Extended Abstract
1. Introduction: Coriander is a crop that is cultivated in irrigation and rainfed conditions for the production of vegetables and seeds in all parts of the world. Waterlogging is one of the abiotic stresses that may damage the growth and performance of most plants, including coriander. Waterlogging occurs as a result of heavy rainfall in a short time, floods, improper irrigation management, low slope of the field, hardness of the subsurface layer, etc. One of the important effects of climate change is the occurrence of heavy rains and floods in dry and semi-arid areas in spring and summer and during the growing season, which can cause waterlogging. The amount of waterlogging damage depends on the type of plant, variety, time, duration, and intensity of stress, the temperature of the environment, etc.
2. Materials and Methods: The experiment was conducted to investigate the effect of waterlogging on the growth and yield of coriander (Kermanshah local variety) under greenhouse conditions at Razi University in 2021. The factors included time (establishment, stem elongation, and flowering) and duration (control, 3, 6, 9, and 12 days) of waterlogging. The experiment was conducted as a factorial design on a completely randomized design (CRD) in three replications. Planting was done in pots with dimensions 50×50×50 cm on May 23, 2021. After emergence and establishment, the density was thinned to 50 plants. m^-2. During the growth period, one week after the end of waterlogging stress treatment were investigated the SPAD value, stomatal conductance, and quantum yield of photosystem II (Fv/Fm) traits were investigated. At the time of ripening were measured biological yield, seed yield, seed number per umbel, 1000-seed weight, umbel number per plant, and plant height were measured. Ripening took place on August 5, 2021. Analysis of the data was performed with SAS and MSTATC software, and the means were compared using the least significant difference (LSD) at the 5% level.
3. Results and Discussion: Based on analysis of variance, the effect of time and duration of waterlogging stress during the growth period of coriander was significant on stomatal conductance, chlorophyll fluorescence, and chlorophyll index, but the interaction effects of these treatments were significant only on the greenness index. The amount of stomatal conductance in the waterlogging treatment in the establishment stage was lower than in the stem growth and flowering stages, but there was no significant difference between the stem growth and flowering stages. With increasing waterlogging duration, the amount of stomatal conductance decreased, and in the 12-day waterlogging treatment, it decreased by 14.7% compared to the control. The value of the quantum yield of photosystem II (Fv/Fm) was higher at the time of establishment than at the stem elongation and flowering stages; however, with the increase in the duration, the amount of chlorophyll fluorescence increased. In the control treatment, Fv/Fm reached 0.79, and in the 12-day waterlogging treatment, it reached 0.50. The interaction effect of the treatments on the SPAD value showed that with the increase of the duration of the waterlogging, the amount of damage in the flowering stage was more than in the stages of stem growth and establishment. Analysis of variance revealed a significant effect of time and duration of waterlogging stress on biological yield, seed yield, harvest index, number of umbels per plant, number of seeds per umbel, and thousand-seed weight. The effect of waterlogging time on the studied traits showed that waterlogging had the most significant damage on biomass yield, seed yield, number of seeds per umbrella, and number of umbrellas per plant at the time of establishment, and the least damage in these traits was observed during the flowering stage. On the contrary, the effect of waterlogging time treatment on the weight of 1000 seeds was the highest in the establishment stage. The effect of waterlogging duration on yield and its yield components showed that, with an increase in waterlogging duration, the values of all these traits significantly decreased. For each day of waterlogging, damage to coriander was for the biological yield 0.29 g plant^-1 (2.5 %), the seed yield 0.14 g plant^-1 (3.8 %), the harvest index 0.4%, the seed number per umbel 0.23 (1.3%), the 1000-seed weight 0.105 g (1.5%), and the umbel number per plant 0.42 (1.4%). In this experiment, the effect of waterlogging on the yield and yield components of coriander was greater in the establishment stage than in the later stages. Probably, waterlogging stress in the early stages of growth, such as establishment, has caused more damage to roots (reduction of respiration) and shoots (reduction of photosynthesis and yield), consequently causing damage and delay in growth. For this reason, the coriander plant has not compensated for the damage caused during the establishment stage after the period has passed, and this has had a significant impact on the reproductive characteristics of the plant, including the number of umbels per plant, the number of seeds per umbel, and seed yield.
4. Conclusion: In general, the results showed that under greenhouse conditions, the effect of time of waterlogging stress on biological yield, seed yield, number of umbels per plant, and number of seeds per umbel of the coriander plant was more sensitive in the establishment stage and more resistant in the flowering stage. The duration of flooding had a significant negative effect on all traits. Waterlogging reduced grain yield by 3.8% per day.