J Plant Growth Regul DOI 10.1007/s00344-017-9728-0
Improving Seed Germination and Early Growth of Garden Cress (Lepidium sativum) and Basil (Ocimum basilicum) with Hydropriming Seyyed Ali Noorhosseini1 · Nargesh Khatun Jokar1 · Christos A. Damalas2
Received: 6 March 2017 / Accepted: 11 July 2017 © Springer Science+Business Media, LLC 2017
Abstract Hydro-priming is a useful method for increasing speed and uniformity of germination in several plants, but pertinent research concerning garden cress (Lepidium sativum) and basil (Ocimum basilicum) does not exist in the literature. The effects of hydro-priming duration (0, 6, and 12 h) and temperature (15 and 25 °C) on seed germination and seedling vigour of garden cress and two varieties of basil (at priming temperature of 20 °C) were evaluated on paper and sand. With reference to garden cress, hydropriming for 6 and 12 h at 15 °C increased uniformity of germination and reduced mean germination time. These improvements were more evident on paper. Moreover, hydro-priming for 6 and 12 h at 25 °C increased radicle length, plumule length, seedling length, and seedling vigour index on paper, but did not affect significantly those variables on sand. Overall, hydro-priming of garden cress seeds for 12 h can improve germination and early growth of this species, but germination medium can play a role due to different capacities for moisture retention. With reference to basil, hydro-priming reduced mean germination time for purple basil, but not for green basil. Also, reduced germination speed and uniformity of germination were observed for green basil on sand, but not for purple basil. Hydropriming for 12 h increased plumule length, seedling length, and seedling vigour index for both basil varieties. Overall, * Seyyed Ali Noorhosseini
[email protected];
[email protected] * Christos A. Damalas
[email protected];
[email protected] 1
Young Researchers and Elite Club, Rasht Branch, Islamic Azad University, Rasht, Iran
2
Department of Agricultural Development, Democritus University of Thrace, 68200 Orestiada, Greece
hydro-priming of basil seeds for 12 h can improve germination and early growth of this species, but variety and germination medium can play a role. Data on improving germination of those species are not available in the literature and could be useful for improving plant establishment and yield of commercial plantations of garden cress and basil. Keywords Priming duration · Seed priming · Seed quality · Seedling length · Temperature
Introduction Seed quality is a paramount parameter in yield improvement of medicinal herbs. It is determined by numerous factors including germination potential and seed vigour. Seed vigour may tremendously influence desirable plant establishment and stand (Basra and others 2002). Priming refers to any pre-sowing treatment of the seeds for enhancing germination, emergence rate, and initial seedling establishment (Shahrousvand 2010). Seed priming shortens the period from sowing to seedling establishment and alleviates potential effects from adverse environmental conditions after seed placement (Ansari and others 2012; Abdolrahmani and others 2011). Priming has different forms depending on the different substances used, including hydro-priming, hydro-thermopriming, osmo-priming, and matric-priming. For instance, plant hormones, polyethylene glycol, and mineral salts are applied in osmo-priming (Azarnia and others 2016; Rezaei Sokhat Abandani and others 2009). Hydro-priming or seed preparation refers to different methods used for the improvement of seed function and quality in adverse environmental conditions in all of which the seeds imbibe water in a controlled manner and they are
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treated as having their germination vigour improved. In hydro-priming, the seeds are treated with distilled water without any use of chemicals. This type of priming is very simple and inexpensive; water uptake commences as soon as the seeds are soaked in water (Eisvand and others 2013; Rehman and others 2015). Standard germination trials on the basis of the International Seed Testing Association (ISTA) guidelines showed that time to 50% germination, mean germination, and germination rate and uniformity were improved significantly in primed seeds of canola, wheat, pea, soybean, alfalfa, maize, watermelon, rice, lettuce, and bean, implying accelerated germination and higher seed vigour in pre-sowing priming of seeds (Basra and others 2002; Bailly and others 1998). Some researchers have studied the desirable influence of priming on the germination of different plants and have reported their impact on improving germination parameters (Mauromicale and Cavallaro 1996; Murungu and others 2003; Kaya and others 2005; Kang and others 2007; Ansari and others 2012). These reports show that seed priming enhances germination parameters in seeds of accelerated ageing (Younesi and others 2014). Priming causes a wide range of biotic and physiological changes in the seeds and the seedlings so that its consequences are reflected in germination, early plant establishment, better crop stand, and early maturity (Najafi and others 2015). Germination is one of the most crucial and sensitive steps of plant growth so that uniformity and emergence percentage can deeply affect the production and quality of the crop (Shahrousvand 2010; Abdolrahmani and others 2011; Najafi and others 2015; Rehman and others 2015). The environment during priming also influences the seed response to priming. Thus, different temperatures must be evaluated for each crop species to determine which provides the best priming result. Studies have already reported the proper temperature of priming as 10–35 °C. The proper duration of priming varies from several hours to several weeks depending on species. The optimal duration and temperature of priming favours germination and seedling establishment (Rezaei Sokhat Abandani and others 2009). A prevailing problem especially in rain-fed regions is water deficiency and precipitation inadequacy. Thus, hydro-primed seeds can germinate and establish faster to cope with this problem (Joudi and Sharifzadeh 2006). Hydro-priming improves the growth of the embryo and the establishment of the plants (Ashrafi and Razmjou 2010). Garden cress (Lepidium sativum L.) of the family Brassicaceae and basil (Ocimum basilicum L.) of the family Lamiaceae are used as medicinal herbs (Zargari 2011; Radwan and others 2007). However, the seeds often lose their vigour and the germination in the field is erratic. Under conditions of low temperatures at planting, erratic emergence and seedling loss lead to reduction of plant
