorokiniana (Teleomorph : Cochliobolus sativus) and itstoxins, PHYTOPATHOL, 91(2), 2001, pp. 127-133
In search of new durable disease resistance traits in barley to control lea
f spot blotch disease caused by the necrotrophic fungus Bipolaris sorokinia
na (teleomorph: Cochliobolus sativus), we developed macroscopic and microsc
opic scales to judge spot blotch disease development on barley. Infection o
f barley was associated with cell wall penetration and accumulation of hydr
ogen peroxide. The latter appeared to take place in cell wall swellings und
er fungal penetration attempts as well as during cell death provoked by the
necrotrophic pathogen. Additionally, we tested the influence of a compromi
sed Mlo pathway that confers broad resistance against powdery mildew fungus
(Blumeria graminis f. sp. hordei). Powdery mildew-resistant genotypes with
mutations at the Mlo locus (mlo genotypes) showed a higher sensitivity to
infiltration of toxic culture filtrate of Bipolaris sorokiniana as compared
with wild-type barley. Mutants defective in Ror, a gene required for mlo-s
pecified powdery mildew resistance, were also more sensitive to Bipolaris s
orokiniana toxins than wild-type barley but showed less symptoms than mlo5
parents. Fungal culture filtrates induced an H2O2 burst in all mutants, whe
reas wild-type (Mlo) barley was less sensitive. The results support the hyp
othesis that the barley Mlo gene product functions as a suppresser of cell
death. Therefore, a compromised Mlo pathway is effective for control of bio
trophic powdery mildew fungus but not for necrotrophic Bipolaris sorokinian
a. We discuss the problem of finding resistance traits that are effective a
gainst both biotrophic and necrotrophic pathogens with emphasis on the role
of the anti-oxidative system of plant cells.