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افزایش میزان تنژگی بذر چهار جنس چمن با استفاده از تیمار اسید

حسن صالحی و مرتضی خوشخوی

بخش علوم باغبانی، دانشکده کشاورزی، دانشگاه شیراز، شیراز، ایران

چکیده:

چمن ها به طور معمول با بذر افزوده می شوند. از مهم ترین مشکل های موجود در افزایش بذری برخی جنس‏های چمن، می توان به کمی درصد تنژگی و یا سرعت تنژگی اشاره نمود. پژوهش حاضر برای یافتن بهترین غلظت و زمان تیمار اسید سولفوریک برای افزودن به میزان تنژگی بذر جنس‏های چمن:Pers.  Cynodon dactylon [L.]، Festuca rubra L. var. rubra ‘Shadow’، Lolium perenne L. ‘Barball’ و Poa pratensis L. ‘Merion’ انجام شد. در آزمون اول، از اسید سولفوریک به غلظت های 0 (شاهد)، 25، 50، 75 و 100 درصد به مدت زمان های 10، 15، 20، 25 و 30 دقیقه استفاده شد. در آزمون دوم، با به کار بردن بهترین تیمار اسید برای هر جنس چمن اثر شرایط وجود یا نبودن نور در محیط بر میزان تنژگی مورد بررسی قرار گرفت. هر تیمار با 4 تکرار، هر کدام با 100 عدد بذر قرار داده شده بر روی کاغذ صافی درون پتری دیش های پلاستیکی، انجام شد. نتایج نشان داد که در Cynodon، تیمار اسید 50% به مدت 20 تا 25 دقیقه با درصد و سرعت تنژگی بیشتر در روشنایی؛ در Festuca، تیمار اسید 25% به مدت 15 دقیقه با درصد و سرعت تنژگی بیشتر در روشنایی؛ در Lolium، تیمار اسید 50% به مدت 10 دقیقه، با سرعت تنژگی بیشتر در تاریکی و در Poa، تیمار اسید 50% به مدت 15 تا 25 دقیقه با سرعت تنژگی بیشتر در تاریکی، مناسب ترین تیمارها می باشند. بیشترین درصد تنژگی در چمن های Poa و Cynodon و کمترین آن در Festuca دیده شد. چمن های Cynodon و Festuca به ترتیب بیشترین و کمترین سرعت تنژگی را دارا بودند. این روش کار ساده با نتایج قابل ملاحظه می تواند جایگزین روش های وقت گیر و پرهزینه ای مانند آماده سازی بذر شود.

Enhancing seed germination rate of four turfgrass genera by acid treatments

H. Salehi and M. Khosh-Khui

Department of Horticultural Science| College of Agriculture| Shiraz University| Shiraz| Iran

Abstract:

Turfgrasses are commonly propagated by seeds. In some genera of turfgrasses| presence of low germination percentages or rates are the main problems in seed propagation. The present investigation was undertaken to determine the best concentration and duration of sulfuric acid treatment for seeds of following turfgrass genera: Cynodon dactylon [L.] Pers.; Festuca rubra L. var. rubra ‘Shadow’; Lolium perenne L. ‘Barball’ and Poa pratensis L. ‘Merion’. In the first experiment| sulfuric acid was used with concentrations of 0 (control)| 25| 50| 75 and 100% for 10| 15| 20| 25 and 30 min. In the second experiment| effects of light/dark (16/8) or dark conditions on germination rates of different mentioned genera were investigated using the best specific acid treatments. Each treatment was replicated 4 times with 100 seeds per replicate kept in plastic petri dishes. Results indicated that in Cynodon| using 50% acid for 20-25 min had highest germination percentage (GP) and mean daily germination (MDG) in light/dark; in Festuca| using 25% acid for 15 min had highest GP and MDG in light/dark; in Lolium using 50% acid for 10 min had highest MDG in dark and in Poa| using 50% acid for 15-25 min had highest MDG in dark. Both Cynodon and Poa had the highest and Festuca had the lowest GPs. Cynodon and Festuca had the highest and lowest MDGs| respectively. This simple procedure| with considerable results| may be replaced to time-consuming and expensive methods such as seed priming.

