Effect of Temperature Treatments on Seed Germination and Seedling Growth of Jute Mallow (Corchorus olitorius)

— Jute mallow (Corchorus olitorius) is one of the common green leafy vegetables used widely throughout Ghana. Jute mallow is cultivated by seeds and the demand for the crop is year-round. Despite the high demand, its efficient production is marred by poor seed germination. Thus, this study seeks to determine the effect of pre-chill, dry and wet heat on germination, seedling emergence and seedling vigor of jute mallow. Results revealed that h ot water at 70⁰C with combination of 70⁰C oven heat for thirty (30) minutes produced the best germination, emergence and seedling vigour. The effect of hot water at 70⁰C only was also significantly higher than other treatments. Jute mallow farmers who pro duce on small scale could use hot water at 70⁰C to treat seeds before sowing. Large scale producers, however, could use a combination of hot water at 70⁰C and oven heat at 70⁰C to treat seeds before sowing.


INTRODUCTION
Corchorus olitorius, also known as Jew or jute mallow or bush okra is one of the popular tropical leafy vegetables in Africa, Asia and some part of the Middle East (Olabode and Sangodele, 2014). Studies have shown that jute mallow is considered as a vegetable in most parts of Africa and is widely consumed among rural communities (Velempini et al., 2003). It is an annual crop popularly known in southern Ghana as "Ademe" and northern Ghana as "Ayoyo". It plays very significant role in household nutrition and it is very affordable. It is used to prepare sauce and soup delicacies and its mucilaginous property when cooked facilitate swallowing of solid foods. Hence most parents introduce it to babies who are learning to eat solid foods for the first time. In Ghana, jute mallow is eaten with starchy foods such as "banku", "akple" and "tuo-zafi" due to its ability to enhance swallowing.
Jute mallow was usually found in the wild but recently the health consciousness of many Ghanaians to eat healthy has increased the demand for its consumption hence making it necessary for farmers to deliberately grow them on commercial scale. However, the hard seed coat of jute mallow seeds cause physical dormancy hence, its delay in seed germination (Tareq et al., 2015). Attempts at breaking seed dormancy in jute mallow include the use of heat under constant temperatures (Wahab, 2011), seed scarification (Emongor et al 2004) and use of chemicals such as sulphuric acid (M. Palada and Chang, 2003). Palada and Chang (2003), reported that when jute mallow seeds are steeped in boiled water, seed germination International Journal of Environment, Agriculture and Biotechnology, 5 (6) 29 1632 and seedling emergence are enhanced. These studies produced germination percentage between 40%-80%.
Mechanical scarification usually makes the surface of seeds permeable to water but reduces seedling vigor. Apart from reducing seedling vigor, the size(small) of the seed makes it difficult to carry out mechanical scarification on jute mallow seeds (Velempini et al., 2003). Some of these treatments involve chemicals which do not only overburden small scale farmers with high production cost but these chemicals are not easily accessible. It is important to exploit feasible and effective methods that can be used by small scale farmers as well as commercial farmers to enhance germination and seedling vigor. Application of heat may be easier than earlier attempts that are more difficult to apply especially by small scale farmers. Thus, this study seeks to assess seed quality of jute mallow in terms of health, purity and viability while assessing rate of seed germination and seedling vigor, following different methods of breaking dormancy using heat treatments.

II. MATERIALS AND METHODS
The experiment was conducted at the laboratory of Ghana Seed Inspection Division (GSID) located at Pokuase, Accra and the Pathology Laboratory of Crop Science Department, University of Ghana. Jute mallow seeds used for the study were farmer saved seeds and were purchased from seed shop in Accra.
Seed viability test was conducted by using floatation method (www.agrifarming.in). In this process, seeds were poured into beaker containing water and allowed to settle for 20 minutes. Viable seeds are usually heavier than unviable seeds hence they settled at the bottom of the glass beaker while the lighter seeds with other impurities floated on the water.
The purity test was conducted according to the rule of International Seed Testing Association (ISTA, 2017). The aim of the purity test was to determine the percentage composition by weight of the seed being used. Two hundred grams (200g) of seeds were weighed and mixed thoroughly by hand. The seeds were poured onto the purity working board with reflected light to enhance vision; this was done with about 150 seeds at a time. Magnifiers were used to aid the separation of seeds into various components by magnifying the seeds and other components. The components were pure seeds, other seeds and inert matter. Pure seeds were seeds with all the features of jute mallow.
Other seeds were defined as seeds of other plants that may be present. Inert matter was the materials that were neither pure seeds nor other seeds.
Purity percentage was calculated by dividing the weight in grams of pure seeds by the total seed weight and multiplied by 100 as shown in the equation 1 below: Where purity percentage is denoted by P, weight of pure seeds as Pws and total seed weight denoted by Tws.

