Сельскохозяйственная биология, 2012, № 3, с. 80-85.

doi: 10.15389/agrobiology.2012.3.80eng

УДК 634.75:631.527.5:581.142

ACHENES DEVELOPMENT AND GERMINATION IN REMONTANT CULTIVARS OF DAY-NEUTRAL STRAWBERRY (Fragaria х ananassa Duch.) IN WESTERN SIBERIA

I.K. Apolinar'eva¹, S.O. Baturin², L.L. Kuznetsova², V.A. Petruk¹

A number of domestic and foreign cultivars of remontant large-fruited strawberry (Lizon'ka F₁, Vechnost' F₁, Sarian F₁, Grandian F₁, Loran F₁, Chezan F₁, Florian F₁, Freska F₁), growing in open ground, were estimated on indices of seed production and quality of achenes. The majority of strawberry cultivars are noted to demonstrate high seed production and germination of achenes taken from berries of August harvest. The authors revealed that the cultivars differ in varying achenes production over one season of fruitage. The Florian F₁, Grandian F₁ and Loran F₁ cultivars were the most stabile. The Grandian F₁, Florian F₁, Loran F₁ and Sarian F₁ cultivars demonstrate the high germination of achenes during the whole fruiting period.

Keywords: Fragaria x ananassa Duch., strawberry, everbearing cultivars, seed set percentage, achene germination ability, plant breeding.

Large-fruited strawberry (Fragaria × ananassa Duch., 2n = 8 x = 56) is one of the leading berry crops by the area of its growing (1, 2). Its current assortment includes about 4000 varieties suitable for growing in different climatic zones, which forms belong to two main groups with different types of fruiting – single and multi-fold, or remontant. About 17% new varieties of the strawberry are remontant forms, and it indicates their high popularity and commercial demand (3). In favorable conditions of pollination and fertilization, large-fruited strawberry develops seeds mainly by a sexual way with double fertilization (gamospermia). In open ground, strawberry may develop seeds through both self-pollination (autogamy) and cross-pollination (xenogamy). According to T.S. Fadeev (4), Fragaria × ananassa is an optional cross-pollinated species.
In breeding practice, strawberry can be propagated both by seeds and vegetative rooted rosettes formed on aboveground stolons-runners. Seed propagation is commonly used in the development of new vegetatively propagated varieties, including remontant ones (5). In modern selection of remontant large-fruited strawberry it is being actively developed the new direction of seed-propagated varieties along with conventional forms whose varietal specificity is maintained through a vegetative propagation (6). Such propagation of remontant strawberry varieties can help to avoid many problems of vegetatively-propagated forms, eg. spread of infectious diseases through seedlings and costs on combating them, a limited period of planting stock sale, as well as storage and transportation problems, etc. (6, 7). However, seed propagation of large-fruited strawberry is complicated by high requirements to conditions of germination, low germinating capacity of seeds and prolonged period of germination (8). These problems are partially solved by different methods of seed pre-treatment improving germination properties of seeds (9-11). Remontant varieties are the first to bloom, which is followed by a fruiting season of 3-4 months when growing in open ground. Such a long period of continuous fruiting is accompanied by conditions more or less favorable for flowering (spring late frost, significant fluctuations of diurnal temperatures in autumn) and undoubtedly affecting seed quality and number of seeds in the berries.
This study was aimed at revealing an optimal time for obtaining of full-value seeds of remontant large-fruited strawberry that will be used to develop the technique of seed propagation of this berry crop in conditions of Western Siberia.
Technique. The berries with achenes were collected in July to October 2009 from plants grown in the collection garden of the Laboratory of experimental studies of the Siberian Physical-Technical Institute of Agrarian Problems. The achenes were obtained through open pollination of large-fruited strawberry remontant varieties of domestic and foreign selection: Lizon’ka F₁, Vechnost’ F₁, Sarian F₁, Grandian F₁, Loran F₁, Chezan F₁, Florian F₁, Fresca F₁ (the symbol F₁ hereinafter is omitted for ease of presentation) intended for seed propagation, along with the achenes developed through open pollination on vegetatively propagated varieties Brighton and Selva.
The yield of seeds was determined as a percentage: the number of developed seeds / total number of ovules in a flower (seed yield, %). To do this, each fruit was cut into 2-4 parts, which were pressed tightly to a cardboard, dried at room temperature to account achenes and ovules in each berry using a binocular microscope Miсromed MS-2 ZOOM (Russia). Mean percentage of seed yield was accounted from the trait performance in 30 berries selected randomly in each month of harvesting.
Germination was examined in 300 achenes of each variety (100 achenes at 3-fold replication). The achenes were pre-treated by stratification at a temperature of 2-3 °C for 14 days, and then germinated at 20-22 °C in Petri dishes on wet filter paper. Using such short stratification period was based on the practice of seed reproduction of remontant strawberry varieties. Germination was evaluated for 65 days after sowing day. Germinating energy was determined on the 15th day of germination.
Statistical analysis of data was performed using standard methods (12).
Results. Even though a classical botany considers a “berry” of  Fragaria as an aggregate accessory fruit with a fleshy part derived not from the plant's ovaries but from the receptacle that holds the ovarieon, or “false berry”, while its “seeds” developed through a double fertilization should be called “achenes” (13, 14), it was more convenient for the authors to call them as “berry” and “seed”  - the terms generally accepted in selection of strawberry (2, 4, 9).
Evaluation of seed yield from berries harvested in different months.  The highest yield of seeds was recorded in berries picked ripe in August (Figure, A), which value was reliably exceeding in all varieties except Sarian and Loran, whose seed yields in  October (cv Sarian) and September-October (cv Loran) were close to those in August. Knowing that it takes 29-30 days from pollination to full ripening, it appears that seeds from strawberries picked ripe in August were the result of flowering in July – the most favorable period for strawberry pollination and fertilization in Western Siberia.

