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Genetic Diversity of the Upland Cotton Varieties Bred in North Xinjiang Region Revealed by Agronomic Phenotypes  

Xiantao Ai , Xueyuan  Li , Junduo  Wang , Juyun  Zheng , Hong  Sha , Tuerxunjiang  , Likun  Duo , Ming  Mo
Economic Crop Research Institute, Xinjiang Academy of Agricultural Sciences, Urumqi, 830091, R.P. China
Author    Correspondence author
Cotton Genomics and Genetics, 2012, Vol. 3, No. 2   doi: 10.5376/cgg.2012.03.0002
Received: 18 Sep., 2012    Accepted: 15 Oct., 2012    Published: 20 Nov., 2012
© 2012 BioPublisher Publishing Platform
This article was first published in Molecular Plant Breeding (2011, Vol.9, No.1, 113-122) in Chinese, and here was authorized to translate and publish the paper in English under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Ai et al., 2012, Genetic Diversity of the Upland Cotton Varieties Bred in North Xinjiang Region Revealed by Agronomic Phenotypes, Cotton Genomics and Genetics, Vol.3, No.2 8-16 (doi: 10.5376/cgg.2012.03.0002)

Abstract

We attempted to reveal the genetic background and phenotypic characteristics of the varieties bred in Northern Xinjiang through the study on genetic diversity of the 38 cultivated varieties approved in Xinjiang. The results showed that the trait of the fruit branch number in the 13 tested phenotypic traits had the highest genetic diversity index; along with the year in different breeding period, the bred cotton varieties exhibited that the growing period gradually shortened, fruit-branch number increased, cotyledon node and plant height significantly increased; and boll weight per boll obviously increased, seed index also showed an upward trend with boll weight changes; the boll number per plant and lint percentage also presented overall increasing trend, however, the lint percentage left a great space to be enhanced; the fiber length and strength gradually increased in the bred varieties, and micronaire values showed a downward trend. Overall the quality traits went to be reasonable with each passing periods. Genetic analysis indicated that 38 domestic bred varieties could be clearly divided into two groups with similar phenotypic traits, similar genetic background, the same breeding unit and the same type varieties were better clustering together. The clustering results would be relatively accord with the evolution trend in their real characteristics and genetic background. Overall, the domestic bred varieties had become major cultivating varieties in Northern Xinjiang, The reason would lie in the reasonable utilization of the genetic composition from the American components and the Yellow River cotton germplasms as well as Liaomian cotton series of special early maturing cotton area, which would provide insights, basis and developing direction to break out the genetic component narrow issues in Xinjiang cotton breeding program.

Keywords
Upland cotton; Domestic bred varieties in North Xinjiang region; Phenotype traits; Genetic diversity

Xinjiang, as the largest high-quality cotton producing region in China, are the commodity cotton production base and export base, the total output of cotton, yield per unit, the cultivating area has been for many years ranked the first in China. In recent years, with the rapid development of cotton production and an increasing expend of cotton planting area, a variety of pests and diseases increasingly developed and spread, the hazard was increasing year by year that seriously influenced cotton yield, quality and benefits of cotton planting. It has become increasingly prominent that the yield potential and resistance level of the existing varieties in Xinjiang region could not meet the requirements in cotton production. In production, most of the released cotton varieties with insufficient yield potential and poor genetic stability resulting in poor quality and low resistance to disease were difficult to meet the demand of the development of cotton production and market demands.

Northern Xinjiang is one of the three major cotton-growing areas in Xinjiang. In recent years, with the continuous development of the cotton production, developing the appropriate varieties with the high-yielding, good quality and disease-resistant cotton adapting to the Northern Xinjiang cotton growing areas become one of the increasingly urgent demands. In other hand, although there were much more studies on genetic diversity in phenotypic traits of the cotton germplasms (Bie et al., 2001; Xu, 2001; Liu et al., 2003; Yu, 2003; Chen, 2005), it was not yet to study more on the genetics and breeding of the Northern Xinjiang.
For above reasons, in the study we attempt to analyze the upland cotton varieties bred in the Northern Xinjiang in the past three decades with means of 13 phenotypic traits analysis to reveal the genetic diversity and background in order to provide breeding experience and know how as well as to provide theoretical guidance for better utilizing the excellent germplasm resources and breeding super new varieties of cotton.
1 Result analysis and discussions
1.1 Quality trait phenotypes and genetic diversity index
Twelve of quality traits were chosen to analyze the diversity index (Table 1), the results showed there were huge difference existing among the tested varieties, in which the main stem hairy presented highest index of genetic diversity (1.362 5), followed by the blades of the leaf cleft and boll size (1.328 7 and 1.310 4, respectively), while the lowest genetic diversity was the leaf color at the blooming stages (0.787 7).


