THE EFFECT OF MATURATION STAGE AND AFTER-RIPENING ON SEED QUALITY IN ORGANICALLY- AND CONVENTIONALLY PRODUCED PEPPER (CAPSICUM ANNUUM L.) SEEDS ABSTRACT

High-quality seed production is essential in organic production as well as in conventional production. Fruit maturity can be observed at different times due to the continuous flowering of pepper plant. Consequently, seeds with different maturity stages were obtained as the fruits were collected during once over-harvesting period. Immature seeds collected in once over-harvest may cause quality losses in the seed lot. Hence, this study was conducted to determine the effect of after-ripening on mature and immature pepper seeds produced in organic and conventional production systems. To see the effect of after-ripening treatment, seeds were harvested in two different periods (immature 45-50 days after anthesis(DAA) and mature 60-65 DAA). Afterripening (AR) was performed by keeping the seeds in fruits for 7 days after harvesting the fruits. Effect of production systems and after-ripening on immature and mature pepper seed lots were assessed for four cultivars harvested in 2015 and 2016. After-ripening increased germination (AR:76.3%, C:28% for organic and AR:88%, C:53.8% for conventional), seedling emergence (AR:70.8%, C:44.3% for organic and AR:82.5%, C:53.8% for conventional) percentages and mean weight of 1000 seeds (AR:6.5, C:6.0g for organic and AR:6.5, C:6.2g for conventional) in both production systems of immature seed lots compared to control (C)(P<0.05) but did not have a similar effect on mature ones. Moreover, organically-produced seed lots have the same quality as conventionally-produced seeds. Consequently, obtained results indicate that after-ripening can be used to enhance the quality of immature seeds of pepper cultivars and seeds can be produced organically without any loss of quality.


INTRODUCTION
Seed is one of the most important elements in terms of increasing yield and obtaining high quality crops. Organic crop growing systems may claim to produce even higher quality reproduction material compared to conventional growing methods DOI: 10.37317/ pbss-2020-0003 (Sripathy et al., 2012). Seeds and other production materials used in organic farming should be produced organically (Anonymous, 2005). Thus, organic seed is the initial material for organic plant production. The demand for organic seed has grown rapidly in recent years. Accordingly, sales of organic products were worth nearly $43 billion in 2015, an 11% increase compared to 2014. The food share of this amount was $39.7 billion (Anonymous, 2016). Accelerated understanding of health and environmental matters accompanied by the intense use of chemicals attracted attention to different methods of agriculture in the world. Organic farming is defined as a production method that protects the natural balance and includes human and environmentally friendly production systems, ensuring soil has sustainable efficiency, increasing the resistance of the plant, and recommending biological methods in plant protection (Tasbasli et al., 2003).
Organic seed production usually involves higher costs than conventional seed production because of losses throughout the seed production period or inadequate quality of seed production (van der Zeijden, 2003). When research about organic vegetable seed production is examined, it was observed that the studies were limited to some vegetable species and this was related to the vegetation period (Bonina and Cantliffe, 2004). The longer vegetation period in vegetable seed production causes the plants to be exposed to ecological conditions for a longer period of time. Hence, research is required to handle these problems and support seed companies in advancing their organic seed production and seed treatment techniques (Groot et al., 2004).
Determination of appropriate harvest time during seed development for high quality is of great importance for seeds that contain high seed moisture during maturation . Pepper (Capsicum annuum L.) seeds contain seed moisture at maturity (Demir and Ellis, 1992a) and a high germination rate is not easily achieved due to the indeterminate flowering seed maturation on the plant. For this reason, the ideal harvest time in terms of fruit maturation directly affects the seed quality of the pepper seed lots (Sinniah et al., 1998;Demir and Samit, 2001;Dias et al., 2006;Vidigal et al., 2011;Caixeta et al., 2014;Nogueira et al., 2017;Demir et al., 2018).
Fruit maturity can be observed at different times due to the continuous flowering of the pepper plant. As a result, seeds with different maturity are obtained as the fruits are collected during one over-harvesting period in commercial seed production. When the seeds with different maturity are mixed, the immature seeds may cause a decrease in the quality of the seed lots by adversely affecting seedling emergence and uniformity (Demir and Ellis, 1992a). For this reason, pepper seed lots can be composed of immature, mature, and over mature seeds due to differences in flowering time and one over-harvesting.
Earlier studies indicate that seed quality was enhanced by keeping seeds in harvested fruits for a while (Edwards and Sundstrom, 1987;Sanchez et al., 1993;Desai et al., 1997;Vidigal et al., 2006;Dias et al., 2006;Vidigal et al., 2009;Passam et al., 2010;Kalyanrao and Singh, 2014;Santos et al., 2015). Accordingly, if the vigor potential of the immature seeds is increased, it may have a positive effect on the overall quality of the seed lot (Vidigal et al. 2009). This may be more important when seed harvesting is done during once-over (harvesting all fruits at different maturation stages due to sequential flowering).
In previous reports, the effect of after-ripening treatment on seed quality was determined under conventional production conditions. However, to the best of our knowledge, there were no studies found about the effects of organic seed production system with after-ripening treatment on seed quality development and seed vigor performance. Hence, this study was carried out to assess the effect of after-ripening treatment linked to the maturation levels on organically-and conventionally-produced pepper seed lots. In addition, organic and conventional production systems were compared in terms of seed quality criteria.

