Dynamics of moisture content and sowing qualities of seeds in rice varieties during post-harvest ripening and storage

. Rice seeds at each stage of ripening are characterized by a certain state, structure and moisture. Such properties of rice as germination, nature, quality and duration of storage depend on moisture content. Biochemical processes in the grain do not end at the filling stage, but continue for some post-harvest period. To safely preserve the rice gene pool, it is necessary to clarify the effect of seed maturity and storage time on seed quality. The varietal characteristics of rice seeds were studied using 8 Kuban varieties harvested on days 35 and 45 after flowering. The structural-phase state of freshly harvested grain and after 5, 10 days of ripening in natural conditions at room temperatures, and then the dynamics of sowing qualities after 1, 6 and 10 months of storage are discussed. The following parameters were studied: moisture, germination, length of the seedling and seed root, mass of 1000 grains. Differences in the moisture yield of grain of different degrees of maturity, varieties with different types of grain are shown. The results of the evaluation of rice physico-chemical indicators at the end of post-harvest ripening are presented. Varieties with slow moisture yield during ripening were distinguished by increased grain size: Yakhont, Rubin, Thaibonne and Zlata. The germination of seeds increased as they ripened, compared with freshly harvested ones, after a month it increased by almost 50%, and reached its maximum value by 6 months of storage, after 10 months, on average, germination for the group of varieties has already decreased by 6%. The stage of seed harvesting significantly influenced the germination rates.


