Potassium is one of the principle plant nutrients underpinning crop yield production and quality determination. While involved in many physiological processes, potassium's impact on water relations, photosynthesis, assimilate transport and enzyme activation can have direct consequences on crop productivity. Potassium deficiency can lead to a reduction in both the number of leaves produced and the size of individual leaves. Coupling this reduced amount of photosynthetic source material with a reduction in the photosynthetic rate per unit leaf area, and the result is an overall reduction in the amount of photosynthetic assimilates available for growth. The production of less photosynthetic assimilates and reduced assimilate transport out of the leaves to the developing fruit greatly contributes to the negative consequences that deficiencies of potassium have on yield and quality production. Goals aimed toward increasing crop productivity and improved quality dictate either increased potassium supply or more efficient use of potassium. Developing plants that more efficiently use potassium might be a worthwhile goal for geneticists.

Potassium influences on yield and quality production for maize, wheat, soybean and cotton.

In cotton (Gossypium hirsutum L) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate (PN) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply Decreased leaf PN of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues

Influence of Potassium Deficiency on Photosynthesis, Chlorophyll Content, and Chloroplast Ultrastructure of Cotton Plants

Each cotton fiber is a single cell that elongates to 25 to 30 cm from the seed coat epidermis within ∼16 days after anthesis (DAA) To elucidate the mechanisms controlling this rapid elongation, we studied the gating of fiber plasmodesmata and the expression of the cell wall–loosening gene expansin and plasma membrane transporters for sucrose and K+, the major osmotic solutes imported into fibers Confocal imaging of the membrane-impermeant fluorescent solute carboxyfluorescein (CF) revealed that the fiber plasmodesmata were initially permeable to CF (0 to 9 DAA), but closed at ∼10 DAA and re-opened at 16 DAA A developmental switch from simple to branched plasmodesmata was also observed in fibers at 10 DAA Coincident with the transient closure of the plasmodesmata, the sucrose and K+ transporter genes were expressed maximally in fibers at 10 DAA with sucrose transporter proteins predominately localized at the fiber base Consequently, fiber osmotic and turgor potentials were elevated, driving the rapid phase of elongation The level of expansin mRNA, however, was high at the early phase of elongation (6 to 8 DAA) and decreased rapidly afterwards The fiber turgor was similar to the underlying seed coat cells at 6 to 10 DAA and after 16 DAA These results suggest that fiber elongation is initially achieved largely by cell wall loosening and finally terminated by increased wall rigidity and loss of higher turgor To our knowledge, this study provides an unprecedented demonstration that the gating of plasmodesmata in a given cell is developmentally reversible and is coordinated with the expression of solute transporters and the cell wall–loosening gene This integration of plasmodesmatal gating and gene expression appears to control fiber cell elongation

The Control of Single-Celled Cotton Fiber Elongation by Developmentally Reversible Gating of Plasmodesmata and Coordinated Expression of Sucrose and K+ Transporters and Expansin

