Title of Thesis

Enhancement of drought tolerance in sunflower (Helianthus annuus L.) by exogenous application of abscisic acid

Author(s)

Safdar Hussain

Abstract
Studies to assess the response of spring planted sunflower (Helianthus annuus L.) to exogenous application of abscisic acid following different irrigation schedules were carried out at the Agronomic Research Farm, University of Agriculture, Faisalabad, Pakistan were conducted for two consecutive years; 2008 and 2009. In one experiment, three irrigation schedules viz. four irrigations (25 DAS, bud initiation, flower initiation and achene formation), three irrigations (25 DAS, flower initiation and achene formation) and three irrigations (25 DAS, bud initiation, and achene formation) were subjected to exogenous application of different concentrations (0, 5μm and 10μm) of ABA at bud initiation or at flower initiation. In the 2nd experiment different irrigation and ABA application schedules i.e. four irrigations (25 DAS, at bud initiation, at flower initiation and at achene formation) and no ABA, three irrigations (25 DAS, at flower initiation and at achene formation) and no ABA, three irrigations (25 DAS, at flower initiation and at achene formation) and ABA spray at bud initiation, three irrigations (25 DAS, at bud initiation and at achene formation) and no ABA, three irrigations(25 DAS, at bud initiation and at achene formation) and ABA spray at flower initiation were tested for three hybrids (DK-4040, S-278 and SF-187). The experiments were laid out in randomized complete block design with factorial arrangement and with three replications in each experiment.In the 1st experiment exogenous application of 5μM ABA under drought at bud initiation stage significantly increased plant height, head diameter, number of achenes per head, 1000-achene weight, achene yield and oil yield over no ABA. It also improved water relations of sunflower by improving water potential and turgor pressure and decreased amount of compatible solutes which indicates that exogenous application of ABA was helpful in enhancing drought tolerance in sunflower. Foliar application of 5μM ABA at flower initiation under drought stress at this stage also increased plant height, head diameter, number of achenes per head, 1000-achene weight, achene yield and oil yield over no ABA but this increase was lesser than exogenous application of 5μM ABA at bud initiation after imposition of drought stress at this stage. In the 2nd experiment exogenous application of ABA under drought at either stage (bud or flower initiation) was helpful in ameliorating drought stress in sunflower hybrids; however response was better when ABA was applied at bud initiation than at flower initiation.Sunflower hybrid DK-4040 showed better enhancement of drought tolerance by exogenous application of ABA than SF-187 and S-278 because it showed more improvement in agronomic parameters, growth, quality, water relations and compatible solutes.

1

2.1 Introduction (Sunflower)

3.1 Site and soil
3.2 Experimental details
3.3 Economic analysis
3.4 Statistical analysis

4.1 Experiment-1: Effect of irrigation scheduling and applied abscisic acid concentrations on growth and yield of sunflower (Helianthus annuus L.)
4.2 Experiment-2: Role of exogenous application of abscisic acid towards drought tolerance in different sunflower (Helianthus annuus L.) hybrids

6