Introduction
Seeds of grain crops are essential to global crop production, human nutrition and food security.Consistently high crop yield depends on germinative power of seeds and the ability to sprout evenly in various environmental conditions [1].
Seed germination is an essential requirement for agricultural production and plays an important role in maintaining genetic diversity.The preservation of seeds of genetic diversity in gene banks and collections is of high importance for ensuring food security, while their initial quality is important.The stage of maturity at the time of rice harvesting greatly affects seed viability.At the same time, mechanized harvesting of seeds is not possible until their physiological maturation is reached and the moisture content in the grain is reduced.It takes about 30 days from flowering and pollination to ripening of rice grains, and grain filling with biosynthetic products generally lasts 20-25 days.[2], and the moisture in this phase is 40-42%.At the stage of filling -in milky ripeness, grain moisture content exceeds 35-50% and the duration of this phase is from 7 to 15 days.In the phase of wax ripeness of the grain, the accumulation of solids decreases and the humidity drops to 21-40%, in the phase of technical maturity, the processes of drying and polymerization take place, the endosperm hardens, and the humidity decreases to 18-20%.Further, respiration and biochemical processes already stop, ripening takes place and the full ripeness of the grain sets in, when the endosperm becomes glassy [3].Filling rate of rice seeds is initially low, then there is a phase of rapid filling, and then growth slows down again with the onset of ripening.
The optimum moisture content range for long-grain rice is considered to be 19 to 22%, and for short-and medium-grain rice -22 to 24%.However, when rice grains of a variety in the field reach a moisture content of 22%, heterogeneous grains with a moisture content of 15 to 45% can be found on the panicle.Lower moisture content reduces yield, leads to the formation of cracks and brittleness of rice grains at the stages of post-harvest processing [4].
The moisture yield of grain of different types is not the same -it depends on the size and anatomical features of the grains: the denser and less porous the shell of the grain is, the less is its moisture yield.For example, buckwheat has a higher moisture yield than wheat and corn, while legume seeds have a lower moisture yield.In large grains, the internal moisture content per unit surface is much higher than in small grains [5,6].
The intensity of seed respiration depends on moisture, while in rice a value above 14% is called critical, since its excess enhances the respiration process [7].According to the moisture content, grain is referred to the state: dry -up to 14%, medium dryness -up to 15.5%, wet -up to 17% and raw -over 17%.The increased moisture content makes it difficult to store rice safely and affects its longevity.For laying seeds for short-term storage, the moisture index should not exceed 12-13%, and for long-term low-temperature storage -6-8% [8].Understanding why, under the same storage conditions, some seeds remain viable for a long time, unlike others, is a fundamental question in seed biology.Earlier, we considered factors such as temperature, conditions and duration of seed storage, and also noted that seed germination depends on the early maturity of the variety and the timing of grain harvesting [9,10].
Scientists note that rice seeds have a wide range of protection systems that allow them to survive in a dry state and maintain high germination [11].The International Rice Gene Bank (IRRI, Philippines) stores more than 127 thousand accessions of Oryza sativa, O. Glaberrima, and to adjust the monitoring intervals and determine differences in the lifespan of seeds of different genotypes, sowing qualities of seeds harvested at 31, 38 and 45 days after flowering were studied [12,13,14].
Seed maturity and moisture are not only decisive for viability and other quality characteristics, but also affect the subsequent reproductive ability of plants [6,15].Freshly harvested seeds have a high physiological and biochemical activity, reduced viability and germination, unstable during storage [13,16].During full ripeness, complex biochemical processes in the grain do not end, but continue for some post-harvest period.At the same time, the amount of proteins, fats, starch increases in grain crops and sowing properties improve [17].
The ability to maintain quality depends not only on the conditions of seed maturation, the state of their ripeness, but also on subsequent storage conditions [5,18,19].Short periods of storage below room temperature are recommended to maintain rice quality [20].
The duration of the ripening process in cereal crops can be up to 2 months, however, it is a varietal trait and depends on the storage conditions of the seeds.Post-harvest ripening occurs if the moisture content is less than the critical value (14%), and no less important condition is the grain temperature in the range of 15-30°С [17].The timing of crop ripening affects the subsequent longevity and quality of seeds [21].
Russian scientists found that freshly harvested wheat seeds had a germination energy of 35% and a germination rate of 46%, and after 2 months of storage, the germination energy was 92%, the germination rate was 97%.This indicates that the seeds have reached full physiological maturity after 2 months of storage [22].Other researchers also confirm that in winter crops, the maximum germination and energy values were obtained from grain harvested at the end of wax ripeness, after a period of post-harvest ripening (1-2 months after threshing).Early harvesting was not conducive to obtaining quality seeds [23,24].
To predict the viability of seeds during storage, studies of genomic associations (GWA) are carried out that correlate with the longevity of seeds, for example, more than 100 genetic markers have been found for barley [11].Dehydrins play an important role in seed maturation, the gene encoding dehydrin (Os02g0669100) is located on chromosome 2 of the QTL [25].
It is assumed that the duration of storage and long viability of seeds is provided by a high level of a number of grain components, including sugars, proteins and antioxidants [26,27,28].From storage stresses, the seed coat performs an important protective function, while antioxidant flavonoids and vitamin E limit oxidative stress and provide a chemical barrier against fungal infections.The accumulation of antioxidant components in the shell of the grain occurs at the late stages of ripening.Seed tolerance to keeping quality is associated with the presence of late embryogenesis proteins (LEA), heat shock proteins (HSP), and seed longevity proteins [29], as well as abscisic acid (ABA), which is the main dormancy-inducing hormone [30].
It is known that moisture content affects the longevity of seeds, which varies significantly between species, differs within a species and between varieties [6].Thus, indica rice varieties have greater seed durability compared to other subspecies.Changes in seed quality during ripening in IRRI (Philippines) were studied on sixteen rice varieties, the germination of unripe seeds varied significantly, but in the phase of mass maturity it increased in all varieties, and it reached its maximum value 2 weeks after the final phase of development of orthodox seeds [31].
Effective conservation of Plant Genetic Resources (PGR) germplasm in international, national genebanks and collections of scientific organizations will ensure future global food security.Therefore, research in the areas of forecasting, monitoring and increasing the lifespan of seeds are relevant at the present time.The development of a reliable system for the conservation of genetic diversity and the technology of sample preparation of seeds, their timely reseeding remain important tasks of modern science [32].

Research goals and objectives
The goal of this research was to identify varietal differences in grain moisture yield, preservation of sowing qualities of seeds and the formation of the physicochemical properties of rice harvested with different degrees of ripeness to optimize the technology for preserving germplasm.Tasks to be solved: 1.
Assessment of the structural-phase state of the grain during ripening on the vine.

2.
Analysis of moisture loss dynamics of harvested grain during storage in natural conditions.

3.
Study of the sowing qualities of seeds with different degrees of maturity during post-harvest ripening and storage.4.
Phenotyping of biological and morphological characteristics of rice varieties.

5.
Express analysis of grain quality parameters of the studied rice varieties.6.
Determination of the influence of the degree of grain maturity of rice varieties of different types on the preservation of the sowing qualities of seeds.

