1. Introduction

Persian shallot is an endemic plant species of Iran that has different uses in the food industry and medician. Persian shallot is rich in different secondary metabolites such as flavonoids and organosulfur. In addition to mountains and rangelands, it grows as a weed in many fields and gardens in different regions, especially in the west of Iran. Considering the irregular harvest of Persian shallot from natural habitats, it is very important to study the domestication of this medicinal plant species. Although the numerous benefits of this plant have been proven, however, there isn't enough information about the appropriate agronomic methods such as irrigation, plant density, bulb size, and fertilization in Persian shallot fields.

2. Materials and Methods

In this research, the effect of bulb size and drought stress on morpho-physiological characteristics of Persian shallot has been investigated. The experiment was laid out in a randomized complete block design with a split-plot arrangement. Experimental treatments were four levels of bulb size (small: <5 g, medium: 5-10 g, large: 10-20 g, and very large: 20-30 g) and two levels of irrigation (full irrigation and drought stress). In drought stress treatment irrigation was done at 50% of field capacity and in order to reduce the experimental error, the area of the plots was covered during the spring rainfalls. Selected bulbs were planted in the last week of October with a planting density of 20 plants/m2.





3. Results and Discussion

The results showed that the highest bulb yield (13.2 t/ha) was related to the largest bulbs under irrigation conditions and the lowest bulb yield (0.4 t/ha) was measured for small bulbs under drought stress conditions. As a result of drought stress, the yield of the largest bulbs decreased by 26%. Drought stress reduced the number of produced bulbs (bulblets); however, only for the large bulbs, this negative effect was significant. In this treatment, the average number of bulblets under drought stress condition were 2.3 whereas in full irrigation conditions on average 6.3 bulblets were produced. Bulb size and drought stress have significant effects on stem length and in the very large bulbs as a result of drought stress, the stem length decreased by 47%. The adverse effects of drought stress on yield and growth characteristics of many plants especially in the Alliaceae family are well documented. The most important reasons for these negative effects are the reduction of plant photosynthesis and also the reduction of uptake and transfer of plant nutrients from the soil to plant leaves. In irrigated plots, the highest amount of Chlorophyll a was related to small bulbs, but under drought stress conditions the highest chlorophyll a was measured in the leave of the largest bulbs. As a result of drought stress, the relative water content (RWC) decreased in all of the bulbs. In normal conditions, the bulb size didn’t affect the relative water content (RWC) but under stress conditions, RWC of the larger bulbs was less affected. During the day under drought stress conditions, because the water potential of meristematic tissues decreases significantly, these cells will experience a drop in turgor pressure, which is necessary for the cells to enlarge, and as a result, their growth rate will be limited. With increasing the bulb size and drought stress, protein content increased, however, in different levels of bulb size, there was no significant difference between full irrigation and drought stress treatment. The results of some previous studies have shown that the increase of some biochemical compounds, including proteins, is a natural reaction of the plant to cope with stress conditions.

4. Conclusion

In general, it seems that in drought stress conditions, planting bulbs weighing 10 to 20 g is recommended because, in this weight range, the rate of yield loss per plant was not significant compared to full irrigated conditions.



















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