Growth Regulator Effects on Wheat Culm Nonstructural and Structural Carbohydrates and Lignin 1

Lodging can be a problem when wheat (Triticum aestivum L.) is grown using high rates of N in intensive management systems. The plant growth regulators (PGRs) chlormequat chloride (CCC) (2-Chloro-ethyl-N,N,N-trimethylammonium chloride) and ethephon [(2-Chloro-ethyl)phosphonic acid] often decrease lodging. Our objective was to determine the influence of CCC and ethephon on lodging and on carbohydrate and lignin composition of wheat culms. Water-soluble carbohydrate (WSC) composition of the peduncle, middle, and lower internodes; and cellulose, hemicellulose, and lignin concentrations in cell walls of the middle and lower internodes were investigated in ‘Arthur 71’ (lodging susceptible) and ‘Auburn’ (lodging resistant) soft red winter wheat. Wheat was planted into a Parr silt loam (fine-loamy, mixed, mesic Typic Argiudolls) in autumn of 1983 and 1984. Plants were fertilized with 45 and 180 kg N ha⁻¹ and sprayed with CCC and ethephon the following spring. Arthur 71 had a higher lodging rating than Auburn, averaging 1.9 and 0.4, respectively (0.2 to 9 scale). Lodging increased as N fertilization rates were increased and decreased with the application of CCC and ethephon. Culm WSC concentrations averaged 20% higher for Arthur 71 than for Auburn. The low N application resulted in increased WSC concentrations (25% in the peduncle, 21% in the middle internode, and 42% in the lower internodes) compared to high N. Ethephon and CCC resulted in increased WSC concentration as compared to controls. Concentrations of cellulose, hemicellulose, and lignin in cell walls of the middle internode and lower internodes changed less than 5% when comparing cultivars, low N and high N, or controls and PGR-treated plants. Lodging could not be associated with changes in concentrations of WSC in the culm or with changes in concentrations of structural carbohydrates and lignin in cell walls of the culm. The arrangement and interaction of the various structural carbohydrates and lignin in the culm cell walls may be more important in lodging resistance than concentrations of these components.