The purpose of the current study was to develop a technique to stabilize the production of seedlings or seed tubers of water yam (Dioscorea alata L.) by using vine cuttings. The effect of the time of collection of the cuttings as scions, application of gibberellic acid (GA) and uniconazol-P (UZP), an inhibitor of GA biosynthesis, to leaves of vine cuttings, on the growth of vine cuttings was investigated. The GA treatments inhibited new shoot formation of vine cuttings,　regardless of the collection time as scions or concentrations of applied GA. On the other hand, shoot and mini-tuber development on the vine cuttings by UZP treatments varied with the collection time as scions. Especially, when cuttings as scions were collected at 130 days after planting, the UZP treatments led to the development of new shoots on the vine cuttings, while shoots were not observed in the control. It was considered that the UZP treatments may reduce endogenous GA synthesis in the scions and promote shoot development. UZP treatments applies to a vine cutting could be effective for the enhancement of shoot formation on vine cutting before rapid tuber enlargement of mother plant.

View full abstract

The Kilombero valley is an inland flood plain located in the southern part of Tanzania. It covers an area of about 11600 km² and is a major rice production area, accounting for about 10 % of all rice produced in Tanzania. There are many types of rice cultivation under various hydrogeological conditions in the Kilombero valley. In this area, rice cultivation on the alluvial fan is very common. This type of rice cultivation depends on rainfall and flood events and farmers use these waters for rice cultivation skillfully. Therefore, the objective of the present study was to elucidate the features of this indigenous rice cultivation, especially water use strategy. The results showed that ridges of paddy field were not built and rice seeds were broadcasted in this type of rice cultivation. Germinated rice plants grew depending on rainfall in fields that were not waterlogged until flooding. The flooding of tributaries occurred occasionally in the late rainy season. In this type of rice cultivation, it was very important that rice plants reach the booting stage during the flood events because rice required a large amount of water at this growth stage. After flooding, rice plants supplied with water headed immediately and ripened using soil moisture toward the dry season. Therefore, the floodwater was remarkably effective for rice growing; and the yield strongly depended on the timing and scale of flooding. In this type of rice cultivation, the cropping systems and selection of rice varieties were determined by flooding. The yield of rice grains was 2 t · ha^-1 in an average year and under good conditions when flooding occurred over a long period of time, the yield of rice grains reached about 4 t · ha^-1.

View full abstract

Pesticide should not threaten the welfare, heath or lives of farmers. Many pesticides that have been banned or severely restricted used in Vietnam where pesticide regulations are often deficient, enforcement of decisions is inconsistent and there is a shortage of trained personnel. Overuse of pesticides is still very common and too many farmers remain unaware of appropriate pest control management. Further, even if farmers can read the pesticide labels, they do not always follow the instructions or use protective clothing, resulting in pesticide exposure and poisonings. It has also been found that poorer farmers apply lesser amounts of pesticides than better-off farmers, but they use more toxic pesticides. In response to these problems, the Vietnamese government was forced to act. There are many new policies and new regulations were promulgated to manage pesticide as well as many national program of training/ education farmer to improve their knowledge on the best use of pesticides.

View full abstract