Oil Palm Bulletin No. 78 (May 2019) p13-23

Population Dynamics of Fusarium oxysporum and Trichoderma spp. in Malaysian and Ghanaian Soils

M Hefni Rusli*, A Seman Idris* and Richard M Cooper**

Fusarium oxysporum f. sp. elaeidis (Foe) is a pathogenic fungus that causes vascular wilt in oil palm. The disease is prevalent in African oil palm plantations, causing devastating losses. Oil palm seeds are used in global breeding programmes, and have recently been shown to be highly contaminated with Foe, with 3% of all Foe-infected seedlings developing Fusarium wilt during growth. Malaysia is the second largest oil palm producer in the world, and palms here are also susceptible to the disease, with Foe posing a potential major threat to the industry. Malaysia and other countries in Southeast (SE) Asia have previously imported seeds from Africa, yet remain unaffected by Foe. This is thought to be caused by the presence of antagonists, such as species of Trichoderma or other micro-organisms that give the soil its Foe-suppressive qualities. This study looks into the levels of Foe and Trichoderma in the soils from Ghana and Malaysia. From colony counts, Malaysian soil samples were shown to have a lower number of Fusarium species per gram, with 25% of these isolates revealed to belong to the species F. oxysporum. These soils were also found to have a higher number of Trichoderma species per gram of soil. Both these results were significantly different from those on the Ghanian soils (P=0.0450 and P=0.0003, respectively), and may be the reason for the absence of the disease in Malaysia. Trichoderma isolates from Ghana were tested in dual culture experiments, and it was found that Foe colony growth was inhibited by 7% to 32%, although the colonies were not killed in the process and no inhibition zones were seen. This indicates the potential, though unlikely, suppression quality of Trichoderma against Foe isolates which can be tested in a field setting. A comparison with Malaysian Trichoderma isolates may reveal significant differences in inhibition strength that may indicate Trichoderma as the antagonist behind Foe inhibition in Malaysia. This would strengthen the hypothesis that Trichoderma has potential as an antagonist against Fusarium wilt. This, among other inhibition studies, may provide a suitable candidate as a biological control agent in Ghana and Malaysia to prevent and control this devastating disease of oil palm.

Penyakit layu vaskular yang disebabkan oleh Fusarium oxysporum f. sp. elaeidis (Foe) merupakan penyakit sawit yang sangat serius di Afrika. Walau bagaimanapun, penyakit ini tidak pernah dilaporkan di Asia Tenggara, walaupun pengimportan biji benih dari Afrika sering dilakukan untuk tujuan pembiakbakaan. Malaysia ialah pengeluar minyak sawit yang kedua terbesar di dunia, dan Foe merupakan satu ancaman utama pada industri ini. Berdasarkan kajian yang lepas, kehadiran agen kawalan biologi seperti Trichoderma yang berpotensi merencatkan infeksi Foe merupakan antara salah satu faktor yang mungkin menyebabkan ketiadaan penyakit layu vaskular sawit di Malaysia dan Asia Tenggara. Kajian ini dijalankan untuk mengenalpasti dinamik populasi Foe dan Trichoderma dalam tanah di Malaysia dan Ghana. Berdasarkan keputusan yang diperoleh, kiraan koloni dari sampel tanah Malaysia ditunjukkan mempunyai bilangan spesies Fusarium yang lebih rendah per gram, dengan 25% isolat terdiri daripada spesies F. oxysporum, dan lebih banyak spesies Trichoderma bagi setiap gram tanah. Kedua-dua keputusan ini berbeza dengan signifikan (P = 0.0450 dan P = 0.0003, masingmasing) dibandingkan dengan keputusan daripada sampel tanah Ghana, dan boleh menjadi penyebab ketidakhadiran penyakit layu vaskular di Malaysia. Kajian in vitro menunjukkan Trichoderma yang diisolat daripada tanah Ghana boleh merencatkan pertumbuhan Foe sebanyak 7%-32%. Ini menunjukkan bahawa Trichoderma mempunyai potensi sebagai agen kawalan biologi terhadap Foe.


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