In order to determine cold requirements for flower induction (vernalization), the adult bulbs of Ghermez Azarshahr and Sefid Qom onion cultivars were studied in four time periods (two, four, six and eight weeks) and three temperatures (5, 10 and 15 °C) in a factorial experiment based on a completely randomized design with three replicates. Scaning electron microscope (SEM) was used to determine swelling of reproductive meristem (meristem dome) after applying the treatments. Also, the temporal expression patterns of flowering integrator gene (AcFT2) were analyzed in cv; Ghermez Azarshahr, using Real-Time PCR. According to obtained results, the maximum meristem inflation of Sefid Ghom was observed in 10 and 15 °C, while in Ghermez Azarshahr at 5 °C. Bulbs showed the lowest meristem inflation (30.53%) after 2 weeks of cold storage, and with increasing vernalization time, up to 6 weeks, the meristem inflation (75.35%) increased. The highest relative expression of AcFT2 was observed in the Ghermez Azarshahr after 6 weeks of cold storage at 5 °C, which coincides with meristem inflation results. Ultimately, the best vernalization condition were determined as 6 weeks cold storage at 10 ° or 15 °C for Sefid Ghom and 5 °C for Ghermez Azarshahr.

Introduction

Planting onion sets instead of seeds or seedlings in situations where factors such as physical and chemical quality of soil and water are very limiting, is the safest planting method to achieve maximum plant establishment in the ground. In order to determine the appropriate planting date and density (in the treasury), storage conditions of bulbs in storage and the response of cultivars belonging to the long day type to this method of onion production, the present plan was implemented to optimize the conditions of production and storage of anions. Appropriate means, it is possible to compare the agricultural problems of this production method with common methods such as direct seeding and planting seedlings in the present study.

In order to determine the optimazation of dry onion sets production and to examine the storage capacity of produced dryonion sets, a field experiment was carried out in Kabutar Abad Research Station in Isfahan during 2015-2016 in a split- split plot experiment based on RCBD with three replication.The effects of nursery planting date (30 March, 30 April, 30 May), plant density (15 and 30 g m-2) and variety (Dorche, White Kashan and Sweet spanish) on dry onion sets pruduction in long day condition, this experiment. In a separate experiment, three planting date (9 May, 9 June and 10 July) and two plant density (15 and 30 g m-2) in a short variaty was examinated. Also, in order to investigate the possibility of using heat treatment to reduce or stop bolting, another experiment was conducted in a completely randomized design with three replications for the three cultivars. In each repetition, 400 anions (randomly with a size of 10 to 20 mm) are distributed in plastic nets and in a warehouse whose temperature is supplied by a gas heater and between 28 and 32°C was, for a period of two months (from February 10 to April 10) and the number of surviving onion sets was calculated after removing those that were rotten, green and hollow. Experimental data were analyzed by SAS software version 9.4 and the means were compared based on Duncan's multiple range test.

According to the results, the best planting date was 30 April by the mean 616 onion sets pruduction for all three variety in long day types and 9 may by the mean 311 inion sets in short day types and the effect of seed weight (15 and 30 g m-2) was nonsignificant. In two separate experiments, storability of onion sets was examinated in ambient storage (6-28 °C) after 118 days and warm storage (> 30 °C) after 60 days. The cause of this phenomenon can be traced to the reaction of the onion plant to the length of the day, so that the cultivar in question, due to its short day, in the face of long and hot days, without being able to develop and produce enough leaves, enters the production stage. They are fried and of course their size will be very small. Results indicated that 84%, 64% and 61% of onion sets survied in the first condition for three population (Dorche, kashan and Sweet Spanish). What was evident in this experiment was that most of the surviving onion sets were those who had completed the maturation process in the field, and conversely, the higher storage losses were in those that had leaves and leaves at harvest. Growth has been observed. Such a phenomenon was also observed in edible bulbs, so that bulbs with thick necks and green leaves are more susceptible to the entry and establishment of pathogens during storage during harvest. An observational estimate in this experiment indicates that the percentage of green onion sets is not more than normal storage and the main losses are due to depletion and water loss. As reported in the storage of edible onions, very high temperatures (about 38 °C) and very low temperatures (about 0 °C) both prevent flowering and sprouting of bulbs.

Based on the results obtained from the four experiments, in the first planting date, due to the existence of sufficient time (from emergence to harvest) and coincidence of leaf production with favorable environmental conditions (high temperature and long day length), a larger share of total yield to shoots Coarse was allocated and as a result the number of onion sets was reduced. Finally, they did not enter the phase of coagulation and anion production. In summary, spring sowing of long-day onion cultivars by onion sets with a treasury date of 10 May and a seed density of 15 g m-2 is recommended.