Abstract-- The germination power of a local variety of rye grain (var. Don Ewald INTA) has been studied. They have been rewetted at different moisture levels, 10, 12.5, 15 and 17.5% wet basis (w.b.), and have been stored at 10, 20, 30 and 40°C. Weekly samples of each moisture and temperature condition were taken, to carry out the germination tests of the material. It has been found that the germination power of the seeds decreases with the storage time, following first order kinetics. Moisture content and temperature during storage affect kinetics, such that any increase in temperature or moisture content manifests itself as an increase in the rate of deterioration of the seed. The best conditions of preservation of germination power were achieved with samples of 10% moisture (w.b.) stored at 10°C. A mathematical expression is presented that models the spoilage.
Keywords-- Rye, germination, moisture, storage, spoilage
I. INTRODUCTION
The Younger Dryas (10,800 BC), is a sudden cooling climate change event that lead to an ice age that lasted about a thousand years (Melott et al., 2010; Mills et al., 2014; Wolbach et al., 2018a; Wolbach et al., 2018b).
Wild cereals were particularly affected by this event causing a reduction in their yields. Consequently, all the cultivation practices that began in the Middle East during the early Natufian (weeding, transplanting, watering, pest control) became essential to ensure adequate nutrition (Bar-Yosef and Belfer-Cohen, 2002)
The domestication of cereals was influenced by natural and anthropic selection, giving rise to a series of biochemical, physiological and genetic changes, which altered the dispersal and fertilization mechanisms, causing a dependence between the plant and human care for its effective reproduction (Harlan, 1987; Munro, 2003). The strongest evidence for anthropic selection comes from the Abu Hureyra site in Syria, excavated in the 1970s. Rounded rye (Secale cereale L.) seeds were found there, an unequivocal sign of prolonged anthropic selection. The researchers concluded that rye (Secale cereale L.) and perhaps other grains were domesticated in that region at the beginning of the Younger Dryas. (Harlan, 1992; Dirzo et al., 2001).
One of the most notable characteristics of rye (Secale cereale L.) seeds and other cereals is their ability to tolerate dehydration, allowing them to be stored without significant loss of viability. The primary purpose of storing cheap plant seeds is to preserve stock for planting from one season to the next.
With the start of agriculture, man expanded his comprehension of seed requisites for maintenance of viability and methodologies to provide adequate storage conditions. In 1832, Augustin Pyramus de Candolle included a chapter on the preservation of seeds in his work “Physiologie Végétale”. In it he pointed out that the vitality of the seeds would be prolonged if they were stored in conditions that protect them from heat, moisture and oxygen (Haferkamp et al., 1953).
Rye seeds as well as those of most crop species are considered mature when they reach maximum dry weight, and are at their highest vigor. From this moment, the vigor gradually diminishes and finally dies out.
Not all life processes take place at the same speed in different seeds of a given batch. Woodstock (1973) has expressed: “When seeds are stored, these vital processes can be stopped in individual seeds at different times. Seed death is a gradual and cumulative process as more and more cells die, until certain critical parts of the seed become unable to perform their essential function”. Germination is the primary and most sensitive factor in assessing the level of spoilage of any stored seed (Justice and Bass, 1978).
Information available in the literature is found in the form of tables, nomographies and graphs, which allow evaluating the safe storage period of different seeds of agronomic interest (Ellis, 1991; Karunakaran et al., 2001; Sathya et al., 2008). The available germination data for rye (Secale cereale L.) was obtained from tests carried out on samples of a small number of seeds and presented in the form of a graph (Sathya et al., 2008; Rajarammanna et al., 2010).
In the present work, the influence of abiotic variables on progress of the deterioration of rye seeds during their storage in different environments (temperature and moisture content) were studied using the germination power as a method for their evaluation. The resulting information is applied to the development of a mathematical model for the prediction of spoilage.
II. MATERIALS AND METHODS
A. Material
A local variety of diploid rye (Secale cereale L.) has been used, registered under the name Don Ewald INTA in the National Register of Cultivar Property (RNPC) and the National Register of Cultivars (RNC) in 2010. The material has been received with a moisture content of 9.90 ± 0.4% on a wet basis (w.b.), a weight of 1000 seeds, of 21.2 g and an initial germination rate of 92% (Moreyra et al., 2014; Gómez Castro et al., 2019).
