Effect of priming with neem seed extract on seeds of four traditional rice varieties of Sri Lanka; Kaluheenati, Kurulurthuda, Madathawalu and Maa-wee

: With the concern for environmentally friendly agriculture, demand for traditional rice varieties in Sri Lanka has been increased. Farmers claim that the seed germination in traditional rice varieties in Sri Lanka is remarkably low. Considering the reported benefits of neem in enhancing the germination, priming of rice seeds with distilled water and neem seed extracts (100, 50 and 25% strength) for 0, 24, 48, and 72 hours was used to enhance the performances in seed germination of four selected traditional rice varieties. Primed seeds were dried under ambient conditions until initial weight was achieved. Seed germination was tested at ambient laboratory conditions (~27 °C). Seed vigour was evaluated by measuring the root, and shoot lengths and seedling emergence in glasshouse conditions. Four replicates of 100 seeds were used in each treatment. Arcsine transformed data were analysed using one-way ANOVA. Germination percentages of un-primed seeds of Kaluheenati, Kuruluthuda, Maa-wee and Madathawalu were 62, 32, 24, and 20%, respectively, while seedling emergence of the same were 65, 10, 12 and 40%, respectively. Half strength neem priming (50%) for 24 hours and 24 hours pre-soaking significantly improved seed germination (83%) and seedling emergence (83%) of Kaluheenati, while quarter strength neem priming for 72 hours and 24 hours pre-soaking improved germination (64%) and seedling emergence (25%) of Kuruluthuda. Quarter strength neem priming for 48 hours, and 48 hours pre-soaking was effective in improving the germination (49%) and seedling emergence (30%) of Maa-wee, while priming with 100% neem extract for 72 hours and 48 hours pre-soaking improved the germination (55%) and seedling emergence (53%) of Madathawalu. Root and shoot lengths were higher in seedlings of neem primed seeds. Thus, priming with neem seed extracts can be recommended to improve the performance in seed germination of studied rice varieties.


