Effect of Temperature and Salinity on Two Eastern Dodder (Cuscuta monogyna Vahl) Ecotypes Seed Germination Characteristics

Knowledge of weed biology helps to optimize weed management strategies and avoid unnecessary weed control input by for example accurate prediction of emergence timing of the weeds. According to the available references, 200 species of dodder have been reported in the world of which 18 species are in Iran. Among the 18 reported species in Iran, Cuscuta campestris and Cuscuta monogyna cause the greatest damage to crops and horticultural products in Iran. Cuscuta monogyna (Vahl), a member of the Cuscutaceae family, is a non-specific aboveground holoparasite, and as such is totally dependent on its host plant for assimilates, nutrients and water supply. Eastern dodder is one of the important dodder species that parasite fruit trees and ornamental shrubs. Each eastern dodder plant produces greater than 3000 seeds of which low percentage germinate in the first year. In the field, dodder started to germinate in March or April when daily average soil temperatures reached 10°C, and maximum germination was observed in May or June when daily average soil temperatures reached 20°C. After germination, seedlings of Cuscuta spp. Undergo a non-parasitic phase of growth, dependent on seed reserves, for 2–3 weeks. To improve management systems for specific weed species, it is critical to have good information on seed dormancy, persistence, production, seasonal germination, seedling emergence, and variations among populations. The objective of the present study was to effect of temperature and salinity on two eastern dodder (Cuscuta monogyna Vahl) ecotypes seed germination characteristics.

In order to study the effect of salinity and temperatures on seed germination chrachteristics of two eastern dodder ecotypes experiments were conducted based on factorial in a completely randomized design with three replications in the Research Laboratory of Ferdowsi University of Mashhad Faculty of Agriculture during 2015 and 2016. Treatments include salinity stress in 8 levels (0 (Control), -0.1, -0.2, -0.4, -0.6, -0.8, -1 and -1.2 Mpa) and temperature at 8 levels (5, 10, 15, 20, 25, 30, 35 and 40oC). After 14 days, seeds in treatment solutions were no longer germinating, so all germinated seedlings were removed and un-germinated seeds of the highest salinity treatment (-1.2 Mpa NaCl) were rinsed with distilled water and placed back in their dishes with 5 mL of distilled water for 14 more days.

Results showed that with increasing salinity at each level of temperature germination rate and percentage reduced in both ecotypes, so that in potential -1.2 Mpa germination was stopped in both ecotypes. In both ecotypes germination stamped at 5, 10 and 40 ̊C temperatures in all levels of salinity. In both ecotypes the highest percentage and rate of germination were indicated at control treatment salinity and 25 and 30 ̊C temperatures. It is believed that the effect of high concentration of NaCl at high temperatures can be attributed to the toxic sodium that causes irreversible damage. According to the results Bardaskan ecotype was better than Qouchan ecotype in view of germination at high levels of temperatures and salinity treatments. The three parameter logistic model provided a satisfactory fit for the response of seed germination to NaCl concentration. The effective salinity for reducing of 50% seed germination in Qouchan ecotype at 15, 20, 25, 30 and 35 ̊C temperatures were -0.79, -0.86, -0.87, -0.77 and -0.68 Mpa and in Bardaskan ecotype were -0.93, -0.93, -0.95, -0.90 and -0.75 Mpa respectively. Recovering the ungerminated seeds from the salinity level of -1.2 Mpa and reincubating them with distilled water resulted in a germination of 70% in both ecotypes, indicating that enforced seed dormancy was mainly because of an osmotic effect, as opposed to toxicity owing to an ionic effect.

This study shows that eastern dodder has capacity to survive and reproduce even under a higher temperature and higher degree of salinity stress. The information of this study would be helpful for estimating the potential of this species to spread to new areas and for the improvement of this parasitic weed species management programs. As is evident from these experiments, the effective, long-term reduction of eastern dodder populations will require the use of an integrated weed management approach.