IMPACT OF BAMBOO DISEASES ON THE ECONOMY

The relative importance of different diseases affecting bamboos in the region is difficult to assess because of the general lack of information accompanying the disease records. Similarly, lack of quantitative data on the extent of damage caused to the bamboo stands makes it onerous to evaluate the economic losses resulting from diseases. However, the overall impression is that the impact on economy is limited for most diseases.

A large number of foliage diseases -- leaf spots, leaf blight, leaf rust, etc. -- of bamboos have been recorded. In general, however, these cause comparatively less damage to bamboo stands than culm diseases.

Diseases affecting the emerging and growing culms are much more serious as they cause extensive damage to bamboo stands. Rot of emerging culms -- reported in various bamboo species from Bangladesh, China, India, Pakistan, the Philippines and Thailand -- appears to be one reason for the large-scale reduction in culm production. In India, the disease is widespread in natural bamboo stands as well as in bamboo plantations in the southern states. Severe infection and large-scale mortality of emerging culms were recorded in bamboo stands in high-rainfall areas in Kerala state. About 34% mortality of emerging culms was recorded in Bambusa bambos natural stands in different locations in Wynad Forest Division of Kerala during 1988-91. In bamboo plantations, mortality of emerging culms ranged from 5.5% to 25.5% during the same period. Usually, very high incidence of disease and mortality occurs in emerging culms of 15-30 cm height. Higher

economic losses have been reported in unmanaged natural stands than in plantations.

Rot of growing culms reported from China and India is another potentially serious disease affecting culm production. In India, the disease has been recorded in different species of bamboos grown in Kerala state, its incidence in different localities varying from 3% to 25% during 1987-91. Young (2-4 years old) clumps of

B. bambos, Dendrocalamus longispathus and D. strictus were found to be the worst affected. The disease
lowers the quality as well as the quantity of the
culms produced.
Bamboo blight, perhaps the most dreaded disease, has been reported as affecting village groves of B. bambos, B. balcooa, B. tulda and B. vulgaris throughout Bangladesh, and B. nutans in the coastal areas of Orissa state in India. In Bangladesh, the disease was first recorded in 1970 as a potentially serious problem of village bamboos. Losses from the disease have been highest in B. vulgaris and the Jawa/Kata Jali variety of B. tulda. From 3% to 66% clump infection has been reported in different localities such as Chittagong, Comilla, Dhaka and Rajshahi. Although the disease severely affects the bamboos in village groves and the village farmers in the affected areas experience considerable setbacks, the available data are not adequate to make an overall assessment of the economic losses or of the impact on culm production.

In India, large-scale mortality of B. nutans owing to blight occurred in 1988 in the coastal areas of Ganjam, Puri and Cuttack in Orissa, causing considerable damage to the village economy. Villagers in these areas earn Rs 3 000 to 5 000 annually from sale of culms in their groves. The infection was so widespread and severe that it threatened to damage all the groves, each

consisting of 50-100 clumps, within a period of 2-3 years. The disease soon reached an epidemic proportion, and about 55-67% of the clumps in Cuttack and Puri Districts were affected. At present, the disease is spreading fast, forcing the desperate village farmers to altogether abandon bamboo cultivation.

Culm brown rot is another disease that affects growing bamboo culms, mainly those of Phyllostachys viridis and P. viridis f. hauzeauana. It was first recorded in 1974 in Nanjing, China, and is at present widespread among Phyllostachys stands in Jiangsu and Zhejiang provinces. Disease incidence in different areas ranged from 9% to 17% during 1974-79, with an annual average of 10% culm mortality.

Top blight (also known as withered tip disease or die-back), which occurs in P. edulis and P. heterocycla stands in China, is another serious disease. It affects the culms of current season, and is widespread in Jiangsu, Zhejiang, Anhui, Jiangxi, Fujian and Shanghai provinces. Top blight caused large-scale mortality of bamboos in 1983. The resultant economic losses

were reported to be very high in bamboo stands growing in drought-affected areas and in poor soils with poor growth.
Branch die-back disease is extensive in natural stands and plantations in Kerala, India. Comparatively, the incidence of disease recorded was higher in young (2-3 years old) B. bambos in plantations (14-67%) than in natural stands (2-37%) during 1987-91. The disease has been reported as adversely affecting the establishment of young clumps. However, economic losses resulting from it have not been assessed yet.