INTRODUCTION
Rice is one of the most important staple foods in the world. Nevertheless, more than 90% of the world's rice is grown and consumed by Asian people (IRRI, 2020). As 60% of the worlds' population lives in Asia, rice could be considered as the worlds' most important food. Rice provides 50% of the dietary calorie supply for ~5 billion Asians (Muthayya et al., 2014). Rice is cultivated in every continent except in Antarctica (Muthayya et al., 2014). Moreover, rice is planted on about 148 million hectares annually, or on 11% of the world's cultivated land (Khush, 1997). Annually > 715 million tons of paddy rice is produced globally (FAO, 2013) showing its significance as a global crop. In Sri Lanka, rice was grown in 1,040,954 ha of land in the year 2018, while the production was 3,929,831 tons. However, only 1.22% of the rice grown lands has been devoted to produce traditional rice varieties of Sri Lanka (Department of Agriculture, 2019).
Traditional rice varieties that have been used by Sri Lankan farmers are with low yields. Thus, rice improvement programs in Sri Lanka have attempted to December 2021 Journal of the National Science Foundation of Sri Lanka 49 (4) develop new rice varieties with higher yields. Most of these new varieties heavily dependent on agrochemicals (Rajapakse et al., 2000). Nevertheless, the introduction of these new rice varieties caused the extinction of many traditional rice varieties from the field (Rajapakse et al., 2000;Kennedy & Burlingame, 2003). Usage of extensive levels of agrochemicals is a significant problem as it has created many health and ecological problems. Most agrochemicals used in rice cultivation are not environmentally friendly (Bambaradeniya & Amarasinghe, 2003). These agrochemicals cause many human health problems (Weeraratne, 1983;Bandara et al., 2008;2010;Jayasumana et al., 2014). Especially, with the emergence of chronic kidney disease with unknown aetiology, a new debate has been initiated in the country on the use of agrochemicals.
In the light of the current debate on health issues, organic farming, as well as traditional rice varieties were promoted as many of the traditional rice varieties are claimed to have health benefits (Dharmasena, 2010). Traditional rice varieties contain variety of chemicals with antioxidant properties. Thus, consumption of traditional rice varieties gives health benefits such as reducing the risk of non-infective diseases (Samaranayake et al., 2017). Therefore currently, these traditional varieties have a good market value especially if they were produced organically (Wickramasinghe & Noda, 2008;Suriyagoda et al., 2011).
However, low germinability and storability of seeds of the traditional rice varieties is a drawback in popularizing these varieties (Personal communication with the organic farming community). Thus, the current research was initiated on the request of the organic farming community to address the low germinability and storability issue of traditional rice varieties of Sri Lanka. In the current study, effect of priming on seed quality of four traditional rice varieties; Maa-wee, Kaluheenati, Kuruluthuda and Madthawalu were studied. No information was available on the improvement of seed quality of these rice varieties in scientific literature. However, few studies were conducted to reveal the medicinal (Samaranayake et al., 2017) and physical (Ranawake et al., 2013;Rebeira et al., 2014) properties of these rice varieties.
Seed priming was used in this research to improve the seed quality of the selected species. Seed priming is a controlled hydration of seeds to initiate the molecular level process towards germination. Hydration is ceased prior to radicle emergence (Bradford & Bewley, 2002). Priming improves seed performance specially under stress conditions, inducing the rapid establishment of vigorous rice seedlings (Tilahun et al., 2013). Moreover, it improves the germination rate, growth of seedlings, and reduces the time to start germination (Drew & Dearman, 1993). Several seed priming methods are used to improve seed quality (Nawaz et al., 2013); hydropriming (use of water), osmopriming (use of solutions with low osmotic potentials), matrix priming (use of solid matrix; Harris et al., 2002), nutrient priming (use of solutions with micronutrients; Johnson et al., 2005) and hormonal priming (use of solutions with plant growth regulators; Ghobadi et al., 2012).
Neem has been used as pesticide and as a treatment for many fungal and bacterial diseases in crops (Girish & Bhat, 2008). Isolated chemicals as well as neem seed extract have shown antibacterial (Coventry & Allan, 2001;Biswas et al., 2002), antifungal (Achimu & Schlosser, 1992;Coventry & Allan, 2001;Biswas et al., 2002;Wang et al., 2010) and anti-viral (Biswas et al., 2002) properties. Further, neem seed extract has been reported to have significant antioxidant activity (Nahak & Sahu, 2011;Revathi & Thambidurai, 2019). Free radicle damage and pathogenic effects are the main factors reducing quality of seeds during storage (Copeland and McDonald, 2001). Thus, we hypothesized that antimicrobial and antioxidant effects of neem seed extract would improve the seed quality of traditional rice seeds. Furthermore, if neem seed extract is effective in improving seed quality it could be used as an organic treatment. Thus, the main objective of our study was to improve the seed quality of four selected traditional rice varieties in Sri Lanka with priming treatments using different concentrations of commercially available neem seed extract.
Four traditional rice varieties were used for the study. Three varieties (Madathawalu, Kaluhenati and Kuruluthuda) are cultivated in both Yala and Maha seasons whilst the other variety (Maa-Wee) is grown only in the Maha season (Ginigaddara, 2018). Kaluheenati and Madathawalu take 3 ½ months from sowing to harvest, while Kuruluthuda takes 4 months. In contrast, Maa-Wee require 5-6 months to get mature. Generally, Maa-Wee have a strong root system and healthy tillers. It is popular in Ratnapura, Kalutara, Galle, Matara and Gampaha districts (Personal communications with farmers). Madathawalu is suitable for muddy rice fields and cultivated in all districts. However, this variety is recommended by the Department of Agriculture for acidic soils. Kuruluthuda is better for flooded and high saline fields. Kaluheenati is suitable for puddled muddy lands and perform well in dry zone conditions (Ginigaddara, 2018

Seed moisture content
Ten replicates of 10 seeds each from each variety were taken randomly and the seed samples were crushed separately using motor and pestle. Fresh weights of these crushed samples were measured using an analytical balance to the nearest 0.0001 g and were oven dried at 121°C for 3 h. Seed samples were reweighed, and moisture content was calculated in fresh mass basis (Fischer, 2007).

