| | Table 1. Perimeter, length and maturity properties of 20 cotton varieties grown under non-irrigated conditions at the Macon Ridge Research Station in 2004 (Winnsboro, LA). |
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| | Table 2. Length and micronaire for cotton grown under non-irrigated and irrigated conditions at the Macon Ridge Research Station in 2003 (Winnsboro, LA) |
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| | Figure 1. Relationship between micronaire and UHM for varieties grown under non-irrigated and irrigated conditions in 2004. |
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Each year, scientists with the LSU AgCenter test cotton varieties at various locations throughout the state. Varieties are grown using practices that follow AgCenter recommendations and conform to commercial operations as closely as possible. One location is the Macon Ridge Research Station in Winnsboro where cotton is grown on non-irrigated and irrigated Gigger silt loam. Cotton Variety Tests were planted in a randomized complete block design. The irrigated trials had four blocks and the non –irrigated trials had three blocks. Prior to 2004, 50-boll samples were hand harvested. In 2004, samples for fiber analysis were harvested with a two-row mechanical harvester. Cotton was ginned on a laboratory saw gin. Fiber quality was determined by the Louisiana Agricultural Experiment Station Cotton Fiber Testing Laboratory using HVI (High Volume Instrumentation) equipment and at the USDA Southern Regional Research Center using HVI and AFIS (Advanced Fiber Information System). A highly discriminating location is one that maximizes the observed varietal differences among cottons. Winnsboro has been designated as a discriminating environment for yield and fiber length (Blanche and Myers, 2006).
High micronaire has been a problem in Louisiana in recent years. Because seed company product guides often present averages for fiber properties, careful consideration of cotton variety trials can help producers identify types of varieties that have the potential to be discounted on micronaire. Identifying fiber maturity properties that fit a specific profile will assist breeders in the selection of low micronaire cottons. The HVI fiber properties include Upper Half Mean length and micronaire. Perimeter and fiber cell wall thickness were calculated from the AFIS Maturity Ratio and Fineness values. Micronaire is a composite of fineness and maturity. The basic fiber constituents are perimeter and cell wall thickness and provide cotton breeders valuable information.
All varieties listed in Table 1 were designated as being long (UHM 1.11 – 1.26in) under irrigated conditions in 2004. Under non-irrigated conditions only nine varieties retain that designation. The varieties were arranged in order of ascending perimeter. When the same variety was compared across several environments a range of perimeters was obtained. This range was about 2 micrometers. The larger perimeter PHY410 R with a micronaire of 5.0 had a thinner cell wall than FM966 LL. Therefore, at the same micronaire FM966 LL was more mature than PHY410 R. Both small and large perimeter varieties had the potential to have micronaire values above 4.9.
The UHM and micronaire values from non-irrigated and irrigated (2004) varieties were plotted together (Fig.1). As fiber length increased micronaire decreased. Irrigation has the potential to reduce micronaire values. Also, irrigation can increase micronaire values. In 2003, irrigation did not increase fiber length in most varieties (Table 2). Two varieties showed an increase in length but no increase in micronaire. Six varieties showed at least a 0.5 micronaire increase with irrigation.
SELECTION OF LOW MICRONAIRE VARIETIES
Lower micronaire varieties are characterized by small perimeter, long fiber or reduced cell wall thickness. Small perimeter varieties are a good choice. In the 2001 Winnsboro Non-Irrigated Variety Trials the mean micronaire for 18 medium maturing varieties was 5.5 but the micronaire for FM832 was 5.2. In the 2004 Winnsboro Non-Irrigated Variety Trials the mean micronaire for 21 medium maturing varieties was 5.1 but the micronaire for FM832 LL was 4.4. An examination of Winnsboro Irrigated Variety Trial data from 2004 and 2005 revealed that longer fiber varieties tended to have lower micronaire values. In 2004 there were 11 varieties with UHM lengths at or below 1.14 in. with a mean micronaire of 4.6 while 9 varieties had a UHM of 1.20 in. and above with a mean micronaire of 4.2. In 2005 there were 9 varieties with mean UHM lengths at or below 1.08 in. with a mean micronaire of 4.5 while 6 varieties had a UHM of 1.14 in. and above with a mean micronaire of 4.2.
Reduced cell wall deposition is another means to achieve lower micronaire. This can be accomplished if the rate or duration of cell wall deposition changes. Fiber lengths for FM966 LL, FM960 B/R, DP444 B/R and DP555 B/R were not significantly different under irrigated conditions in 2004. Cell wall thicknesses were 2.7, 2.7, 2.8 and 2.7 micrometers, respectively. Under non-irrigated conditions in 2004 fiber lengths were shorter and micronaire increased. Cell wall thickness for DP444 B/R was significantly thinner than the other three varieties (Table 1). In 2003, non-irrigated fiber lengths for FM966, DP444 B/R and DP555 B/R were not significantly different. Cell wall thicknesses were 2.5, 2.6, and 2.6 micrometers, respectively. Cell wall thickness for FM966 was significantly different from the other two varieties. Under irrigation fiber lengths were not significantly different (Table 2). Cell wall thickness for FM966, DP444 B/R and DP555 B/R were 2.7, 2.5 and 2.6 micrometers, respectively. Cell wall thickness for DP444 B/R was significantly different from the other two varieties. Although PHY410 R had the same cell wall thickness as DP444 B/R, the large perimeter contributed to a micronaire of 5.0 ( Table 1). In order to identify varieties with reduced cell wall deposition in high micronaire environments it is necessary to test them in high micronaire environments.
Prior to variety release, selections can be made in environments where micronaire values are below 4.9. Fiber perimeter and cell wall thickness can be determined and compared to test varieties grown at the same location. Varieties suitable for test cottons can be obtained from Table 1. A range of perimeters can be obtained if FM800 B/R, DP488 B/R and PHY 410 R are selected. For example in 2004, variety T57 was grown under irrigated conditions and had a micronaire of 4.4. The perimeters for FM800 B/R, DP488 B/R and PHY410 R were 47.3, 51.1 and 53.0 micrometers, respectively. Cell wall thicknesses were 2.4, 2.7 and 2.7 micrometers, respectively. The perimeter for T57 was 52.3 micrometers and cell wall thickness was 2.6 micrometers. Since fiber length of T57 was not significantly different from PHY410 R it would be expected that T57 under high micronaire conditions would have a micronaire above 4.9.
CONCLUSIONS
Selection of varieties with HVI micronaire values below 4.5 depends on consideration of variety trial data supplemented with AFIS fiber perimeter and wall thickness data.
REFERENCES
Variety Trial information is available at: www.lsuagcenter.com/en/communications/publications/Publications+Catalog/
Crops+and+Livestock/Cotton/Cotton+Varieties+for+Louisiana.htm
Blanche, S.B., and G.O.Myers.2006. Identifying discriminating locations for cultivar selection in Louisiana. Crop Sci. 46:946-949.