Table 1 The performance of the quality traits and the genetic diversity index of the domestic bred varieties in Northern Xinjiang

1.2 Variation parameters of phenotypic trait and genetic diversity
Based on investigation data of agronomic traits and fiber quality, the variation status of thirteen phenotypic traits were carried out the statistical analysis (Table 2). The variation of the boll per single plant maximum reached 24.56% in eight of major agronomic traits, followed by plant height, height of cotyledon node and the number of fruiting branches, which were 17.32%, 13.02% and 11.90%, respectively, while the minimum coefficient of variation was the trait of the length of growth period, that was only 3.23%. The size and range of variation coefficient of the traits presented positively correlationship (Li et al., 2005), demonstrating that there were plenty of the variation of yield traits existing in varieties developed Northern Xinjiang.


Table 2 The comparison between the variation parameters of the phenotype traits and diversity index of the domestic bred varieties in Northern Xinjiang
The analysis of quality traits indicated that the variation coefficient of cotton micronaire was 10.48% with the range of variation from 3.2 to 5.2, followed with fracture strength and fiber velvet length that ranged from 26.0 mm to 37.2 mm and from 27.7 mm to 34.6 mm, respectively. The variation coefficient of uniformity index and elongation rate were the smallest, 1.63% and 1.33% respectively.

The highest genetic diversity index was the number of the fruiting branches in the 13 phenotypic traits, which reached 2.077 739, followed by micronaire value, seed index and single boll weight. While the lowest genetic diversity index was the rate of elongation, that was only 0.867 286.
1.3 The phenotypic trait difference of the varieties in Northern Xinjiang in different periods
In order to understand the phenotypic differences among the series of Xinluzao varieties in different periods, 38 varieties of roughly divided into three breeding periods according to the released Year of these varieties (Table 3). Three varieties were grouped to the first breeding period from 1981 to 1990, accounting for 7.9% of the total 38 varieties; nine varies were grouped to the second breeding period from 1991 to 2000, accounting for 23.7% of the total; and twenty six were group to the third breeding period from 2001 to 2008, accounting for 68.4% of the total.


Table 3 The differences of phenotype traits of the domestic bred varieties in Northern Xinjiang

In
view of the changes in phenotypic traits, the trait of the growth period the varieties gradually shortened overall (130, 125, 126), which indicated that the maturity should gradually adapt the climates of the Northern Xinjiang; The number fruiting branches (8.8, 8.4, 9.3) overall gradual increased, and the height of the cotyledon node (5.2 cm, 5.8 cm, 6.3 cm) and plant height (52.6 mm, 62.4 mm, 78.9 mm) had an obvious increasing trend. Therefore, the changes of these traits related to genetically yield improvement led to change in the traits of variety maturity and plant height in breeder’s selection strategy.
In view of the yield traits, the yield changes were the most evident during the breeding periods. The boll weight bred varieties (5.4 g, 6.4 g, 6.9 g) was significantly increased, presenting the smallest of the boll weight in the first period, while the biggest of the boll weight in the third period with an average of 6.9 g, ranged from 5.4g to 8.4 g, which might be close related to the enriching types of the bred varieties in the third period. Seed index (10.7, 11.0, 11.6) changed with boll weight change also showed an upward trend. Boll number per plant (5.4, 6.4, 6.1) presented the trend of the increase overall. It was not difficult to see that from the coefficient of variation (25.73, 26.15, 24.32) in the three periods, the boll number change was closely related to cultivar characteristics and cultivation conditions. The trait of lint percentage (38.4%, 40.7 %, 39.0%) also showed the trend of the increase overall, in which the biggest change happened in that third period with the range from 35.2% to 45.2%. Overall, the changes of the self-bred varieties were obvious in the yield traits, and with the breeding period growing the yield potential continues to increase, the traits affecting the yield such as boll number, boll weight and lint yield were continuing to be improved and optimized.
In view of the quality traits, three periods of self-fertile varieties the length of fiber (29.4 mm, 29.4 mm, 31.6 mm), the strength (cN/tex) (27.8, 28.6, 31.3), uniformity index (84.0%, 84.4%, 85.2%) showed a steady improvement trend; especially happening in the third period, the changes of fiber length and strength were in the ranges from 27.7 to 34.6 and from 26 to 37.2 , respectively. The average of the Micronaire (4.9, 4.5, 4.2) showed a downward trend that the change were becoming more rational overall to meet the reasonable needs of the market direction toward. However, there was little change in elongation traits. Overall, fiber quality the third period was better than that in the second period, while the fiber quality the second period was better than that in the first period, indicating the breeders made the continuing efforts to increase the quality of cotton.
1.4 Different distribution of the number of the bred varieties in Northern Xinjiang based on the major phenotypic traits
In order to figure out the differences of the phenotypic traits among the bred varieties in Northern Xinjiang, the traits of boll number, boll weight, lint percentage, fiber length and so on were divided into five groups, that is:
â… , â…¡,â…¢,â…£, and â…¤, and then statistically analyze the distribution of the number of the bred varieties in Northern Xinjiang within five groups (Table 4).
 