Seed Moisture Test
Seed moisture test was done by weighing one hundred grams (100g) of seeds on a weighing scale. The seeds were poured into a digital moisture meter and calibrated to shallot seed. The calibration did not have jute mallow seeds on the machine so shallot was used since it has similar seed size.
To conduct health test on the seeds, ten (10) glass petri dishes were sterilized in a hot oven sterilizer at 175⁰C for 90 minutes. Ten milliliters (10 ml) of Potato Dextrose Agar (PDA) media was poured into each sterilized petri dish. Ten (10) seeds were placed in each petri dish and covered. This was replicated ten (10) times, making a total of hundred (100) seeds. The petri dishes were labeled and incubated for five days to observe the presence of pathogens on the seed surface.
Two grams (2g) of seeds were placed in a conical flask and 1% sodium hypochlorite was poured into the flask for sixty (60) seconds to sterilize the surface of the seed.
The contents in the flask were sieved and the seeds were poured onto a tissue paper to absorb the remaining moisture on it. Ten (10) glass petri dishes were sterilized in a hot oven sterilizer at 175⁰C for 90 minutes. Ten milliliters (10 ml) of PDA media was poured into each sterilized petri dish. Ten (10) seeds were placed in each petri dish and covered. This was replicated ten (10) times, making a total of hundred (100) seeds. The petri dishes were labeled and incubated for five days to observe the presence of pathogens within the seed.

Seed Treatments to Break Dormancy
Seeds were subjected to Ten (10) temperature treatments (T) and assessed for germination, emergence and seedling vigor as shown in were sown without temperature treatment was included in the study. For oven treatments, the oven was pre-heated.

Germination Test
Germination was done by using the top of paper method. Hundred seeds from each treatment were sown on filter paper. This procedure was replicated four (4) times. Germination counts started on the third day after planting and continued for a total period of 14 days when most of the seeds had germinated. Radicle (root) emergence was used as the criterion for germination (Denton et al., 2013). The percentage germination was calculated by dividing the total number of seeds that germinated over the number of seeds sown and multiplied by hundred (Denton et al., 2013) as shown in equation 2 below.
( ) where germination percentage is denoted by GP, total number of seeds germinated is denoted by Tsg, and total number of seeds sown denoted by Tssn.

Seedling Emergence and Seedling Vigor Index
The experiment was a complete randomized design. One hundred seeds were taken from each treatment and sown in a germination tray which was filled with sand to about 3cm thick. Each treatment had three (3) replications.
The set up was irrigated lightly every day to ensure adequate water supply for germination and to prevent the seed from drifting away from the planted rows.
The numbers of seedling emergence were recorded on daily basis, starting from the third day after sowing until 14 days after sowing. Seedling was scored as emerged when the cotyledons break through the soil surface and the percentage seedling emergence was calculated by dividing the total number of seedlings that emerged by the number of seeds sown and multiplied by hundred.
On the 14th day, measurements of seedling length were carried out on 10 randomly selected seedlings from each replicated tray (Denton et al., 2013). The seedling vigor index was calculated by multiplying the seedling length by percentage seedling emergence (Denton et al., 2013).
where emergence percentage (%) is denoted by EP, total number of seeds emerged denoted by Tse, and total number of seeds sown denoted by Tssn

Seed Quality
The seed quality tests revealed that ninety two percent (92%) of the jute mallow seeds were viable and eighty seven percent (87%) pure. Seed health test within the seed revealed no contaminants however test on the seed surface showed that seeds carried 10% fungal pathogens and 5% bacterial pathogens refer to table 2. Seed health (seed surface) 85