Witches'-broom disease reported from China, India, Indonesia, Japan, Taiwan-China and Vietnam is considered a potentially serious disease that affects a

large number of bamboo species in the genera Phyllostachys, Ochlandra, Bambusa, Gigantochloa and Sasa. In China, the disease is widespread in Hunan province, causing 95-100% infection in Phyllostachys stands. Although the disease causes malformation of the culms and affects culm production, data on economic losses are not available from any affected countries. In Kerala, India, the disease is fairly extensive in areas where reed bamboo grows, and 6-15% disease incidence was recorded in different localities during 1988-92. Severe infection leads to the production of thin, wiry shoots. Even though no assessment of economic losses are available, the extensive and systemic nature of the infection is expected to adversely affect culm production and stand productivity of reed bamboos in the near future.

Little leaf disease, caused by a phytoplasma (mycoplasma-like organism), reported from the southern states of India is another critical bamboo disease. Severe infection causes the emerging culms to be stunted and deformed, causing clumps to become bushy. In Kerala, very high incidence (90%) of the disease is reported in dry tracts and sandalwood reserves. A survey during 1988-92 recorded 6% to 12.5% increase in the disease occurrence over the four-year period in different localities of the state. Economic losses caused by the disease are very high in dry

tracts, where the farmers hardly get any culm from their groves.
Bamboo mosaic disease, caused by the bamboo mosaic virus, has been reported as affecting the two major cultivated species in Taiwan-China -- D. latiflorus and B. oldhamii. The disease is widespread in bamboo-growing areas in Taiwan-China, and 70-82% disease incidence has been reported from different localities. The diseased shoots become hard in texture, their

internal tissue gets discoloured, and their edible and canning quality declines markedly. The disease is reported to be spreading fast because of the large-scale use of vegetative propagules for raising plantations. As the disease affects industries based on the export of edible shoots as well as its canning, the economic losses resulting from the disease are very high.

Culm rust caused by Stereostratum corticioides poses a major threat to P. glauca and P. meyeri stands in Jiangsu, Hunan, Zhejiang and Anhui provinces in China. The incidence of rust infection ranged from 30% to 90% in different provinces, and the disease affects the production of edible shoots. Culm rust is reported as causing serious economics losses, and a current major outbreak of the disease in Yangzhong County is destroying about 200 ha of P. glauca.

Culm staining and die-back in B. vulgaris and

D. longispathus stands, reported from the Kerala state of India, acts as a limiting factor for the establishment of clumps in plantations, especially in high-rainfall areas. Although 10% to 98% incidence was recorded during 1980-92, the disease has a patchy distribution and economic loss from it is negligible.
Microorganisms invade bamboo seeds during their different development stages in plant as well as after the seed fall. Seeds are also infected during storage and subsequent handling prior to sowing. Poor quality of seeds in terms of viability and vigour has been the cause of a high degree of failure in nurseries. Few of the seed-borne fungi are also capable of causing seedling diseases in nurseries. Considering the usual flowering and seeding cycle of bamboos, the seeds are so valuable and any losses owing to microbial deterioration is of great concern. Although data on such losses are not available from any of the bamboo-growing countries in the

region, it is evident from some of the disease records that large quantities of bamboo seeds deteriorate at different stages from various microorganisms.

Large quantities of bamboo culms stored in forest depots, mill yards and other storage facilities are decayed and deteriorated by microorganisms. The onslaught on culms is mainly caused by fungi, which include those that cause soft-rot, white-rot, brown-rot and staining. Bacterial degradation of culms also occurs, but is a slow process unlike that caused by fungi. Bamboos used for structural purposes in rural and tribal housing deteriorate within a couple of years, putting heavy pressure on the resource because of the frequent need for replacement. The natural durability of bamboo culms is low and varies from 1 to 36 months, depending on species and environmental conditions. During storage for up to 12 months, 20-25% damage of culms has been reported in India. Decay and deterioration are major problems in bamboo culms stored for making pulp. Decay fungi affect the pulp yield by up to 25% over a storage period of one year, and the pulp strength is reduced by 15-40%. Although data on economic losses owing to culm decay and deterioration are not available, fungal attacks on culms, in general, increase pulping costs because of the increased alkali requirement and higher bleach consumption.

Apart from the infectious diseases, non-infectious diseases -- which are caused by abiotic factors -- also play a major role in limiting culm production. Severe damage caused by glazed frost has been reported from mainland China and Taiwan-China. About 3 800 ha of P. pubescens stands in Qianshan County of Anhui province in China suffered destruction from glazed frost in 1988, causing losses worth 9 million renminbi yuan.