Materials and methods
The rice growing zone in Krasnodar region, Russia is located in the third agro-climatic region, characterized by moderate moisture with an annual rainfall of 600-700 mm.The agro-ecological region of the location of the experimental plot of FSBSI "Federal Scientific Rice Centre" is characterized by a temperate continental climate, hot summers and relatively warm winters.The duration of the frost-free period in Krasnodar reaches 193 days.
The experiment was carried out in the period 2022-2023 on the basis of a collection nursery and demonstration sowing of rice varieties of different breeding stages in the laboratory of USI "Collection of Rice Genetic Resources".The collection of the "Federal Scientific Rice Centre" contains more than 7.3 thousand samples of cultivated rice from 42 countries of the world, indica and japonica subspecies [22].

Methods of field experiment
The field experiment was carried out on the irrigated plot of Federal Scientific Rice Centre (Belozerny settlement), when plants were grown under the same conditions at an equal planting density and on the agricultural background N90P60 K60 kg a.r./ha or 46 kg of nitrogen per 1 ha.Seeding rate -5 million viable seeds per ha.The size of the experimental plots was 12.0 m 2 , the distance between the rows in the plot was 15 cm, and between the plots -40 cm.The use of fertilizers, pesticides and herbicides was consistent with local rice production practices.
Plots were plotted in a randomized full block configuration with three repetitions, with 50 individual panicles randomly selected from each plot and hand threshed.Filled spikelets were separated from empty ones by sifting through sieves for further research.Experiment establishment, records, visual assessments, phenological observations were carried out according to the methodology of the scientific center ("Methods of experimental work on breeding, seed production, seed studies and quality control of rice seeds" / A.P. Smetanin V.A. Dzyuba, A.I. Aprod // Krasnodar, 1972.-156 p.).
The development phases of rice plants were recorded: seedlings, flowering, milky ripeness, waxy and full grain ripeness, when 75% of the plants on the plot reached the development phase; the description and measurement of vegetative traits of plants were carried out according to the method: "Standard Evaluation System for rice"/ INGER-IRRI, 1996.
Eight Kuban rice varieties of different ripeness groups (from 110 to 128 days) were grown and analyzed as experimental material.To develop the basis for monitoring the state of the biological component (seeds) of different subspecies composition, we assessed the seed and sowing qualities of 5 japonica varieties (Khazar, Rubin, Favorit, Yakhont, Azovsky) and 3 indica varieties (Thaibonne, Mars, Zlata) ("Composition and classification of rice Oryza sativa L." / Lyakhovkin, 1994.-72 p.).

Assessment of the structural-phase state of the grain
Rice panicles of each variety were harvested from plants at different grain moisture content in two options: on day 35 after flowering at the end of the wax ripeness phase (option I) and on day 45 after flowering at the full stage of ripeness (option II).The mass of the sample was 0.15 kg; panicles were delivered to the laboratory, threshed by hand, and empty spikelets were removed.Humidity, temperature, mass of 1000 grains, germination were determined for freshly harvested grain and it was left for natural drying in paper bags.Grain mass storage mode: at room temperature (25+2°C and air humidity 50-55%), with the analysis of grain moisture dynamics on the 1st, 5th and 10th day after harvesting.On the 5th and 10th day after harvesting, the evaluation of the studied parameters in the drying grain was repeated.Measurement of moisture, nature and temperature of the grain was carried out by a non-destructive method according to the instructions for the Wile-200 device (Moisture naturometer).

Determination of seed germination
Rice seeds were germinated using a Barnstead Lab-Line General Purpose incubator and Petri dishes.In total, 50 grains of each variety were tested in duplicate.Dry seeds were placed in Petri dishes (9 cm in diameter) with two sheets of filter paper and 20 ml of distilled water were added, germinated at 28±1°C for 7 days in accordance with the methods: Russian Standard 12038-84 "Seeds of agricultural crops.Methods for determining germination".Seeds were washed and moistened every 2 days.The standard germination of seeds was determined when the seeds had a coleoptile that reached half the length of the seed and when the length of its root reached the length of the grain.The percentage of germination was calculated for the viable proportion of the seed population of each variety, from 50 seeds the number of normally germinated seeds was counted and then multiplied by 2.