Introduction:

The turfgrass industry has undergone rapid growth in its attempts to meet the public’s increasing demands for products and services (Turgeon| 2002). The rate at which a new turf becomes established is influenced by specific procedures used during propagation (Turgeon| 2002).

Direct seeding is the least expensive and most efficient method for revegetating large parcels of land with herbaceous species such as grasses (Trask and Pyke| 1998). Different turfgrass species and cultivars vary substantially in the normal percentage of viable seed contained in a seed lot (Simpson| 1990; Turgeon| 2002). Previously| germination characteristics of some perennial grasses have been studied (Beckman et al.| 1993; Fujikura et al.| 1993; Young et al.| 1977; Trask and Pyke| 1998; Tigabu and Oden| 2001). Mechanical scarification and concentrated sulfuric acid treatment have been widely used to improve seed germination of several hard-seeded species (Tigabu and Oden| 2001). Generally| turfgrass seeds have not hard seed coat| but their caryopses are sandwiched between lemma and palea (Turgeon| 2002). There are few reports on using mechanical scarification for seeds of grasses (e.g.| Trask and Pyke| 1998)| but in turfgrasses| sulfuric acid treatment had been used only for tall fescue in tissue culture studies for callus production (Bai| 2001).

Optimum acid concentration and exposure time vary with species (Argel and Paton| 1999). The main aims of this study were to find an effective and practical treatment| and to obtain the best cultural conditions to enhance seed germination rates in each of four common turfgrass genera.

Materials and Methods:

Turfgrass genera

In this investigation| four turfgrass genera| common bermudagrass Cynodon dactylon [L.] Pers. (California origin); red fescue| Festuca rubra L. var rubra ‘Shadow’; Perennial ryegrass| Lolium perenne L. ‘Barball’ and Kentucky bluegrass| Poa pratensis L. ‘Merion’ were used.

Experiment 1. Sulfuric acid treatments

Sulfuric acid was used in concentrations of 25| 50| 75 and 100% for 10| 15| 20| 25 and 30 min along with control treatment.

Seeds were soaked in cold sulfuric acid solutions (or distilled water in control treatment) and then were thoroughly rinsed three times with tap water. The rinsed seeds were kept under running tap water overnight.

Experiment 2. Light/dark or dark treatments

Based on data obtained in experiment 1 for each genus| effects of light/dark (16/8 h) or dark conditions on germination rates| mean daily germination (MDG)| were studied and compared to controls.

Germination tests

A total of 400 seeds| 5 replications of 100 seeds| each was used in all treatments. The seeds were placed on filter papers in 9 cm ?- sterilized plastic ptri dishes| which kept moist with distilled water. Petri dishes were kept at 25±2 °C with 1000 lux illuminance (cool white fluorescent lamps) and 16/8 h light/dark or dark conditions. They were monitored every day and moistened with distilled water when needed. Seeds were considered germinated when the radicles were about 3 mm long and discarded after counting. Germination tests were continued up to 25 days. In each genus and treatment| the final germination date was the time in which seed germination percentage (GP) was completed| or when the seeds failed to germinate in 3 previous days.

Data recording and statistical analysis

Number of germinated seeds was daily recorded in all the experiments. Final GP and MDG were calculated for each trial. Experiments were conducted as complete randomized design with factorial arranging. The percentage data were arcsine transformed before analysis (Zar| 1996). The presented percentage data in Tables l and 3 are back-transformed. Data were analyzed by Factor analysis of variance in experiment 1 and One-way analysis of variance in experiment 2 using MSTATC program. Means were separated by Tuckey’s test at 1% level (P<0.01).

Results and Discussion:

Experiment 1.

Seed GP was markedly increased using acid treatments especially in Cynodon| Festuca and Lolium genera (Table l). Poa had the highest total mean of seed GP followed by Cynodon| Lolium and Festuca. Turgeon (2002) reported the variability among seed GP of different turfgrass species and cultivars similar to these findings. According to ISTA (1999) some turfgrass species such as Kentucky bluegrass (Poa pratensis L.) are slow to germinate under optimal seed germination conditions and treatments. In present study| using 50% acid for 15-25 min resulted in 100% seed GP in this genus. It may be concluded that acid treatment can improve seed GPs of turfgrass genera even in slow germinating ones.

