Effect of High-Temperature Treatments on the Breaking of Dormancy in One-Year-Old Asparagus (Asparagus officinalis L.)

In Japan, asparagus is produced throughout the year, except in November (Benson, 2008), using three cultivation methods: open field, semi-forced mother fern culture, and “Fusekomi” forced culture. “Fusekomi” forced culture is conducted during the winter and the production area for this method is increasing in the northern part of Japan (Jishi et al., 2012). This method was developed during the 1960s in Gunma Prefecture (Gunma Prefecture Vegetable Technology Workshop, 1992). Asparagus seeds are sown from January to February, and seedlings are raised in the nursery until March or April. Seedlings are then planted in open fields. The seedlings are subsequently removed by digging from open fields and planting densely in the greenhouses with a heating system. Spears can be harvested in the winter for two to three months (Koizumi et al., 2002). “Fusekomi” forced culture is different from other methods in that plants are removed in the autumn. Asparagus is a perennial plant that enters a dormant period in the autumn (Hayashi and Hiraoka, 1978; Hayashi and Hiraoka, 1983; Haruyama et al., 1985; Kobayashi and Shinsu, 1990; Yamaguchi, 2012; Koizumi et al., 2013). Thus, it is necessary to break dormancy to begin spear germination in “Fusekomi” forced cultures. To break dormancy, a suitable severity and period of chilling are necessary (Hayashi and Hiraoka, 1983). In Japanese markets, the price of asparagus is relatively higher in December than in January. Therefore, the earlier breaking of dormancy enables earlier digging up and planting, which leads to an earlier harvest and increased income. Therefore, it is very important to maintain chilling temperatures for breaking dormancy in “Fusekomi” forced cultures because this method requires chilling temperatures. Therefore, it is suitable for cold northern areas of Japan such as Tohoku and Hokkaido. However, recent climatic instability, particularly warm autumn temperatures, has reduced yields by delaying the chilling temperature period. Conversely, Hayashi and Hiraoka (1978) have indicated that, even if asparagus is in dormancy, bud breaking occurs at temperatures over 23.0°C (‘California 500W’). Matsubara (1980) also reported that the dormancy of asparagus is broken by high-temperatures. When breaking dormancy by chilling temperature, asparagus germination continues at the assigned temperature following the chilling treatment period. Furthermore, experimental results suggest that germination continues under high-temperature treatments. If the dormancy of asparagus can be broken by high-temperature treatments, then the germination of spears should continue after high-temperature treatments. However, reports did not clarify whether high temperatures actually break dormancy. If the autumn dormancy of asparagus can be broken early using, this breakthrough technique may allow the harvest of asparagus in November with “Fusekomi” forced cultures. Thus, the objective of this study was to clarify the effects of high temperatures on the early breaking of dormancy in asparagus using ‘Welcome’ (Sakata Seed Ltd.,