Cotton resistance against Bemisia tabaci: What compounds and regulators have a role to play?

Whitefly, Bemisia tabaci, is threatening global cotton (Gossypium hirsutum) production. Our understanding of plant defense mechanisms against this pest remains limited. We evaluated herbivore-induced plant volatiles in resistant (cv. 13-102, 13-93) and sensitive (cv. 13-68) cotton under laboratory and field conditions. Levels of catechin, quercetin, isoquercitrin, and tannin were measured to support plant defense data. GC/MS and HPLC analyses detected volatile and non-volatile compounds in the three whitefly-damaged cotton cultivars. Eight herbivore-induced volatiles were identified, with alpha-pinene and caryophyllene highly emitted in cv. 13-93. Catechin, isoquercitrin, and tannin were synthesized at higher levels in cv. 13-93. Electroantennal and behavioral responses of whitefly to 20 volatile compounds were investigated. Nine showed behavioral and electroantennal activities. Caryophyllene elicited a response in whitefly antenna receptors, and behavioral trials confirmed attraction to this compound. Choice tests showed that cv. 13-102 and 13-93 were less preferred for oviposition by B. tabaci. The role of flavonoids in conferring resistance to whitefly in cv. 13-102 and 13-93 is discussed. Transcriptomic differences between the three cotton cultivars were compared at 48 hours post-infestation using RNA-Seq. Approximately 786 million paired-end reads were obtained through Illumina sequencing. Gene ontology and KEGG pathway analyses revealed the involvement of metabolite synthesis, protein kinases, transcription factors, and phytohormone signaling in cotton's response to whitefly infestation. This study provides insights into cotton's defense mechanisms against whitefly and identifies potential insect-resistant candidate genes.