Location: Crop Genetics Research2012 Annual Report
1a. Objectives (from AD-416):
Improve the value of cotton fiber for the grower by identifying key temporal and spatial cellular events which affect the development of ovule epidermal cells into fiber initials, and add value to seed cotton by modifying the amount and distribution of gossypol in the seed and vegetative plant parts.
1b. Approach (from AD-416):
Identify pleiotropic effects associated with a reduction in the number of fibers initiated on the ovule and the number and morphology of leaf trichomes or root hairs in pilose x fuzzless or pilose x fiberless seed crosses; identify key genetic components (transcription factors/enzymes) and cellular events occurring during the development of an ovule epidermal cell into an elongating fiber; determine the genetic control of gossypol content and the proportion of plus/minus forms via transmission genetics and mapping with molecular markers; evaluate if selection in early generations, using a half seed method to test gossypol content, is as effective for identifying the desired genotypes as testing progeny in later generations.
3. Progress Report:
A leaf trichome survey identified putative genetic linkages between the trichomes (hairs) of cotton leaves and ovules (fiber). Near isogenic lines (NIL) to evaluate this linkage are under development. This linkage is important in that it literally provides an understanding the cellular mechanism of cotton ovular trichomes (fiber) initiation. The first rounds of NIL production have established and validated the association of smooth leaves with fiberless cotton seed and pilose (ultra-hairy) leaves with the production of ovular fiber. NIL production is in the 2nd year of development and these NILs will be a valuable asset for the cotton community for use as tools for mapping and trait evaluation studies. Cotton plants contain a variety of related toxic compounds classed as terpenoid aldehydes (TA) that protect the plant from pests. Cotton seed is a source of high quality protein that could be used for animal feed if the anti-nutritional TA compounds could be reduced. In the seed, the predominant TA compound is gossypol which has two forms (plus and minus) with the minus form being more toxic. Evaluation of progeny from crosses between adapted cultivars and high plus gossypol lines determined that the “plus/minus gossypol” trait could be transferred into adapted lines. Selected lines were tested to determine if high plus gossypol lines were as resistant to attack by tobacco budworms (Heliothis virescens F.) and bollworms (Helicoverpa zea Boddie) as normal lines. The high plus gossypol lines proved as tolerant as normal lines to tobacco budworm and bollworm infestation.
1. New sources of low toxicity cotton seed. Cotton growers would like to get more money for their seed, but the cotton seed contains an anti-nutritional compound called gossypol that prevents the seed from being fed to animals except cows, which have a special digestive system that can tolerate gossypol. This project has already developed low gossypol lines (less than 0.5 percent seed gossypol) with insect tolerance ratings comparable to existing cultivars that have 1 to 2 percent seed gossypol. The feeding value can be further improved by altering the type of gossypol in the seed; previous research indicates that the plus form is less toxic to animals than the minus form. Using rapid assay methods developed by ARS scientists at Stoneville, MS, for analyzing the seed, germplasm was identified among more than 100 cotton Plant Introduction (PI) accessions with a range of seed gossypol content and isomeric form including accessions with greater than 90 percent gossypol in the plus form and total seed gossypol less than one percent. The high plus gossypol lines proved as effective as the minus lines in inhibiting tobacco budworms (Heliothis virescens F.) and bollworms (Helicoverpa zea Boddie). The trait is being transferred to elite lines that can be used to develop cultivars more suitable for animal feed.