The rehabilitation or intensified use of lmperata grasslands will require a much better understanding of their area, distribution, and characteristics. We generated estimates of the area of Imperata grasslands in tropical Asia, and suggested a typology of Imperata grasslands that may be useful to define the pathways toward appropriate land use intensification. We conclude that the area of lmperata grasslands in Asia is about 35 million ha. This is about 4% of the total land area. The countries with the largest area of Imperata grasslands are Indonesia (8.5 million ha) and India (8.0 million ha). Those with the largest proportion of their surface area covered with Imperata are Sri Lanka (23%), the Philippines (17%), and Vietnam (9%). Laos, Thailand, Myanmar, and Bangladesh evidently all have similar proportions of their land area infested with lmperata (about 3 to 4%). Malaysia (< 1%), Cambodia (1%), and the southern part of China (2%) have but a minor proportion of their total land area in lmperata. The species was found widely distributed on the full range of soil orders. It occupied both fertile (e.g. some of the Inceptisols and Andisols) and infertile soils (Ultisols and Oxisols) across a wide range of climates and elevations, lmperata lands fall into four mapping scale-related categories: Megagrasslands, macro-grasslands, meso-grasslands, and micro-grasslands. The mega-grasslands are often referred to as 'sheet lmperata'. They are the large contiguous areas of Imperata that would appear on small-scale maps of say 1:1,000,000. We propose that this basic typology be supplemented with a number of additional components that have a key influence on intensification pathways: land quality, market access, and the source of power for tillage. The typology was applied in a case study of Indonesian villages in the vicinity of lmperata grasslands. We propose an international initiative to map and derive a more complete and uniform picture of the area of the Imperata grasslands. This should include selected studies to understand conditions at the local level. These are critical to build the appreciation of change agents for the indigenous systems of resource exploitation, and how they relate to local needs, values, and constraints.

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The release of an insect pest-resistant variety and subsequent adaptation of the insect species to that variety through the process of biotype selection has occurred on many cultivated crops. The present study was designed to obtain detailed information on some of the processes involved in the selection of biotypes of Nilaparvata lugens (Stål) on two rice varieties with different major genes for resistance. The N. lugens population selected for the study, which had originally been collected in the field and reared on a susceptible variety for 12 years (ca. 140 generations), initially had a low survival on the resistant rice varieties Mudgo (Bph 1 gene) and ASD7 (bph 2 gene) and high survival on the susceptible variety, Taichung Native 1 (TN1). Monitoring the survival and length of the developmental period for seven generations indicated a progressive increase in the survival and shortening of the nymphal period in each generation on the heretofore resistant varieties until they were similar to those on TN1. The shift in the population to a more virulent biotype was also confirmed by the seedling bulk test. The selected populations reared on Mudgo or ASD7 were not able to kill Mudgo or ASD7, respectively, in the fifth generation but by the eighth generation were able to do so. In addition, adult longevity and fecundity on the resistant varieties increased during the selection process. Nilaparvata lugens (Stål) is one of the major insect pests of rice and has had a distinct economic effect on rice production in many Asian countries (Dyck and Thomas 1979). It is a monophagous pest, limited to feeding on Oryza sativa and wild rice species. The epidemic of outbreaks of N. lugens in 1972, 1973, and 1974 in several Asian countries including the Philippines stimulated rice scientists to accelerate the development of rice varieties resistant to this pest. Genetic analysis of several rice varieties resulted in identification of two

As the resistance of rice varieties to the brown planthopper is based on major genes it has been widely assumed that there is a gene for gene correspondence between resistance on the part of the plant and virulence on the part of the hopper. However, the mode of inheritance and response of the biotypes to selection. together with the previously reported wide variation within each “biotype” and large overlap between them in virulence, is all consistent with polygenic determination of virulence. RÉSUMÉ LA GÉNÉTIQUE DES “BIOTYPES” DE NILAPARVATA LUGENS Comme la resistance des variétés de riz à N. lugens est due à des gènes majeurs, on considere généralement qu'il y a une correspondance gène à gène entre la résistance de la plante et la virulence de l'insête. Cependant, le type d'héritabilité et la réponse des biotypes à la sélection, ainsi que la grande variabilité antérieurement signalée dans chaque biotype et l'important chevauchement de leur virulence, sont tous conformes à une détermination polygénique de la virulence.

The present study was conducted to know the smallholder pig production system in tribal areas of Sikkim State, India. Two hundred tribal farmers were selected randomly from the North and East District of the state. Information on socio-economic characteristics of farmers (gender, occupation, educational status, and farming experience), management practices, disease prevalence, and economics in pig production was collected. The study recorded the mean land holding as 1.2 ± 0.8 ha, and the number of pigs per farm was 5.0 ± 0.28. Pigs were mainly kept as a source of income, and 70 % of farmers reared crossbreed pigs. Ninety percent (90 %) of respondents practiced the intensive system of management whereby kitchen wastes along with cooked mixture comprising maize bhusa, mustard oil cake, pseudostem of banana, tuber, stem, and plant leaves were used to feed their animals. About 40.5 % of farmers procured their breeding stock from government farms that had good records and utilized veterinary services like timely vaccination and deworming. The diseases prevalent in the study area were swine fever, diarrhea, helminthoses, sarcoptic mange, pneumonia, etc. The litter sizes at birth (local, 4.3 ± 0.45; crossbreed, 7.2 ± 0.33), at weaning (local, 2.79 ± 0.24; crossbreed, 6.1 ± 0.21), and age at first farrowing (local, 365.39 ± 7.96 days; crossbreed, 337.24 ± 8.79 days) were recorded. Production costs of meat extracted from local and crossbred pigs were 1.08 $/kg and 0.86 $/kg, respectively.

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Effect of rapeseed drying temperature on oil quality was investigated over the range 50-250°C. Total oil content was not significantly affected at 5% probability. Amounts of free fatty acids were significantly affected but remained much below the maximum permissible limit. Oil color was also significantly affected but had no specific trend of variation with temperature, and visual differentiation was difficult. Further, visual cracks and blackening were observed in rapeseeds dried at 250°C. Based on this study, elevated drying temperature up to 200°C was recommended for rapeseed without adversely affecting oil quality. This would save up to 80% drying time compared to the present practice of drying rapeseed at a maximum temperature of 93°C.

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