Imbibition of seeds
This experiment was conducted to evaluate the imbibition pattern of seeds to determine the suitable priming time. Four replicates of 20 seeds from each variety were weighed using a digital chemical balance to nearest 0.001 g. The seed samples were immersed in 30 ml of distilled water in beakers with aluminium foil lids and incubated at 25 °C. Seed samples were retrieved after 2, 4, 6, 8, 24, 48 and 72 h, surface blotted, reweighed and returned to the beakers. Imbibition curves were prepared.

Initial seed germination
Three samples containing three replicates of twenty seeds from each rice variety was taken randomly and incubated on tissue papers moistened with distilled water in 9 cm diameter Petri dish. One samples of each variety were incubated at 25 o C in a temperature-controlled incubator [Model-MGC-450BP, Company-Qualitron (Pvt) Ltd., Rajagiriya], at 35 o C in a temperature-controlled incubator [Model-MGC-250P, Company-Qualitron (Pvt) Ltd., Rajagiriya] and the other at the ambient room temperature conditions. Samples were watered every day with distilled water and germinated seeds were counted for two weeks. Germination rate and the percentage were calculated.

Hydro-priming
Four replicates of 100 seeds from each variety were used for each priming treatment. Seed samples were weighed and immersed in 100 mL of distilled water in a 250 mL beaker. Seed samples were kept in distilled water for 0, 24, 48 and 72 h separately and were retrieved and reweighed. Then the seed samples were air dried until they came to their initial weight.
After the priming treatments, the vigour of the primed seeds was determined using the seedling growth test. Further, seed germination under laboratory conditions and seedling emergence under plant house conditions in rice field soils were studied after four pre-soaking treatments, i.e., 0 (no soaking), 24, 48 and 72 h soaking in distilled water as practiced by the traditional farmers.

Seed germination under the laboratory conditions
Hydro primed seed samples (from each priming treatment) and a non-primed sample from each species were incubated on manila papers moistened with distilled water. Manila papers with seeds were rolled and kept for germination under room temperature. Seeds were observed for germination after 7 d. The same experiment was conducted at 25 and 35 o C in temperature-controlled incubators.

Seed vigour test
Seed vigour of the primed seed samples were determined using the seedling growth criteria (Hampton & TeKrony, 1995). Twenty-five seedlings from each replicate of each sample mentioned above were selected randomly and were placed on a black coloured cloth and photographed. Root length and shoot length of the seedlings were measured using the images with the aid of Image J software.

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Journal of the National Science Foundation of Sri Lanka 49(4)

Seedling emergence under the plant house conditions
Four replicates containing 100 primed (from each priming treatments separately) and non-primed seed samples of each species were pre-soaked in distilled water as explained above and incubated on moistened paddy field soil in separate 30 × 45 cm 2 plastic trays at ambient plant house temperature conditions. Trays were watered every day for 7 d. Emerged seedlings were counted after 7 d. This experiment was conducted using only the best distilled water priming treatment and the best neem priming treatment as identified from seed germination and from seed vigour tests. Thus, the experiment was initiated two weeks after the initiation of the seed germination and seed vigour tests.

Seed priming with neem seed extract
Commercially available neem seed extract (Kohomba Saraya, 322/7, Negombo road, Kurunegala) was used, as neem seeds were not available at the time of initiation of the experiment. This commercially available neem seed extract is 100% natural as verified by the producers.
According to the producer, neem seed extract has been prepared by crushing 5 kg of neem seeds and mixing with 10 L of water. This mixture has been kept overnight (12 h) and filtered. The filtrate was made up to 100 L by adding water.
Three samples containing four replicates with 100 seeds in each were selected randomly from each study rice variety and weighed with a digital chemical balance to the nearest 0.001 g. Seed samples were immersed in 100 mL of three different neem extract concentrations prepared (50 mL of neem solution mixed with 1 L of distilled water -full strength, 25 mL of neem solution mixed with 1 L of distilled water -half strength and 12.5 mL of neem solution mixed with 1 L of distilled waterquarter strength) from the commercially available neem seed solution.
Seed samples were allowed to imbibe neem solutions for 24, 48 and 72 h, after which seed samples were reweighed and air-dried until they came to their initial weight. Neem primed seeds samples were subjected to pre-soaking treatments as mentioned in hydro-priming. Then, seed germination at laboratory conditions, seed vigour, and seedling emergence under plant house conditions were studied as explained above. Different treatment combinations of priming and pre-soaking are depicted in figure 1.