Testing the sowing qualities of seeds during storage
After harvesting, the seeds were cleaned and placed in kraft paper bags before dry storage at a constant temperature of 25+2°C for up to 12 months.Sowing qualities were analyzed immediately after harvesting, as well as after 1, 6 and 10 months of storage.
In order to obtain comprehensive information on the dynamics of the parameters of rice sowing qualities, the following measurements were carried out: germination, length of the seedling and roots.Growth power was determined: according to Russian Standard R52325-2005 "Seeds of agricultural plants, varietal and sowing qualities".The length of seedlings and primary roots of ten randomly selected normally germinated seeds was measured on day 10 in terms of replication.

Phenotyping method
Rice sowing in the Kuban is carried out in the first ten days of May, flowering of early ripening varieties occurs in July, medium and late ripening -in August, seed harvesting occurs from September to October.A visual assessment of the onset of the flowering phenophase in the plots and maturation was recorded for each variety separately.
Morphological characteristics of grain (shape, color, size) were evaluated in the laboratory after harvesting using a computer, an HP Scanjet G4050 scanner and an image analysis system.The spikelet shape was determined visually: short-grain varieties, depending on l/b (grain length to width ratio), have a rounded or oval-rounded grain shape, medium-grain varieties have an oval, semi-spindle grain shape, and long-grain varieties have an elongated, long, and spindle-shaped grain.
Mass of 1000 grains was determined by counting two samples of 500 grains in a row, without selection, using an automatic seed counter SLY; Weighing was carried out on a Scout laboratory balance with an accuracy of 0.01 g.
To measure the indicators of physicochemical characteristics of rice grain by a nondestructive method, the Bruins "Universal Express Analyzer MultiCheck Plus" operating in the near infrared range in the "transmission" mode was used.An infrared analyzer in triplicate obtained the percentage of the total amount of starch, amylose, protein and free fats, the total vitreousity of rice.Standard quality assessment methods: Russian Standard 10987-76 "Grain.Methods for determining vitreousity", Russian Standard 10843-73."Grain.Method for determining filminess".
Statistical analysis was performed using the Excel -2016 program.Data are presented as the mean value ± standard error of triplicate measurements.Significance level is expressed for P < 0.05.

Moisture yield of rice with different degree of maturity
Grain ripening does not end in the field, so freshly harvested seeds of the rice gene pool require careful monitoring and preparation before storage.Rice is harvested in the phase of technical ripeness, when the grain reduces moisture and the process of cracking is not yet high.The optimal harvesting time for early-ripening varieties is considered to be 35 days after flowering, and for mid-and late-ripening varieties -40-45 days.However, varietal differences in terms of moisture loss at the ripening stage and the achievement of full maturity should be taken into account.Phenotyping of moisture yield during grain maturation for all the studied varieties was carried out upon reaching these terms (Fig. 1).Further, after harvesting, the dynamics was observed and the rate of moisture loss was determined for 10 days during the ripening of freshly harvested grain at room temperature.

Characteristics of grain size of rice when ripening on the stalk
During the period of rice ripening on the root from 35 to 45 days after flowering, the change in the mass of 1000 grains in the studied 8 Kuban varieties was evaluated (Fig. 2) Fig. 2. Dynamics of the mass of 1000 grains (grams) on the root in 8 rice varieties in the range from 35 to 45 days after flowering

The results of assessing the sowing qualities of seeds of rice varieties during storage
For the safe preservation of the crop gene pool in the structure of the collection, it is equally important to assess the sowing qualities of seeds of different degrees of maturity.How the harvest time and post-harvest ripening affected the sowing qualities was determined using an experiment with storage periods.It is known that freshly harvested grain has a reduced germination capacity, as well as after a year of storage of seeds, sowing qualities are reduced.Therefore, we controlled the sowing qualities in the interval from one month (during post-harvest ripening), 6 and 10 months of seed storage after harvesting.The average values of the results of the evaluation of germination, seedling length and root length are presented in table 1. Note: A* -factor "variety", B** -factor "seed harvesting period", C*** -factor "seed storage time"

Characteristic of biological and morphological properties of rice varieties
The results of phenotyping of biological, morphological and technological indicators of the studied rice varieties, which showed significant differences between the studied varieties, are presented in Table 2.

