Germination of seeds of Avena fatua L . under different storage conditions

Storage conditions have a strong influence on the germination of seeds of Avena fatua L, especially at variable conditions, the germination decreased. Seeds stored at a constant low temperature maintained the germination capability for 5 years. Under greenhouse conditions, seeds matured and germinated more rapidly comparing to field conditions, but individuals from these seeds were weaker and produced fewer seeds. The higher temperature in the greenhouse accelerated the development and maturing of plants. Field emergence varied depending on seed storage conditions, sample, further reproduction, and weather conditions. It was observed that individual specimens of A. fatua were able to form ripe seeds with high thousand grain mass (TGM), regardless of the occurrence of fungal diseases. The knowledge of the biology of A. fatua is very important due to its status as a restricted weed in certified seed of crop plants.


Introduction
Proper storage conditions are essential to maintain high viability of seeds, both of crops and weeds.There is a lack of information about storage conditions of weed seeds and therefore research was conducted on a very expansive weed, Avena fatua L. (Poaceae) a restricted weed in certified seed of crop plants [1].
Avena fatua is an annual spring plant, germinating in early spring, though some authors claim it is also a winter plant [2].Grains of A. fatua are hulled, their glumes are generally dark with numerous seed hairs, and the awn grows more or less in the middle of the lemma.When mature, the ear falls apart into flowers showing the scar shaped as a horseshoe with a smooth, roller-like fold in each flower -which is the characteristic of this species [3].
Avena fatua can be observed both in alkaline and sour soils.It can spread by hairy seeds carried by wind.Seeds may germinate even at a depth of 20 cm.Grains mature irregularly and as they ripe they fall off, contaminating the soil.Some of the grains, not fully ripe, are collected together with the crop plant and contaminate the harvest, while grains left in straw may germinate immediately, without undergoing the dormancy stage.
The aim of the study was to evaluate the seed germination potential of A. fatua depending on storage conditions and to compare the growing period under greenhouse and field conditions.

Material and methods
A part of seed material was collected from crop fields in Poland during the expeditions organized by the National Centre for Plant Genetic Resources (from 2007 to 2008), while a part of it came from the Gene Bank collection.Seeds used in laboratory experiments and in the greenhouse were collected in crop fields.In the field experiment, in the first year of sowing seeds came from the Gene Bank and after that they were stored at room temperature (from 20 to 25°C) until the end of the experiment.

Laboratory experiment
In 2008, after determining the germination ability, seeds were placed in two types of storage conditions: treatment A -long-term storage (constant temperature: 0°C with a low humidity of 5-7%) and treatment B -variable storage conditions (ambient temperature and humidity) with variable temperature (from 5 to 30°C) and humidity (from 40 to 80%).During 5 years of storage, seeds from particular treatments were tested.Every year, the germination ability was determined and 3 × 50 seeds were sown.In accordance with the current ISTA Rules [4], the percentage of normal seedlings, abnormal seedlings, dead seeds, and fresh nongerminating seeds were estimated.Figures were made using Excel software and the trend function for the studied parameters was determined to analyze the germination ability in the laboratory.An analysis of variance was conducted using R language for statistical computing (R Core Time).

Field experiment
A field experiment was established on soil complex 3, class III b, on experimental fields in Radzików, between 2009 and 2011.Pre-sowing fertilization was performed: NPK (= nitrogen, phosphorus + potassium).Seeds were sown in 1.5 m 2 plots, in 7 rows, 1.5 m long each.In each plot, six hundred (600) seeds were sown.No herbicides were used and weeds were removed manually.During the growing period, the following parameters were observed: dates of sowing, panicle formation, maturity, plant height (3 replications with n = 10 individuals each), and panicle length (3 replications with n = 10 individuals each).Resistance to diseases (disease assessment range: 1-9, 9 = resistant) and lodging (observed on two dates, assessment range: 1-9, 9 = no lodging) was observed according to James (1971) [5].Seeds were collected manually from panicles and isolation bags (which were applied to prevent seed loss), following the cutting of panicles.Seeds were sorted out manually and then the seed yield from one plot was weighted.The thousand grain mass (TGM) was determined by triple counting of 100 grains and multiplication by 10.The term "growing period" refers to the number of days from sowing until collective maturity.The climate data was taken from the weather station in Radzików.

Greenhouse experiment
In March 2012 and in June 2013, 3 × 50 seeds of A. fatua were submitted to germination on Petri dishes at a variable temperature from 20°C to 30°C.Once germinated, seedlings were planted in pots and moved to a greenhouse.Using 10 specimens (each year), plant growth was observed and measured, i.e.,: date of germination, panicle formation, maturity, and plant height.Finally, all seeds of each specimen were collected and 10 seeds of each specimen were weighted, then TGM was determined by multiplication: 10 grains × 100 (this was an estimated method, due to the lack of seeds).