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density in the field and may affect crop yield at harvest. On the other hand, early planting can help the crop to avoid various biotic or abiotic stresses during growth, such as the unfavourable effects of insects, diseases, weeds, or drought. By contrast, primed seeds are stimulated up to the initiation of cell division and after drying and re-imbibition, restore their activity from the spot they have dried (Nabi and others 2014) and they get biologically and biochemically prepared for germination. Proper standardization of the pre-sowing seed treatment method for individual crops and cultivars is the most important determinant of the success of seed priming. The duration of seed soaking is critical and should always be less than a safe limit for each crop species or cultivar. If the priming time exceeds that limit, it may lead to damage due to premature germination (Harris and others 1999). The specific temperatures at which seeds are kept during priming or dried after priming are also important determinants of effective priming (Ashraf and Foolad 2005). Given that data on hydro-priming of garden cress and basil seeds are not available in the literature, the objective of the present study was to examine seed germination traits and early growth parameters of garden cress and basil as affected by hydro-priming.
Materials and Methods Experimental Setup and Growth Conditions The experiments were carried out in the Botany Laboratory of the Agriculture Training Center of the University of Applied Science and Technology in Guilan Province, Iran in 2014 as factorial trials based on a randomized complete block design (RCBD) with three replications. The studied factors included germination medium at two levels (paper and sand), hydro-priming duration at three levels (0, 6 and 12 h), and hydro-priming temperature at two levels (15 and 25 °C). Temperature was not included as a factor in the basil experiment, where hydro-priming was implemented at 20 °C for all treatments. A seed lot of garden cress and seed lots of two varieties of basil (green and purple) were prepared under uniform and controlled conditions, and 50 seeds were counted for each experimental unit. Then, they were disinfected with sodium hypochlorite 0.05% for 5 min. The seeds were soaked in distilled water as per the predetermined durations. A part of them was placed in an incubator at 25 °C and a part at 15 °C. It should be noted that all seeds of all treatments were taken out of hydro-priming conditions and were prepared to be placed in germination media simultaneously. After hydro-priming, the seeds were placed in open air (25 °C) to dry to a moisture content below 10% of the dry weight
J Plant Growth Regul
of the seeds, resembling the original moisture content of the seeds, that is, equilibration conditions for safe storage (Black and Bewley 2000; Di Girolamo and Barbanti 2012; Hussain and others 2016; Wang and others 2016a). At the next step, 50 seeds per experimental unit were placed on paper and sand media. Specific containers, towel paper, and sand were used to prepare the germination media. At first, the containers were disinfected with sodium hypochlorite 1%. Then, their openings were firmly closed with parafilm and they were transferred to a germinator with 70% relative humidity at 25 °C. The germinated seeds were counted daily at specific times from day 4 to 14. The number of normal seedlings (the seedlings that could produce a healthy plant in soil under optimal moisture, temperature, and radiation conditions) and abnormal seedlings (seedlings that were not viable enough to turn into a healthy plant under optimum conditions) was specified in accordance with ISTA criteria (Anonymous 2003).
The determined parameters included mean speed (MS) of germination, uniformity (U) of germination, mean daily germination (MDG), mean germination time (MGT), and seedling vigour index (SVI). These parameters were estimated as described below:
Mean speed of germination (MS) = Σ(nt)∕Σn (also known as mean (1)
where n = number of normal germinated seeds at time t. (2) where GP = germination percentage and T = number of days after the start of the test (it is the mean number of seeds germinating per day).
Mean daily germination (MDG) = GP∕T,
(3) where n = number of germinated seeds until day d (the number of days from the start of germination).
Mean germination time (MGT) = Σdn∕Σn,
(4) where GP = germination percentage and SL = Seedling length.
Seedling vigour index(SVI) = GP × SL
(5) where GP = germination percentage and MGT = mean germination time. To measure seedling length traits, ten normal seedlings were randomly sampled from each culture medium and their radicle, plumule, and seedling lengths were measured with a ruler in mm, when the numbers of germinating
Uniformity of germination (U) = GP/MGT,
Data Analysis Data were analysed separately for each species. For garden cress, data were subjected to analysis of variance (ANOVA) using a 2 (media) by 2 (temperatures) by 3 (priming periods) factorial approach with three replications. For basil, data were subjected to ANOVA using a 2 (varieties) by 2 (media) by 3 (priming periods) factorial approach with three replications. Differences between means were compared with Fisher’s protected LSD test at P
