Semiochemicals from ex situ abiotically stressed cactus tissue: a contributing role of fungal spores

Authors: Beck, John; Cook, Daniel; Baig, Nausheena; Mahoney, Noreen; MARSICO, TRAVIS - Arkansas State University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2014
Publication Date: 12/7/2014
Publication URL: https://handle.nal.usda.gov/10113/60169
Citation: Beck, J.J., Cook, D., Baig, N., Mahoney, N.E., Marsico, T.D. 2014. Semiochemicals from ex situ abiotically stressed cactus tissue: a contributing role of fungal spores. Journal of Agricultural and Food Chemistry. 62(51):12273-12276.

Interpretive Summary: Odors given off by plants play a central role in communication between plants and insects. For many insects plant volatiles are cues to locate a suitable host. Fungi on host plants can play an influential role in communicating certain plant vulnerabilities to an insect. Conophthorin is a chemical compound with the overall structure that is called a spiroketal. Conophthorin is an important semiochemical produced by developing fungal spores on almond tissues. Spiroketals also play roles in communication between some beetles and their hosts. Plants and fungi are known to produce various odors under biological and non-biological stressors. Provided herein are distinctive odor profiles over time from three abiotic treatments (room temperature, -15 oC, and -15 oC to room temperature) of Opuntia humifusa (prickly pear) tissue plugs. Odors from the three treatments were primarily: compounds known as monoterpenes from room temperature plugs; compounds of varying classes and origin at later stages for plugs at -15 oC; and, known chemical cues (semiochemicals) at varying later stages for the -15 oC to room temperature plugs. The results highlight the importance of considering biotic and abiotic influences on plant-produced semiochemicals, as well as plant-insect-microbe interactions. These findings have high impact regarding various odors produced by agricultural commodities at vulnerable stages and how insect pests such as the cactus moth may perceive these signals from its host Opuntia species.

Technical Abstract: Semiochemicals play a central role in communication between plants and insects, such as signaling the location of a suitable host. Fungi on host plants can also play an influential role in communicating certain plant vulnerabilities to an insect. The spiroketal conophthorin is an important semiochemical produced by developing fungal spores. Spiroketals are also used as signals for scolytid communication. Plants and fungi are known to emit varying volatile profiles under biotic and abiotic stress. This paper reports distinctive temporal-volatile profi les from three abiotic treatments, room temperature (control), - 15 ° C (cold), and - 15 ° C to room temperature (shock), of cactus tissue plugs. Volatiles from the three treatments included monoterpenes from control plugs, compounds of varying classes and origin at later stages for cold plugs, and known semiochemicals, including spiroketals, at later stages for shock plugs. The results highlight several important findings: a unique tissue source of the spiroketals; abiotic cold-shock stress is indicated as the cause of spiroketal production; and, given previous findings of spirogenesis, fungal spore involvement is a probable biosynthetic origin of the spiroketals. These findings suggest an important role of fungal volatiles as signaling plant vulnerability to insects.