Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2000
Publication Date: N/A
Interpretive Summary: Cotton fiber length is an important component of quality. Each fiber is a single elongated cell that extends from the seed coat. It was hypothesized that elongating cotton fiber would be as responsive to extra far-red light (FR) as elongating cells in seedling stems, which grow longer in response to FR reflected from nearby growing plants. The amount of FR affects the FR/R photon ratio which acts through the plants natural phytochrome system to regulate its development. Cotton plants were grown in trickle irrigated field plots over panels that reflected high or low FR/R photon ratios and low or high amounts of photosynthetic light to developing bolls. Some bolls were left bare and others were shielded from any light during fiber development. Fibers that developed in bolls that received the increased FR/R photon ratios were longer than those that received elevated photosynthetic light. The difference in fiber length between shielded and bare bolls was influenced more by elevated FR/R than by increased photosynthetic light. This is important in developing new plant spacing and conservation tillage systems because the amount of FR received by the developing boll is influenced by FR reflected from nearby green plants and even from some dead plant residues.
Technical Abstract: Cotton (Gossypium hirsutum L.) fibers are single elongated cells whose length is an important component of quality. It was hypothesized that elongating cotton fiber would be as responsive to far-red light (FR) as elongating cells in seedling hypocotyls, which grow longer in response to FR reflected from nearby growing plants. Spaced plants were grown in sunlight in trickle irrigated field plots over soil covers that reflected low amounts of photosynthetic light and higher FR/R photon ratios than were present in incoming sunlight, or covers that reflected much photosynthetic light and low FR/R ratios. Randomly selected young bolls on plants growing over the reflectors were covered with aluminum foil envelops to shield them from light during development. Others of the same age served as unshielded controls. After the bolls matured, one hundred seeds were randomly selected per rep per color, brushed to extend the fibers, and measured for length. Fibers that developed over panels that reflected the higher FR/R ratios were significantly longer than those that developed over panels that reflected more photosynthetic light. Within the shielded bolls, slightly longer fibers over panels that reflected the higher FR/R ratios suggest that extra FR impinging on nearby leaves contributed a small additional amount to fiber elongation. Transmission through carpels of developing bolls was measured showing that substantial amounts of FR passed through carpel walls to the developing fibers. It is concluded that FR reflected to developing cotton bolls can penetrate through the carpel walls to the developing fiber and influence elongation. Reflected FR should be considered when developing new production systems that involve nontraditional row spacing and plant population densities.