Laboratory experiment
The germination capability of the initial seed material of A. fatua was 64%.At the constant low temperature (treatment A), the value of germination capability increased reaching 80% in 2012 (Fig. 1).There was no significant variation in germination capability between years during seed storage in low temperature.Under the variable conditions (treatment B), the germination capability of seeds increased in 2010.A significant decrease in seed germination was observed throughout the storage time starting after two years of storage.In the fifth year, it reached zero.The analysis of variance showed that both factors -storage conditions and storage longevity as well as the conditions × longevity interaction -were highly significant for the seed germination capacity with P < 0.000 (Fig. 1).
In treatment A, the percentage of dead moldy seeds was constant (Fig. 2).At the variable temperature and humidity (treatment B), the germination capability decreased and the proportion of dead seeds increased.In the first two years of storage, the percentage of dead seeds was lower than in the initial material, but later it increased to a value of 99% in 2013.The analysis of variance showed that for the number of dead seeds both factors -storage conditions and storage longevity as well as the storage conditions x storage longevity interaction -were significant with P < 0.000 (Fig. 2).
Fresh non-germinating seeds constituted 22% of the initial material at the beginning of the experiment (Fig. 3).At the low constant temperature (treatment A), fresh nongerminating seeds gradually decreased down to 8% in 2012.Under the variable storage conditions (treatment B), the percentage of fresh non-germinating seeds fell to zero after 2 years of storage.For viable non-germinating seeds, a significant effect of storage longevity was observed (with P < 0.000), while the storage conditions and the storage × year interaction were not significant (Fig. 3)

Field experiment
Under field conditions, germination capability varied depending on the conditions in which seeds were stored, the sample, and further reproduction of the same research material (Tab.1).
Fig. 2 Percentage of dead seeds under long-term storage and variable storage conditions.Significance: storage conditions (SC) P < 0.000; year (Y) P < 0.000; SC × Y P < 0.000.
Seeds after long-term storage (0°C) and sown directly in the field showed the worst germination.Out of 600 seeds sown in 2009, 13 581 seeds were collected (267 g harvested), while with the same number of seeds sown in 2010 and 2011, 20 590 and 37 690 seeds were collected, respectively.
Under the field conditions in 2009, a longer growing period was observed (114 days), panicles formed later, and the seed yield was poorer compared to 2010 and 2011.In 2010 the growing period was slightly shorter (by 14 days); the average air temperature (Fig. 4) during the growing season was slightly higher than in the previous year.However, in 2011 the growing period was comparable to the previous year.
In 2011, the precipitation during the growing period was very high and Puccinia coronata and Septoria diseases occurred more frequently than in the others years of the experiment.However, the weather did not affect the TGM, despite that the yield was high.
During all the research years, it was observed that plants were able to produce ripe seeds with high TGM despite the fact of being affected by fungi.