Analysis of data
Arc-sine transformed germination percentage data, shoot and root length data and conductivity data were analysed using one-way and two-way ANOVA procedures. All the data were statistically analysed using Minitab 17 statistical software. All the graphs were drawn for nontransformed data using Sigma Plot 10.0 software.

Seed moisture
Dry weights of studied rice varieties were between 1.72-2.33 g. Seed moisture contents of four traditional rice varieties were between 13-15% (Table1).

Analysis of data
Arc-sine transformed germination percentage data, shoot and root length data and conductiv analysed using one-way and two-way ANOVA procedures. All the data were statistically a Minitab 17 statistical software. All the graphs were drawn for non-transformed data using Si software.

Seed moisture
Dry weights of studied rice varieties were between 1.72-2.33 g. Seed moisture contents of four varieties were between 13-15% (Table1). Table 1: Average (± SD: standard deviation) seed moisture content of the four rice varieties stud

Imbibition of seeds
Seeds of all the rice varieties increased in mass during the imbibition (Figure 2). Even afte imbibition none of the seeds of different varieties reached the lag phase of seed germination.

Imbibition of seeds
Seeds of all the rice varieties increased in mass during the imbibition ( Figure 2). Even after 72 hours of imbibition none of the seeds of different varieties reached the lag phase of seed germination.

Seed germination
Seeds with Kaluheenati germinated to ~ 80% at 25 o C and at ambient laboratory temperature conditions ( Figure 3). Seeds of Madathawalu, Kuruluthuda and Maa-Wee germinated to ~60, 70 and 50%, respectively at these temperatures. However, at 35 °C, seeds of all the tested varieties germinated to < 20%.    Seeds of these four rice varieties, except Kaluheenati, had germination percentage <70% within 7 days at all the temperatures tested. The remaining seeds were soft and rotted within a short period. Low initial germination indicated that the initial quality of seeds of these four varieties was low. Further, observed low germination percentages of seeds in studied varieties confirmed the claims of the traditional rice-growing farmers that seeds of traditional varieties had lower germinability. Even though the seeds were stored < 2 weeks by the supplier  (Krishnan et al., 2011). Several researchers have shown that the temperature requirement of rice seeds for germination depends on the rice variety (Tanida, 1996;Krishanan et al., 2011).
Preliminary imbibition experiments showed that seeds of all the studied rice verities would not have attained the lag phase (Bewley, 1997) of seed germination within 72 hours of the study period. Thus, we used seed priming treatments 24-, 48-and 72-hours duration in all the priming experiments conducted during the research.

Seed germination at laboratory conditions
Kaluheenati: Non-primed Kaluheenati seeds germinated to 63% within 7 days, while most of the priming treatments improved the germination percentage. However, the significantly highest germination percentage was observed in seeds primed for 24 hours with distilled water subjected to 24 hours pre-soaking treatment (86%) and 24 hours priming with a half strength of neem extract subjected to 24 hours pre-soaking treatment (85%, F = 5.6, p < 0.01, Table 2).
Kuruluthuda: Non-primed Kuruluthuda seeds reached only 32% cumulative germination within 7 days. However, significantly higher germination percentage was observed after 72 hours priming of seeds in distilled water followed with no pre-soaking treatment (55%), 72 hours priming of seed in half strength neem extract with no pre-soaking treatment (57%), 72 hours priming of seed in half strength neem extract followed by 48 hours soaking treatment (56%) and 72 hours priming of seed in quarter strength neem extract followed by 24 hours soaking treatment (64%, F = 7.31, p < 0.01; Table 2).

