Cochliotoxin, a Dihydropyranopyran-4,5-dione, and Its Analogues Produced by Cochliobolus australiensis Display Phytotoxic Activity against Buffelgrass (Cenchrus ciliaris)

Abstract

Buffelgrass (Pennisetum ciliare or Cenchrus ciliaris) is a perennial grass that has become highly invasive in the Sonoran Desert of southern Arizona. In the search for novel control strategies against this weed, strains of the foliar fungal pathogen Cochliobolus australiensis from buffelgrass have been screened for their ability to produce phytotoxic metabolites that could potentially be used as natural herbicides in an integrated pest management strategy. A new phytotoxin, named cochliotoxin, was isolated from liquid culture of this fungus together with radicinin, radicinol, and their 3-epimers. Cochliotoxin was characterized, essentially by spectroscopic methods, as 3-hydroxy-2-methyl-7-(3-methyloxiranyl)-2,3-dihydropyrano[4,3-b]pyran-4,5-dione. Its relative stereochemistry was assigned by H NMR techniques, while the absolute configuration (2S,3S) was determined applying the advanced Mosher's method by esterification of its hydroxy group at C-3. When bioassayed in a buffelgrass coleoptile elongation test and by leaf puncture bioassay against the host weed and two nontarget grasses, cochliotoxin showed strong phytotoxicity. In the same tests, radicinin and 3-epi-radicinin also showed phytotoxic activity, while radicinol and 3-epi-radicinol were largely inactive. All five compounds were more active in leaf puncture bioassays on buffelgrass than on the nontarget grass tanglehead (Heteropogon contortus), while the nontarget grass Arizona cottontop (Digitaria californica) was more sensitive to radicinin and 3-epi-radicinin. Cochliotoxin at low concentration was significantly more active on buffelgrass than on either native grass, but the difference was small.

Spatial-temporal profiling of prodiginines and serratamolides produced by endophytic Serratia marcescens harbored in Maytenus serrata

“…The phytotoxicity assay was performed according to previously published methods 74 , suitably modified. Fresh leaves were collected from living plant material from the INFU greenhouse ( M .…”

Pyriculins A and B, two monosubstituted hex‐4‐ene‐2,3‐diols and other phytotoxic metabolites produced by Pyricularia grisea isolated from buffelgrass (Cenchrus ciliaris)

“…Recently, from the culture filtrates of one of these pathogens, Cochliobolus australiensis, a new phytotoxin, named cochliotoxin, was isolated together with the known compounds radicinin, radicinol, and their 3‐epimers. Cochliotoxin showed strong phytotoxicity when bioassayed in a buffelgrass coleoptile elongation test and by leaf puncture bioassay against the host weed . A second buffelgrass foliar pathogen is Pyricularia grisea (teleomorph Magnaporthe grisea ), which is now considered distinct from the rice blast pathogen M. oryzae .…”

Fungal Metabolites Antagonists towards Plant Pests and Human Pathogens: Structure-Activity Relationship Studies

“…However, buffelgrass has become a very serious invader in the Sonoran Desert of southern Arizona where it increases the frequency of fire and has the potential to destroy the iconic saguaro woodland ecosystem. Considering that buffelgrass is difficult to eradicate with chemical herbicides without major damage to native vegetation, two primary foliar pathogens in its introduced range, namely Cochliobolus australiensis and Pyricularia grisea , were studied to evaluate their ability to produce phytotoxic secondary metabolites which could be used as potential natural herbicides [ 103 , 104 , 105 ]. In particular, from the liquid culture of C. australiensis , a new phytotoxin named cochliotoxin ( 216 , Figure 16 ) was isolated together with radicinin, radicinol, and their 3-epimers ( 217 – 220 , Figure 16 ).…”

“…Cochliotoxin was characterized by spectroscopic methods as 3-hydroxy-2-methyl-7-(3-methyloxiranyl)-2,3-dihydropyrano[4,3-b]pyran-4,5-dione. Its relative stereochemistry was assigned by 1 H NMR techniques, while the absolute configuration (2 S ,3 S ) was determined by applying the advanced Mosher’s method by esterification of its hydroxy group at C-3 [ 103 , 109 ].…”