Cotton Fiber Length Is Affected by Far-Red Light Impinging on Developing Bolls

Cotton (Gossypium hirsutum L.) fiber length is an important component of quality as defined by the textile industry. The fibers are single elongated cells that extend from the seed coat during development within bolls. It was hypothesized that elongating cotton fibers would be responsive to the far-red (FR) to red light (R) photon ratio (FRIR) reflected to developing bolls. To test the hypothesis, plants were grown in trickle irrigated field plots over different colored soil covers that reflected high FRIR and low photosynthetic photon flux (PPF), or low FRIR and high PPF to developing bolls. Newly opened flowers were tagged over three replicate plots of each of four colors. After the flowers were fertilized, randomly selected young bolls were covered with aluminum foil to shield them from light during development. Others served as unshielded controls. The FRIR and PPF impinging on developing bolls affected biomass per area of carpel walls and the amount of FR transmitted into the bolls to the developing fibers. Fiber lengths were determined after the bolls matured. Fibers in unshielded bolls that developed over green and red (higher reflected FR/R) soil covers were significantly longer than those that developed over aluminum and white (higher reflected PPF). The difference in length of fiber developed in unshielded versus shielded bolls was greater over green and red than over aluminum and white indicating a greater response to increased FR/R than to increased PPF impinging on the developing bolls. These results suggest that reflected FR should be considered along with other environmental factors when developing innovative production systems that involve nontraditional row spacing, plant population densities, or soil surface conditions that can affect the photon ratios to which the developing plants are exposed.