Project Summaries

10-692TX  Project Manager: D. C. Jones


Jane K. Dever, Texas AgriLife Research

This project was intended to demonstrate that work-to-break characteristics of cotton fibers and yarns can be improved through breeding, specifically selecting for elongation. Cotton fiber is an important natural resource used for multiple purposes, widely used in industry for textile processing.  With the advancement and acceleration in spinning speed and processing, the requirement of improved cotton fiber quality is of great importance to the textile industry because it directly relates to processing performance, productivity and yarn quality.

Fiber elongation is a property of the fibers measured during the determination of bundle strength.  Elongation refers to the amount of elasticity of the bundle sample before breaking, tested on tensile strength instrument like the stelometer or HVI (High Volume Instrument). Backe (1996) studied the effects of fiber elongation on yarn and textile manufacturing.  He determined that fiber bundle elongation is important for producing better yarn's quality and resistance to stresses in weaving.  However, fiber elongation has never been a selection criterion during line or cultivar development mainly because of the lack of calibration of HVI instruments and a weak negative correlation with fiber strength.  Nevertheless, as spinning technologies evolve and speed in processing increases, fiber elongation might become a more important property in the cotton improvement breeding process.  

The primary walls of cotton fibers are formed during the fiber trichomes elongation phase and contain less than 30 percent of cellulose, noncellulosic polymers, neutral sugars, and various proteins.  Spirals and angles are formed during elongation of fibers before boll opens, or primary cell wall deposition, which is known to affect secondary cell wall deposition and later, fiber strength.  The same mechanisms of spirals and angles might affect the degree of stretching of post-harvest fibers.  However, there is lack of understanding regarding the relationship between primary cell wall formation and fiber structure and properties.  According to Hsieh (1999) primary cell wall development appears to contribute two-thirds or more of the fiber strength.  However, no data is reported on fiber elongation.  Nonetheless, he reports that elongation is affected by the development of the fibers before boll opening.  Yet, secondary cell formation (cellulose deposition and crystallination) is more directly related to tensile properties than primary cell formation.  Nevertheless, fiber development is highly influenced by genetics and the environment which at the same time affect fiber properties important for fiber and yarn processing.  As pre-harvested fiber elongation determines the length of the fibers, likewise it is probable to have a direct impact on post-harvested fiber elongation. However, since cotton fiber elongation (post-harvest) has never been a selection criterion, studies of the relationship between fiber development and cell wall deposition to post-harvest fiber elongation has not been extensively studied.  Therefore, to better understand fiber quality and the effect of fiber elongation on yarn processing and weaving, the linkages between fiber development and fiber elongation (post-harvest) should be more extensively studied.

To determine the effect of fiber elongation (post-harvest) on yarn properties, Benzina et al. (2007) produced 3 standard cottons with known values of tenacity and elongation (measured with the instron).   Reference material was created that could be used to calibrate the HVI instrument.  This allowed elongation levels to be held constant over an extended period of time which is indispensable for a breeding program selecting for the measured character. The CV% for elongation were below the target value of 5% (5% is the maximum CV% allowable for the fiber testing) and no instrument drift or malfunction was observed during the testing period. Therefore reliable fiber elongation measurements were obtained. 

In addition, the elongation property of fibers has not been emphasized in breeding programs because it has been shown to have inconsistent genetic contribution to fiber and yarn tenacity. In addition there is a perceived negative correlation between fiber elongation and strength, which makes breeders more skeptical to focus on this particular trait. Nevertheless, the negative correlation is weak and does not preclude a simultaneous improvement of fiber strength and fiber elongation. The work of rupture, or combination of breaking strength and fiber elongation, is very important to spinning quality.  The best way to improve it is to work on genetically improving both tenacity and elongation. By genetically improving fiber properties, breeders are contributing to productivity gains in the textile industry. This project included development of similar lines with different levels of elongation through divergent selection in a typical pedigree breeding scheme to use for spinning studies and heritability studies to help determine if elongation can be impacted through breeding using improved measurement technology.

