Effect of Water Deficit Stress on Growth, Yield and Aloin Concentration of Aloe vera L. at different harvesting dates

Abstract
Background and objectives: Aloe vera is one of the most economically important medicinal plants in many countries which used in food, cosmetics and pharmaceutical industries; it is widely cultivated throughout the arid and semi-arid regions. Therefore, the current study was aimed to evaluate the effects of different water stress on growth, yield and aloin concentration during plant growth stages.
Materials and methods: This study was conducted in research greenhouse of Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. The experimental design was a randomized complete block design with a split plot in time arrangement of treatments in four replicates. Treatments including water deficit stress (irrigation after depleting of 20%, 40%, 60% and 80% field capacity (FC)) and harvesting dates ( 90, 180 and 270 days after imposing the irrigation treatments). Irrigation treatments and harvesting dates were considered as main- and sub-plots, respectively. Growth changes, yield and aloin concentration were evaluated during growing period.
Results: The results demonstrated that the growth and yield values decreased with increasing water stress severity. Generally, the highest number, width and thickness of leaf were observed when the plants were irrigated at 20% FC, which was higher increased by 19, 22 and 16%, respectively compared with irrigation after depleting 80% of the field capacity, respectively. Irrigation at 40% FC increased plant height and leaf length by 16% and 21%, respectively, compared with the irrigation at 80% FC. The highest leaf and gel fresh weight were observed in 270 days after imposing the irrigation at 40% FC which increased by 44 and 49% compared with irrigation at 80% FC. Results also showed that the pup number decreased with increasing water stress, the maximum pup number was observed when plants were irrigated at 40% FC at 90 days after imposing the irrigation treatments. aloin concentration and Total Soluble Solids (TSS) increased in Aloe vera plants under severe water stress. The highest aloin and TSS content was observed when the plants were irrigated at 80% FC at 90 and 270 days after imposing the irrigation treatments, respectively.
Conclusion: In general, severe water stress decreased leaf yield and plant growth while caused a significant increase in aloin concentration and TSS. Finally, irrigation after depleting of 40% of soil water content was the best treatment for growth and yield, also depleting of 80% of soil water content was the best treatment for aloin and TSS during all growth period.
Keywords: Aloe vera, Growth, Field capacity, Yield, Harvest date