The minimum proportion of full-value seeds was found in berries collected in July, which was significantly different from that of berries picked in August.  Probably, it was the result of unstable weather conditions in June during the first bloom of remontant varieties. In Western Siberia, vegetation season of strawberry usually begins against significant fluctuations of day and night temperatures, night frosts in the first ten days of June, short periods of air cooling (8-12 °C) adversely affecting fertilization and development of seeds in remontant varieties. Such effect of environmental factors was clearly shown by the coefficients of variation (Cv,%) of seed yields in different months of a growing season (Table). In most of the studied cultivars variation in seed yield from berries harvested in July, September and October exceeded that of August (respectively 33-35% and 25%). The highest variation in seed yield during a growing season was manifested by cv Sarian, while the smallest – by cv Selva. It should be noted that Cv values up to 44% correspond to the variation of a biological trait within the norm of reaction. Thus, the formation of achenes in studied remontant varieties of large-fruited strawberry grown in open field was affected by external conditions, but the recorded fluctuations in seed yield can be considered as normal for the described biological events (12).

Differences in seed formation of berries harvested in September and October were unreliable in most of the varieties, moreover, in October cv Selva, Vechnost’ and Sarian showed much higher seed yields than in September. Apparently, large-fruited strawberry under adverse environmental conditions enters a modified asexual seed reproduction – agamospermy – instead of gamospermia (15) thereby providing the development of full-value achenes. This fact was indirectly confirmed by the absence of significant differences in weight of 1000 seeds developed in different months of growing season by cv Chezan, Vechnost’, Brighton, Grandian, Selva and Fresca (Table). Perhaps, a part of achenes from the October harvest were of agamospermic origin (15).
Germination of seeds from berries harvested in different months. Almost all studied cultivars showed the best germination of seeds from berries harvested in August, which confirms the recommendation of T.I. Volkova (16) for using in seed collections the seeds from strawberries picked ripe in August. The exception were cultivars Brighton and Grandian (Fig., B). In cv Brighton, the highest germination showed the seeds collected in July, while cv Grandian had no significant differences in germination of seeds harvested in July, August and September. Along with it, Brighton and Grandian showed a significant excess of germinating energy in seeds collected in July relative to other months (Table). In general, germination of achenes from berries harvested in August amounted from 72,6 to 89,0%. The minimum germination was found in seeds from berries picked in October: in cv Selva – 23,8; Fresca – 41,0; Vechnost’ – 46,3; Loran – 47,0; Chezan – 48,6 and Lizon’ka – 49,0%. In varieties Lizon’ka, Fresca, Florian and Chezan germination of seeds from the harvest of July was significantly lower (30,7-37,6%) than in October (41,0-67,3%). Agamospermic origin of seeds with low germination capacity was described in the earlier authors’ work (17), and, possibly, it was what occurred in such seeds. In this experiment, there should be mentioned varieties Vechnost’, Chezan, Lizon’ka and Fresca. Cv Grandian showed stably good germination of seeds from berries picked ripe in different months.
So, the experimental study of large-fruited strawberry grown in open ground conditions of Western Siberia has shown that the best seed yield and quality seeds with high germination capacity can be obtained from berries picked ripe in August. Seed yields of remontant strawberry cultivars can vary significantly during a fruiting season, and the most stable of those were Florian, Grandian, and Loran. Good germination of achenes throughout a fruiting season was observed in varieties Grandian, Florian, Loran and Sarian.