Effect of Treatments on Percentage Germination and Emergence
Seeds that were treated with hot water and oven heat combination resulted in the highest percentage of  (see table 3).
The untreated seeds resulted in the lowest percentage germination (2.5%) and there was no seedling emergence.   T1: soak seeds in water at 21⁰C for 15hours, T2: Soak seeds in water at 21⁰C for 15 hours followed by oven heat, T3: Hot water at 70⁰C, T4: Hot water at 70⁰CFollowed by oven heat at 70⁰C, T5: Pre chill at 5⁰C for 24 hours, T6: Pre-chill at 5⁰C for 24 hours followed by oven heat at 70⁰C, T10: Control). (T1: soak seeds in water at 21⁰C for 15hours, T2: Soak seeds in water at 21⁰C for 15hours followed by oven heat, T3: Hot water at 70⁰C, T4: Hot water at 70⁰C followed by oven heat at 70⁰C, T5: Pre chill at 5⁰C for 24 hours, T6: Pre chill at 5⁰C for 24 hours followed by oven heat at 70⁰C)

Health Status and Contributing Factors of Farmer Saved Seeds
African indigenous vegetables are usually cultivated with other crops where the same plot is divided into sub plots and different crops are cultivated in each subplot; this agrees with (Maseko et al., 2018) who reported that African leafy vegetables are cultivated under a mixed cropping system. Farmers with a variety of crops are able to make sales every time compared to farmers who grow single crops because a crop is always available for sale notwithstanding, it also comes along with its challenges. It is however easy for pest and diseases to spread on such farms, especially when crops from the same family are found on the subplots. Pest easily migrate from one crop to another. The presence of fungi on the seed but not within the seed indicated that the seeds may have been kept with other contaminated seeds during storage. Seeds may also have been contaminated during the extraction process or through harvesting equipment or even via storage environments as seeds were not certified. Fungus is usually associated with stored grains and legumes; it also grows well where there is water (moist) and temperature interaction. Fungal infestation of seed coat decreased viability of seeds causing abnormal seedlings.
However, methods of sterilization such as hot water, natural compounds, commercial bleach and ethylene are able to get rid of the seed's infestation. Farmers are able to eradicate the fungal contamination on the seed coat of jute mallow unconsciously during the period of breaking dormancy by steeping the seeds in hot water (Selcuk et al., 2008). The seed is thus sterilized while dormancy is being broken and this reduces the risk of disease infestation in jute mallow. Disease causing bacteria present on the seed coat showed that the farmer saved-seeds did not go through any standard check, therefore, there is potential yield loss as a result of disease infestation in the life of the plant.

