Сельскохозяйственная биология, 2012, № 1, с. 46-51.

doi: 10.15389/agrobiology.2012.1.46eng

УДК 633.854.78:631.52:57.08

USE OF ULTRA EARLY AND LATE SOWING DATE IN SUNFLOWER SELECTION ON EARLINESS, PRODUCTIVITY AND ECOLOGICAL RESISTANCE

S.G. Borodin, O.I. Voloshina

The main stages of faster creation of early-ripe sunflower variety with the use of natural contrasting environment conditions, ultra early and late sowing date as differentiative background for selection, were presented. The efficiency of modified technique for estimation of selected determinants is considered during creation of early-ripe sunflower variety with high productivity and broad diapason of ecological resistance. It was shown, that the selection on a reduction of vegetation period and an increase of 1000 seed mass is one of the ways of improvement sunflower productivity and expansion of the range of application of this culture.

Keywords: sunflower, variety, breeding, vegetation period, evaluation, selection, productivity.

Sunflower occupies a large area of Russia with very diverse edaphic and climatic conditions. New cultivars entered the market recently (large-kernel cv SPK - since 1993, cv Lakomka – 2000) and soon extended a range of usage of sunflower seeds and caused a high demand for snack varieties.  However, sunflower is grown for seed mainly in the southern region since its growing season (86-90 days) limits an assured yield of high quality seeds without desiccation in the north-eastern part of the country. In this regard, a task for plant breeders is creating the early-ripe varieties with medium-sized seeds.  Varieties with a short growing season, great weight of 1000 seeds and other improved productivity traits are necessary for growing in both north-eastern and southern areas.
There are several approaches to create various crops varieties with a short growing season. The most common is growing original forms in artificially shortened photoperiod. Differentiation of plants to early- and late-ripening in some cases is obtained by the use of regulated artificial lighting conditions (1, 2), in others (when using costly environmental chambers is not suitable) - light-tight boxes or mobile chambers allowing detection of plants with a weak or neutral reaction to photoperiod  in vivo (3, 4). Selection of early-ripening forms in contrasting natural environmental conditions is performed through a comparative testing by growing a source material in different geographical areas (5).
The purpose of this study was to evaluate the efficiency of very early and late sowing in order to accelerate selection and improve certainty of detection of early-ripe large-fruited sunflower genotypes with high adaptability potential, as well as to test a modified method for assessment of commercially valuable traits in nurseries with directed cross-pollination.
Technique. The study was performed in the main experimental station of V.S. Pustovoyt All-Russia Research and Development Institute of Oil-producing Crops (VNIIMK, Krasnodar) in 2003-2007. Two generations of sunflower were grown at extra-early and late sowing in a single year in one geographic location (6).
Source parental forms were chosen among the best families from a large-fruited early-ripe variety Lakomka selected upon their commercially important features in nurseries of the 1st and 2nd year of study. Extra-early sowing of the first generation (F1) was done on March 1, 2003 (thickness of sowing - 20 thousand units/ha). Dates of budding (early formation of inflorescence), flowering, flowering termination and ripening were recorded for each plant. The best early-flowering plants were isolated for further cross-pollination in groups with open flowering at a spatial isolation, while late-flowering, abnormal and sick plants were removed. Among the progeny of plants with short interphase periods of seedlings-flowering and flowering-ripening obtained at extra-early sowing there were chosen the outstanding families with high weight of 1000 seeds, oil content, yield and low humidity of achenes, in order to isolate the best plants at late sowing time. The second generation (F2) was sown on test plots individually by families on August 1 (10 days after harvesting the early sown plants). Evaluation and selection of early-ripe biotypes in F2 were performed the same as in F1.
In 2004, seeds from the best early-ripe high-productive plants selected from F2 were sown in optimum time in the nursery of directed cross-pollination individually by families; phenological events, biometric measurements and productivity characteristics of these plants were accounted. In the nursery of directed cross-pollination, commercially valuable traits were assessed according to the technique of competitive trials aimed at more stringent control of ripening time and productivity indices in order to isolate the best genotypes on one field in a single year.
A mixture of seeds from the best plants selected in the nursery of directed cross-pollination were sown to be propagated in a spatially isolated seed nursery using a standard method (7).
In 2005-2007, the preliminary seed growing of a new variety Oreshek was performed (reproduction on seed sites) simultaneously with assessing at optimum sowing time in the nursery of competitive variety testing.
Statistical processing of data was performed in Statistika 6.0. using analysis of variance and correlation analysis.
Results. To obtain early-ripe varieties, a temporary isolation of plants was performed in order to provide a directed cross-pollination of plants with a mixture of pollen from early-flowering forms, which is contrast to commonly applied artificial isolation peculiar to many conventional techniques.

Vegetation of extra-early sown sunflower plants occurred at a moderate average daily temperature (18,2 °C) (Table 1), while at late sowing date the lack of heat was observed in the period flowering-ripening  (13,6 °C). Moisture conditions varied significantly as well: total precipitation during the growing season of plants sown on March 1 amounted to 56,2, on August 1 – 226,4 mm. At extra-early sowing, daylight became longer by 2 h by the start of mass flowering and then gradually decreased. At late sowing, daylight duration decreased from 14 h 25 min to 10 h 14 min.