REFERENCES

1. Govorova G.F. and Govorov D.N., Zemlyanika: proshloe, nastoyaschee, buduschee(Strawberry: Past, Present and Future), Moscow, 2004.
2. Zubov A.A., Teoreticheskie osnovy selektsii zemlyaniki (Theoretical Fundamentals of Strawberry Selection), Michurinsk, 2004.
3. Faedi W., Mourgues F. and Rosati C., Strawberry Breeding and Varieties: Situation and Perspectives, Acta Horticulturae, 2002, vol. 567, pp. 51-59.
4. Fadeeva T.S., Genetika zemlyaniki (Genetics of Strawberry), Leningrad, 1975.
5. Arkhipov Yu.B., Selection of Seeds and Pre-Sowing Treatment in Strawberry Breeding, Extended Abstract of Cand. Sci. Dissertation, Leningrad-Pushkin, 1969.
6. Bentvelsen G.C.M., Bouw E. and Veldhuyzenvan Zanten J.E., Breeding Strawberry (Fragaria × ananassa Duch.) from Seed, Acta Horticulturae, 1997, vol. 439, no. 1, pp. 149-53.
7. Baturin S.O., Apolinar’eva I.K. and Kuznetsova L.L., About Some Achievements in Seed Reproduction of Remontant Large-Fruited Strawberry, in Mat. Mezhd. nauch.-metod. distantsionnoi konf. “Aktual’nye problemy razmnozheniya sadovykh kul’tur i puti ikh resheniya (Proc. Int. Sci.-Method. Distance Conf. “Propagation of Garden Crops: Urgent Problems and Their Solutions”), Michurinsk, 2010, pp.  32-39.
8. Baturin S.O., Apolinar’eva I.K. and Petruk  V.A., Evaluation of Seed Germination and Varietal Uniformity in Seed Progeny of Remontant Commercial Varieties of Large-Fruited Strawberry, Sibirskii vestnik sel’skokhozyaistvennoi nauki, 2010, vol. 1, pp. 40-45.
9. Zubov A.A. and Arkhipov Yu.B., Methods of Improving Germination of Strawberry Seeds, Tr. TsGL im. I.V. Michurina, 1969, vol. 10, pp. 72-77.
10. Hamdouni E.M.El., Lamarti A. and Badoc A., In Vitro Germination of the Achenes of Strawberry (Fragaria × ananassa Duch.) cvs. “Chandler” and “Tudla”, Bull. Soc. Pharm. Bordeaux, 2001, vol. 140, pp. 31-42.
11. Hongxiang M.A., Guihong Y.U., Weimin W.U. and Xiulan C., Effects of Achene in Vitro Culture on Seed Germination Percentage of Strawberry, Jiangsu J. Agricul. Sci., 2001,  vol. 17, no. 2, pp. 87-90.
12. Zaitsev G.N., Metodika biometricheskikh raschetov (Procedure of Biometric Calculations), Moscow, 1973.
13. Levina R.E., Morfologiya i ekologiya plodov (Morphology and Ecology of Fruits), Leningrad, 1987.
14. Lotova L.I., Morfologiya i anatomiya vyschikh rastenii (Morphology and Anatomy of Higher Plants), Moscow, 2001.
15. Baturin S.O., Experimental Apomixis in Strawberry (Fragaria × ananassa Duch.), Extended Abstract of Cand. Sci. Dissertation, Novosibirsk, 1997.
16. Volkova T.I., Remontantnaya zemlyanika (Remontant Strawberry), Moscow, 2000.
17. Baturin S.O. and Ambros E.V., Peculiarities of the Seed Germination of Agamospermic Seedlings Fragaria × ananassa Duch. in Different Breeding Systems, S.-kh. biol., 2010, vol. 5, pp. 87-91.