Citrus scab disease caused by Elsinoe fawcettii is one of major disease in
citrus cultivation, resulting in fruit blemishes that reduce quality and the
economic value of fruits. Like other disease in citrus, citrus scab was
mainly protected by chemical fungicides. Recently, interests of safe
products were increased so that alternatives of chemical control were
highly required. Elsinoe fawcettii was suppressed by rhizobacterial strains
such as Burkholderia gladioli MRL408-3, TRH423-3 and Pseudomonas
fluorescens THJ609-3, TRH415-2 having antifungal activity. In order to
investigate inhibition-behaviors of citrus scab pathogen, the leaf surface of
Satsuma mandarin, which was pre-treated with the rhizobacteiral strains,
was observed on the Satsuma mandarin leaves by a scanning electron
microscope (SEM) after inoculation with Elsinoe fawcettii. The number of
lesions was reduced on the leaves pre-treated with the rhizobacterial
strains compared to those of untreated leaves. Especially, the lesions
numbers was apparently reduced on the leaves pre-treated with B. gladioli
MRL408-3. The observation by SEM revealed that not only the
germination rate but also the length of germ tube of the pathogen were
decreased on the rhizobacterial strains pre-treated leaves. These inhibition
of the fungal growth was more strongly expressed on the leaves pretreated with commercial fungicide Imibenconazole, by which the lesions was
rarely found on the leaves. Based on these results, it was suggested that
rhizobacterial strains may inhibit the germination and growth of the Elsinoe
fawcettii on the surface of citrus leaves, resulting in decrease of disease
severity. Lastly, in order to test resistance of various kinds of citrus cultivar
against E. fawcettii, some citrus cultivar Jigak, Frost eureka, Washington
navel, Jugyeon and Satsuma mandarin (negative control) were inoculated
with E. fawcettii. Consequently, The number of lesions was significantly
reduced on all tested citrus cultivar leaves compared with Satsuma m
mandarin. Particularly Jugyeon was the most resistant to citrus scab, but
Frost eureka was the least.