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Development of synthetic cultivar of alfalfa (Medicago sativa L.) on the basis
of polycross progeny performance in the Southern Anatolia
Article in Journal of Food Agriculture and Environment · April 2011
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Journal of Food, Agriculture & Environment Vol.9 (2): 404-408. 2011
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Development of synthetic cultivar of alfalfa (Medicago sativa L.) on the basis of
polycross progeny performance in the Southern Anatolia
Mustafa Avci 1*, Arif Aktaş 1, Numan Kılıçalp 1 and Rüştü Hatipoğlu 2
1 Cukurova Agricultural Research Institute, Adana, 01321, Turkey. 2 Department of Field Crops, Faculty of Agriculture, University of Cukurova, Adana, 01330, Turkey. *e-mail: mavci61@hotmail.com
Abstract
This research was carried out to develop synthetic cultivar of alfalfa with high forage yield and high quality under Mediterranean environment of Turkey during 2002-2009. To ensure a broad range of genetic variability, different alfalfa entries including cultivars, introductions and bulked populations, collected from different sources, were used to establish source nursery. From the original source nursery 380 superior plants (genotypes) out of 7680 individuals were selected and cloned. Thirty-two selected plants from the clonal line nursery were cloned and transplanted to an isolated polycross seed production nursery and were allowed to intermate randomly. Seeds were harvested from all propagules within a clone, composited and sown in replicated progeny test plots. In the progeny plots 32 lines and two standard check cultivars (Mesa-Sirsa and Artal) were evaluated for dry matter yield (DMY), crude protein (CP) content, crude protein yield (CPY), acid detergent fibre (ADF), neutral detergent fibre (NDF) and estimated digestible dry matter yield (EDDMY) during the 2008 - 2009 growing seasons. According to average of two years progeny test results, there were significant differences among alfalfa lines and cultivars in terms of above all mentioned components. Mean DMY, CP content, CPY, ADF and NDF concentrations and EDDMY were 8184 kg ha-1, 18.1%, 3271 kg ha-1, 40.7%, 46.7% and 10,290 kg ha-1, respectively. The results indicated that selection for most vigorous tall-growing plants during the selection phases generally increased DMY, CPY and EDDMY but slightly decreased digestibility and intake potentials. It was concluded that lines 31, 15, 2, 20, 16, 24, 17, 25, 23, 13, 30, 28, 32, 5, 10 and 18 showed good adaptation and performed well under Cukurova ecological conditions by producing more EDDMY and CPY. These genotypes were chosen as components for establishment of a high-yielding nondormant synthetic variety.
Key words: Alfalfa, synthetic cultivar, dry matter yield, herbage quality.
Introduction
Alfalfa, Medicago sativa L., is one of the most important forage crops in the world and used primarily as dried hay, pasture or green chop for a wide variety of livestock. Since 1940, alfalfa forage yields have increased dramatically and breeding has been directly responsible for an important portion of this increase. Progress in improving resistance to disease and insect pests, adaptation to specific environments, and tolerance to frequent harvest have made substantial contributions to the yield performance of alfalfa cultivars. However, the genetic increase in alfalfa yield has been small compared with most grain crops. There is abundant genetic variability within and among alfalfa cultivars, that could be used to develop alfalfa varieties with high yield potential and wide adaptation to different environmental conditions 1.
The development of synthetic cultivars in cross-pollinated forage crops like alfalfa is the common objective of most breeding programs 2. The term synthetic variety has been defined in several
different ways. Busbice 3 defined it as a cultivar produced by
random mating of several parents so that all possible mating between parents have an equal probability of occurring. He excluded the requirement of selecting for combining ability and
improvement in advanced generations. However, Allard 4
emphasized that the parents of a synthetic variety must be selected on the basis of combining ability.