Plant cultivation and seed harvest in organic and conventional production systems
The study was conducted in 2015 and 2016 in the organic and conventional production parcels of Atatürk Horticultural Central Research Institute -Yalova / TURKEY. "Surmeli", "Kandil Dolma", "Yaglik" and "Corbaci" open-pollinated pepper cultivars were used as plant materials.
During the vegetation period for seed production, different fertilizers were used depending on plant growth periods and the amount of plant nutrients in the soil. 'Gentasol' (30% total organic matter, 5% N, 3% K 2 O, 2% P 2 O 5 ), 'Ormin K' (30% K 2 O, %5 organic matter), and 'Biofarm' organic fertilizers were used in organic seed production parcels and 20:20:20 (NPK), potassium sulfate (50% K 2 O) and 15:15:15 (NPK) compound fertilizers were used in conventional seed production parcels. Table 1 Soil properties of organic and conventional seed production parcels in [2015][2016] According to the results of soil analysis, the soil structures of the production parcels belonging to both vegetation periods (2015-2016) have a clayey structure. The soil pH was determined to be between 7.09-7.79. Therefore, the structures of the production parcels have slightly alkaline character. Soil salinity is between 0.07% and 11.11%, while the available phosphorus values in the soil range from 7.2 to 20.0 ppm. The amount of organic matter in parcels was found to be between 1.41-3.51% and the amount of exchangeable potassium in the parcels was between 202.5-310.0 ppm ( Seeds of four different pepper cultivars were sown in the second week of March in both vegetation periods. The medium used for seedling production is organic origin and contains 1:1:1 burned sheep manure, loam soil, and biofarm chicken manure. These materials were steam sterilized before use. The study was conducted according to the randomized complete block design with 4 replicates and each replicate contained 150 plants. Seedlings were planted in organic and conventional production fields in the second week of May in both seasons. Plant spacing was 0.8 m between rows and 0.4 × 0.5 m between plants with double rows. Before planting, biofarm chicken manure at a rate of 50 kg per 1000 m 2 was added to the organic parcels and 15:15:15 NPK at a rate of 50 kg per 1000 m 2 was applied to conventional parcels. Weekly fertilization was done depending on the plant growth and the amount of plant nutrients in the soil. "Gentasol" 20 L per 1000 m 2 was applied to the organic seed production parcels and 20:20:20 (N-P-K) 2 kg per 1000 m 2 of compound fertilizer was given by drip irrigation to the conventional seed production parcels. Potassium fertilization was done during the fruit phase. Accordingly, "Ormin K" 2 kg per 1000 m 2 was used in organic production parcels and potassium sulfate 1.5 kg per 1000 m 2 was given to conventional production parcels.
Plants began flowering in June in both production systems and both vegetation periods. Flowers were labeled on the day of flowering and fruits were harvested with two different maturities; 45-50 (immature) and 60-65 (mature) days after anthesis for each cultivar in both vegetation periods. The seeds from each harvest were kept in the fruits for 7 days under indoor conditions (about 23 °C and 70% RH). Afterward seeds were extracted and dried at 30 °C until the seed moisture content declined to 8%. Moisture content of dried seeds was determined according to the ISTA (2016) method. The mean weight of 1000 seeds was determined after the drying process. The dried seeds were kept in the dark at 4 °C in hermetically-sealed aluminum foil packets until use.

