Differential impact of crown rust (Puccinia coronata) infection on photosynthesis and volatile emissions in the primary host Avena sativa and the alternate host Rhamnus frangula

Rust infection results in decreases in photosynthesis and stress volatile emissions, but how these changes vary among host species has not been studied. We demonstrated that the impact of the obligate biotrophic fungus, Puccinia coronata f. sp. avenae, on foliage physiological processes is stronger in the primary host, Avena sativa (cultivated oat), than in the alternate host, Rhamnus frangula (alder buckthorn). Photosynthesis decreased with increasing percentage of damaged leaf area (D-A) in both species, but reductions were greater in A. sativa. In A. sativa, photosynthetic reductions resulted from reductions in stomatal conductance and photosynthetic capacity; in R. frangula, reductions were due to reduced capacity. Infection reduced photosynthetic biomass and key nutrients in A. sativa, but not in R. frangula. In A. sativa, stress-elicited emissions (methyl jasmonate, green leaf volatiles, long-chain saturated aldehydes, mono- and sesquiterpenes, benzenoids, and carotenoid breakdown products) increased with increasing D-A from 0% to 40%, but decreased with further increases in D-A. In R. frangula, volatile emissions were slightly elicited but, surprisingly, constitutive isoprene emissions were enhanced. Different hosts had characteristic volatile fingerprints, indicating differential activation of biochemical pathways. Fungal-elicited reductions in photosynthesis scale uniformly with stress severity. In the sensitive host, biphasic scaling of volatiles indicates that heavy spread of chlorosis/necrosis leads to an overall cessation of physiological functioning. Crown rust infection reduced photosynthesis via different underlying mechanisms in Avena sativaand Rhamnus frangulaand elicited major volatile emissions in A. sativabut minor emissions in R. frangula.

Automated summary

Rust infection has a stronger impact on foliage physiological processes in Avena sativa than in Rhamnus frangula. Photosynthesis decreases with increasing damaged leaf area (D-A) in both species, but the reductions are greater in A. sativa. In A. sativa, reductions in photosynthesis result from reductions in stomatal conductance and photosynthetic capacity, while in R. frangula, reductions are due to reduced capacity. Infection also leads to decreased photosynthetic biomass and key nutrients in A. sativa, but not in R. frangula. In A. sativa, stress-elicited volatile emissions increase with increasing D-A up to 40%, but decrease with further increases, while in R. frangula, volatile emissions are slightly elicited but constitutive isoprene emissions are enhanced.