The theory of the synthetic variety is to exploit hybrid vigor by combining superior clones, while avoiding loss of vigor from close
inbreeding by restricting the number of generations. When there are few individuals in the syn 0, relatives will mate in advanced generations, resulting in inbreeding. From the viewpoint of depression in advanced generations, there appears to be little advantage of including more than 16 parents in a synthetic variety so long as the parents are noninbred and unrelated. Busbice et al. 5
pointed out that selection of a plant on the basis of its phenotype would be effective only when a character is highly heritable, such as resistance to many diseases and some insects. However, selection based on progeny testing is more effective than phenotypic selection for characters of low heritability like forage yield. Forage breeders have traditionally used dry matter yield, winter survival and disease resistance as the primary criterion for cultivar selection.
Although alfalfa is one of the highest quality forages available to livestock feeders, it is not perfect forage, and breeding should be devoted for improvement of quality of alfalfa forage. Many parameters have been used to estimate forage quality. Among these, CP, ADF and NDF concentrations and total digestible nutrients are the most useful for predicting forage quality. A long- term selection increased CP concentration by an average of 6.9%, decreased ADF concentration by an average of 4.4% and resulted in increased digestibility by 2.1%. However, despite selection of the most vigorous plants during the selection phase, forage yield
Journal of Food, Agriculture & Environment, Vol.9 (2), April 2011 405 The importance of alfalfa as a cash crop is rapidly increasing
and every year more alfalfa is grown for direct sale in Southern Anatolia, so cultivar development has received emphasis from public or private agencies to maximize yield and quality. Conventionally, introduced cultivars from USA and Europe are grown in the region but sometimes their poor adaptation to the local environmental conditions and susceptibility to multiple-pest resistances can cause significant yield losses. Therefore, a breeding research program was initiated by Cukurova Agricultural Research Institute for development of cultivars to make a significant contribution to the successful production of alfalfa in the region.
Materials and Methods
Five consecutive field experiments were conducted at the Cukurova Agricultural Research Centre, Adana, Turkey (36°51.675 N, 035°20.662 E, altitude 14 m above sea level) under irrigated management conditions during 2002–2009 growing seasons. The soil of the experimental area was classified as silty clay in the 0-30 cm profile, which had an average of 2.51% of organic matter, pH 7.62 and P 87.0 kg/ha and was rich in lime. The mean long-term annual temperature is 18.7°C, the lowest and highest average temperatures occur in January and August. Minimum-maximum mean monthly average temperatures were 8.9-28.6, 4-30.0 and 6.0- 29.0°C; annual average temperatures were 18.7, 18.9 and 18.4°C in the 2006, 2007 and 2008, respectively. Long-term average rainfall is 651 mm 7.
The polycross progeny performance procedure was used for development of synthetic alfalfa cultivar. The procedure involves several distinct embodies and field experiments as illustrated below.
Source nursery: Sixteen different alfalfa entries including cultivars,
introductions and bulked populations, collected from different sources (Turkey, Europe and USA), were used to establish source nursery. Initially an original population containing 7680 individuals was planted as spaced plants in April 2002. The nursery consisted of 64 rows each with 96 m length and 0.8 m row spacing. Superior plants were identified by visual evaluation for vigour, persistence, flowering, disease, insect resistance and other desired features using index selection criteria as described by Rumbaugh et al. 8
Individual plants were scored and approximately 400 plants determined during 2002-2003 growing season.
Clonal line nursery: From the source nursery 384 superior plants
were digged and multiplied as clones (genotypes were propagated by stem cuttings and directly planted in moist soil, and they readily rooted) for establishing a clonal line nursery during 2004 spring. Each clonal line in the nursery comprised 12 plants propagated vegetatively from the original plant and planted in rows with spacing of 0.8 m. In the nursery, genotypes were evaluated in terms of plant height, flowering time, leaf/stem ratio, fall dormancy rating, dry matter yield and seed yield potential during 2004-2005 growing seasons. There were total of 5 harvests in 2004 and 6 harvests in 2005. Genotypes were also screened for the presence of alfalfa mosaic viruses (AMV). Serological DAS-ELISA tests were done as described by Clark and Adams 9. The virus-infected
plants were discarded and 32 AMV free nondormant genotypes were selected for polycross nursery.
The polycross nursery: The general combining ability of superior
clones from clonal line nursery was evaluated by a polycross test. Randomized complete block design with multiple replications was used to maximize the change of random interpollination as suggested by Fehr 10. It was established in isolation by clonal
propagation of selected 32 superior clones. Sixteen replications with six propagules per plot were established in spaced nurseries during March, 2006. Open-pollinated seeds were harvested and bulked by clones maintaining the identity of each clone.