Germination test
The experiment was established with 4 replicates and each replicate had 50 seeds for each production system, after-ripening and harvest periods (i.e. 4 cultivars = 2 production systems × 2 harvests × 1 after-ripening and 1 control). Two pieces of Whatman No: 1 blotting paper were placed in 9 cm Petri dishes. Then 4 ml of 0.2% KNO 3 solution was added after the seeds were placed in the Petri dishes (ISTA, 2016). The germination test was carried out at 25 ºC in the dark and the percentage of germination was calculated using daily counts for 14 days. The germination papers were moistened as needed. Normal and abnormal seedlings were determined at the end of the germination experiment. Mean germination time was calculated based on the daily counts made during the experimental period (Ellis and Roberts, 1980).

Seedling emergence test
The seedling emergence test was conducted with the same protocol as the germination test (described above). Seeds from organic and conventional systems were sown in vials at a depth of 2 cm including a mixture of peat and per-lite (1:0.5). The vials were put in a climate-controlled chamber at 23 ± 2 °C and 60-70% relative humidity with 16 hours of light and 8 hours dark conditions. Emergence counts were made daily for 25 days. The seedling emergence percentages (the appearance of hypocotyls at the surface) were determined after 25 days. Mean emergence time was recorded by virtue of the daily counts made during the experimental period (Ellis and Roberts, 1980).

Weight of 1000 seed
Using a seed counting machine, 1000 seeds from each seed lot were counted with four replicates and subjected to statistical analysis.

Statistical analysis
The laboratory tests in the study were established in accordance with the experimental randomized parcel design. Field trials were conducted according to the randomized complete block design. The percentage of values obtained from these tests were subjected to transformation. JMP 8.0 Statistical package program was used for anal-ysis. Data were assessed with analysis of variance for the main effects, whereby the means of values were compared using the Duncan Multiple Range Test and Least Significant Difference test (p=0.05).