Maa-wee:
Germination percentage of Maa-wee (unprimed 25% within 7 days) has significantly increased by many priming treatments. The highest germination was recorded after priming with quarter strength neem extract for 48 hours + 48 hours soaking (49%) ( Table 2). Germination percentage after these priming treatments are significantly higher than the control (F = 11.4, p < 0.01).

Seed vigour of primed seeds
Kaluheenati: Root length (121.3 mm) of the seedlings developed from seeds primed in ½ strength neem extract for 24 hours + 24 hours soaking were higher than those developed from non-primed and non-soaked seeds (86.8 mm), and those developed from seeds subjected to other priming and pre-soaking treatments (F = 90.4, p < 0.001, Figure 4). Shoot length followed a similar trend (F = 17.5, p < 0.001).
and non-soaked seeds ( Figure 5). Same trend was observed in shoot length data (F = 27.8, p < 0.001).  Kuruluthuda: Seedlings with significantly higher root lengths (F = 12.1, p < 0.001) were produced by seeds primed with ¼ strength neem extract for 24 hours + 0 hours soaking, than those developed from non-primed  Error bars mean ± SD. Only results of treatments that resulted in > 60 mm root length and >20 mm shoot length are shown in the figure.
Maa-wee: Root (F = 17.7, p < 0.005) and shoot lengths (F = 33.4, p < 0.005) of seedlings developed from seeds primed in quarter strength neem for 48 hours + 48 hours soaking were significantly higher than those developed from non-primed and non-soaked seeds and those developed from seeds subjected to other priming and pre-soaking treatments ( Figure 6).

Madathawalu:
Root lengths of seedlings developed from seeds primed with full strength neem extract for 72 hours + 48 hours soaking, and with full strength neem extract for 48 hours + 0 hours soaking were significantly higher than non-primed and non-soaked seeds (63 mm) and those developed from the seeds subjected to other priming and soaking treatments (F = 9.1 p < 0.005, Figure 7). Shoot length (70.4 mm) of seedlings developed from seeds primed in full strength neem extract for 72 hours + 48 hours soaking was significantly higher (F = 4.90, p < 0.005) than those of non-primed and non-soaked seeds (32.4 mm). Figure 6. Mean of root (A) and shoot (B) lengths of Maa-wee seedlings developed from seeds subjected to different priming and soaking treatments. Different upper-case letters indicate significant differences between treatments. Error bars mean ± SD. Only results of treatments that resulted in > 60 mm root and > 20 mm shoot length were shown in the figure.

Kaluheenati
The seedling emergence percentage of non-primed seeds (65%) improved, significantly after priming with distilled water or neem extract ( Figure 8A). However, the seedling emergence percentage of seeds primed in half strength neem extract for 72 hours followed by 24 hours soaking was significantly (F = 28.9, p < 0.01) higher than that of all the other treatments (82.5%).

Maa-wee
Seedling emergence of non-primed Ma-wee seeds was very low (12%, Figure 8C). However, when seeds were primed with quarter neem extract for 48 hours, seedling  Madathawalu: Root lengths of seedlings developed from seeds primed with full strength neem extract for 72 hours + 48 hours soaking, and with full strength neem extract for 48 hours + 0 hours soaking were significantly higher than non-primed and non-soaked seeds (63 mm) and those developed from the seeds subjected to other priming and soaking treatments (F = 9.1 p < 0.005, Figure 7). Shoot length (70.4 mm) of seedlings developed from seeds primed in full strength neem extract for 72 hours + 48 hours soaking was significantly higher (F = 4.90, p < 0.005) than those of non-primed and non-soaked seeds (32.4 mm).