The polycross progeny test: The open-pollinated seeds were
planted in a replicated manner in November, 2006 in a progeny test. Yield, quality and other characteristics were evaluated during the 2007-2008 growing seasons.
Synthetic generation: The 16 superior clones were vegetatively
propagated and randomly transplanted in isolated field with 16 replications to produce Syn. -1 seed during April 2009. In the first production year 1500 g of seed was produced for research purpose and seed multiplication. The breeding project is still being carried out. Because lot of data was obtained from the distinct embodies of this research project, only the polycross progeny test data and results are shown in this research paper.
Thirty-two superior nondormant alfalfa lines and two check cultivars were used to establishment of the progeny test plots. The check cultivars, Mesa-Sirsa and Artal (Pioneer- 5888), are high-yielding, well-adapted cultivars commonly grown in the Southern Anatolia region 11. Plots were arranged in a randomized
complete block design with three replications and fertilized with 120 kg ha-1 of P
2O5 and 50 kg ha-1 of N prior to sowing. Seeds at
a rate of 15 kg ha-1 were sown in the fall into the plots, each
containing 5 rows with 4 m length and 25 cm row spacing. Forage yield was evaluated on six harvests in 2007 and seven harvests in 2008. Plants were harvested at a cutting height of 5 cm when the majority of plants in the plots reached the early flowering stage. Plots were irrigated after each cutting during the growing season. Forage production was estimated by manually harvesting and weighing plants from the centre of each plot 2 m length of three rows. Forage quality was measured at all harvests for two growing seasons. A sample of about 500 g was dried at 70°C and ground with mill using 1 mm screen for determination of DM content and sub samples were taken for chemical analysis. Forage CP contents
were estimated by multiplying total N by 6.25 12. The ADF and
NDF contents in the samples were determined by using ANKOM Fiber Analyzer filter bag method 13. Estimated digestible dry matter
(EDDM) was calculated according to the following equation adapted from common formulas for forages 14:
EDDM (%) = 88.9 - (0.779 x ADF%)
CP yield and EDDMY were calculated by multiplying total dry matter yield of each line and cultivars with CP and DDM ratios. Analysis of variance was performed using the MSTAT-C statistical analysis program and differences were compared using Duncan’s multiple range test.
Results and Discussion
Analysis of variance based on the average values over two years showed that there were significant differences (P<0.05) among
alfalfa entries in terms of DMY (Table 1). The highest DMY (20,233 kg ha-1) was obtained from the line 31. Cultivars Artal and
Mesa-Sirsa and line 29 produced relatively less DMY and were
significantly different from lines 31 and 15. DMY results are consistent with those obtained by previous workers 15-17. In this
study the old cultivars Mesa-Sirsa, released in 1965, and Artal, released in 1991, were lower-yielding (16,543 and 16,525 kg ha-1,
respectively) when compared with mean yield of all lines (18,962 kg ha-1). It is clear that selection produced a general increase in
dry matter yield (average 12.8%). Lines with better adaptation to Cukurova environments, improved stand survival and protected yield potential had a yield advantage over older cultivars. Lamb
et al. 18 also stated that recently released cultivars had a yield
advantage over older cultivars.
Crude protein content was significantly changed by genotypes (Table 1). Average CP ratio of two years for alfalfa ranged from 16.9 to 19.0%. Lines 11 and 26 had the highest and the lowest CP ratio, respectively. Relatively lower mean content of CP in lines 31, 26 and 30 may be due to plants being slightly more mature at sampling time indicating that the increase in stem diameter and length decrease the leaf/stem ratio, with a reduction of CP concentrations, consequently large variations in quality of alfalfa herbage have been reported 19. CP content values determined in
the present study are similar with those reported by previous
researchers 17, 20, 21. Hill et al. 1 suggested that breeding efforts
should be focused on improving the protein content and yield of alfalfa.
