Journal of Medicinal Plants and By-products (2023) 2: 145-157 https://doi.org/10.22092/jmpb.2021.341798.1182 * Corresponding author: Department of Agronomy and Plant Breeding, Sabzevar Branch, Islamic Azad University, Sabzevar, Iran Email Address: Armin@iaus.ac.ir The Effect of Times and Type of Stress Modulator on Quantitative and Qualitative Yield of Cumin under Rainfed and Irrigated Conditions Feridon Timachi 1 , Mohammad Armin 1* , Matin Jamimoeini 1 and Abbas Abhari 2 1 Department of Agronomy and Plant Breeding, Sabzevar Branch, Islamic Azad University, Sabzevar, Iran 2 Department of Agronomy, Payame Noor University, Tehran, Iran Article History ABSTRACT Received: 02 Feb 2021 Accepted in revised form: 01 December 2021 © 2012 Iranian Society of Medicinal Plants. All rights reserved. Keywords Brassinosteroids Cumin Drought stress Glycine Betaine Sodium Nitroprusside A split-plot factorial experiment was conducted with 3 replications to evaluate the impacts of different type and time applications of stress modulators on the yield and yield components of cumin (Cuminum cyminum L.) under rainfed and irrigated conditions during 2016-2018. The studied factors were the cultivation method at 2 levels (rainfed and irrigated conditions) as the main plot and times of foliar applications with 2 levels (vegetative and vegetative + flowering growth stage) and sources of stress modulators with the 4 levels (control, 1.5 M Glycine Betaine (GB), 10-7 mM Brassinosteroids (BRs), and 1.5 mM Sodium Nitroprusside (SNP)). The results showed that irrigated cultivation led to the productions of higher plant heights, more lateral branches, larger numbers of umbrellas and seeds per plant, greater 1000-seed weights, more grain and essential oil yields, and less essential oil contents as compared to the treatments undergoing the rainfed condition. The lateral branches, umbrellas per plant, seeds per plant, and 1000-seed weights were affected by the application times. The foliar applications of Brassinosteroids (BRs) increased plant heights, lateral branches, umbrellas per plant, seeds per plant, 1000-seed weights, and grain and essential oil yields with less essential oil contents compared to those of the control. Under the irrigated condition, spraying of BRs enhanced plant height (7.64%), lateral branches (3.57%), umbrellas per plant (14.3%), seeds per plant (47.4%), 1000-seed weight (3.69%), and grain yield (74.5%), and lowered essential oil content (11.22%) when compared to those undergoing the rain-fed condition. Overall, the modulators for reducing drought stress impacts by elevating the yields and yield components could be classified as BRs>GB>SNP. INTRODUCTION Cumin (Cuminum cyminum L.) is an annual plant belonging to the Apiaceae family. It is one of the most important medicinal plants, which is cultivated in arid and semi-arid climates in many countries, such as those located in the Mediterranean environments, Iran, India, and Egypt [1]. Environmental stresses like drought are considered as one of the major factors limiting the growths and productions of medicinal plants in many parts of the world, as well as Iran. Drought stress restricts plant growth more than any other environmental stresses [2]. Such characteristics as a short growing season, leaf shape, canopy structure, and low water requirement enable the rainfed cultivation of cumin [3]. However, when the rainfall is lower than the crop requirements, its rainfed cultivation does not produce proper economic yields. In a related study, it was reported that cumin phenology, yield, and yield components were influenced by drought stress. An increasing drought level from 70 to 200 mm was seen to decrease the days to flowering and maturity by 4.66 and 3.83 days, respectively. Branches/plant, number of umbels/plant, and number of umbellets/umbel were observed to have no responses to the drought stress levels, whereas the number of seeds and biological yield dramatically decreased by increasing drought stress [2]. Armin and Miri [4]