RICE PEST AND DISEASE ISSUES IN MALAYSIA

RICE GROWING IN MALAYSIA are an important industry in agriculture sector after Oil Palm and Rubber. Rice (Oryza sativa) was grown mostly in granary area with good infrastructure and governments subsidies. There are pests and diseases across Malaysian rice granaries and other non-granary area. Pests and diseases such as the rice blast disease, bacterial leaf blight, tungro and brown plant hopper are constant threats to the rice production systems in Malaysia. In 2015 reported by Department of Agriculture  Malaysia (DOA) in which accounting for 43% of total rice disease incidence and reported blast disease as the most predominant disease affecting rice cultivation. Blast disease caused by the Pyricularia oryzae Carava or Magnaporthe grisea (Herbert Barr) fungus is categorized into two types based on host preference known as (i) foliar blast; infects at the rice seedling stage and (ii) panicle blast; infects the panicle during the reproductive stage. The disease occurrence, distribution and infestation is weather-driven. The first incidence of blast disease in Peninsular Malaysia was reported in 1945 following a 70% yield loss observed on Jaya, a susceptible rice variety in which involves varieties such as Jaya, Sekencang and Setanjung too succumbed to panicle blast which reduced grain filling, panicle breakage and subsequent yield loss. In 2011 reported by DOA in which the blast resistant MR219 succumbed to panicle blast in MADA granary while in 2017 also reported that a total of 1,453 ha and 957 ha of rice fields were infected by leaf blast and panicle blast, respectively. The most infected granary was KADA followed by MADA and IADA BLS. MARDI had since then released MR253, MR263, MR269 and MR284 with improved disease resistance. Besides these varieties, MR297 also known as Siraj conferred blast resistant, tungro resistant and BPH moderate resistant. This article in "Anim Agriculture Technology" blog I would like to write a report regarding the rice and disease issues in Malaysia.

The Bacterial Leaf Blight Disease (BPH) that was caused by Xanthomonas oryzae pv. oryzae (Xoo) is assumed to be the oldest and most important disease in rice history including in Malaysia (See photo above). BPH is characterized with wilting of paddy seedlings and/or yellowing or drying of the leaves. Farmers first encountered BPH in 1980s however, over the decade there is no reports of the disease incidence were observed. In the recent years in which the disease re-emerged and reared its ugly head on at least 12,080 ha of rice fields in Peninsular Malaysia (Source: DOA, 2019). Similar to blight disease in which DOA reported about 30 - 50% potential loss of yield due to bacterial leaf blight (BLB) disease infection. The most severe leaf blight disease outbreak in the last 30 years occurred in the paddy field of Sekinchan, Selangor, in 2016 causing 50 - 70% loss of yield. During the outbreak from the report that the farmers had planted the new variety MR284 that was released just a year ago. In 2017 the report shows that there are another type of blight, namely Bacterial Panicle Blast (BPB) caused by Burkholderia glumae showed up at Ache River, Penang and a year later in Kelantan. BPB infected rice plants have upright panicles, florets with darker basal portion of the glumes, and reddish-brown border across the florets. According to MARDI in which for the granaries in various states in Peninsular Malaysia have recorded up to 50% losses due to BPB. As for sheath blight (ShB) or caused by Rhizoctonia solani is the soilborne necrotrophic fungal causative agent that is responsible for yield loss of up to 45%. The symptoms are the formation of lesions on the sheath leading to softness and lodging of the sheath and inhibition of grain filling. Besides blast and blight, the rice plants have always been prone to tungro disease (Penyakit virus merah) that is transmitted by green leafhopper also known as Nephotettix virescens. The disease results from an infection by two distinct viruses, Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). Although the symptoms of yellow-orange leaf discoloration, plant stunting and reduced yield were recognized since 1934, but its viral nature only came to light in 1965. Despite the significance of tungro disease, very little work has gone into understanding it except for the first genome sequencing of RTBV undertaken in 1999. Annually almost US$1.5 billion is lost worldwide while in Asia about 10% of loss in rice yield had been attributed to this disease.

Besides Green Planthopper reported that the other insect known as the Brown Planthopper has been a constant menace. Nilaparvata lugens causes the notorious brown plant hopper (BPH) disease that is touted to cause a loss of 90,000 ton/season which is valued at about RM 72 million. BPH reported that it directly feed on rice plants and transmits the grassy stunt disease. As for brown spot disease, the causal agent is Bipolaris oryzae (or known as Cochliobolus miyabeanus). It affects direct seeded rice plants and could potentially lead to 90% yield loss if water supply is scarce or limited and there is an inadequate supply of nitrogen. Although brown spot is commonly observed on the leaves and glumes (grain husks) it could also affect other plant parts, namely leaf, coleoptile, sheaths, panicle branches and grain. According to the pathogen causes brown to dark brown lesions on panicle stalk at the joint of flag leaf to stalk. As the disease progresses, the pathogen retards plant growth, forms visible grain discoloration, reduces the number of grains per panicle and grain weight, and increases the number of empty grains. However, the common disease management approach is cultural practices and use of chemical but often times it fails to combat the disease at the bud. It is imperative to use disease resistant rice varieties as host resistance is the best strategy to cut yield losses and ensure the sustainability of rice and paddy industry. Additionally, the use of certified quality seeds is mandatory to curb yield losses. Thanks...

By,

M Anem,

Senior Agronomist,

Putrajaya,

Malaysia.

(August 2023).