The Javanese long pepper, Piper retrofractum, has been used as a traditional spice and medicinal plant in the Yaeyama region of Okinawa Prefecture, the westernmost territory of Japan. We examined geographic distribution of P. retrofractum and characteristics of its habitat in Okinawa Prefecture. A broad distribution range of P. retrofractum was confirmed, while the frequency of occurrence varied geographically; i.e., this plant was frequently observed in the southwestern area (Sakishima Islands including Yaeyama region), less frequently found in the northern area (Okinawa Islands), and not found on the eastern area (Daitou Islands). Although P. retrofractum has been regarded as dioecious, plants bearing male spikes were not found in the field, and all plants sampled and grown by cutting bore only female spikes, suggesting male plants do not occur in Okinawa Prefecture. Occurrence of P. retrofractum was restricted almost exclusively to environments developed by humans such as residential areas and farmland; this plant was rarely found in natural vegetation such as forest edges. Vines of P. retrofractum frequently attached to substrates of concrete, mortar, limestone, wood, and trees; other substrates such as metal and synthetic resin were uncommon. When plants were grown for sexing in a glasshouse, infestations of the spider mite Tetranychus okinawanus and unidentified mealybugs repeatedly occurred, suggesting these are potential pests in P. retrofractum cultivation. All of the newly obtained knowledge of P. retrofractum will be useful for future studies on cultivation and cultivar selection of this plant.
To meet the increasing demand of food due to population increase in Egypt, intercropping is expected to increase the yield per unit area. The present study focused on maize- soybean intercropping, and the objective was to investigate the effects on the growth, photosynthesis and yield of the two crops. The cultivation experiments were conducted in Zankalon and Sakha fields in Egypt, and monocultured maize, monocultured soybean and intercropping were compared. The furrow irrigation interval was 10-15 days. Plant length, leaf number, dry weight of the above-ground parts were measured every month, and the photosynthetic rate and SPAD value were determined at the vegetative and reproductive stages. Yield components and LER (Land Equivalent Ratio) were determined after harvest. No differences in the growth of maize between monoculture and intercropping could be detected. However, intercropped soybean grew spindly and showed a decrease in the dry weight, caused by interception of sunlight by the shading of the maize plants. The photosynthetic rates at vegetative stage under monoculcure and intercropping were similar in both fields. On the other hand, since intercropped soybean at the reproductive stage could not adapt to the monoculture light conditions, the photosynthetic rate of intercropped soybean was lower than that of the monocultured crop. Yield of intercropped soybean was about 40%〜60% of that of monocultured crop, while in maize such a difference was not observed. LER of each field ranged from 1.29 to 1.79, showing that intercropping increased the total production per unit land area.