Table 4 The quantitative distribution of the key traits of the domestic bred varieties in Northern Xinjiang
In view of the yield traits, the boll number of the varieties were ranged from 3.3 to 4.5, accounting for 15.8% of the bred varieties, and the boll number of most of the bred varieties were distributed from 4.7 to 7.2, accounting for 68.4%, whereas only 15.8% of the bred varieties presented the boll number per plant distributed between 7.8 to 9.7. The bred varieties for the boll number per plant were still much lower due to high shedding of the bolls, which might be one of the important factors to limit the increase in yield, requiring to be further improved.
Boll weight is also an important factor constituting the yield of cotton in production. Distribution, 50% of the bed varieties were distributed in range of from 6.5 g to 7.1 g of the boll weight, particularly the bred varieties since 2000 were located in this rang. The boll weight significantly more increased than that of the varieties bred in the first period, indicating the breeders continuing strengthened the selection for the boll weight per cotton boll, which was in line with the change trend of the seed index.
There was greater variation in the trait of the lint percentage from the lowest 35.2% up to 45.2%, indicating that the breeders should strengthen to select this trait. Most of the bred varieties had lint percentage at about 40%, only 10 varieties had high lint percentage, definitely, there might be much potential for improvement.
50% bred varieties had their fiber length distributed from 28.9 mm to 30.8 mm, of which eight varieties (21.1%) reached the standard of high-quality and mid-to-long fiber cotton, fiber length ranged between 33.4 mm to 34.6 mm and the strength ranged between 32 to 37.2 cN/tex, such as the series of Xinluzao No. 16, No. 20, No.24, No.27, No.29, and No.39, these varieties were released since 2000, indicating that the northern bred cottons were forced in the selection of the quality traits.
Micronaire is considered as the comprehensive performance in the traits of the fiber fineness and maturity. 18.4% of the bred varieties ranged between 3.7 to 4 in the values of micronaire, 36.8% between 4.1 to 4.5 in the values of micronaire, and 31.6% between 4.6 to 5, (the micronaire A grade ranging between 3.7 to 4.2), which indicated that the bred varieties in Northern Xinjiang were not yet reasonable in the trait of micronaire value and need to pay attentions about the micronaire growing trend.
There was greater variation in the trait of the strength ranging from 26 to 37.2 cN/tex, 42.1% of the bred varieties ranged between 27.4 to 29.6 cN/tex in the values of the strength, while 36.8% between 30 to 32.5 cN/tex.
1.5 Clustering analysis on the bred varieties in Northern Xingjiang based on the phenotypes
Dendrogram was built based on the sum of squares method (Figure 1), and Euclidean genetic distance between the different species were calculated (Table not showed). Euclidean genetic distances of different varieties ranged from 1.599 8 to 25.108 5 with an average of 4.941 7. There was biggest genetic distance (25.1085) existing between Xinluzao No1 and No 16, which might be caused due to the genetic basis of different varieties. Whereas the smallest genetic distance (1.599 8) existed between two varieties of Xinluzao No. 6 and No. 7.


Figure 1 Clustering tree of the domestic bred varieties in Northern Xinjiang based on the main agronomic traits

Series varieties of Xinluzao were divided into two groups based on the threshold as 15.07 (Figure 1). The group one contained 30 varieties and the groups two contained eight varieties. The threshold value was set at 10.04, the group one can be sub-divided into two sub-groups, wherein the sub-group one consisted of 16 varieties and the sub-group two consisted of 14 varieties. Statistical results from phenotypic traits showed that differences in phenotypic traits in each group owned their representative (Table 5) and presented the different characteristics of the bred varieties in Northern Xinjiang.
 

