Biological characterization and molecular diagnosis of exserohilum rostratum, and rice defense mechanisms towards the pathogen

Name: Yatavee Boonkorn

LCSH: Kasetsart University -- Dissertations. Ph.D. (Plant Pathology) 2023.

Classification :.LCCS: SB608.R5

LCSH: Kasetsart University. -- Department of Plant Pathology -- Dissertations.

LCSH: Rice -- Diseases and pests.

LCSH: Rice -- Disease and pest resistance.

LCSH: Phytopathogenic microorganisms.

Abstract: Rice, a principal crop of economic importance in Thailand, is significantly affected by several fungal diseases, including leaf spots and seed discoloration caused by Exserohilum rostratum (teleomorph = Setosphaeria rostrata). In this study, thirty-five isolates were obtained from leaves exhibiting tiny spot symptoms collected from various Thai paddies. Pathogenicity was confirmed through Koch's postulates. The Infected leaves exhibited reddish-brown spots and developed necrotic tissue within 48 hours. Morphological identification through molecular analysis based on nucleotide sequences of internal transcribed spacer (ITS), translation elongation factor 1 alpha (tef1a), and glyceraldehyde-3- phosphate dehydrogenase (gadph) confirmed that all isolates were E. rostratum. Histocytological observation on E. rostratum-infected rice leaf sheaths revealed that E. rostratum developed penetration hyphae originating from hyaline appressoria to penetrate host tissues. Both intercellular and intracellular invasions were evident, leading to the development of necrotic cells. In addition, E. rostratum has a wide range of hosts, including barnyard grass, corn, banana, beans, and cucumbers. Diagnostic primer sets for E. rostratum were developed for conventional PCR using the sequences of actin (act) and gadph genes, and for real-time PCR using gadph, cytochrome b (cytb), and cytochrome c oxidase subunit 3 (cox3) genes, enabling specific detection and quantification of E. rostratum in rice samples. Fungicide inhibition assays identified flusilazole as the most effective against E. rostratum mycelial growth. Additionally, the response of various Thai rice cultivars to E. rostratum indicated that JHN exhibited the lowest disease severity, while KDML 105 displayed the highest disease severity. Gene expression analysis in KDML 105 and JHN indicated that rice plant hormone-responsive genes, including OsPR1b and OsPBZ1 (salicylic acid-responsive defense genes), JiOsPR10 (jasmonic acidresponsive defense gene), and OsEBP89 (ethylene-responsive gene) played a role in the rice response to E. rostratum infection. However, the resistance mechanism may not be regulated through jasmonic acid and ethylene pathways. This study provides critical insights into E. rostratum's impact on Thai rice, its interaction mechanisms, and potential control strategies, including chemical control and breeding for resistant cultivars.

Kasetsart University. Office of the University Library

Address: Bangkok

Email: tdckulib@ku.ac.th

Name: Pattavipha Songkumarn

Role: Thesis Advisor

Name: Veeranee Tongsri

Role: Thesis Co-Advisor

Created: 2023

Modified: 2025-06-26

Issued: 2025-06-26

วิทยานิพนธ์/Thesis

วิทยานิพนธ์/Thesis

application/pdf

URL: http://www.lib.ku.ac.th/KUthesis/2566/yatavee-boo-all.pdf

CallNumber: SB608.R5.Y38

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Plant Pathology

Grantor: Kasetsart University

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