Sains Malaysiana 52(3)(2023): 683-691

http://doi.org/10.17576/jsm-2023-5203-01

Molecular Characterization and Pathogenicity of Stagonosporopsis cucurbitacearum Causing Gummy Stem Blight Disease of Watermelon (Citrullus lanatus L.) in Malaysia

(Pencirian Molekul dan Kepatogenan Stagonosporopsis cucurbitacearum Penyebab Penyakit Hawar Batang Bergam Tembikai (Citrullus lanatus L.) di Malaysia)

ABDUL AZIZ WAZIRI¹, DZARIFAH ZULPERI¹ & SITI IZERA ISMAIL^1,2,*

¹Department of Plant Protection, Faculty of Agriculture, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia

²Laboratory of Climate-Smart Food Crop Production, Institute of Tropical Agriculture and Food Security (ITAFoS), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia

Received: 24 March 2022/Accepted: 7 February 2023

Abstract

Watermelon (Citrullus lanatus L.) is a popular fruit crop with high economic value and widely grown in Malaysia. In January 2020, gummy stem blight (GSB) has become a threat for production of watermelon in Malaysia particularly in warm and humid climates, but the causative agent of GSB infecting watermelon is unknown. This disease decreases the fresh fruit marketability. Watermelon plants cultivar Red Rocky showing varied degree (40-90%) of suspected GSB, were collected from two main watermelon growing areas in Malaysia. Initial symptoms appeared as marginal brown necrotic lesions on leaves, while on the stems showed water-soaked, necrotic lesions and exuded reddish-brown gummy exudate on the stems. A total of ten isolates were isolated from lesions on leaves and stems of watermelon plants affected by GSB. All ten fungal isolates were identified as Stagonosporopsis cucurbitacearum on the basis of morphological characteristics and phylogenetic analysis of combined sequences of the internal transcribed spacer (ITS) and β-tubulin regions. All isolates were proven to be pathogenic when inoculated on the leaves and stems of the watermelon plant and the the fungal isolates were consistently reisolated from the diseased watermelon plants confirming Koch’s postulates. Pathogenicity tests indicated that there were significant differences in virulence among the S. cucurbitacearum when inoculated on the leaves and stems of the watermelon plant. Understanding the etiology of the pathogen will help in disease management of gummy stem blight disease in Malaysia.

Keywords: Cucurbits; gummy stem blight; Stagonosporopsis cucurbitacearum; watermelon

Abstrak

Tembikai (Citrullus lanatus L.) ialah tanaman buah-buahan yang popular dengan nilai ekonomi yang tinggi dan ditanam secara meluas di Malaysia. Pada Januari 2020, penyakit hawar batang bergam (GSB) telah menjadi ancaman kepada pengeluaran tembikai di Malaysia terutamanya dalam iklim panas dan lembap, tetapi agen penyebab GSB yang menjangkiti tembikai tidak diketahui. Penyakit ini mengurangkan kebolehpasaran buah segar. Kultivar tanaman tembikai 'Red Rocky' yang menunjukkan pelbagai darjah (40-90%) GSB yang disyaki dikumpulkan dari dua kawasan penanaman tembikai utama di Malaysia. Simptom awal muncul sebagai luka nekrotik coklat marginal pada daun, manakala pada batang menunjukkan luka nekrotik yang direndam air dan eksudat bergetah coklat kemerahan pada batang. Sebanyak sepuluh pencilan telah diasingkan daripada luka pada daun dan batang pokok tembikai yang terjejas oleh GSB. Kesemua sepuluh pencilan kulat telah dikenal pasti sebagai Stagonosporopsis cucurbitacearum berdasarkan ciri morfologi dan analisis filogenetik bagi jujukan gabungan kawasan spacer transkripsi dalaman (ITS) dan β-tubulin. Semua pencilan telah terbukti bersifat patogen apabila disuntik pada daun dan batang pokok tembikai dan pencilan kulat diasingkan semula secara tekal daripada tumbuhan tembikai berpenyakit yang mengesahkan postulat Koch. Ujian kepatogenan menunjukkan bahawa terdapat perbezaan yang ketara dalam kevirulenan dalam kalangan S. cucurbitacearum apabila disuntik pada daun dan batang pokok tembikai. Memahami etiologi patogen akan membantu dalam pengurusan penyakit penyakit hawar batang getah di Malaysia.

Kata kunci: Hawar batang bergam; kukurbit; Stagonosporopsis cucurbitacearum; tembikai

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^*Corresponding author; email: izera@upm.edu.my