At extra-early sowing, a period from seedlings to the start of fruit formation varied  between the families from 40 to 45 days (Table 2), and they differed by dates of flowering and flowering termination in 3-4 days. The interphase period seedlings-ripening was the most diverse characteristic (87-96 days), most likely owing to non-typical growing conditions and different rate of finishing oil formation in achenes.
Average daily temperature, total precipitation, duration of daylight and growing season were closely correlated (r = 0,84-0,99). At the same time, changes of growing conditions resulted in a pronounced diversity of other quantitative traits. Reduce in yield and oil content in seed obtained at a short growing season is a serious problem in breeding work on early-ripe varieties (4, 7-9). To overcome this negative dependence, there were selected early maturing genotypes with a minimum moisture content in achenes and maximum oil content and weight of 1000 seeds, which were sown on August 1 of the same year.
In the case of late sowing, better on-field germination was exhibited by plants with greater weight of 1000 seeds (r = 0,34, p <0,05). The period seedlings-flowering reduced by 10 days against a gradually increasing average daily air temperature and reducing daylight (Table 1). The period flowering-ripening was 3 days shorter than in the case of extra-early sowing date. Visually healthy sunflower plants which started to bloom in the first 4 days were left for the directed pollination of early-ripe genotypes, other late forms were removed.
Lower temperatures and shorter daylight in the period of flowering-ripening became a differentiating background to detect differences between plants within a population. Seeds from the best plants with outstanding weight of 1000 seeds, oil content and resistance to diseases and broomrape were sown in the nursery of directed cross-pollination (2004), which allowed to fix early ripening and restore seed productivity. It was assumed that a serial selection of early maturing genotypes with high yields of seeds from a splitting population of sunflower against the background of seasonal variability of hydrothermal and photoperiodic conditions contributes to better ecological adaptability of a new variety.
Selection of genotypes and assessment of inheritance of desired features in offspring was carried out during early flowering and ripening. Early flowering was the main common characteristic in selection for early maturity, though its necessity to consider diversity of genotypes in period from the beginning of flowering to physiological ripening (oil synthesis proceeding at this period ultimately determines commercial quality of resulting seeds). Other accounted features were: uniformity of plant height, head slope, lesion from diseases and pests, size of achenes estimated by weight of 1000 seeds and oil content, because these characteristics are negatively correlated (p <0,05). Seeds of snack varieties can substitute raw nut, so desired genotypes of this type were selected by weight of 1000 seeds (at least 120 g) and the achenes of optimum shape, high protein content and low oil content (40-43%).
The main target in the period of variety propagation was preservation and improvement of hereditary properties by accurate elimination of deviant genotypes. During 3 years distinct by weather conditions, plants of the new variety maintained high level in weight of 1000 seeds (151-161 g) and oil content (41,2-42,0%). The trait most variable from year to year (from 160 to 207 g) and within a population (± 25,3 g) was number of achenes per head (inflorescence). High rates of seed production (weight of 1000 seeds - 161 g, oil content - 42%) were developed by the new variety in 2006 at optimum combination of heat and moisture. Low fluctuations in yield value and product quality from year to year were achieved through the selection of a source breeding material in stressful conditions of atypical sowing time and further rejection of unwanted biotypes.
After two cycles of selection against different environmental conditions (extra-early and late sowing, 2003), major commercially valuable traits were evaluated in the resulting early-ripe large-fruited variety Oreshek in the nursery of competitive variety trials at optimum timing of growing season. The variety was compared with an extra-early ripe variety Rodnik (R-453) and a large-fruited early-ripe snack variety Lakomka from the collection of VNIIMK (Table 3).

A comparative study during the 4-years competitive trial has proved high efficiency of the own developed method for evaluation and selection of genotypes with desired traits (Table 3). In 2004-2005 cv Oreshek exhibited a longer growing season than R-453, but in following 2 years this difference was leveled. Therefore, the source breeding material obtained from cv Lakomka in a short period has passed from early ripening to extra early maturation.
This reduce in time needed for ripening was accompanied with decrease in plant height. Weight of 1000 seeds significantly (30-40%) exceeded that of R-453 and slightly exceeded cv Lakomka. Cv Oreshek developed yields similar to those of Lakomka, and on average by 10% higher than in R-453, which indicates overcoming the inverse relationship between early maturation and productivity. Oil content in cv Oreshek varied from 42,2 to 47,3% vs. 48,8% in cv R-453 on average for 4 years of trials. No reliable differences in oil yield between the compared cultivars were found. In 2007, cv Oreshek was assigned to state variety trials, and in 2009 it entered the State register of breeding achievements of the RF and approved for growing in the 5th, 6th, 7th, 8th and 10th climatic zones of the Russian Federation .
Thus, the authors have developed the effective method for selection of a source early-ripening breeding material of sunflower by means of extra-early and late (summer) sowing which enables the reserves of phenotypic variability in periods of flowering and maturation, seed production indices and resistance to adverse environmental factors. The effectiveness of this method was confirmed by rapid creation of a new variety upon two generations grown in one year in natural environmental conditions. When growing plants in the nursery of directed cross-pollination, a number of traits must be recorded: phenological observation, biometric measurements, laboratory analysis of oil content, moisture content, weight of 1000 seeds. The use of serial individual selection in breeding of a variety and at its further reproduction in the system of primary seed growing according to the classical scheme of V.S. Pustovoyt were found to be quite effective in obtaining a new early-ripe, highly productive and highly adaptive snack variety Oreshek.

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