Significant differences among the alfalfa were found for CP yield. Based on average of two years, the highest CPY was obtained from the line 20 with 3543 kg ha-1. It gave statistically significant
higher CPY than the lines 9, 14 and 29 as well as the check cultivars. Cultivar Artal having the lowest DM yield (16,525 kg ha-1) and
relatively lower CP ratio (17.6%) exhibited the lowest CP yield (2940 kg ha-1). Cultivar Mesa-Sirsa with relatively higher CP ratio (18.3%)
produced lower CP yield (2988 kg ha-1) because of its lower DM
yield. Relatively higher total CP yields for lines 31, 15, 17 and 20 were largely due to higher DM yield contribution from those lines. Significant differences were recorded among alfalfa entries, and mean content of ADF ranged from 38.6 to 42.7% for two year average (Table 1). Line 10 had the lowest content and was statistically different from the lines 7, 28, 19, 31, 5, 30, 17, 26, 20, 21, 6, 25, 1, 8 and 18. Line 7 had higher ADF content than the lines 3, 4, 9, 10, 11, 12, 13, 16, 23, 24, 29 and 32, as well as check cultivars. ADF values determined in the present study were found similar to those of previous studies 11, 17, 22. ADF is the percentage of highly
indigestible plant material in the forage. Therefore, low ADF values are desirable because they are correlated with increased digestibility. Means of ADF content of two check cultivars and
_________________________________________________________________________________ Line/cultivar DMY (kg ha-1) CP (%) CPY (kg ha-1) ADF (%) NDF (%) EDDMY (kg ha-1)
1 17332bd* 18.2b-g 3119a-f 41.0a-h 46.5a-e 9897c-g
2 19292a-c 18.2b-g 3491a-c 40.7a-ı 47.2a-e 11040a-c
3 17128bd 18.5a-d 3138a-f 40.1c-ı 45.0ef 9846d-g
4 17223bd 18.4a-f 3158a-f 39.8d-ı 46.4a-e 9975c-g
5 18515a-d 17.6fh 3252a-f 41.7a-e 46.7a-e 10440a-g
6 17638bd 17.7e-g 3117a-f 41.1a-h 47.2a-e 10030c-g
7 17848a-d 18.2bg 3223a-f 42.7a 47.6a-d 9932c-g
8 18088a-d 18.1b-g 3264a-f 41.0a-h 46.0c-f 10300a-g
9 17415bd 17.7e-h 3076c-f 39.5f-ı 45.4df 10160b-g
10 17692bd 18.7ab 3293a-f 38.6ı 45.4df 10390a-g
11 17357bd 19.0a 3296a-f 39.2g-ı 45.7c-f 10140b-g
12 17235bd 18.6a-b 3185a-f 39.6e-ı 43.6f 9993c-g
13 19037a-c 17.7e-h 3358a-f 40.3b-ı 47.5a-e 10720a-f
14 17578bd 17.8c-g 3106b-f 40.3a-ı 46.6a-e 10110b-g
15 19592ab 18.1b-g 3353ab 40.3aı 47.5a-e 11250ab
16 18822a-d 18.5a-d 3462a-d 39.6e-ı 45.3d-f 10950a-d
17 19365a-c 18.2bg 3510ab 41.7a-e 46.8a-e 10910a-e
18 18322a-d 18.6ab 3386a-e 40.9a-h 46.8a-e 10440a-g
19 17732b-d 18.0b-g 3190a-f 42.1a-c 46.7a-e 9939c-g
20 19363a-c 18.3a-f 3543a 41.3a-g 48.0a-c 10970a-d
21 18097a-d 18.4a-f 3324a-f 41.2a-g 46.9a-e 10280a-g
22 17642bd 18.6ab 3256a-f 40.6a-ı 46.2a-e 10130b-g
23 18842a-d 18.0b-g 3393a-e 40.1c-ı 47.7a-d 10870a-e
24 18993a-d 18.3a-f 3469a-d 40.3b-ı 47.1a-e 10930a-d
25 19097a-c 18.4a-e 3516ab 41.1a-h 46.1a-e 10870a-e
26 18533a-d 16.9ı 3118a-f 41.5a-f 47.4a-e 10450a-g
27 18003a-d 17.6f-h 3156a-f 40.8a-ı 48.1a-c 10250a-g
28 18948a-d 17.4g-i 3292a-f 42.4ab 48.7a 10590a-g
29 16932cd 18.1b-g 3055d-f 40.3b-ı 46.7a-e 9758e-g
30 18935a-d 17.0hı 3226a-f 41.7a-e 48.6ab 10660a-g
31 20233a 16.9ı 3413a-e 41.9a-d 48.2a-c 11400a
32 18343a-d 18.5a-c 3372a-e 40.4b-ı 45.9c-f 10520a-g
Artal 16525d 17.6d-g 2940f 40.3b-ı 46.0b-e 9500g
Mesa Sirsa 16543d 18.3a-f 2988ef 38.9hı 45.0ef 9646fg
Mean 18184 18.1 3271 40.7 46.7 10390
Table 1. Dry matter yield (DMY), crude protein content (CP), crude protein yield (CPY), acid detergent fiber
(ADF), neutral detergent fiber (NDF) and estimated digestible dry matter yield (EDDMY) of alfalfa. Data collected from the polycross progeny performance. Values are averages of 2008 and 2009 data.