Efficient and Effective Methods of Breaking Dormancy on Germination and Seedling Vigor of Jute Mallow
Hot water caused thermal shock to the embryo or leaching of inhibitors to enhance germination, however the embryo may be destroyed as a result of prolong contact with high temperatures which is consistent with (Velempini et al., 2003) who reported that, longer soaking times result in drastic reduction in germination.
Treatments included dipping jute mallow seeds into hot water when it starts to bubble and this caused germination. Based on the observations, the effect of temperature treatments on germination and seedling emergence followed similar trend with seeds dipped into hot water at 70⁰C followed by oven heat at 70⁰C for 30minutes showing the highest germination and seedling emergence. Seed dormancy in jute mallow is physical dormancy and is usually as a result of hard seed covering which prevent water from entering into the seed (Abukutsa-Onyango, 2005). The hot water thus scarified the seed coat and caused water imbibition hence facilitating germination and emergence. The high temperature also provided good medium for enzymes to catalyze the breakdown of seed coat and this allowed the water imbibition and gaseous exchange thereby enhancing germination and emergence.
Exposing seeds to oven heat at 70⁰C showed moderate seedling emergence, which increased with temperature at 80⁰C. Dry heat produced may have cracked the hard seed coat making it permeable to water when moistened similar to method of breaking dormancy in some Acacia tree species (Walters et al., 2004). This explains why seeds in the wild readily germinate and produce seedlings during the rains on farms that were burned during land preparation (Denton et al., 2013). No significant increase in seedling emergence and germination were obtained when oven heat temperature was increased from 80⁰C to 90⁰C for 30minutes. This could be as a result of embryo damage due to the excessive high temperature and this observation was contrary to Denton et al., (2013) who reported that irrespective of how long jute mallow seeds were subjected to bush fire, there were seedling emergence on the field after the first rain. The difference in germination and emergence when temperature increased from 80⁰C to 90⁰C may also be as a result of embryo damage due to the prolong exposure of the seed to dry heat causing seeds to dehydrate hence increased mortality.
The control treatment and seeds soaked in water at 21⁰C for 15 hours did not enhance germination at all. The seed coat could not be modified to imbibe water for germination to occur due to physical dormancy. Pre chilling seeds at 5⁰C for 24 hours resulted in poor germination and emergence which agrees with (Nkomo et al., 2009b) who reported that there was no germination for seeds that were pre-chilled for one(1) day. However, seeds that were prechilled with oven heat combination showed significant difference in germination. This finding agrees with (Nkomo & Kambizi, 2009b) who reported that germination occurred when seeds were exposed to temperature of 35⁰C and above.
Hot water followed by oven heat treatment showed high seedling vigor for both germination and emergence indicating that, hot water and dry heat enhanced germination, emergence and seedling length. Though the seeds had high viability, the treatments for breaking dormancy favored the plant establishment. The term "seed vigor" has a concept associated with aspects of seed performance which include rate and uniformity of seed germination, seedling growth and emergence. Seeds soaked in water at 21⁰C (T1), seeds soaked in water followed with oven heat (T2) and control (T10) produced low seed vigor. This was as a result of poor seedling performance in terms of height and germination which agrees with the International rules for seed testing's explanation of seedling vigor as the total properties that determines the activity and acceptable germination performance of seed (ISTA, 2015).
Germination rate is a necessary parameter in crop establishment on the field. The effect of treatments on the seed varied significantly, seeds dipped into hot water only (T3) and seeds dipped into hot water followed by oven treatments (T4) were the only treatments that started germination from the first day of germination count. This is consistent with other findings that hot water treatments enhance germination (Maina et al., 2011). Germination started on day one and increased by day two but the rate of germination decreased in the subsequent days. About 85% of the total seeds' germinations occurred from day one (1) to two (2) while the remaining treatments started germinating between day two (2) and fourteen (14). The trends of germination rates of the various treatments indicated their effectiveness in breaking dormancy with the control taking the longest time to germinate. A low germination of 2.5% is an indication of the importance of treating seeds of jute mallow prior to planting.
Also soaking seeds in water at 21⁰C alone is equally not very effective. Maximum germination rate for treatment (6 and 1) occurred on day three, treatment (2) was on day four, treatment (7and 8) was on day eight, treatment (9) was on day six and treatment (10) started germinating on day fourteen. This revealed that, though the other treatment enhanced germination at some point, there was delay in germination which makes the treatment method ineffective for breaking dormancy. Treatment 10 which was the control had its maximum germination on day fourteen with germination percentage of 2.5% revealing that jute mallow seeds will not germinate at all or have poor germination and seedling vigor when it is not treated before sowing. Soaking seeds in ordinary water at room temperature (T1) resulted in 5% germination and was not an effective method of breaking dormancy. It agrees with the report by (Maina et al., 2011) that soaking jute mallow seeds in ordinary water will not break dormancy.

V. CONCLUSION
The quality of farmer saved-seeds in terms of purity and viability is adequate as it was above 80% for both 87% and 92% respectively. For seed health quality, no seed borne pathogen were observed. Hot water followed by oven heat treatment can be adopted on large scale production while small scale producers can employ hot water treatment for uniform growth and development.
The best treatment for breaking dormancy in jute mallow from the study was dipping seeds in hot water treatment at 70⁰C for five (5) minutes followed by oven heat at temperature of 70⁰C for thirty (30) minutes as it gave the highest seedling germination, emergence and vigour. Hot water treatment and hot water combination with oven heat enhanced germination and good germination rate.
Hot water followed by oven heat treatment should be used by large scale producers while small scale producers use only hot water treatment.