EVALUATION OF THE QUALITY OF TOMATO SEED POPULATIONS FROM THE ORGANIC PRODUCTION SYSTEM DURING AGING

A total of six tomato seed populations, collected in the autumn of 2016 at different locations in Serbia (West (3), South (1), North (1) and East (1)), were enrolled in this study. Seeds of the tomato populations considered were produced in the organic growing system in the area of Zaovice (76 m a.s.l., chernozem), Stara Pazova, Northern Serbia (44 ̊ 47 '19.6" N, 20 ̊ 27' 56.2" E) in 2017. Analyses of the germination parameters of the tomato seed populations examined (namely the germination energy, total germination, abnormal seedlings and dead seeds of the tomato seeds considered) indicated significant (р < 0.01) differences according to the production year (A) and the tomato seed population (B). The impact interactions (р < 0.01) of these factors (A × B) proved significant only relative to dead seeds. A highly significant positive correlation was found between the germination energy and the total germination of the seeds considered (r = 0.8711, p < 0.001), as well as between the amounts of their abnormal seedlings and dead seeds (r = 0.92297, p < 0.001). The germination energy and the total germination of the tomato seeds considered were found to decrease with the increasing seed age, in contrast to the numbers of their abnormal seedlings and dead seeds which continued to increase with seed aging.


INTRODUCTION
Seeds are one of the basic preconditions of successful agricultural production and regular yields of high quality. Therefore, the identification and testing of seed quality, i.e. vigor, is of paramount importance to crop production (Poštić et al., 2019). Vigor or biological viability is used to describe the physiological properties of seeds responsible for their ability to germinate rapidly in the soil (Tabaković et al., 2013). There is a deficit in organic seeds both in Serbia and worldwide, which is being increasingly compensated for by conventional non-treated seeds. However, the EU experts have announced that organic production will not be able to use untreated seeds from conventional production as of 2021. Over the past twenty years, the global organic production has rapidly expanded due to growing concerns about human health and a great demand for "healthy" food (Postic et al., 2018). Organic farming and organic tomato production have recently been receiving increased attention in Serbia. However, there are no accurate data on the organic production of tomatoes in Serbia to date.
Nowadays, a 0.9 % share of the total agricultural land in the world is devoted to organic agriculture. However, the largest share of 6.2 % of the agricultural land devoted to organic farming is recorded in Europe. As many as eight EU countries have an average of more than 10 % of their agricultural land devoted to organic farming. However, only a 0.4 % share of the total agricultural land is devoted to organic farming in Serbia. A total of 13,423 ha were devoted to organic production in Serbia in 2017, or 0.4 % of the total Serbian arable land, with 6,022 registered organic producers (FiBL, 2020). Tomatoes are one of the most common and economically significant vegetable crops in Serbia, grown in the open field or in protected areas. The conventional production of tomatoes in Serbia approximates to 180,000 t, covering a land area of 20,000 ha. Owing to the lack of organic seeds in the market, domestic producers use seeds from their own production and/or local seed populations adapted to the agroecological conditions in Serbia (Ugrenović et al., 2015).
A continuous decrease in the number of well-established local seed populations in Serbia poses a great threat to the local biodiversity and genetic resources. In the face of increasing production issues caused by climate change, it is necessary to collect and preserve as many well-established local seed populations and plant varieties as possible because they carry many genes for resistance to various adverse environmental conditions and plant diseases (pathogens). The purpose of this study is to evaluate the effects of production year and seed population on the most significant indicators of the quality of organic tomato seeds. The results obtained emphasize the overriding importance of domestic seed populations and plant varieties of tomatoes and other vegetable crops for organic agriculture.

