Effect of water deficit stress on proline contents, soluble sugars, chlorophyll and grain yield of sunflower (Helianthus annuus L.) hybrids
The objective of the present work was to determine the mechanisms of tolerance of four sunflower hybrids; H1 = Azargol, H2 = Alstar, H3 = Hysun 33 and H4 = Hysun 25 to water stress under three different levels of irrigation regimes; WD1 = irrigation after 50 mm (normal irrigation), WD2 = 100 mm (mild stress) and WD3 = 150 mm (intense stress) cumulative evaporation from evaporation pan class A. The results showed that water deficit stress significantly (P≤0.01) increased proline, soluble sugars and chlorophyll b but decreased chlorophyll a, total chlorophyll and grain yield in all sunflower hybrids; therefore increase of the proline, soluble sugar, chlorophyll b and decrease of the chlorophyll a, total chlorophyll and grain yield occurred when water input decreased. Although, at different level of water stress, each hybrid behaved differently according to their genetic makeup. Alstar hybrid exhibited the highest value for all the mentioned characteristics, except for soluble sugars. Under both mild and intense water deficit stress conditions, the highest value of proline, soluble sugars, chlorophyll a and chlorophyll b were recorded in Alster, Azargol, Hysun 33 and Alstar hybrids, respectively. Also, the highest value of total chlorophyll in both mild and intense water deficit stress conditions was acquired by Hysun33 and Alstar, respectively. The results also indicated that under normal irrigation, mild and intense water deficit stress, maximum grain yield was obtained in Azargol (3448 kg ha-1), Alstar (2121 kg ha-1) and Alstar (829 kg ha-1), respectively. Therefore, among all of sunflower hybrids, Alstar hybrid under both levels of water deficit stress had the best tolerance to water deficiency stress.
Key words: Proline, soluble sugars, chlorophyll, grain yield, sunflower.