In Japan, white asparagus spears are grown using two blanching methods to block sunlight: the traditional soilmound and the film-cover methods. The objective of this study was to investigate the influence of the film-cover and soil-mound methods on components of white asparagus spears related to flavor, especially sweetness and bitterness. We investigated the effects of the two blanching methods on sugar (fructose, glucose, and sucrose) and protodioscin (a major furostanol saponin in white spears) contents in white spears by conducting a spring field survey and an experiment using winter-forcing cultures. No significant differences were observed in sugar content or composition in spears cultivated by the two methods in either the field survey or the experiment. Protodioscin content tended to be higher in spears blanched by the soil-mound method than in spears blanched by the filmcover method in both the field survey and the experiment. These results suggest that differences in the flavor of white spears grown using the two blanching methods are caused mainly by bitterness associated with saponin content, and saponin content may be influenced by soil-borne stresses.

The objective of this study was to clarify the factors that influence saponin biosynthesis, with an emphasis on protodioscin, a major saponin compound in white asparagus spears. We investigated the effects of methyl jasmonate (MeJM) treatment on protodioscin content in white spears harvested by spring semi-forced and winterforced cultivation. Protodioscin content was determined using high performance liquid chromatography equipped with an evaporative light scattering detector. Protodioscin was mainly localized in the lower region of the spears. In the spring semi-forced cultivation system using the film-cover method, the protodioscin content in white spears harvested from the MeJM plot was significantly higher than in those harvested from the control plot throughout the sampling period. MeJM also significantly enhanced protodioscin biosynthesis in a dose-dependent manner in the experiment conducted under winter-forced cultivation. These results suggest that saponin biosynthesis in white spears is associated with plant defensive reactions triggered by jasmonate. In addition, bitterness in filmcovered white spears could be artificially controlled in commercial fields by MeJM treatment.

To facilitate the production of white asparagus (Asparagus officinalis L.) spears in winter, we studied spear blanching in rootstock planting forcing culture. A strong correlation was observed between the fresh weight of one-year-old rootstocks and their yields. Light conditions during the harvesting time had little influence on the yield, but, they influenced anthocyanin pigmentation in the spear. When asparagus spears were harvested under darkness maintained by an opaque film covering, anthocyanin pigments in the spears disappeared. There were differences between cultivar yields; these were caused by the differences in the extent of chilling exposure, which is necessary for each cultivar to break the dormancy of its rootstock. These results suggested that white asparagus spears can be produced with no anthocyanin pigment in forcing culture by using oneyear-old rootstocks of cultivars with a low level of dormancy ('UC-157 F 1 ', 'GrandeF 1 '), if spears are harvested under dark conditions maintained by opaque film covering.Key Words：anthocyanin, dormancy, light condition, opaque film covering

This study produced white asparagus (Asparagus officinalis L.) spears by covering plants with a shading film during semiforcing spring harvest cultivations of asparagus. White asparagus spears with no anthocyanin pigment were produced in plastic houses, when a 2.0 m-highwalk-in tunnel covered with a shading film was set up in the houses before the spears sprouted. The number of marketable white spears was smaller than that of marketable green spears. However, the weight of white spears was greater than that of green spears. Consequently, there was no difference between white and green asparagus production with regard to marketable yield. The characteristics of white asparagus spears produced in plastic houses with a shading film covering differed from those of green spears. Their tips were tighter and mid-section diameters were greater. Further, white asparagus spears that had been boiled for 10 minutes tended to be tougher than similarly treated green spears. Key Words：characteristics

To clarify the differences between white asparagus (Asparagus officinalis L.) spears produced by two different blanching methods, the soil-mound method and film-cover method, the external appearance and hardness of spears were examined in forcing culture with two-year-old rootstocks. The blanching method had an obvious influence on the color and tightness of the spear tip. Color in the portion 2 cm below the spear tip was more yellowish in the film-cover method than in the soil-mound method. The spear tips tended to be tighter in the soilmound method than in the film-cover method. These results suggest that both the spear tip color and tightness might be striking visible features to help us discriminate between the two blanching methods. Spears produced by the soil-mound method were greater in diameter in the upper (4 cm from tip) and middle (10.5 cm from tip) portions, and heavier by weight than those by the film-cover method. Spears boiled for 10 minutes from the soilmound method were significantly tougher in the upper (4 cm from tip) and middle (10.5 cm from tip) sections than those from the film-cover. Therefore, the blanching method was thought to affect spear hardness, which is closely associated with eating and cooking quality.