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  • Author or Editor: Hiroaki Kitazawa x
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Head tightness, soluble solid content (SSC), and rutin level were investigated in asparagus spears harvested at different lengths. We found no correlation between spear length and SSC per dry weight (DW) in spearheads. Spearheads became looser and the rutin content of the spearhead increased as spear length at harvest increased, although appearance quality decreased. These findings revealed that spears previously discarded, because their length did not meet the length specifications, contained abundant rutin. Therefore, spears for which the optimum harvesting time has been missed are a useful rutin source.

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To control asparagus harvest timing, we investigated the effects of short-term low (5%) oxygen (O2) treatment in the cultivation area on asparagus growth and yield using a closed cultivation system. During 120 days of cultivation, low O2 treatments were initiated at 0 to 4, 20 to 24, and 40 to 44 days after planting (DAP). The sprouting spears and control crown yield gradually decreased with increasing DAP. However, low O2 treatment at 0 to 4 DAP significantly delayed the decrease until 80 DAP, although the total yield did not change during cultivation. In contrast, low O2 treatments at 20 to 24 and 40 to 44 DAP did not affect yield performance. Taken together, short-term low O2 treatment immediately after planting can change the harvest timing of white asparagus and can be used for effective asparagus culturing in a closed system, such as a plant factory.

Open Access

Autotoxicity in some ornamentals was investigated. The plants were grown by hydroponics with or without the addition of activated charcoal (AC) to the nutrient solution. The AC was used to trap the exuded organics from roots. Among the 37 plants under study, growth of lily, prairie gentian, corn poppy, farewell-to-spring, rocket larkspur, and carnation was drastically reduced in the absence of AC compared with those in the presence of AC in the nutrient solution. Root exudates of some plants were analyzed and several organic compounds were detected. The strong growth inhibitors such as lactic acid in pot marigold, benzoic and p-hydroxybenzoic acid in lily, o-hydroxyphenylacetic acid in rocket larkspur, benzoic and p-hydroxybenzoic acid in sweet pea, and maleic and benzoic acid in prairie gentian were detected in the root exudates. The reduced growth of prairie gentian after prolonged cultivation in a field might be avoided by amending the soil with AC at a rate of 60 kg·10a−1.

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Root exudates from strawberry plants are known to cause autotoxicity and benzoic acid (BA), a potent growth inhibitor, was found in the exudate. BA (400 μm) was easily decomposed by electrodegradation (ED) treatment at 10.0 V and 2.0 A after the addition of BA into nutrient solution. The growth of strawberry plantlets in nutrient solution containing BA (400 μm) or in control nutrient solution varied significantly depending on the use of ED treatment. The growth inhibition of plantlets in the BA-containing nutrient solution or in nutrient solution used for strawberry culture was significantly ameliorated by ED treatment. This growth recovery resulting from ED treatment was most pronounced in terms of the yield of strawberry fruit. These results suggest that ED treatment of the culture nutrient solution could result in the decomposition of toxic root exudates, including BA from strawberry plants, and mitigates the autotoxicity observed in closed hydroponic culture. In addition, the supplementation of Fe-EDTA is recommended after ED treatment as a result of the rapid decomposition of Fe-EDTA by ED.

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