Jack C. McCarty, Paul A. Hedin, and Russell W. Hayes
Various
plant growth hormones and regulators have been reported to increase
the yield of cotton (Gossypium hirsutum L.) lint when applied
to foliage in field tests. We observed positive effects in individual
years, but multi-year results were not significant. However, some
field tests with gibberellic acid and carbohydrate isolates had shown
occasional promise and were the subject of further investigations in
1996 and 1997. In expanded tests in 1996, gibberellic acid did not
provide statistically significant increases in lint yield. In a 1997
test, glucose provided a statistically significant increase in lint
yield at one location but not at another, while fructose and sucrose
did not increase yields at either location. If growth regulators are
to consistently affect cotton lint yield, factors such as geography,
climate, and procedures must be more precisely
defined.
In recent years, we have evaluated many kinetin-based commercial plant growth regulators for their effects on cotton plants. In a study at Mississippi State during 1986-1992, five commercial plant growth regulators and urea were evaluated as foliar sprays on growing cotton plants for their effects on yield. Of the five tested at the levels recommended by the providers, the stated activities of three were attributed to cytokinins (Burst, Burst Agritech, Overland Park, Kansas; Foliar Triggrr [FT], Westbridge Agricultural Products, San Diego, California; and Maxon, Terra International, Blytheville, Arkansas). FPG-5 (Baldridge BioResearch, Inc., Cherry Fork, Oklahoma) contained cytokinins, IAA, gibberellic acid, and several inorganic micronutrients. PG-IV (Microflo, Lakeland, Florida) contained IBA, gibberellic acid, and micronutrients, but it contained no cnytokinins. FPG-5 and Foliar Triggrr gave small, consistent yield increases in 1 or more years and significant increases in 1992. Urea had a consistent negative effect on yield. Formulations containing IAA/IBA, gibberellic acid, and inorganic micronutrients also failed to increase yields (Hedin and McCarty 1994a).
Our attention was drawn to one of these commercial plant growth regulators, FT, which gave small, consistent yield increases in field tests each year. In 1992, FT provided statistically significant increases in lint yield. While several cytokinin constituents and preparations performed poorly for us (Hedin and McCarty 1991, 1994a, 1994b), we assume that geographical, climatic, and procedural differences may have been contributing factors to the successful tests with FT by Parker and Salk (1988). They had attributed the activity to cytokinins. However, because we were not able to show yield increases with cytokinins, we hypothesized that, alternatively, one or more unknown components were responsible. This possibility was indirectly supported by the report of Parker and Salk (1988), which described FT as "the product of a fermentation process that is then combined with extracts from a variety of plants which contain naturally occurring growth stimulating substances."
Over a period of several years (1989-1995), we prepared fractions of FT and tested them by foliar application. These fractions, which we found to be rich in carbohydrates, gave consistent, small increases in the lint yield, but they were not statistically significant (Hedin et al. 1997). This report describes our further efforts in 1996 and 1997 to investigate the effects of foliar applications of an occasionally effective growth regulator, gibberellic acid, and of three sugars (glucose, fructose, and sucrose) on the yield and boll size of cotton.
The gibberellic acid test in 1996 was conducted at two locations. At Location 1, the test was planted on May 7. Gibberellic acid was applied on July 2 and July 16. The plot was harvested on October 18. At Location 2, the test was planted on May 30. Gibberellic acid was applied on July 10 and July 24. The plot was harvested on October 30. In each test, gibberellic acid was applied at the rates of 1, 3, and 10 grams per acre. Each test consisted of six replicates with three rows per replicate.
The carbohydrate test in 1997 was also conducted at two locations. The test was planted on May 12 at Location 1. Applications of glucose, fructose, and sucrose were made on July 3 and July 17. The plot was harvested on October 16. At Location 2, the test was planted on May 14. Applications of glucose, fructose, and sucrose were made on July 11 and July 24. The plot was harvested on October 17. In each test, the same three sugars were applied at the rates of 2 and 10 grams per 0.01526 acre (323.8 and 1,619 grams per hectare). Each test consisted of five replicates with one row per replicate.
Procurement of Test Chemicals. The gibberelic acid (GA3), glucose, fructose, and sucrose were obtained from Fluka Chemical Corporation, Ronkonkoma, New York, and used as received.
Statistical Procedures. Data obtained from the various analyses and measurements were subjected to the analysis of variance (ANOVA), and least significant difference (LSD) values were calculated according to SAS (1985) methods.
Table
1. Effects of foliar applications of GA
level Lint
yield Boll
size Lint
fraction g/a lb/A g % Location
11 0 643 5.24 39.99 1 699 5.39 39.59 3 689 5.27 40.19 10 724 5.10 39.96 F
0.05 NS NS NS Location
22 0 896 4.96 38.18 1 845 4.80 38.01 3 910 4.82 38.81 10 837 4.69 37.75 F
0.05 NS NS NS 1The
first application at Location 1 was made on July 2; the
second, July 16. This test was harvested on October 18.
gibberellic acid (GA) to cotton plants, 1996.
2The first application at Location 2 was made on
July 10; the second, July 24. This test was harvested on
October 30.
Statistically significant results were obtained in one instance from the 1997 carbohydrate tests (Table 3). At Location 1, the lint yield was increased by 14.4% and 9% when glucose was applied, while at Location 2, the yield was not significantly increased by glucose application. No statistically significant increases were obtained when either fructose or sucrose were applied. At Location 2, lint yield was increased by 2% at the lower application level of glucose.
