Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 3/5/2019
Publication Date: 5/20/2019
Citation: Perez, J.L., Suh, C.P., Bell, A.A. 2019. Chemotypic variation of caryophyllene derivatives in cotton germplasm. National Cotton Council Beltwide Cotton Conference. pp. 467-471.
Interpretive Summary: Previously, three wild species of cotton were shown to produce three unique compounds that appeared to play a role in deterring insects from the plants. These compounds are absent in commercial upland cotton, but through traditional breeding techniques, Unit scientists were able to breed these wild cottons with a commercial upland cotton variety to form a tri-species cotton hybrid. A series of experiments have been planned to evaluate this new cotton hybrid against a variety of insect pests. However, as is the case with traditional breeding efforts, the desired trait is not always expressed in subsequent offspring and genetic methods to test for the presence of the desired trait involve tedious sample preparation steps and expensive reagents. As such, we developed an accurate, rapid, and relatively inexpensive screening method based on gas chromatography-mass spectrometry (GC-MS) analysis of leaf tissue to determine which plants produced the unique compounds. In doing so, we are now able to proceed with our insect evaluations and select which plants to move forward in our ongoing breeding program to ultimately develop a cotton line that is resistant to a multitude of diseases, environmental stresses, and insects. Moreover, our developed technique may be useful for expediting other breeding programs by allowing breeders to select only plants that express the desired chemical profile needed for resistance.
Technical Abstract: ß-caryophyllene is a ubiquitous secondary metabolite found in many plant species, including cotton. Several studies have reported that ß-caryophyllene affects the activities of insect pests in various crops. While ß-caryophyllene is present in most cotton species, including commercial upland cultivars, ß-caryophyllene derivatives are not. Interestingly, the diploid cotton species Gossypium armourianum, G. harknessii and G. turneri have been reported to produce three unique ß-caryophyllene derivatives identified as 12-hydroxy-ß-caryophyllene, 12-hydroxy-ß-caryophyllene acetate, and 12-hydroxy-ß-caryophyllene-4,5-oxide acetate. Furthermore, these diploid species have been reported to possess resistance to various biotic and abiotic stresses. Hence, these wild cotton species may be used to produce new cotton hybrids with resistance to multiple pests and adverse environmental conditions. USDA recently developed several tri-species cotton lines having G. armourianum or G.turneri in their genetic background. The tri-species hybrids are HAA ((G. hirsutum x G. arboreum)2 x G. armourianum), HHA ((G. hirsutum x G. herbaceum)2 x G. armourianum ), and HAT ((G. hirsutum x G. arboreum)2 x G. turneri). Backcrosses with G. hirsutum have resulted in promising hybrids with good agronomic characteristics. However, the trait for the production of ß-caryophyllene derivatives is not always expressed in subsequent progeny. As such we have developed a chemotypic method using 12-hydroxy-ß-caryophyllene and 12-hydroxy-ß-caryophyllene acetate as biomarkers to aide in the identification of hybrids containing the genes responsible for their production. Gas chromatography-mass spectrometry (GC-MS) was used for the separation and identification of ß-caryophyllene extracted from terminal leaves of hybrid plants. Initially, the presence of 12-hydroxy-ß-caryophyllene acetate in G. armourianum was confirmed by using the molecular weight and fragmentation patterns obtained from GC-MS analysis. Tri-species hybrids were developed and grown under both greenhouse and field conditions. The terminal leaves of plants were analyzed for the presence of 12-hydroxy-ß-caryophyllene and 12-hydroxy-ß-caryophyllene acetate, and plants containing these compounds have been selected for further breeding efforts. Given the ease, sensitivity and reproducibility of this GC-MS analytical procedure, breeding efforts may be expedited to fulfill industry needs for cotton cultivars with multiple pest resistance platforms and appealing agronomic traits.