MATERIAL AND METHOD
Production of tomato seeds in the organic farming system. A total of six tomato seed populations, collected in the autumn of 2016 at different locations in Serbia (West (3), South (1), North (1) and East (1)), were enrolled in this study. Seeds of the tomato populations considered were produced in the organic growing system in the area of Zaovice (76 m a.s.l., chernozem), Stara Pazova, Northern Serbia (44˚ 47 '19.6" N, 20˚ 27' 56.2" E) in 2017. The soil properties are shown in Table 1.
Seed sowing was performed using containers in early April, whereas planting in the open field was carried out in mid-May (at a distance of 0.4 × 0.7 m and in a plot area of 10 m 2 ). Crop management was conducted according to the commonly accepted recommendations for growing tomatoes in the organic production system. Tomatoes were harvested at full physiological maturity during August and September, followed by seed extraction and 24-hour seed fermentation. Seed drying was performed in the shade at room temperature. The seeds were stored in PVC bags at a temperature below 15ºC, RH 50%. The data on meteorological conditions are shown in Table 2. Seed quality assessment. The evaluation of tomato seed quality (namely the germination energy, total germination, abnormal seedlings and dead seeds of the tomato seeds considered) was conducted in 2017, 2018 and 2019 at the Laboratory for Seed and Planting Material Testing of the Institute for Plant Protection and the Environment in Belgrade.
The germination testing of six seed populations considered was performed using a standard laboratory method involving filter paper moistened with a 0.2 % aqueous KNO 3 solution at 4 × 100 seeds. The seeds were incubated for 14 days at a temperature of 20-30 °C and a relative air humidity of 95 %. The germination energy after 5 days of incubation, the total germination and the numbers of abnormal seedlings and dead seeds after 14 days of incubation of the tomato seeds considered were determined according to the Rules on the Quality of Seeds of Agricultural Plants ("Official Gazette of SFRY ", no. 47/87), which are in accordance with the ISTA Rules (ISTA, 2002(ISTA, -2018. Statistical analysis. The experimental data obtained were processed using the statistical package STATISTICA 8.0 for Windows. Differences between the treatments were determined using the analysis of variance (ANOVA), whereas the least significant difference (LSD) test was used for individual comparisons. Correlations between the parameters observed were determined using the Pearson correlation coefficient (r).

RESULTS AND DISCUSSION
Analyses of the germination parameters of the tomato seed populations examined (namely the germination energy, total germination, abnormal seedlings and dead seeds of the tomato seeds considered) indicated significant differences (р < 0.01) according to the production year (A) and the tomato seed population (B). The results obtained in the present study are consistent with the results of Stanisavljević et al., (2018). The impact interactions (р < 0.01) of these factors (A × B) proved significant only relative to dead seeds.  The total germination of the tomato seed populations considered ranged from 81 % to 98 % ( Table 5). As expected, the highest average total germination of 94 % was determined in 2017, followed by 88 % in 2018 and 84 % in 2019. After harvest (2017), the decreases in the overall germination of the tomato seed populations considered ranged on average from 6 % in 2018 to 10 % in 2019. The results obtained are consistent with the results of Poštić et al., (2011). Lower variability was found in the germination energy (Table 4) and the total germination (Table 5) of the tomato seeds considered, ranging from 3.15 % to 11.43 %. The number of abnormal seedlings of the tomato seeds considered was found to increase with the increasing age of tomato seeds, ranging from 0 % in the first year to 9 % in the third year (Table 6). The smallest average number of abnormal seedlings of 3.33 % was observed in the Jabučar East population (Negotin), whereas the largest number of abnormal seedlings of 7.33 % was observed in the Jabučar West population (Šabac). The number of dead seeds of the tomato seeds considered increased with seed aging, ranging from 2 % in the first year to 10 % in the third year (Table 7). High variability was found for abnormal sprouts (Table 6) and dead seeds (Table 7), ranging from 13.32 % to 91.65 %.
The coefficients of correlation (r) computed express the interdependence between the seed quality parameters observed ( Table 6). As expected, a highly significant positive correlation was found between the germination energy and the total germination of the tomato seeds considered (r = 0.8711, p < 0.001), as well as between the numbers of their abnormal seedlings and dead seeds (r = 0.92297, p < 0.001). The results obtained are consistent with the results of Stanisavljević et al., (2017). Table 4. Effects of the production year and seed population on the germination energy (%)

Population (B) / Origin
Year (  The strongest negative correlation was found between the germination energy of the tomato seeds considered and the numbers of their abnormal seedlings (r = -0.82930, p < 0.001) and dead seeds (r = -0.87727, p < 0.001), as well as between the total germination of the tomato seeds considered and the numbers of their abnormal seedlings (r = -0.97903, p < 0.001) and dead seeds (r = -0.98202, p < 0.001).

CONCLUSION
Production year, seed population and plant variety exerted strong effects on the quality of organic tomato seeds (namely the germination energy, total germination, abnormal seedlings and dead seeds of the tomato seeds considered). The tomato seed populations examined exhibited lower variability in the germination energy and the total germination with seed aging. However, high variability was observed in the numbers of their abnormal seedlings and dead seeds. A highly significant positive correlation was found between the germination energy and total germination of the tomato seeds considered (r = 0.8711, p < 0.001), as well as between the numbers of their abnormal seedlings and dead seeds (r = 0.92297, p<0.001). The germination energy and the total germination of the tomato seeds considered were found to decrease with the increasing seed age, in contrast to the numbers of their abnormal seedlings and dead seeds which continued to increase with seed aging.