Traditionally, ideal cotton (Gossypium ssp.) fibers are said to be as white as snow, as trong as steel, as fine as silk and as long as wool. It is difficult to incorporate these specifications favored by cotton processors into a breeding program or to set them as quantitative goals for cotton producers. Since the 36 JOURNAL OF COTTON SCIENCE, Volume 4, Issue 1, 2000 early 1980s in the USA, the USDA-AMS cotton classing offices have become the primary connection for fiber quality between cotton producers and processors. The high volumes of cotton passing through the classing offices every year have forced workers there to make compromises for the sake of speed and productivity, and to develop rapid, semiautomatic classing techniques that have blurred some fiber-quality definitions in ways that may favor one industry segment over another. The vertical integration of the U.S. cotton industry from field to fabric depends on efficient use and cooperative refinement of the existing line of communication. Fiber-classing technologies now in use and under development and evaluation allow quantitation of fiber properties, application of improved standards for end-product quality, and, most importantly, creation of a fiber-quality language and a system of fiber-quality measurements that can be meaningful and useful to producers and processors alike. A cotton physiologist working in production research examines the interface between cotton production and processing in terms of the fiber properties currently quantified by the USDA-AMS cotton-classing offices, describes the measurement protocols available, and investigates possible environmental sources of the significant variations in fiber quality that reduce grower and processor profits. The interaction of growth environment, genetic potential, and fiber properties quantified at harvest are discussed where appropriate data or references exist. From the physiologist’s perspective, the fiber quality of a specific cotton genotype is a composite of fiber shape and maturity properties that depend on complex interactions among the genetics and physiology of the plants producing the fibers and the growth environment prevailing during the cotton production season. Fiber shape properties, particularly length and diameter, are largely dependent on genetics. Fiber maturity properties, which are dependent on deposition of photosynthate in the fiber cell wall, are more sensitive to changes in the growth environment. The effects of the growth environment on the genetic potential of a genotype modulate both shape and maturity properties to varying degrees. Anatomically, a cotton fiber is a seed hair, a single hyperelongated cell arising from the protodermal cells of the outer integument layer of the seed coat. Like all living plant cells, developing cotton fibers respond individually to fluctuations in the macroand microenvironments. Thus, the fibers on a single seed constitute continua of fiber length, shape, cell-wall thickness, and physical maturity (Bradow et al., 1996b,c, 1997a). Environmental variations within the plant canopy, among the individual plants, and within and among fields ensure that the fiber population in each boll, indeed on each seed, encompasses a broad range of fiber properties and that every bale of cotton contains a highly variable population of fibers. Successful processing of cotton lint depends on appropriate management during and after harvest of those highly variable fiber properties that have been shown to affect finished-product quality and manufacturing efficiency (Bradow et al., 1996b). If fiber-blending strategies and subsequent spinning and dyeing processes are to be optimized for specific end-uses and profitability, production managers in textile mills need accurate and effective descriptive and predictive quantitative measures of both the means and the ranges of these highly variable fiber properties (Moore, 1996). In the USA, the components of cotton fiber quality are usually defined as those properties reported for every bale by the classing offices of the USDA-AMS, which currently include length, length uniformity index, strength, micronaire, color as reflectance (Rd) and yellowness (+b), and trash content, all quantified by the High Volume Instrument (HVI) line. The classing offices also provide each bale with the more qua litative classers’ color and leaf grades and with estimates of preparation (degree of roughness of ginned lint) and content of extraneous matter. The naturally wide variations in fiber quality, in combination with differences in end-use requirements, result in significant variability in the value of the cotton lint to the processor. Therefore, a system of premiums and discounts has been established to denote a specified base quality. In general, cotton fiber value increases as the bulkaveraged fibers increase in whiteness (+Rd), length, strength, and micronaire; and discounts are made for both low mike (micronaire less than 3.5) and high mike (micronaire more than 4.9). Ideal fiber-quality specifications favored by processors traditionally have been summarized thusly: “as white as snow, as long as wool, as strong as steel, as fine as silk, and as cheap as hell.” These 37 BRADOW AND DAVIDONIS: FIBER QUALITY, COTTON PRODUCTION, AND PROCESSING specifications are extremely difficult to incorporate into a breeding program or to set as goals for cotton producers. Fiber-classing technologies in use and being tested allow quantitation of fiber properties, improvement of standards for end-product quality, and, perhaps most importantly, creation of a fiberquality language and system of fiber-qua lity measurements that can be meaningful and useful to producers and processors alike. GENETIC POTENTIAL, GENETIC CONTROL, AND ENVIRONMENTAL VARIABILITY Improvements in textile processing, particularly advances in spinning technology, have led to increased emphasis on breeding cotton for both improved yield and improved fiber properties (Meredith and Bridge, 1972; Green and Culp, 1990; Patil and Singh, 1995). Studies of gene action suggest that, within upland cotton genotypes there is little non-additive gene action in fiber length, strength, and fineness (Meredith and Bridge, 1972); that is, genes determine those fiber properties. However, large interactions between combined annual environmental factors (primarily weather) and fiber strength suggest that environmental variability can prevent full realization of the fiberquality potential of a cotton genotype (Green and Culp, 1990). More recently, statistical comparisons of the relative genetic and environmental influences upon fiber strength suggest that fiber strength is determined by a few major genes, rather than by variations in the growth environment (May, 1999). Indeed, spatial variations of single fertility factors in the edaphic environment were found to be unrelated to fiber strength and only weakly correlated with fiber length (Bradow et al., 1999b,c; Johnson et al., 1999). Genetic potential of a specific genotype is defined as the level of fiber yield or quality that could be attained under optimal growing conditions. The degree to which genetic potential is realized changes in response to environmental fluctuations such as application of water or fertilizer and the inevitable seasonal shifts such as temperature, day length, and insolation. Season-related shifts in cotton plant metabolism and fiber properties take the form of higher levels of fiber maturation in upland and pima bolls from July flowers, compared with the maturity levels of fibers in bolls from August flowers on the same plants (Sassenrath-Cole and Hedin, 1996; Bradow et al., 1996c; Bradow et al., 1997a). Similar effects of environment on genetic potential have been quantified in plant and field maps of micronaire and maturity (Bradow et al., 1996b, 1999b; Johnson et al., 1999). In addition to environment-related modulations of fiber quality at the crop and whole-plant levels, significant differences in fiber properties also can be traced to variations among the shapes and matur ities of fibers on a single seed and, consequently, within a given boll. Comparisons of the fiber-length arrays from different regions on a single seed have revealed that markedly different patterns in fiber length can be found in the micropylar, middle, and chalazal regions of a cotton seed at either end and around the middle (Delanghe, 1986). Mean fiber lengths were shortest at the micropylar (upper, pointed end of the seed) in G. hirsutum, G. barbadense , and G. arboreum genotypes (Vincke et al., 1985). The most mature fibers and the fibers having the largest perimeters also were found in the micropylar region of the seed. After hand ginning, the percentage of short fibers less than 0.5 inch or 12.7 mm long on a cotton seed was extremely low. It has been reported that, in ginned and baled cotton, the short fibers with small perimeters did not originate in the micropylar region of the seed (Vincke et al., 1985; Delanghe, 1986). Further, AFIS-A2 (Advanced Fiber Information System, Model A-2, Zellweger, Knoxville, TN) measurements of fibers from micropylar and chalazal regions of seeds revealed that the location of a seed within the boll was related to the magnitude of the differences in the properties of fibers from the micropylar and chalazal regions (Davidonis and Hinojosa, 1994). Significant variations in fiber maturity also can be related to the seed position (apical, medial, or 1 Trade names are necessary for reporting factually on available data. The USDA neither guarantees nor warrants the standard of the product or the service. The use of the name USDA implies no approval of the product or service to the exclusion of others that may be suitable. 38 JOURNAL OF COTTON SCIENCE, Volume 4, Issue 1, 2000 basal) within the boll and locule. Degree of secondary wall thickening (quantified by the AFISA2 as the fiber cell-wall maturity measurem