Characteristics of the physico-chemical properties of grain of 8 rice varieties
The results of assessing the moisture content, grain size and nature and biochemical composition of rice of the studied varieties by non-destructive methods after 10 months of storage are presented in Table 3. Note: * The average results of the evaluation of the biochemical composition of grain in five repetitions on an infrared analyzer are presented.Values are in Mean ± SEM, n = 5.

Discussion
When analyzing the moisture content of grain at an early degree of maturity, it was revealed that, depending on the harvesting time, the grain lost moisture with different intensity.It was found that on the 35th day after flowering, the moisture content of freshly harvested grain varied by variety within 21.6-25.0%,and after 10 days of storage it decreased to 15.0-16.8%.In grain with ripening on the root up to 45 days after flowering, the initial moisture content was 18.3-23.5%,and after 10 days of natural drying, it decreased to 13.8-17.9%.On average, for the group of varieties, for 10 days of grain standing on the root, its moisture content decreased by 2.02%.And for 10 days of storage of seeds in laboratory conditions, the average group decrease in moisture in the 1st selection option was 7.1%, and in the 2nd option -5.4%.The highest harvesting moisture on the 35th day after flowering was observed in the varieties Khazar and Favorit, and the lowest in Azovsky, Mars and Zlata.On the 45th day after flowering, increased harvesting moisture in the range of 22-23% was noted in the varieties Favorit and Rubin, and relatively low in the varieties Mars and Thaibonne (18-19%).It should be noted that the varieties Mars, Zlata and Thaibonne belong to the longgrain indica subspecies.Thus, it was revealed that by the 35th day after flowering, the varieties Azovskiy, Mars and Zlata had intensive moisture loss.And in such varieties as Khazar, Yakhont, Favorit and Thaibonne, intensive moisture loss was observed (from 2.5 to 4.0%) in the next 10 days of standing on the root, i.e., the longer the grain retains moisture, the longer the filling takes of this variety.
After reaching the technical ripeness of the grain in the period from 35 to 45 days after flowering and ripening on the root, the moisture content decreased in the varieties Yakhont by 0.4% and Azovskiy -by 0.7%, and in varieties Khazar -3.7% Thaibonne -4 .0%.The deceleration of moisture yield on the root shows that the grain is almost ripe for this period.Thus, it is shown that the best time for harvesting seeds of varieties Khazar, Favorit, Rubin, Thaibonne is recognized as 45 days after flowering.
When studying the dynamics of moisture yield in rice varieties for 10 days of storage of freshly harvested seeds in laboratory conditions, it was revealed that the moisture leveled off and reached an average of 16.3% for grains of the 1st harvesting option, 15.6% for the 2nd option.The maximum loss of moisture during this period was recorded in varieties Khazar, Thaibonne and Favorit (by 8.4-8.8%), and in the first 5 days the moisture yield was within 2-3%.Under laboratory conditions, the maximum moisture yield of grain is the 2nd harvesting period for varieties Yakhont, Rubin, Zlata (5.5-9.1%).Uniformly rapid drying of grain under natural conditions was noted in the varieties Azovsky, Zlata and Mars, in the varieties Khazar, Favorit, Yakhont and Rubin, relatively slow moisture loss was noted.This may be due to the different biochemical composition of the grain (Table 3), starch and proteins interact well with water, and the longer the filling, the denser the starch structure and less moisture transfer.
The rate of moisture loss in grain during ripening is due to the interaction of many factors that determine the differentiation of samples by grain moisture in the early stages of development and the rate of drying after reaching physiological ripeness.Before the onset of physiological ripeness, the rate of moisture loss is constant, and then there is a slowdown in the rate till grain harvesting.
The intensity of moisture yield during storage in grains of different degrees of maturity differs by variety and the following patterns have been identified:  The grain of the second harvesting period has already ripened on the root, reduced moisture content to 18-22%, and subsequently reduces moisture more evenly during storage. Drying of early harvest grain averages 0.76% per day, and second harvest grain -0.54% per day. Long-grain varieties, in contrast to short-and medium-grain rice, by the 45th day after flowering, reached the state of dry grain (14.0%), which is necessary for its preservation, more quickly.An assessment of the structural-phase state of the grain showed that for a number of varieties, early harvesting is not desirable, not only because of high moisture.The moment of maximum accumulation of dry weight of seeds is the moment of harvesting seeds with maximum physiological quality.From Figure 2, which shows the change in the value of the "mass of 1000 grains", it can be seen that the varieties Favorit, Yakhont, Zlata with increased grain size (29.8-34.3g) still continue to accumulate reserve substances of grain during the period of overmature standing, and they slowly lose moisture.The mass of 1000 grains in a number of varieties harvested on day 45 exceeded the indicator of the trait of an earlier harvesting date by 0.4-1.2grams.Due to the decrease in moisture content, the weight of grain on average for the group of varieties decreased by 0.55 g over a ten-day period of overmature standing.Thus, it can be seen that the rice varieties Azovsky, Khazar and Rubin had free water and during the period of overmature standing reduce the mass of 1000 grains.The issue of the accumulation of substances in the grain is important in connection with the determination of the optimal timing of harvesting.Having reached the technical ripeness of the grain, a number of varieties are not yet ready for harvesting, and the optimal time for them can be considered: 40-45 days after flowering.
