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Rice Diseases in the Flood-prone Ecosystem and Their Management

M. A. Taher Mia
Bangladesh Rice Research Institute, Joydebpur, Gazipur-1701, Bangladesh

M. A. Nahar
Bangladesh Rice Research Institute, Joydebpur, Gazipur-1701, Bangladesh

Abstract/ Executive Summary:

In Bangladesh, the total area of deepwater rice (DWR) and a vast area of T. aman and boro fall under the flood-prone ecosystem. Among the major constraints, disease is one of the most important for rice production in this ecosystem. Among the diseases, ufra, sheath blight (ShB), blast, and tungro are the most important ones causing considerable yield losses. In the past, ufra was restricted to the deepwater ecosystem, but, now, this disease affects all rice crops. Yield loss varies depending on disease severity and may reach 100% in some cases. This disease is found in 18 districts of Bangladesh. Ufra could be controlled by the integration of crop rotation, stubble cleaning or burning, alternate wetting and drying, deep plowing, soil amendment with neem-seed dust, and avoiding growing seedlings in infested fields. The application of nematicide under the carbofuran group is also effective. Sheath blight disease is found throughout the country. It can cause up to 31% yield loss. Panicle initiation to the booting stage of the rice plant is the most susceptible stage for this disease. There is no resistant variety for it. It could be managed by some cultural practices, such as burning of infected straw and stubble in the field, planting seedlings at wider spacing, using balanced fertilizers, etc. Some fungicides are also effective against this disease. A study shows that blast disease could reduce yield by 11% to 46.4% under low to moderate disease severity. Leaf blast is the major problem in the boro season, whereas node and neck blast are major problems in the T. aman season. Several BRRI-released varieties are resistant to this disease. Other measures to protect from the disease include collection of seed from disease-free fields, avoiding the excess use of nitrogenous fertilizers, keeping standing water in the field, and using effective fungicides. Tungro is a virus disease transmitted by the green leafhopper (GLH). Under the flood-prone ecosystem, T. aman is the most vulnerable to this disease, which can infect the rice plant from the seedling stage. The earlier the infection of tungro, the higher the yield loss is. This disease could be managed by using resistant varieties, destroying infected plants and alternate hosts, and controlling in- sects by a light trap or insecticides.

Keywords: Rice diseases, Flood-prone, Ecosystem, DWR

Location: Narshingdi, Comilla and Faridpur districts, Bangladesh

Start Date: 00-00-1977

End Date: 00-00-1983

Program Area: Crop-Soil-Water Management

Commodity: Diseases and insects, Rice, Pesticide

Objectives:

To determine the ufra, sheath blight (ShB), blast (BL), and tungro diseases in the flood-prone ecosystem, and
To resolve the epidemiology, symptoms, and management aspects of these diseases.

Methodology:

The disease in some parts of Narshingdi (Dhaka), Chandina (Comilla), Matlab (Comilla), and Hajiganj (Comilla) from 1977 to 1983 revealed that the status of the disease in most areas remained unchanged or decreased to some extent. A recent survey indicated that this disease occurred in epidemic proportion in the T. aman season in Faridpur District among other nonflood-prone districts. In Faridpur, about 20 ha of T. am an fields were totally damaged (Anonymous 1999). Ufra disease is found in 18 districts of the country in all rice seasons. Some varieties/lines were found to be resistant to this disease when inoculated artificially. Progenies developed through crosses using Bazail 65 or Rayada 16-06 as resistant sources revealed that in the F₆ generation 14 lines of DWR type and seven lines with modem plant types were resistant to ufra disease (BRRI 1994). ShB disease is generally a concern for T. aman rice under the flood-prone ecosystem. ShB is a fungal disease caused by Rhizoctonia solani. In the early 1970s, it was considered to be a minor problem for rice cultivation. But, after the introduction of modem, high-nitrogen-responsive rice varieties, the intensity and severity of this dis- ease increased gradually. Dense and luxuriant growth of the plants and warm humid conditions favor disease development. This is now one of the most devastating dis- eases of rice and it is distributed throughout the country. The pathogen as sclerotia survives in the soil for a long time. Mycelium in the infected plant tissues also serves as a primary source of the inoculum. So far, thousands of varieties, germplasm accessions, and breeding lines have been tested against R. solani and none was found to be resistant to this disease. However, the intensity and severity of the disease were found to vary with transplanting time. Blast is another important disease under the flood-prone ecosystem in the T. aman and boro season. It is important because of its wide distribution, rapid spread, and destructiveness under a favorable environment. The causal agent of this disease is Pyricularia grisea. This pathogen can cause disease at any stage of the crop, from seedling to maturity. If the variety is susceptible and the environmental conditions are favorable, it can cause complete damage to the crop. However, information on the exact yield losses from this disease is scarce. Rice tungro is one of the most serious and damaging virus diseases in Southeast Asia. Periodic outbreaks have affected thousands of hectares of rice fields in Bangladesh in the past. The incidence and spread of rice tungro disease in the tropics are determined by the dispersal, movement, number, and migration of viruliferous vector insects, such as the green leafhopper (GLH), Nephotettix virescens (Ling 1966). Usually, boro rice in this country is free from tungro incidence compared with other crops, mainly because of cool weather conditions that cause high mortality of vector insects.

Source of Information: Rice Research and Development in the Flood-prone Ecosystem. Proceeding of the international workshop on flood-prone rice systems held in Gazipur, Bangladesh, 9-11 January 2001. International Rice Research Institute. 283 p. P-269279, ISBN 971-22-0197-X

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Disease severity is higher and consequent yield lower in soil deficient in Zn or S (BRRI 1980, 1985). Therefore, correction of the soil deficiency by applying Zn or S helps reduce disease severity. Soil amendment with Ca-silicate and rice husk increased silicon content in the leaf sheath of both resistant and susceptible cultivars and in stems of only resistant cultivars. Ufra infestation decreased because of the increase in silicon content in the leaf sheath. The yield loss from ShB disease was estimated to be up to 31 % under natural disease incidence. Recent studies revealed that the rate of spread of the disease was higher when 10% of the hills were infected at the maximum tillering stage compared with 5%, 20%, and 40% hill infection. Yield loss at 5%, 10%, 20%, and 40% hill infection at the maximum tillering stage was 6.0%,10.2%,19.3%, and 20.9%, respectively. Most of the time, infected grains remain symptomless. In some cases, elliptical lesions are produced on the husk. In rice tungro twisting of young leaves, stunting (slight to severe) of plants depending on the growth stage, reduction in tiller number, delayed flowering or panicle emergence, and degeneration of roots may occur. Infected leaves may also be mottled, the leaf angle may become wider, and the texture of the leaf may become stiff.

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