The batch of seeds received is suitable for testing as it complies with Resolution No. 2270/93 of the secretariat of Agriculture, Livestock and Fisheries (Argentine Republic), which determines 75% as the minimum value for the germinative power of rye. (Secale cereale L.).
B. Material Conditioning
Four batches of 1.5 kg have been prepared, each one being rewetted to levels of 10, 12.5, 15 and 17.5% on a wet basis (w.b.) respectively. For this, water was sprayed on the material, controlling the amount added gravimetrically. The added water was calculated through a mass balance for each condition. The rewetted material was placed in covered containers that were cooled in a refrigerator at 3-5°C, mixing them every 8 h for 2 days to ensure uniform moisture content.
Each of these batches then has been divided into 10 g samples that have been packed in sealed plastic bags.
Twenty heat-sealed bags of each moisture content were taken and stored at 10 °C. This methodology was repeated at 20, 30 and 40°C. Table 1 shows the relative humidity (R.H.) existing during storage for each tested condition. Every week a sample was taken from each humidity and temperature condition, to carry out the germination test of the material.
C. Moisture content
Moisture content was determined according to Association of Official Agricultural Chemists (AOAC) methodology no. 934.06 (AOAC, 1990), using a vacuum oven. About 5 g of samples were placed in aluminum dishes in a vacuum oven and kept at 70°C for 72 h. The dried samples were then removed from the oven, cooled in a desiccator and weighed using an electronic balance with a sensitivity of 0.0001 g. The initial and final weights were used to calculate the moisture content.
D. Germination Power
Plastic boxes were used for these tests. The seeds were placed on 4 layers of filter paper soaked in water, in a 12x17 grid drawn, one seed per square (2 x 2 cm).. The boxes have been kept at 15-17°C, and were inspected on the fourth and seventh days. It was considered that rye (Secale cereale L.) seeds to have germinated when the radicle length reached at least 5 mm. (Rao et al., 2006; ISTA, 2015).
E. Kinetic model
The kinetics of loss of germination power can be modeled by the following expression:
(1)
where 
is the number of germinated seeds, 
is the
storage time, 
is the
kinetic constant, and 
is the order
of the process.
In this work, it was found that the first order model
(
) is the most
appropriate to describe the changes in germination power.
The integration of the Eq. (1) for n = 1, gives:
(2)
where 
is the
initial quantity of germinated seeds (
).
Figure 1: Reduction of the germination power at 10°C for different moisture content of the rye seed.
Towards the end of the 19th century, Arrhenius (1889), based on the work of Van't Hoff (1884), proposed that the kinetic constant could be described by the following differential equation:
(3)
where T is the absolute temperature, R is the universal gas constant, and Ea is the activation energy. After its integration, equation (3) results in the following exponential form:
(4)
where 
is a constant
called the frequency factor (Glasstone et al., 1941). Equation (4) is
known as the Arrhenius equation. This expression has been remarkably successful
in describing the dependence of kinetics, in different degradation processes,
with temperature (Demiray, 2019).
III. RESULTS
Figure 1 shows the reduction in germination power with storage time at 10 °C. This reduction in germination power increases as the moisture of the seed increases.
It is observed that the germination power decreases with increasing storage time, gradually approaching the time axis. This behavior is reproduced at 20, 30 and 40°C.
If the ordinate axis is represented on a logarithmic scale, it can be seen that now the reduction in germination power is linear for the different temperatures studied, as can be seen in Fig. 2.
The linear behavior observed in this form of representation indicates that the reduction in the germination capacity of the seeds follows first-order kinetics (Eq. (2)). The behavior is similar for 10, 15 and 17.5% moisture on a wet basis.
It can be seen that the proportion of seeds that germinate decreases with increasing grain moisture level, temperature and storage time. Similar behaviors have been previously observed in this and other cereals (Ellis, 1991; Karunakaran et al., 2001; Sathya et al., 2008).
Table 1 shows the values of the kinetic
constant k, for different values of temperature and moisture of the grain
during storage. The value of this parameter increases