The results from this project demonstrate that it is possible to improve fiber elongation and to break the negative correlation between elongation and strength. Furthermore, it was demonstrated that improving fiber elongation results in the increase of uniformity index and decrease of short fiber content.  Additionally, directed divergent selection was a successful methodology for the improvement of fiber elongation; and it was useful to demonstrate that higher fiber elongation has a positive effect on yarn tensile properties and processing.  Preliminary results showed that in the F2 generation there was a wide range of variation for fiber elongation; with a maximum value of 12% and minimum value of 6%.  This variability in fiber elongation made possible the use of divergent selection.  In the F3 generation, an excellent diversity in fiber elongation was maintained with a wide range of maximum values of 9% and minimum values of 4%. Therefore, it was possible to keep divergent selections.  In the following generation, the F4, it was observed that high and low levels of elongation were kept through generations of selection, still maintaining a high range of variation for fiber elongation.  All selections for high fiber elongation were higher than the check cultivar.

A weak negative correlation was observed between fiber elongation and strength in early generations; -0.32 in the F2, -0.36 in the F3 and -0.0889 in the F4. However, with consistent targeted selection this relationship changed towards a positive relationship (0.424) for the lines selected for spinning tests. In the early generations, selection pressure was applied only to elongation while keeping other fiber properties constant, with the purpose of developing lines for spinning that isolate the influence of elongation specifically.  However, in the final round of selections, other fiber properties were considered.  Therefore, the positive correlation between fiber strength and elongation at the end, compared to negative correlation in the early generations, indicated that the two properties that constitute the work-to-break can be improved simultaneously.  In addition, it was demonstrated that improving fiber elongation increases uniformity index.  A positive though weak correlation was observed between them in every generation; 0.319 in the F2, 0.0042 in the F3 and 0.162 in the F4.  In the selected lines for spinning test the positive correlation remained constant (0.182).  Data from HVI shows a steady improvement of fiber length and strength, however, length uniformity remained stagnant.  Nevertheless, this research shows that the ability to select for improved fiber elongation has the potential to impact length uniformity indirectly.  Fiber elongation was also negatively correlated with short fiber content by weight and by number.  However, AFIS data was only obtained in later generations and for the lines selected for spinning.  Nevertheless, the results indicated that improving fiber elongation reduces short fiber content; -0.080 in the F4 (short fiber content by weight) and -0.111 (short fiber content by number) in the lines selected for fiber spinning. 

Spinning performance and yarn quality on the selected F4 lines suggest that improving fiber elongation improves yarn tensile properties and evenness.  Lines selected for high and low elongation had better tensile properties than the check cultivar 'FM958'.  For instance, fiber elongation was positively correlated to yarn tenacity (0.383), breaking elongation (0.594) and work-to-break (0.596). On the other hand, fiber elongation was negatively correlated with thin places (-0.272), thick places (-0.494), nep count (-0.493), hairiness (-0.635) and total number of imperfections (-0.563).  All selections for high elongation were superior for all tensile properties compare to the low selections and the check in the analysis over locations and in each location.  Furthermore, selections for high elongation were significantly different from the selections for low elongation and the check.  Additionally, fiber strength was kept constant in the selection process, and the final lines used for spinning had high levels of strength that positively correlated with fiber elongation.  Therefore, fiber elongation and fiber strength can be simultaneously improved.  Results from this project will lay the foundations for future efforts to breed new varieties with improved work-to-break. Including breeding lines with improved elongation and selection pressure for work-to-break characteristics in new variety development programs is important and will reduce the amount of short fiber content and increase uniformity index.   The development of new varieties with improved fiber elongation will improve the quality and reputation of U.S. grown cotton.  The ultimate result will be better yarn quality and improved weaving efficiency, and particularly address current weaknesses in U. S. grown cotton varieties, especially from the High Plains of Texas, of more short fiber content, lower uniformity ratios, and weaker yarn strength.

Yield tests were planted to determine the productivity of the selected lines. The test was initially planted in four locations; however, one location at Lamesa was not established and the location at the Texas Tech Research Farm did not produce enough lint due a severe drought during 2011.  Nevertheless, lint was harvested in this location and yield data was analyzed along with yield data from the other two locations, Halfway and Lubbock, TX. The results from the yield test showed negative correlations between lint yield and fiber elongation (-0.193) and lint yield and fiber strength (-0.285). The analysis of variance over locations indicated that there was no interaction between entries and locations, and the check cultivar Deltapine DP491 had the highest yield (745.89 kg/ha), followed by the selection for low elongation from family 10b (686.86 kg/ha), and the selection for low elongation from family 7 (664.72 kg/ha).  The selections for high elongation were in the middle to the lower range of yield.  Furthermore, locations were significantly different with the Texas Tech Research Farm having the lowest value. In the analysis for each location, Halfway had the highest yield among all locations.  The low selection from family 10b with a yield of 885.99kg/ha and the low selection from family 10a with 862.74kg/ha were the highest yielding in this location. In Lubbock and the Texas Tech Research Farm, the commercial check Deltapine 491 was the highest yielder with 871 kg/ha and 525.94 kg/ha in Lubbock and the Tech Farm respectively. The yield from the Texas Tech Research Farm was considerably lower due to a severe drought during 2011 coupled with inadequate irrigation.

