Prohexadione calcium is herbicidal to the sunflower root parasite Orobanche cumana

Abstract

BACKGROUND The obligatory sunflower root parasite Orobanche cumana Wallr. deprives its host of essential nutrients, resulting in a dramatic reduction in yield and biomass. A post‐emergence application with an imidazolinone herbicide on an imidazolinone‐tolerant sunflower is highly effective against O. cumana. The herbicide inhibits the enzyme acetohydroxy acid synthase and consequently, growth of the parasite is inhibited, although the sunflower survives the treatment through mutations in the target enzyme. Interestingly, field studies have shown that a combined application of an imidazolinone herbicide with prohexadione resulted in reduced emergence of O. cumana compared with the sole application of the herbicide. The aim of this study was to investigate whether prohexadione is herbicidal to O. cumana. RESULTS Prohexadione was rapidly distributed within the sunflower, reaching the roots, the site of O. cumana attack, as early as 6 h after application (HAA) on sunflower leaves. A direct impact of prohexadione on O. cumana germination was investigated and a half‐maximal inhibitory concentration (IC50) of 84 μm prohexadione was found. In addition, the inhibition of germination by prohexadione was terminal, meaning that O. cumana seeds died after prohexadione contact as soon as they were primed for germination. Additionally, excretion studies showed that a small proportion of the applied prohexadione was excreted by sunflower roots. CONCLUSION We show that prohexadione is an inhibitor of O. cumana germination and that the growth regulator is found in sunflower roots shortly after application. We hypothesize that prohexadione is excreted in sufficient amounts from the sunflower roots, therefore having a direct impact on O. cumana germination. © 2020 Society of Chemical Industry

Silicon Fertilization Improves Sunflower Rhizosphere Microbial Community Structure and Reduces Parasitism by Orobanche cumana Wallr.

“…is an obligate holographic parasite that is currently one of the major hazards to sunflower crops, causing significant production losses. O. cumana has a complex life cycle that begins with sensing chemical signals secreted from the host roots [3,4], followed by seed germination and radicle elongation towards the sunflower root [5]. Once it reaches the target tissue, the radicle penetrates the sunflower's Agronomy 2024, 14, 1312 2 of 20 root system and forms a haustorium [5].…”

“…O. cumana has a complex life cycle that begins with sensing chemical signals secreted from the host roots [3,4], followed by seed germination and radicle elongation towards the sunflower root [5]. Once it reaches the target tissue, the radicle penetrates the sunflower's Agronomy 2024, 14, 1312 2 of 20 root system and forms a haustorium [5]. This invasive organ receives all essential nutrients through direct phloem connections during its host-dependent life cycle [6][7][8].…”

Iridoid Glycosides Isolated from Bellardia trixago Identified as Inhibitors of Orobanche cumana Radicle Growth

“…On the other hand, the chemical solution to control O. cumana is the use of imidazolinone herbicides that inhibit the enzyme acetohydroxy acid synthase [8,11]. However, the capacity to evolve imidazolinone-resistance in weeds, and the lack of alternative chemical methods for O. cumana threatens the sustainability of chemical control of O. cumana in sunflower [12]. Characterization of novel modes of allelopathic action against O. cumana in previously known natural compounds is an alternative solution to provide efficacy and sustainability in strategies for parasitic weed management [13].…”