RESULTS
There were statistically triple interactions found between production systems, harvest periods and after-ripening treatment for all viability and vigor tests. The difference between organic and conventional production systems was found to be statistically insignificant using germination and seedling emergence tests in consecutive years.
Evaluation of seed vigor with the mean germination and emergence times gave analogous outcomes to the germination and seedling emergence percentages. AR treatment for immature seed lots shortened the germination and emergence time in both production systems and years (Table 5 and 6). Consequently, seed vigor of immature seed lots was enhanced by AR treatment in organic and conventional production systems. On the other hand, mature seed lots were not affected by AR treatment in both production systems. The mean germination times for AR-treated immature seed lots were 4.9 and 4.2 (days), while it was 5.8 and 5.4 (days) in the control group for the organic system in 2015 and 2016. AR-treated immature seed lots were 4.6 and 4.3 (days), whilst the control group was 6.0 and 5.5 (days) for the conventional system.
There was no statistical difference found between organic and conventional production systems in terms of mean germination and emergence times for all the cultivars in both years (Tables 5 and 6).
The mean weight of 1000 seed (all cultivars) values remained constant for AR-treated mature seed lots from organic and conventional systems (6.6 -7.1 and 6.5-7.2 g respectively) compared to control groups (6.8-7.2 and 6.6 -7.2 g respectively) in 2015-2016 (Table 7). Yet, AR treatment significantly improved the accumulation of dry matter content in immature seed lots for both production systems (C: 6.0, AR: 6.5 for organic and C: 6.2, AR: 6.5g for conventional) in the first year (P<0.05). But, this influence was not seen statistically in seed lots from the second year (C: 7.0, AR: 7.1 for organic and C: 7.1, AR: 7.2 g for conventional).
There was no statistical difference found between organic and conventional production systems for the means of the weight of 1000 seeds for all the cultivars in subsequent years as well. DISCUSSION Our research study examined the effect of AR treatment for different seed maturity levels from organically-and conventionally-produced pepper seed lots. In addition, the comparison was made with a conventional production system in order to determine whether the organic production system has an effect on quality of pepper seeds.
Each species and cultivars has specific needs for seed germination including certain features of seeds and environmental conditions (Baskin and Baskin, 1998). Our study indicates that similarities were recorded in the responses of all the cultivars to AR treatment, harvest periods, and production systems. This trend is seen in the results obtained by Yanmaz et al. (1994), Mavi et al. (2010), Kenanoglu et al. (2013), Demir et al. (2016), and Demir et al. (2018) who worked with more than one cultivar to see the influence of different treatments on these cultivars.
Many studies have been done to reveal the effect of after-ripening treatment on many species under conventional production conditions. Seed maturation of these species can continue for some time especially when harvested in the green fruit phase (Barbedo et al., 1994;Dias et al., 2006;Vidigal et al., 2009;Passam et al., 2010;Kalyanrao and Singh, 2014;Kumar et al., 2014;dos Santos et al., 2016). Yet, seed production using organic growing methods may influence seed quality (Yildirim and Demir, 2018). Thus, evaluating the treatment under organic production conditions has to be considered. Our findings indicate that the after-ripening treatment enhanced the germination and seedling emergence percentages and decreased the mean germination and emergence time of immature seed lots of all the cultivars belonging to organic and conventional production systems in both harvest years compared to the control group (P<0.05). However, the same effect was not monitored in mature seed lots. It was observed that the application of after-ripening had no effect on the mature pepper seed lots in both production systems. This could be due to the continuous growth of immature embryos reaching the physiological maturity of seed during after-ripening (Weston et al., 1992).
There was no statistical difference found between organic and conventional production systems in terms of germination and seedling emergence tests. Consequently, Duman (2009) reported similar results that differences between seeds produced in organic conditions and conventionally-produced seeds were insignificant according to viability tests. Seeds achieve their maximum quality some days after the maximum seed dry weight is reached (Welbaum and Bradford, 1988;Demir and Ellis, 1992b). Therefore, maximum seed germination and vigor is observed some days after maximum dry weight in fleshy-fruited species such as pepper. In our study, the data for the mean weight of 1000 seeds states that AR treatment slightly increased the seed weight of all the cultivars from the immature harvest period in both production systems in the first year. But this effect was not seen in the second year. Carvalho and Nakagawa (2000) reported that owing to high moisture content when seeds are stored in fleshy fruits, they are prone to respire more by consuming the endosperm; hence decreasing dry matter content. Conversely, some other reports suggest that considerable enhancement was recorded for a dry matter of seeds through nutrient transfer from fruit to seed during storage in fleshy fruits (Passam et al., 2010;dos Santos et al., 2016). It can also be claimed, and our results indicate that this may be the case, that it is caused by the climatic differences between the vegetation periods (Table 2).

CONCLUSION
In this study, triple interaction of production systems, harvesting periods and after-ripening treatment on the quality of pepper seed lots was demonstrated. It is suggested that the production of pepper seeds consider these interactions. It was concluded that pepper seed production can be done effectively with the use of organic inputs and there will be no significant losses in the viability and quality characteristics of the seed lots compared to the conventional production systems. AR treatment induced the development of immature seeds to a certain level, but the same effect was not seen in mature seed lots. Therefore, in order to improve the overall quality of pepper seed lots, the harvested fruits should be left for 7 days of after-ripening treatment before seed extraction in both production systems.