Journal of Food, Agriculture & Environment, Vol.9 (2), April 2011 407 32 selected lines were 39.6% and 40.8%, respectively. This
indicates that selection has negative effect on hay quality because ADF concentration increased by an average of 2.9% when compared with those of check cultivars. Julier et al. 23 also
suggested that the development of high-yielding, highly digestible cultivars is complicated by the negative relationship between digestibility and forage yield.
Significant differences (P≤0.05) were found among alfalfa entries for NDF content. Based on average of two years, the lowest NDF concentration was obtained from line 12, while line 28 showed the highest NDF content. Higher NDF contents in the lines 28, 30 and 31 were largely due to advancing morphological development. The NDF fraction is the cell wall structure of the forage that is partially available to animals. Low NDF values are desirable and associated with increased animal intake. NDF contents of alfalfa were 45.9-51.1, 47.5-50.3 and 39.4-47.8% in the previous studies 11, 21, 22, depending on cultivars and years. The values related to
quality traits observed in this study were lower than those reported
by Lamb et al. 19 and Kallenbach et al. 24 indicating that
environmental conditions and harvest frequency have great influence on forage quality. Avcı et al. 11 also stated that forage
quality tends to be highest at the last harvests of the season (during the fall), having low temperature and shorter day length. However, first 5 or 6 harvests during spring and summer are potentially of lower quality when compared with that of fall harvest, because of relatively higher mean annual temperature 8 in Southern
Anatolia.Means of NDF content of two check cultivars and 32
selected lines were 45.5% and 47.1%, respectively. These results suggested that selection of the most vigorous plants during the selection phases had negative effect on hay quality because NDF content increased by an average of 3.4% when compared with those of check cultivars.
Several studies 25, 26 have demonstrated that forage quality of
alfalfa can be altered by selection for quality traits. Large genetic variations within and among alfalfa cultivars for quality traits have been described in previous researches 23, 27. Selection focusing on
nutritive value, intake and digestibility without consideration of forage yield often results in high-quality, low yielding experimental populations. However, yield and quality are negatively correlated in practice, and optimum profitability rarely occurs at maximum yield or maximum quality, complicating genotype selection. Integration of yield and quality factors as selection criteria is a challenge for breeders and agronomists. Hill et al.1 stated that
alfalfa is such a high quality forage that some may argue that breeding efforts should be placed on increasing yield and improvement of those characteristics that influence yield, and concentrated efforts on breeding for quality alone is not recommended.
Estimated total digestible dry matter yield values for the alfalfa entries are presented Table 1. Significant differences (P<0.05) were observed among them in EDDMY. Based on average of two years results, the highest EDDMY was recorded at the line 31 (11,400 kg ha-1), but it was not significantly different from the entries with an
EDDMY as low as 10,250 kg ha-1. The greater EDDMY was
largely due to greater yield contribution from lines and cultivars.
Conclusions
Although the detrimental effects of inbreeding and some natural selection with each advanced generation could reduce the yield
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Acknowledgements
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