Our attention to carbohydrates arose indirectly through our tests with the previously discussed commercial plant growth regulator, Foliar Triggrr. FT gave small, consistent yield increases in field tests each year beginning in 1989. In 1992, FT provided statistically significant increases in lint yield lint: 15.5% at 8 ounces per acre (528 milliliters per hectare); and 12.6% at 16 ounces per acre (1,056 milliliters per hectare) (Hedin and McCarty 1991, 1994a, 1994b). The provider had attributed the activity to cytokinins (Parker and Salk 1988). However, as stated earlier, in a series of tests conducted from 1986 to 1992, the synthetic cytokinin kinetin was evaluated along with kinetin riboside, IAA, and gibberellic acid. The effects of these plant growth hormones were near zero over the 7-year period. Although, in some individual tests, statistically significant differences in yield were obtained (Hedin and McCarty 1991, 1994b).
In our initial investigations with FT, we found that the liquid formulation as supplied by the provider consisted of a black suspension (5% of solids) that could be precipitated and then chromatographed to give a fraction rich in carbohydrates. This fraction provided significant yield increases of 10% at 0.2 kilogram per hectare and 26% at 0.5 kilogram per hectare (Hedin et al. 1997). Over several years (1989-1995), foliar applications of a succession of sugar-containing fractions of FT gave consistent, small increases but not statistically significant lint yield increases. The composition of the active carbohydrate fraction upon acid hydrolysis was found mainly to be a mixture of monosaccharides and disaccharides, with some sulfated polysaccharides. Equal molar formulated mixtures of sugars (mannose, galactose, glucose, and sucrose) and of several isomeric carrageenans (linear sulfated polysaccharides) provided small, consistent increases, but they were not statistically significant (Hedin et al. 1997).
Therefore, our tests with carbohydrates in 1997 were carried out to determine whether any of three widely distributed sugars in nature (glucose, fructose, and sucrose) would have a statistically significant impact on yield. Unfortunately, we were able to demonstrate only a minimal positive impact. We apparently have been unable to define the precise application regimens required to elicit consistent positive responses. These requirements may include factors such as geography, temperature, sunlight, nozzle pressure, cultivar, timing of application, and status of soil and plant nutrients.
Table
2. ANOVA of foliar applications of GA
Level Means
over two locations Lint
yield Boll
size Lint
fraction g/a lb/A g % 0 769 5.10 39.08 1 772 5.09 38.80 3 800 5.05 39.50 10 780 4.89 38.85 F
0.05 NS * NS LSD
0.05 0.12 Loc
1 872 4.82 38.19 Loc
2 689 5.25 39.93 LSD
0.05 42 0.09 0.96 ANOVA Loc * * * Lev NS * NS Loc
*Lev NS NS NS Table
3. Effects of foliar applications of glucose, Chemical Level
Lint Boll
size Lint
yield g/0.01526
A g/ha moles/ha % g lb Location
11 Glucose 0 0.0 0.0 39.77 4.95 1,265 2 323.8 5.4 38.98 5.36 1,448 10 1,619.0 27.0 38.31 5.02 1,380 LSD
0.05 1.15 NS 149 Fructose 0 0.0 0.0 39.77 4.95 1,265 2 323.8 5.4 39.65 5.07 1,293 10 1,619.0 27.0 39.83 5.16 1,345 LSD
0.05 NS NS NS Sucrose 0 0.0 0.0 39.68 4.95 1,295 2 323.8 2.7 40.07 4.97 1,305 10 1,619.0 13.5 39.16 4.77 1,236 LSD
0.05 NS NS NS Location
22 Glucose 0 0.0 0.0 39.23 5.08 975 2 323.8 5.4 40.93 4.97 894 10 1,619.0 27.0 39.01 5.01 835 LSD
0.05 1.63 NS NS Fructose 0 0.0 0.0 39.23 5.08 975 2 323.8 5.4 38.12 4.93 842 10 1,619.0 27.0 37.97 5.08 963 LSD
0.05 NS NS NS Sucrose 0 0.0 0.0 39.86 4.99 927 2 323.8 2.7 40.25 5.06 906 10 1,619.0 13.5 39.79 4.76 962 LSD
0.05 NS NS NS 1Location
1 was planted May 12, using the variety Deltapine 50. The
first application was made July 3; the second, July 17.
Cotton was harvested October 16. This test consisted of five
repetitions, one row per repetition.
gibberellic acid (GA) over locations for 1996.
fructose, and sucrose to cotton plants, 1997.
2Location 2 was planted May 14, using the variety
Deltapine 50. The first application was made July 11; the
second, July 24. Cotton was harvested October 17. This test
consisted of five repetitions, one row per
repetition.
Hedin, P.A., and J.C. McCarty, Jr. Effects of several commercial plant growth regulator formulations on yield and allelochemicals of cotton (Gossypium hirsutum L.). J. Agric. Food Chem. 1994a, 42, 1355-1357.
Hedin, P.A., and J.C. McCarty, Jr. Multi-year study of the effects of kinetin and other plant growth hormones on yield, agronomic traits, and allelochemicals of cotton. J. Agric. Food Chem. 1994b, 42, 2305-2307.
Hedin, P.A., J.C. McCarty, Jr., and D.A. Dollar. Effects of foliar applications of carbohydrates on the yield cotton (Gossypium hirsutum lint. J. Agric. Food Chem. 1997, 45, 2763-2767.
Parker, L.W., and P. Salk. Foliar Triggrr® and Soil Triggrr®, new plant growth regulators to increase cotton yields. In Proceedings of the 1988 Cotton Production Research Conference, New Orleans, LA, Jan. 3-8, 1988; National Cotton Council: Memphis, TN.
SAS User's Guide: Statistics, version 5 rd.; SAS Institute: Cary, NC, 1985; p. 956.
Key Words: Cotton, Gossypium hirsutum, gibberellic acid,
glucose, fructose, sucrose.
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