The effect of interval irrigation and growth regulators on some morphophysiological traits of cotton (Gossypium hirsutum L) cultivars

To study the effect of interval irrigation and growth regulators on morphophysiological traits of cotton cultivars, an experiment was conducted as a split factorial in randomized complete block design in 2017 and 2018 in Hashemabad Cotton Research Station in Gorgan, Iran. Treatments consisted of intervals of irrigation at two levels (two weeks and four weeks) as the main factor and six-level growth regulator treatments (control, benzyl adenine, abscisic acid, salicylic acid, brassinosteroid, and cycocel) and three cotton cultivars (Golestan, Kashmar, and Shayan) were also considered as sub-factors. The results of this study showed that proline content and relative water content of leaf decreased with water deficit stress. Maximum proline content (3.55 µg/g fresh weight) was obtained from Shayan cultivar with salicylic acid. Benzyl adenine and brassinosteroids increased relative leaf water content. The highest cell membrane stability (2.998%) was observed in Kashmar cotton cultivar and two-week interval irrigation, and Cycocel increased the membrane stability by 15%. Plant height, number of flowers, and number of bolls were affected by growth regulators, irrigation intervals, and cultivars. With increasing irrigation period, plant height, flower number, and boll number decreased in all cultivars, but under drought stress, Golestan cultivar had more flowers and boll number than other cultivars. Cycocel, salicylic acid, and brassinosteroids significantly increased flowering of cultivars at both years and both irrigation intervals. Benzyl adenine and brassinosteroids increased plant height more than 7% and abscisic acid, cycocel, and salicylic acid decreased plant height compared with control. Application of abscisic acid reduced the number of bolls by 22% compared with the control. Overall, growth regulators, especially cycocel and salicylic acid, increased the morphophysiological traits of cotton cultivars indicating their positive effect on drought tolerance and it could play a role in moderating stress effects under stress conditions.