Hiroshima Prefectural Technology Research Institute Agricultural Technology Research Center, Higashihiroshima, Hiroshima (Japan)

Allium × wakegi Araki belongs to the genus Allium in the Amaryllidaceae based on APG (Angiosperm Phylogeny Group). It is first filial Fsub(1) generation between A. fistulosum L. and A. cepa L. Aggregatum group as maternal and paternal parents, respectively. Since the plant can not produce seeds because of the sterility of macro- and micro-spores, propagation for commercial production is carried out vegetatively. Production of bulbs is carried out as follows: Bulbs are planted in September, and dug in spring after their growth. The harvested bulbs are stored by hanging under the eaves, and then used for cultivation in the summer, autumn, winter, and in spring, by planting the bulbs from June to December. Allium × wakegi Araki is one of the regional specialties in Hiroshima Prefecture and the amount of the crop production in Hiroshima Prefecture is largest in Japan. The cultivation area, however, tends to decrease year by year, so that improvement of productivity and maintenance of the production area are urgent. In this study, long-day treatments to obtain sufficiently hypertrophied seed bulbs in Chapter 2, cold storage to improve quality of seed bulbs in Chapter 3 and practicality of new method of planting bulbs using a simplified transplanting machine in Chapter 4, were investigated. 【Chapter2】Bulbs were planted from March to May for early summer -harvesting cultivation, so that the plant growth became inferior because of the insufficient bulb hypertrophy. Effects of long-day treatments were, therefore, investigated to obtain hypertrophied seed bulbs of Allium × wakegi Araki for early summer-harvesting cultivation. In the first section, effects of light sources, photosynthesis photon flux density and addition of far-red light in long-day treatment were investigated to obtain hypertrophied seed bulbs. Lighting with the range from 0.5 to 2.7μmol・/square m・/s PPFD by incandescent lamps made bulb hypertrophy index 2.5 similar to the value in conventional production to be planted in October and harvested in May. The addition of far red light to an incandescent lamp could not promote bulb hypertrophy. From these results, the author decided to use an incandescent lamp with low initial investment at present. In the second section, effects of supplemental lighting, night break and period of long-day (16h) treatments were investigated to obtain hypertrophied seed bulbs. Day length of 15-16 hours accelerated bulb hypertrophy, and similar effects were observed by giving 3-4 hour night break treatment, an effective method to reduce the cost of electricity. Long and early long-day treatment increased bulb hypertrophy index, and the effect decreased in the short period treatments. It was concluded that supplemental lighting treatment for 80 days from January 1 is preferred for the high productivity. In the third section, effect of time zone of night break treatment for three hours, equivalent to long day (15 hour day length) treatment, on bulb hypertrophy was investigated in seed bulb production. It was found that bulb hypertrophy was promoted by night break treatment for 3 hours from 9 hours after twilight after sunset, comparing to that at the center of the dark period, and planting the treated bulbs consequently gives vigorous growth. In the fourth section, effects of heating temperature and start of heating on growth and bulb hypertrophy were examined. Higher temperature and earlier heat treatments resulted better growth and more number of bulbs. It is practically preferred that heating should be started before the beginning of December and minimum temperature should be more than 2℃ in consideration of the cost of the fuel oil. 【Chapter3】 Sufficiently hypertrophied bulbs were harvested in June, and stored by hanging under eaves until use for seed bulbs. The quality of seed bulbs often decreases because of drying and softening as the storage period becomes longer. The number of transplantable bulbs consequently reduced drastically at the end of the final planting time for spring-harvesting cultivation, and germination and growth after planting were inferior. Effect of cold storage on the quality of seed bulbs of Allium × wakegi Araki was investigated for improving the seed bulb quality, for spring-harvesting cultivation. In the first section, effect of shading in hanging storage under the eaves on the quality of seed bulbs was investigated. Harvested bulbs were dormant until mid-August, and then increases of respiration rate, consumption and softening of bulbs were observed from early September. Shading during storage, however, suppressed the increase of respiration rate, and also prevented the decrease of the total sugar content of dry bulb in September. The bulb weight and rate of softened bulbs under shading were 10% higher and 20% lower than those in the control, respectively, and shading increased the rate of transplantable bulbs by 20% in the end of the year. In the second section, effects of temperature and humidity on bulb quality and sprouting after planting were investigated as compared with the conventional storage method by hanging under eaves. It was found that the cold storage of the bulbs at 0 or 5℃, humidity 70 to 90% from July reduced bulb deterioration and promoted sprouting. In the third section, effects of cold storage duration and pre-treatment temperature on bulb deterioration and growth after planting were investigated. Cold storage of the bulbs after harvesting inhibited the deterioration of the bulbs. The rate of softened bulbs in the end of December was approximately 45% under conventional storage method, and cold storage of the bulbs at 5℃ from mid-July reduced the value to less than 15%. It is, therefore, preferred that seed bulbs should be stored at 5℃ until the end of October or later, being shorter than 60 days before planting, and they should be pre-treated at uncontrolled temperature afterward. In the fourth section, effect of the operation time of the dehumidifier in pre-cooling chamber was investigated to maintain humidity from 70 to 90 RH% suitable for seed bulbs of Allium × wakegi Araki. The usefulness of a brown rice storage room for Allium × wakegi Araki bulbs was also investigated. The operation time of commercial dehumidifier for 15 to 45 minutes per hour in a pre-cooling chamber was suitable for storing bulbs. In addition, a storage room for brown rice by setting the temperature to 3 to 5℃ and high humidity mode was suitable for storage of bulbs. 【Chapter4】Planting work for Allium × wakegi Araki bulbs is harsh to the body since it is performed manually in a squatting position. The planting density is especially high in summer-harvesting cultivation, and the number of bulbs planted reaches 5000 /a. Reduction of labor and improvement in planting efficiency were attempted. A new method of bulb planting and applicability of simplified transplanting machine were investigated for planting Allium × wakegi Araki bulbs. In the first section, a planting method for Allium × wakegi Araki bulbs using an existing simplified transplanting machine and its practicality were investigated. The method was highly applicable to Allium × wakegi Araki, since the rate of bulbs that can be loaded into the connected paper pot before planting was more than 90% of the seed bulbs. Nevertheless, an existing simplified transplanting machine resulted less uniform planting depth, turned-down bulbs, and tangling the bulbs with the machine. Therefore, these problems were designated as subjects to be resolved for the development of planting machine that was adapted to bulb planting. In the second section, the author has developed a improved simplified planting machine. The new model had been downsized, and was light in comparison to an existing machine. The accuracy of bulb planting by the improved simplified planting machine had been evaluated. The uniformity and precision of planting depth had been significantly increased. In addition, none of the bulbs fell from the connected paper pot and entangled with the machine. These results indicate that the improved simplified planting machine is of practical use. This new simplified planting machine was award a patent and was put to practical use as "bulb-compatible simple transplanter Hippari-Kun HP-12H". In the third section, effects of using the improved simplified planting machine on practicality of workability and productivity were investigated. Improvement of rating of perceived exertion and work posture of laborers were realized with the improved simplified planting machine for Allium × wakegi Araki bulbs. The growth and yield by using the improved simplified planting machine were comparable to the bulbs that were manually planted, so that practicality of the machine has been indicated.