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Quantitation of fiber quality and the cotton production-processing interface: a physiologist's perspective.

Leaf photosynthesis and carbon isotope discrimination of cotton in response to potassium deficiency

Although results from in vitro ovule culture studies have demonstrated a specific K requirement for fiber growth, a direct association between the K status of the cotton (L.) plant and fiber quality has not been established under field conditions. To evaluate this relationship, a single cultivar (1985) and two cultivars (1986 and 1987) were grown with 0, 120, 240, or 480 kg K ha in 10 blocked replicates of each K level on an irrigated, vermiculitic soil. There was a significant seed-cotton yield response to applied K in each year. Lint yield, however, increased relatively more than seed yield, resulting in a greater lint percentage as plant K supply increased. The greater lint percentage reflected increased fiber length and secondary wall thickness (measured as a micronaire index) obtained from plants that received fertilizer K. For both cultivars, the fiber length, micronaire index, fiber strength and percent elongation, and fiber length uniformity ratio (dependent variables) were each positively related to (i) fiber K concentration at maturity, (ii) leaf K concentration at early bloom, and (iii) an index of soil K availability as independent variables in regression analyses. Comparison of cultivar regressions, however, indicated that fiber quality of ‘Acala GC510’ was higher than that of ‘Acala SJ2’ at low fiber, leaf, or soil K levels. We conclude that K supply to cotton fruit is an important determinant of fiber quality under field conditions, and that the K requirement for producing high lint yield with acceptable quality may differ among genotypes.

D. C. Bryant

Papers

Potassium Nutrition Effects on Lint Yield and Fiber Quality of Acala Cotton