Shukri, Izah Adlina Mohamad
(2024)
Rhamnolipid As Antifungal Agent
Against Pyricularia Oryzae And Rhizoctonia
Solani Causing Blast And Sheath
Blight Diseases Of Paddy.
Masters thesis, Universiti Sains Malaysia.
Abstract
Pyricularia oryzae and Rhizoctonia solani are fungi causing blast and sheath
blight diseases of paddy (Oryza sativa) in Malaysia. The use of disease resistant rice
varieties and fungicides to control both diseases might increase the fungal resistance
and the discharge of chemicals into watercourses. This research evaluates the
antifungal activity of rhamnolipid, a biosurfactant produced by Pseudomonas
aeruginosa USM-AR2 which is more sustainable than chemical fungicides. Seven
isolates of Pyricularia sp. and eight isolates of Rhizoctonia sp. from thirty isolates
were successfully obtained from blast and sheath blight symptoms in a paddy field in
Alor Setar, Kedah, Malaysia. Pathogenicity test confirmed that all Pyricularia sp. and
Rhizoctonia sp. isolates were pathogenic by showing a typical blast as an orange brown
edge diamond-shaped and sheath blight as an irregular water-soaked. Morphological
characterisation and molecular identification of one representative isolate from each
group confirmed the identity as P. oryzae USM-PD1 and R. solani USM-PD2.
Moreover, antifungal evaluation of rhamnolipid against both fungi demonstrated
retarded mycelia with lysis and lesion, as well as slow growth on plates. The highest
percentage inhibition of diameter growth (PIDG) for P. oryzae USM-PD1 was
achieved at 2000 ppm (48.30 ± 1.18%). Meanwhile, PIDG and percentage inhibition
of sclerotia (PISC) number of R. solani USM-PD2 were obtained at 10 000 ppm (60.00
± 2.35%) and 800 ppm (100%), respectively.
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