Maleic hydrazide residues in the onion bulbs induce dormancy and hamper sprouting for long periods

Sprouting of stored onions in Serbia is not a great problem until the beginning of April following the year of harvest. For longer terms of storage growth regulators such as maleic hydrazide (MH) have been used commercially to increase the storage life of onions. In this work, we investigated the effect of foliar application of MH (Royal MH-30) at 8 litres ha(-1) (MH1) and 12 litres ha(-1) (MH2) and harvest in three intervals (one, two and three weeks) after MH application on prolonged onion storage. Use of MH should be combined with selection of a good keeping local Serbian variety ('Kupusinski jabucar' +/- 14% D.M.). After harvest onions bulbs were stored at 0-1 degrees C in cooling room and shallow layers in an open-ventilated storage under ambient conditions, during 6 months. MH residues in the bulbs immediately after harvest depend of time of application and doses of MH. The maleic hydrazide was analyzed by HPLC with UV detection of 313 nm. The detection limits of MH was 0.4 mu g.ml(-1), and the quantification limit was 1.25 mu g.ml(-1). The highest content of MH (7.10 mg.kg(-1)) was recorded with 12 litres ha(-1) Royal MH-30 with harvest at II week after application. The lowest content of MH (3.09 mg.kg(-1)) with 8 litres ha(-1) Royal MH-30 in harvest at I week after application. The determined maleic hydrazide residues after 7, 14 and 21 clays after the treatment were below the maximum amounts permitted in Serbia (10 mg.kg(-1)) and in the EU (15 mg.kg(-1)). Of three harvest dates, MH sprays made second and third weeks before harvesting were effective in prolonging the storage life of onion bulbs. These results indicate that preharvest application of MH and storage at 0-1 degrees C significantly improved the storability of bulbs onion.