The control of seed germination showed that the initial germination of freshly harvested seeds was in the range of 47-60%, and after a month of storage, its value reached 80-100% by varieties (Table 1).The best germination rates were noted for varieties Khazar, Yakhont, Favorit and Rubin (100%), i.e. in varieties with slow moisture yield.Experimental data confirmed that ripening under laboratory conditions of a grain with later harvest period was completed earlier than that of seeds of an early harvest period.This is evidenced by high rates of seed germination after a month of storage in uncontrolled conditions.There are significant differences in factor B "seed harvesting period": the average germination of the first term for the group of varieties is lower after 1 month of storage (90.8%) than for seeds of the second harvesting term (97.7%).After six months of storage, the germination of seeds of different degrees of maturity almost leveled off and reached 98%, and after 10 months, the average group indicator deteriorated to 90.6%.According to the factor C "storage time", there are significant differences in the germination of seeds of different phases of maturity: after 10 months, there was a tendency to decrease in the indicator for varieties of early harvesting to 87.6% and to 93.5% for later harvesting.According to factor A, the "variety", significantly worse germination rates for the storage period among the studied varieties were in the early ripening Azovsky, red-grained Rubin, long-grained variety Zlata and medium-grained Favorit.Which may be due to lower fat accumulation compared to other varieties according to Table 2. Long Xinkang and Guan Chunmin (2023) report that the sorption properties of grain are due to its capillary-porous structure and chemical composition.As part of the grain components, proteins are the most hydrophilic (retain up to 200% of water by weight), starch absorbs up to 70% of water, and fats practically do not retain moisture.[33].
The results of assessing the sowing qualities of seeds of rice varieties, presented in Table 1, demonstrate significant differences in the length of the seedling both between harvesting and storage periods.The correlation coefficient between the length of the seedling and the length of the root for the first harvesting period was 0.59 and r=0.43 for the second harvesting period, and the interdependence between the seed storage periods is negative and weak.The average group value of the "root length" in the seeds of the early harvesting period was significantly inferior to the indicators of the seeds of the late harvesting period, however, after 6 months of storage, this indicator began to significantly decrease.The length of the seedling varied by variety from 1.8 to 3.4 cm (option I) and from 2.2 to 4.1 cm (option II), and the length of roots from 4.5 to 9.6 cm (option I) and 6.5-10.2cm (option II).The experiment showed that if the grain is harvested ahead of time, then at least a month is required to achieve a stable seed quality, which should be taken into account when laying the germplasm for long-term low-temperature storage.
Of the studied varieties, the best sowing qualities were demonstrated by the varieties Khazar of the early harvesting period, and Yakhont, Favorit and Zlata -of the late seed collection period.On the contrary, late-harvested varieties Azovsky and Rubin demonstrated the best seed qualities only after reaching the six-month storage period.The long-grain varieties Mars and Thaibonne were comparatively inferior to the seeds of other varieties in terms of growth vigor.The observed increase in germination by six months of post-harvest storage may be associated with a gradual disruption of the dormant state, which was observed in freshly harvested seeds, and a change in the qualitative composition of starch and protein substances.So, in the studies of Akram M. (2009), in the variety Basmati 370, the dormant period was fixed within 50 days after harvesting, in other varieties, starch metabolism was completed within 4 weeks after ripening [34].The length of seedlings under conditions of short-term six-month storage tended to increase on average in the group by 0.29 cm for seeds of early selection and 0.98 cm for more mature grains.Seeds with a shelf life of 1 month were recorded to show the maximum root length (7.38 cm) compared to six-month-old seeds (6.91 cm).The shortest seedlings were noted in varieties Khazar, Azovsky and Thaibonne, and seed roots in varieties Mars, Rubin and Thaibonne.In the studied group of varieties, the most powerful roots and seedlings were observed in varieties Yakhont, Favorit and Zlata.In our study, the influence of the degree of maturity and shelf life on the length of seedlings and rice roots was found: the seeds of later harvest and after 6 months of storage had significantly better indicators.
Grain quality is evaluated in terms of its physical factors such as grain size, weight, moisture content and chemical composition.Studies show that changes in the physical properties of rice largely depend on its variety, storage conditions and amylose content, the durability effect is more pronounced in vitreous rice than in waxy one [16].When rice ripens, the qualitative composition of accumulated endogenous substances changes all the time, fats accumulate, proteins are synthesized at the expense of amino acids, and proteins have a low hydration capacity [27].It is noted that the higher the moisture content of the grain is, the lower its density and nature are.The high nature (bulk density) of the grain indicates its good filling, the degree of filling, therefore, maturity and high rates of starch endosperm; in rice, the nature value varies within 470-560 g/l.
The qualitative composition of the grain was determined at the time of completion of post-harvest ripening, according to tables 2 and 3, it can be seen that rice varieties reached an equilibrium moisture content in the range of 12.4-13.2%,and genetic differences in the mass of 1000 grains between varieties ranged from 22, 6 to 32.1g.Large-grain varieties have a lower grain filminess.The largest proportion of protein was registered in varieties "Mars" (10.76%) and varieties "Azov" (10.65%), amylose -in Zlata (21.9%) and Thaibonne (24.6%), free fats -in Mars (24 ,9%).
Of the studied, the best indicators of the grain nature (530-560g / l) and starch score (72-74%) were noted in the varieties Rubin, Thaibonne, Favorit, Zlata and Yakhont, which was confirmed in our experiment by a longer filling of grain, slow moisture yield and high initial moisture in these varieties, in contrast to the early maturing quickly losing moisture varieties Azov and Mars, and Khazar.