In general| using 50% acid for 10 to 25 min were the best treatments and resulted to highest seed GP (Table 1). This result is in accordance to that reported by Bai (2001) using 50% acid for 20 min with seeds of tall fescue in tissue culture studies.

Table 1. Effects of different turfgrass genera| acid treatments and their interactions on seed GP.

¹Data followed by the same small letters (capital letters for Means) are not significantly different according to Tukey’s test at 1% level.

Seed MDG was significantly different among turfgrass genera (Table 2). Cynodon had the highest MDG and thereafter were Poa| Lolium and Festuca| respectively (Table 2). These results are similar to those of GP| except for the superiority of Cynodon to Poa (Tables 1 and 2).

Table 2. Effects of different turfgrass genera| acid treatments and their interactions on seed MDG.

¹Data followed by the same small letters (capital letters for Means) are not significantly different according to Tukey’s test at 1% level.

Among acid treatments| similar to seed GP results| 50% acid used for 10-25 min resulted in the highest seed MDG| especially in 20 and 25 min treatments (Tables 1 and 2). Usually| with the greater seed GP| the higher seed MDG was obtained. Acid concentrations higher than 50% is hazardous to turfgrass seeds and can not be recommended (Tables 1and 2).

Each turfgrass genus responded significantly to acid treatments in regard to both seed GP and MDG (Tables 1 and 2). The best treatments were: Cynodon| 50% acid for 20-25min; Festuca| 25% acid for 15 min; Lolium| 50% acid for 10 min and Poa| 50% acid for 15-25 min (Tables 1 and 2).

Experiment 2.

Effects of light and/or dark conditions on seed GPs and MDGs are shown in Table 3. Cynodon and Festuca had the highest seed GPs and MDGs in 16/8 light/dark treatment. In Lolium| light and/or dark conditions did not affected seed GP| but had the highest MDG in dark condition. In Poa| without acid treatment| the 16/8 light/dark condition was the best| but with acid treatment| dark condition resulted in highest seed MDG. This may be attributed due to interaction between light and acid treatments in this genus.

Table 3. Comparison between seed GP or MDG in four turfgrass genera under light and/or dark conditions.

¹Cynodon: 50% acid for 20 min; Festuca: 25% acid for 15 min; Lolium: 50% acid for 10 min and Poa: 50% acid for 15 min.

²In each column| means followed by the same letters are not significantly different according to Tukey’s test at 1% level.

In present study| acid treatments raised the seed GPs to| or near to| 100% (except in the Festuca) (Table 3). With regard to MDGs| total germination periods in Cynodon| Poa and Lolium were only 2| 4 and 10 days| respectively (Table 3). ISTA (1999) recommended 21 days germination period for Cynodon seeds after KNO₃ treatment. ISTA (1999) also have known Poa pratensis L. as a slow to germinate turfgrass. According to results obtained in this experiment| acid treatment can be a very good and simple procedure for enhancing seed germination of turfgrass genera| especially for Cynodon and Poa. Seed priming have been used successfully for better emergence of some turfgrass genera (Young et al.| 1977; Fujikura et al.| 1993; Yamamoto et al.| 1997). Apparently| acid treatment dehulled the seeds (figure 1). Dehulled seeds can absorb water easily| and rinsing and placing under running tap water after acid treatment can prepared them for germination. This treatment is in part similar to “accelerated germination” a seed hydration treatment suggested by Young et al.| 1977| in addition to seed dehullation.

Figure 1. Comparison between control (left) and acid-treated (right) seeds in each turfgrass genus (Cynodon: 50% acid for 20 min; Festuca: 25% acid for 15 min; Lolium: 50% acid for 10 min and Poa: 50% acid for 15 min).

Acknowledgements:

Authors wish to convey their appreciation to Mr. H. Azarakhsh and Mr. F. Nikbakht for technical assistance and Mrs. Z. Seddighi for pretyping the manuscript.

References:

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