Search for the Conditions of Hot Air Treatment to Inhibit Root and Sprout Growth of Garlic Bulbs after Subzero Storage

Garlic bulbs are stored at about −2°C for year-round shipping. After storage, the bulbs start to develop roots and sprouts, which lowers their commercial value. The conventional hot air treatment to inhibit the growth of roots and sprouts after the storage, which aims to keep the temperature inside bulbs at 48°C for 6 h, sometimes causes heat injury. Here, we searched for a more favorable condition of hot air treatment for practical use. Bulbs that had been stored at −2°C from August for various periods were then treated at 40–50°C for 4–48 h in 26 temperature-duration combinations, and then kept at 15°C for 4 weeks. In the bulbs stored until October, 5 temperature-duration combinations inhibited root growth, and 3 combinations inhibited sprout growth. On the other hand, in those stored until April, all combinations inhibited root growth, and 15 combinations inhibited sprout growth. An increase in the duration of treatment intensified the inhibitory effect in many cases, but a higher treatment temperature often did not. Treatment at 40–44°C given in December inhibited root growth more intensely than that at 46–48°C. The effectiveness of hot air treatment at 48°C for 8 h (an equivalent to the conventional treatment) and that at 41°C for 12–48 h given to the bulbs removed from the storage periodically from September to June was compared. Treatment at 41°C for 12–48 h inhibited root growth more effectively than that at 48°C for most of these 10 months. Treatments at 41°C for 48 h and at 48°C were sometimes injurious, while treatment at 41°C for 12–24 h caused no injury. These results indicate that hot air treatment at 41°C is markedly effective and safe, and is more practical than conventional treatment.