Conclusion
The structural and phase state of the grain of 8 Kuban varieties as part of the gene pool of the rice collection was studied to implement the tasks of creating proper conditions for preparing seeds of new genotypes for storage, understanding the optimal time for seed collection, reducing the cost of the breeding process and ensuring food security.
In the aggregate of all experiments, it was shown that the timing of harvesting and the stage of grain maturity affect the sowing qualities of seeds, and moisture is a sensitive diagnostic indicator of the accumulation of dry matter, but is not decisive.At the same time, significant genotypic differences were observed between varieties.
For 10 days of overmature standing on the vine, the moisture content decreased by an average of 2.2%.During natural storage (temperature 23 ± 4 °C) for 10 days of freshly harvested grain, the rate of moisture loss from early harvest grain is 0.76%/day and for late harvest -0.54%/day.
In fresh seeds of the studied varieties, a state of dormancy was maintained, which was eliminated already after a month of post-harvest ripening, in mature seeds, germination gradually increased up to 6 months, however, further storage under uncontrolled conditions led to a decrease in sowing qualities.Better viability was noted in seeds harvested at full maturity, as evidenced by seedling vigor and seed root length.Seeds of a number of varieties harvested on the 45th day after flowering reached 100% germination after a month of storage.
The loss of moisture in rice grain depends on the degree of maturity, grain size, characteristics of the morphology of the variety and biochemical composition.Rice varieties with high harvest moisture (Rubin, Thaibonne, Favorit, Zlata, Yakhont) and slow moisture loss on the root showed increased grain size, better endosperm starch content and high nature, indicating better grain performance.
There was also a tendency to improve the quality of starch, the nature of grain and the sowing qualities of seeds in varieties with a longer growing season.Research on local varieties can provide valuable information on the application of rice storage practices at a basic level.

Table 1 .
Change in sowing qualities of seeds of 8 rice varieties depending on the period of harvesting seeds and the duration of their storage

Table 2 .
Vegetation period, grain type, panicle type and average values of rice quality indicators of the studied 8 Kuban varieties at the end of post-harvest grain ripening, 2023 (n = 3)

Table 3 .
Characteristics of the physico-chemical properties of grain of 8 studied Kuban rice varieties, 2023