The negative correlations between lint yield and fiber elongation contrasted with the results from Tang et al. (1996). The authors reported positive correlations (0.26) between lint yield and elongation. However, it has been demonstrated that yield components are negatively correlated with fiber quality (Desalegn et al., 2009; Green and Culp, 1990; Smith and Coyle, 1997) in accordance with the results from this project. The low elongation parent used in all of the crosses, 'FM 958', is a high yielding cultivar on the High Plains, and the negative yield association with elongation could be an artifact of this particular data set in the Texas High Plains environment.  Nevertheless, the use of more complex crosses, such three way crosses, modified backcrosses, inter-mating or recurrent selection could be used in future experiments to improve fiber quality characteristics and yield at the same time (Coyle and Smith, 1997; Green and Culp, 1990; Schwartz and Smith, 2008).  Additionally, since fiber elongation has not been emphasized in breeding programs, future efforts should include the simultaneous improvement of tensile properties, fiber strength and elongation, along with improvement of yield and yield components.  Lines developed in this project are being used in molecular marker studies and tools could be forthcoming that assist in introgressing improved fiber elongation in higher yielding breeding lines.

In addition to using divergent selection for fiber elongation to test the hypothesis that fiber elongation is important for spinning, this project was intended to evaluate and determine the heritability of fiber elongation. Little is known about the genetics and the heritability of fiber elongation because its improvement has been ignored due to its perceived negative correlation with fiber strength (Backe, 1996). However, knowledge on the heritability of fiber elongation will help breeders understand the genetic action that controls this trait. Heritability estimates help breeders elucidate the best strategy for selection and to predict gains from selection (Holland et al., 2003; Nyquist, 1991).

Three different methodologies were used to obtain estimates of heritability; 1) variance components, 2) parent off-spring regression, and 3) realized heritability.  Broad sense heritability was estimated from the variance component method. Genetic variation estimated by broad sense heritability cannot be partitioned into its components (additive and dominant), and therefore, information on the type of variation cannot be obtained. Nevertheless, broad sense heritability provides information needed to determine the amount of genetic variability in the population.  Heritability was estimated in each generation because no family relationships could be determined. The results indicated that about 40 to 50% of the variation was due to non-genetic effects.  Estimates of heritability from parent off-spring regression indicated there is a 50 - 60% resemblance from parents to off-spring for fiber elongation.  Parent off-spring regression method for estimating heritability is closely related to narrow sense heritability. Therefore, fiber elongation has a high possibility to be improved in early generations.  In addition estimates of realized heritability were obtained to determine the progress realized from selection for the low and high selection for fiber elongation.  Estimates were intermediate (0.44-0.55), indicating moderately good progress from selection. These results indicate that targeted selection was a successful method for the improvement of fiber elongation in early generations while keeping other fiber characteristics constant.

The results demonstrated that divergent selection for fiber elongation was successful in indicating that elongation is important for spinning.  It was also verified that elongation responded to selection while keeping other fiber properties constant; hence elongation can be improved through classical breeding techniques. Likewise fiber strength and elongation can be simultaneously improved using targeted selection. Additionally, the improvement of fiber elongation has a positive effect on yarn tensile properties. Higher fiber elongation resulted in higher yarn tenacity, work-to-break and breaking elongation, improving spinning performance and yarn quality.  Therefore, improving elongation in combination with breaking strength significantly improves spinning quality of cotton compared to the check cultivars.  Furthermore, it was demonstrated that improved elongation resulted in higher uniformity index and reduce short fiber content.  Finally, estimates of heritability demonstrated that fiber elongation would benefit from selection.


Project Year: 2012

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