BACKGROUND: The use of plant growth regulators is a agronomic strategy that researchers are interested in to compensate or moderate the negative effect of environmental stress. One of the most important physiological effects of these factors is increasing the tolerance of plants to environmental stresses.OBJECTIVES: This research was conducted with the aim of investigating the effect of delay in planting on leaf area index and seed growth process and yield formation of three wheat cultivars and how these cultivars respond to paclobutrazol consumption.METHODS: Current research was done in two cropping years 2020-21 and 2021-22 in a farm located in Izeh city, in the northeast of Khuzestan province. It was implemented as a split factorial in the form of randomized complete block design (RCBD) with three replications. The main factor included planting date (November 16, December 11, and January 5) and the secondary factor factorially included bread wheat cultivars (Karim, Mehregan, and Chamran 2) and the use of paclobutrazol (0, 60, 120 mg.lit-1).RESULT: The results showed that with the application of paclobutrazol, the length of the filling period and seed yield increased significantly. The leaf area index increased up to the application of 60 mg.lit-1, but the seed filling rate was not affected by the application of paclobutrazol. The highest seed filling period was observed on the sowing date of November 16 (21 days) and the lowest on the sowing date of January 5 (19 days). With delay in planting, the duration of seed filling period decreased. On the planting dates of November 16 and December 11, the use of 60 mg.lit-1 of paclobutrazol and on the delayed planting date of January 5, the use of 120 mg.lit-1 of paclobutrazol led to an increase in seed yield compared to the conditions of not using paclobutrazol. The effect of using paclobutrazol on seed yield is positive, and by increasing the use of paclobutrazol (120 mg.lit-1), it moderates the negative effects caused by the delay in planting.CONCLUSION: With the application of 60 mg.lit-1 of paclobutrazol, the seed yield of Chamran 2 cultivar was higher on the two planting dates of November 16 (6940.85 kg.ha-1) and December 11 (6779.47 kg.ha-1) compared to other treatment levels. Manuscript profile