Table 5 The mean of the trait values in different clustering groups of the domestic bred varieties in Northern Xinjiang
 
In the group I, the varieties with a similar genetic background, the same breeding unit, and the same types were preferably clustered together. For example, two low gossypol cotton varieties bred by Nongyishi agricultural Institute, Xinluzao No. 3 and No. 15 were clustering in Group I.
The group II as an independent groups owned distinguished characteristics that the varieties such as Xinluzao No. 16, No. 20, No. 27, No. 28, No. 31, and No. 39 contained high-quality Bellsiro genetic component of the American cotton genetic background (Table 6), performing excellent quality, fiber quality had reached the index of mid to long fiber cotton.


Table 6 Genetic components of the domestic bred varieties in Northern Xinjiang
 
Therefore, the cluster analysis in this study were in line with the true characteristics of the bred varieties, the varieties with similar phenotypic traits and or with the same genetic basis were clustering in the same branches, which was consistent to the genetic evolution trend in the Xinluzao series.
1.6 Changes and replaces of the major cultivated varieties and the introduction of genetic components in Northern Xinjiang
The major cultivated cotton varieties were roughly experienced three replacements in Northern Xinjiang regions, which resulted in variation of the genetic component changes in the Northern bred varieties.
The First large scale cultivar replacement would be in 1976, when the northern Xinjiang began to promote the bred variety Xinluzao No. 1. due to the variety with high yield potential idea size of the boll, concentrated boll opening and white fiber, particular in its character of early maturity, the planting area gradually expanded and gradually replaced of the old bred varieties or lines, such as 61-72, 66-241 Qudan, Nongkan No. 5 etc. which became a major cultivating cultivars in Northern Xinjiang in 1983. Since 1985 Northern Xinjiang began to plant Xinluzao No. 2, and No. 3, and in the early 1990s began to promote Xinluzao No. 4 and No. 5 and some varieties or lines, yet the planting area was not very limited and the existing planting time was also limited in this period.
The second large scale cultivar replacement would be in 1996, when the Xinluzao No. 6, No. 7, and 8th replaced the Xinluzao No 1. Because of the Xinluzao No. 6 with high yield and lint percentage (42.7%), while Xinluzao No. 7 with early maturity and resistance to fusarium wilt as well as tolerance to verticillium wilt.
The third large scale cultivar replacement would happen since 2000, the Xinluzao No. 12 and No. 13 with the characteristics of disease resistance and high yield has gradually become the main cultivars in Northern Xinjiang. Xinluzao No. 12 in 2002 was planting up to 250 000 hectare, while Xinluzao No. 13 in 2004 was planted 200 000 hectare in total (Guoy ea al., 2005).
It was not difficult to see that the bred varieties in the northern of Xinjiang (Xinluzao series from No. 1 to No. 8) were introduced mostly with the genetic components of the Su-mian KK-1543, 611Bo, Tashkent No. 2 (Ai X.T., 2005). Obviously, the genetic basis of the varieties was narrow.
In the later of the breeding program, the main varieties gradually showed the trend of diversification, the genetic introductions came from both domestic varieties and introduction, resulting in exhibiting relatively rich genetic components in the domestic varieties. Especially, the genetic components of the American cotton was introduced in the breeding process,such as Bellsiro, deltapine cotton, Acala cotton and King cotton (Huang, 2007), as well as the introduction of Yellow River cotton series and Liaomian series in special early maturing cotton region, which makes the genetic basis of domestic varieties expanded and enriched as well as yield potential continuous improved.
Since 1970's, the domestic bred varieties had been become the main varieties in the Northern Xinjiang, and the yield was steadily increased. The genetic reason would be contributed to the introduction of the genetic components from the American germplasms, which was proven to be the effects by expending the reasonable genetic component in one side (Sun J., 1999). It would provide insights, basis and developing direction to break out the genetic component narrow issues in Xinjiang cotton breeding program.
2 Materials and methods
2.1 Experimental materials
38 cultivars used in this research were developed during the periods from the year of 1981 to 2008 approved and promoted in Xinjiang. All of materials were provided by Nongqishi Agricultural Scientific Institute and the variety breeder’s organization, which represents the overall breeding level of upland cotton varieties in the northern Xinjiang.
2.2 Experimental Methods
Design of field trials, investigation of phenotypic traits and methods as well as phenotypic data processing were following up the descriptions (Ai et al., 2009).
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