Kaluheenati
The seedling emergence percentage of non-primed seeds (65%) improved, significantly after priming with distilled water or neem extract ( Figure 8A). However, the seedling emergence percentage of seeds primed in half strength neem extract for 72 hours followed by 24 hours soaking was significantly (F = 28.9, p < 0.01) higher than that of all the other treatments (82.5%).
Non-primed Kaluheenati seeds had ~60% germinability. Among hydro-priming treatments, distilled water priming for 24 hours+ 72 hours pre-soaking treatment resulted the highest germinability, while among neem priming treatments half strength neem extract priming for 24 hours+ 24 hours pre-soaking resulted the highest germinability. Neem priming treatment has improved the germination percentage of Kaluheenati seeds to about 85%. This percentage germinability was significantly higher than that of the hydro-primed seeds too. Further, the highest root and shoot length were observed after seeds were subjected to ½ strength neem extract priming for 24 hours + 24-hour pre-soaking. Under glasshouse conditions, half strength neem extract priming for 24 hours+ 24 hours-pre-soaking treatment resulted the highest seedling emergence too. Therefore, Journal of the National Science Foundation of Sri Lanka 49 (4) December 2021 Percentage seedling emergence of non-primed Kuruluthuda seeds (10%) improved significantly (F = 76.4, p < 0.01) by distilled water (72 hours) or neem (quarter strength for 72 hours) priming (25%, Figure 8B).

Madathawalu
Seedling emergence percentage of non-primed Madathawalu seeds was~40%. When seeds were primed with full strength Neem extract for 72 hours, seedling emergence percentage has significantly (F = 29.9, p < 0.01) increased to 54% ( Figure 8D). half strength neem extract priming for 24 hours + 24 hours pre-soaking could be recommended as the best treatment to improve seed quality of Kaluheenati.
Kuruluthuda had a very low initial germination ~35%. When seed germination percentage was considered, the best hydro-priming treatment was distilled water priming for 24 hours with no pre-soaking and the best neem priming treatments were quarter strength neem priming for 72 hours + 24 hours pre-soaking and half strength neem priming for 72 hours with no pre-soaking treatments. Neem priming treatments have improved the seed germinability significantly to ~ 65%. However, no significant difference was observed between distilled water priming for 24 hours with that of the two neem priming treatments. However, the highest root and shoot length were observed in seedlings of seeds primed with quarter strength neem extract for 72 hours + 24 hours pre-soaking treatment. However, quarter strength neem extract priming for 72 hours + 24 hours pre-soaking treatment as well as distilled water priming for 24 hours with no pre-soaking treatment has increased the seedling emergence over that of non-primed or primed with other treatments. Further, there was no significant difference between seedling emergences of these two treatments. When all the germination parameters were considered, half strength neem extract priming for 72 hours + 24 hours pre-soaking was the best treatment for Kuruluthuda. Maa-wee also had a low initial germinability (~ 25%). Distilled water priming for 72 hours+ 72 hours presoaking treatment was the best hydro-priming treatment that resulted the highest germinability. However, there were several neem priming treatments which improved the germinability of seeds of Maa-wee. Nevertheless, the germination percentage of seeds within seven days of this variety was always < 50% indicating the initial low quality of the seeds. Although neem priming has significantly increased the shoot and root lengths of seedlings, there were no significant differences between the shoot and root lengths of seedlings of neem primed seed with that of distilled water primed once. However, quarter strength neem extracts priming for 48 hours+ 48 hours pre-soaking treatment resulted in significantly the highest seedling emergence percentage. Therefore, it revealed that the best treatment to improve seed quality of Maa-wee is the quarter strength neem extract priming for 48 hours+ 48 hours pre-soaking treatments.

