The antioxidation capacities of green `Welcome', green and white `Gijnlim', and purple `Purple passion' asparagus spears were evaluated. Analyses of rutin and total polyphenols, and assays of DPPH radical absorbing and low-density lipoprotein (LDL) antioxidation were conducted. Varietal differences associated with the colors of spears were observed both in the amounts of rutin, total polyphenols and in DPPH radical absorbing activities, although not in LDL antioxidation activities. DPPH radical absorbing activities seemed to be affected by both rutin and other polyphenolic compounds. However, LDL antioxidation activities were likely to be influenced more by other polyphenolic compounds than by rutin. Total polyphenol content showed a fairly close relationship with rutin content, DPPH radical absorbing activity and LDL antioxidation activity. To determinate total polyphenol content using the Folin–Denis' method seemed to be useful for selecting the breeding lines that show high antioxidative capacities.

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We investigated the variation in rutin and total polyphenol contents in asparagus spears under different conditions of mother-fern culture. Rutin and polyphenol contents were highest at early spring harvest at all test sites. The contents gradually decreased during the harvest season. In particular, a considerable decrease was observed after the growth of mother ferns. The absorption of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical was weaker in summer. Rutin content in the spears of plants grown outdoors was generally higher than in these grown in a greenhouse, except at early spring harvest. Rutin contents decreased in the spears of plants grown under a shading net or an ultraviolet (UV) radiation-filtering film. These results suggest that cultivation conditions, especially light conditions, have a great influence on rutin and polyphenol contents. We evaluated two new methods to increase rutin content by improving light conditions. Light conditions in asparagus rows were improved by using light-reflecting sheets and net screens; however, a significant increase in rutin content was observed only when net screening was used, implying that this method is better than light reflecting sheets to increase the rutin content.

Environmental conditions, specifically heat stress, are important factors in asparagus crop production. Arbuscular mycorrhizal fungi (AMF) have been shown to increase plant growth. Effects of heat stress on nutrient uptake have rarely been examined in intact plants, but the limited results indicate that heat stress will decrease uptake; no studies have examined heat stress effects on asparagus nutrient uptake. We examined the effects of AMF, Glomus intraradices, on the growth, nutrient uptake, heat stress responses, and antioxidative activity in asparagus (Asparagus officinalis L.). We grew AMF-inoculated or non–AMF-inoculated asparagus plants in sand culture at 20 to 25 °C for 14 weeks in a greenhouse and subsequently subjected to three temperature conditions (control = 20 °C/25 °C night/day, mild heating = 30 °C/35 °C night/day, and severe heating = 37 °C/42 °C night/day) in growth chambers. Morphological and physiological growth parameters were compared between AMF-inoculated and non–AMF-inoculated plants. The mycorrhizal symbiosis markedly enhanced biomass production and heat stress responses negatively in plants compared with that in the non–AMF-inoculated plants. Plants grown under non–AMF-inoculated treatment had severe rate of leaf browning (80% to 100%), whereas the mycorrhizal plants showed a minimum rate of leaf browning under heat stress conditions. The results indicated mycorrhizal-inoculated plants showed an increase activity of antioxidative enzymes, such as superoxide dismutase and ascorbate peroxidase. The 2,2-diphenyl-1picrylhydrazyl radical scavenging activity also showed a greater response in mycorrhizal plants than in the control plants under each temperature treatment. Application of AMF enhanced plant growth and mineral nutrients and alleviated heat stress damage through an increased antioxidative activity and the mycorrhizal symbiosis significantly enhanced heat stress tolerance of asparagus.

Replanting of asparagus (Asparagus officinalis L.) often results in lower yields and extensive damage of young plants. One of the causes is considered allelopathy. In this study, we examined the participation of allelopathy on injury by continuous cropping of asparagus in alluvial soil. The presence of strong allelochemical substances, which have the growth-inhibitory activity, was detected by bioassay of rhizosphere soil around asparagus. This growth-inhibitory activity was not attributed to salt accumulation, pH fluctuation, or inorganic nutrient imbalance in the rhizosphere soil. Asparagus foliage incorporated into the soil did not demonstrate a close relation to the growth inhibition or decreased yield of asparagus. However, strong growthinhibitory activity was demonstrated in the storage roots of asparagus. It is assumed that an allelochemical is exuded from the storage roots and is one of the causes of unsuccessful continuous cropping of asparagus.