Impact of Jasmonic Acid on Radiation Use Efficiency and Dry Biomasses of Sugar Beet (Beta vulgaris L.) under Water Deficit Conditions

Drought stress is a major limitating factor on crop production and plant distribution worldwide. Reduction of RUE, water stress also affects foliage expansion and eventually radiation capture. Water stress almost decreases fresh root weight. Sugar beet (Beta vulgaris L.) is an important commercial crop that supplies approximately 30% of the world’s sugar. Research has showed reduction in the leaf area and a smaller decrease in the taproot growth of sugar beet when subjected to drought stress. Phytohormones are part of signaling pathways or their presence may stimulate signaling reactions molecules that are responsible for plants to response stresses. Exogenously applied jasmonates elicit several different physiological responses to stress and therefore increase plant resistance. For instance, MeJA was reported to improve resistance against drought in rice. This research was carried out in 2015 in the research field station of Shahrekord University, Shahrekord, Iran (50051/N, 32019/E and 2050 m a.s.l). A field experiment was conducted as split-plot arrangement in a randomized completely block design with three replications on sugar beet (Monogerm Castille seed). The main plot included three irrigation treatments 100% (control), 75% and 50% of water requirement and the sub plot included 3 levels of jasmonic acid applied sprayed with water (control), 5 and 10 µM jasmonic acid. Foliar spray was done at 6-8, 12-16 and 20-24 leaf stages. Plants were grown under full irrigation until the 16-20 leaf stage, when water stress was applied. The result showed that light absorption percent and extinction coefficient were significantly affected by irrigation level, jasmonic acid applications and their interactions. The interaction between drought level and jasmonic acid application showed the highest increase in light absorption percent (73.07) and extinction coefficient (0.58) were recorded in 100% of water requirement and 10 µM jasmonic acid application. Drought levels led to decrease of radiation use efficiency. Jasmonic acid increased radiation use efficiency. In terms of the trend of the leaf area index, dry matter accumulation of shoot and root had the highest in 100% of water requirement and application 10 µM jasmonic acid. The improvement of leaf characters of sugar beet by jasmonic acid of treatment may be due to the fact that jasmonate antagonistically regulates the expression of stress inducible proteins, associated with drought stress in rice. With the increase in leaf area index, dry matter accumulation increased. Jasmonic acid improved sugar beet growth under drought stress by inducing plants to increase organic osmoprotectants. JA spray could be adopted as a potential growth regulator or antioxidant to improve growth under water deficit stress on sugar beet.