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Journal of the National Science Foundation of Sri Lanka 49 (4) Madathawalu had initial germination of ~20%. Distilled water priming for 48 hours+ 48 hours pre-soaking treatment was the best hydro-priming treatment for Madathawalu to increase the seed germinability. Whereas full strength neem priming for 72 hours + 48 hours pre-soaking resulted the highest germinability among neem priming treatments. These treatments have significantly improved the germinability of Madathawalu seeds to about 55% but with no significant differences of germinability between the best hydro-priming and neem priming treatments. However, seed vigour (as determined with the shoot and root length) of seeds with full strength neem priming for 72 hours + 48 hours presoaking was significantly higher than that of the seeds hydro-primed for 48 hours + pre-soaking for 48 hours. Thus, full strength neem seed extract priming for 72 hours + pre-soaking for 48 hours could be considered as the best treatment for Madathawalu. However, there is no significant difference between seedling emergences of seed primed with full strength neem extract for 72 hours + 48 hours pre-soaking and that of 72 hours hydropriming + 72 hours pre-soaking.
The results of the priming experiments revealed that neem priming has a higher ability than water priming to improve seed quality of Kaluheenati, Kuruluthuda, Maawee and Madathawalu. There could be basically three reasons for reduced seed quality: imbibition stress during germination, antioxidant stress and pathogenic activity. During imbibition, if water enters to seeds without a control, it could cause reactive oxygen species (ROS) accumulation ( (Liu et al., 2007, Paparella et al., 2015. ROS could damage cellular components (Paparella et al., 2015). The reasons for the increment of seed quality (seed germination and seed vigour) with distilled water may be that it reduces imbibition stress. Neem extract has a lower water potential than distilled water. Therefore, it controls (reduces) water uptake. It could limit ROS formation and thereby reduce cellular damages and oxidative injuries. Further, neem seed extracts show antioxidant properties (Nahak & Sahu, 2011;Revathi & Thambidurai, 2019) and may reduce the effect of ROS during germination. Moreover, the anti-microbial activity of neem seed extract (Biswas et al., 2002) may reduce the pathogenic activities in the seed during germination. These may be the reasons for seed quality improvement shown after neem priming in our experiments. However, a detailed study has to be conducted to determine the mode of action of the neem seed extract during seed priming.
No studies on seed germination/vigour tests have been reported on the studied four rice varieties. However, several studies have been conducted to determine the effects of hydro-priming, dehydration priming and osmo-priming (by NaCl and KH 2 PO 4 ) on germination of rice seeds. Galappaththi et al. (2020) have reported that hydro-priming for 72 hours significantly improve the seed germination, vigour and emergence of two traditional rice varieties; Suwadal and Batapola-el. Illangakoon et al. (2016) have showed that seed hydropriming has improved the survival of both traditional and newly developed varieties under anaerobic conditions. They further reported that, hydro-primed seeds showed increased synthesis of soluble sugars, starch degradation and α amlylase activity compared to non-primed seeds under anaerobic conditions. They suggested that these enhanced activities are the modes by which hydropriming enhanced seed quality. Islam et al. (2012) have reported that CaCl 2 was the best osmo-priming agent. Priming using CaCl 2 enhanced all germination parameters of BRRI dhan41 rice variety in Bangladesh. Seeds of BRRI dhan41, when treated with NaCl, showed the highest germination percentage, germination energy, germination speed. However, vigour index was found to be highest in BRRI dhan40 when it was treated with KCl. BRRI dhan41 produced the largest root when seeds were treated with NaCl. BRRI dhan40 and BINA dhan7 produced the highest shoot length at the controlled and CaCl 2 treated seed, respectively. Esmeili and Heidarzade, (2012) have found that the osmo-priming mainly with PEG could improve seed germination and seedling development parameters of many rice genotypes.
Heretofore, neem priming has not been used to improve seed quality of any species. Our experiments showed the high potential of neem priming in the improvement of seed quality of traditional rice varieties. This finding is especially important as neem can be used as an organic agrochemical in organic farming. Thus, our experiments provide a solution to a basic problem of low seed quality faced by organic farmers who produce organic traditional rice.
According to the results obtained from our experiments, it revealed that hydro priming and neem priming are promising methods to enhance seed quality of all four traditional rice varieties studied. Priming treatments increase seed germinability, seed vigour and seedling emergence. Neem priming gives a more significant improvement of all these seed parameters thus, neem priming is more promising than hydropriming in improving seed quality of traditional rice varieties. However, it is necessary to determine how the antioxidant activity and other properties of neem affect the seed quality of rice.