Greenhouse experiment
Avena fatua individuals in the greenhouse had a shorter growing period compared to plants growing in the field.The number of days from sowing to panicle formation ranged from 47 to 56, whereas in the field from 68 to 82 (Tab. 1, Tab. 2).However, the number of days from sowing to maturity varied from 70 to 84 days, while in the field ranged from 86 to 114 days.
Under the greenhouse conditions, the height of A. fatua specimens was in the range of 44-69 cm (Tab.2), whereas in the field varied from 118 to 138 cm.
In the greenhouse, where the temperature is much higher than in the field (both during the day and at night), every single plant of the A. fatua species developed weaker and produced fewer seeds.However, the mass of 10 seeds (converted into the "thousand grain mass") of each specimen was between 19.2 to 26.3 g, while in the field varied from 19.7 to 27.2 g.The above calculation indicates that the TGM of the plants in the greenhouse is similar to the TGM of plants that grew under natural conditions in the field.
of this species germinate better in the temperature range 0-30°C.Grains are produced by the species in a wide range of temperature, yet the maximum is obtained at +22/16°C [7] and those produced at a higher temperature (+20°C) prove to have higher germination capability [8].
The germination capability of the initial material was only 64% in ambient conditions and then it gradually increased to reach the maximum (92%) after 2 years.This happened because of breaking dormancy due to variable temperature and humidity.This is confirmed by Kieć's [6] who reported that approximately 90% of live grains of wild oat at the maturity stage are in dormancy whose aim is to prevent autumn germination and freezing of young seedlings.According to the same author, dormancy depends on 3 genes and air temperature during grain maturation and later.A low temperature at the time of maturation extends the dormancy, although after maturity the dormancy period shortens.This has an impact on whether grains will be in dormancy in the next year or longer, while it must be remembered that dormancy may be shortened by different external factors, such as high temperature, damage of grains, etc.The extreme flexibility of this species was shown in the field research in Radzików (Tab. 1) where the same sample, i.e., the same behaved differently in individual years, producing a non-uniform thousand grain mass, a different yield or a different height of individual specimens.This is supported by the research of Trzcińska-Tacik [2] and Trzcińska-Tacik and Stachurska-Swakoń [9].
Seeds taken directly from low-temperature storage germinated worse in the field (Tab.1: sample No. 01 in 2009), whereas in the next years 2010 and 2011, when seeds were stored at room temperature, seeds germinated much better.According to Foley [10], seeds of this species must experience a warm and dry period to germinate.In the present research, where temperature and humidity were changeable, an increase in germination ability was observed in the first two years.However, while the germination ability of seeds stored at constant temperature increased more slowly, but it was maintained throughout the entire duration of the experiment, i.e., for 5 years.
In the field experiment, the kernels taken directly from long-term storage produced individuals with small grains (TGM 19.7 g; Tab. 1).The same seeds sown in the next year produced plants with bigger seeds (TGM 23.4 g).It is not confirmed by Peters [11] who found that the germination capability of A. fatua also depends on the size of grains; the bigger they are the weaker their dormancy stage, the higher germination capability, and the bigger plants they form.
At the beginning (2008-2010) of the laboratory experiment under different storage conditions, the germination capability increased, while the dormancy of seeds was breaking.The number of fresh non-germinated seeds decreased to reach zero in 2010.After 2010 seed viability at ambient temperature (treatment B) decreased, because the proportion of dead (moldy) seeds increased.This situation was caused by the development of storage fungi to which variable humidity and ambient temperature contribute [12].
Rooney et al. [13] claim that the growth and production of the dry mass of above-ground parts depend mainly on light, whereas temperature impacts root development, which will be better in lower temperature.The smaller amount of light in the greenhouse could explain why plants developed less abundantly in the greenhouse than in the field [14].Irrespective of this fact, plants produced a high thousand grain mass, which suggests that they accumulated their energy to develop the generative part instead of the vegetative one.Therefore, in the greenhouse we had shorter individuals with a similar TGM as in the field.
Under the field conditions in 2009, a longer growing period was observed (114 days), panicles were formed later, and the seed yield was lower compared to the next years of the research.In 2010 the growing period was slightly shorter (by 14 days) and most probably the better weather conditions caused the formation of more ripe seeds with a higher TGM.In 2011 the average total precipitation during the growing season, mostly in April, was higher than in the preceding years and additionally Puccinia coronata and Septoria occurred.However, this had no impact on the yield.It was observed that plants were able to produce ripe seeds with a high TGM despite the fact of being affected by fungi.
Avena fatua has been of limited use in breeding.It can however be a valuable donor of a number of interesting genes.This species may constitute a source of genes determining the earliness of maturing, rapid growth, ripeness of grains, a high content of proteins, and resistance to Puccinia graminis and Puccinia coronata.There are attempts to transfer the above properties onto crop plants to improve their quality [15][16][17][18][19][20].
It must be reminded that A. fatua is a restricted weed in certified seed of crop plants.All guidelines may be found in the ordinance of the Ministry of Agriculture and Rural Development dated April 18, 2013 [1].We can read the following guidelines: the produced seed material of crop plants or fodder plants is considered meeting all special conditions as regards the content of wild oat seeds (Avena fatua and A. sterilis) if: 1. during an official field assessment it was found that the seed plantation is free from wild oat plants (Avena fatua and A. sterilis); 2. no presence of wild oat seeds (Avena fatua and A. sterilis) was observed in the official sample.

Conclusions
Storage conditions significantly affected the seed germination of Avena fatua which decreased with increasing the time of storage.Seeds stored in ambient conditions (variable temperature and humidity) exhibited the growing number of dead moldy seeds.After five years of such storage, the loss of viable seeds was 80%.However, seeds stored at constant low temperature were able to maintain their germination capability for a long time -above five years.
Under field conditions, seeds germinated depending on the weather and seed storage conditions.Seeds stored at constant low temperature did not germinate all at once in the first year of sowing.A high percentage of such seeds remained in dormancy.In the following years, seeds germinated better despite of the occurrence of field pathogens and A. fatua plants produced seeds with a higher TGM.
In the greenhouse, the life cycle of A. fatua was shorter by almost one month than in the field.Greenhouse specimens were weaker and produced fewer seeds, yet the seeds were well-formed and with a TGM similar to those growing in the field.The higher temperature in the greenhouse accelerated the development and maturation of plants which did not concentrate on the development during the vegetative phase but on forming ripe seeds (generative phase).
Growing period of Avena fatua under greenhouse conditions (mean n = 10 individuals in 2012 and 2013).