Rapid necrosis: a novel plant resistance mechanism to 2,4-D

Abstract

Plants of Sumatran fleabane [Conyza sumatrensis (Retz.) E. Walker] were identified in a field with an unusual rapid leaf-injury herbicide symptoms after application of 2,4-D in mixture with glyphosate. The objectives of this study were to confirm the occurrence of resistance to 2,4-D herbicide and to characterize the occurrence of rapid necrosis as the mechanism associated with the herbicide resistance in C. sumatrensis. The studies performed were an initial screening, effect of 2,4-D alone and associated with glyphosate, cross- and multiple-resistance evaluation, effect of commercial formulation and analytical product, and rate of H2O2 evolution. The Marpr9-rn accession was identified with rapid necrosis symptoms and survival to 804 g ae ha−1 of 2,4-D. The resistance factor to the herbicide 2,4-D was 18.6 at 49 d after spraying. The analytical product 2,4-D and the commercial formulation resulted in similar symptoms of rapid necrosis. This symptom did not occur for the six other auxinic herbicides (dicamba, florpyrauxifen-benzyl, fluroxypyr, halauxifen-methyl, picloram, and triclopyr), indicating absence of cross-resistance. Multiple resistance to the herbicides paraquat, saflufenacil, and ammonium glufosinate was not identified in the Marpr9-rn population. However, survival following treatment with the herbicides glyphosate and chlorimuron-ethyl occurred. The evolution of H2O2 began at 15 min after application and was less pronounced in low light. These results indicate the first case of resistance to 2,4-D and occurrence of rapid necrosis in C. sumatrensis.

Mechanisms of evolved herbicide resistance

“…Rapid necrosis followed by regrowth was also identified as a resistance mechanism to 2,4-D in a Sumatran fleabane (Conyza sumatrensis) biotype from southern Brazil (96). The symptoms after 2,4-D application are similar to those observed in glyphosate-resistant A. trifida (i.e., necrosis in older leaves and absent in younger leaves, followed by regrowth from meristems).…”

Management of Glyphosate-Resistant Hairy Fleabane and Contribution of the Physiological Potential of Seeds to Resistance

“…However, at stage III of development, contact herbicides markedly reduced MSPA due to their rapid action, whereas systemic herbicides (e.g., chlorimuron-ethyl, metsulfuron-methyl, diclosulam, and 2,4-D) had little overall effects on MSPA, specifically in biotype R (Table 3). C. canadensis is highly susceptible to 2,4-D at doses below 70 g ha -1 (MCCAULEY; YOUNG, 2019), but C. sumatrensis is resistant to 2,4-D (PINHO et al, 2019;QUEIROZ et al, 2020). However, in the present study, the recommended dose of 2,4-D achieved over 85% control in biotype R at 28 DAT when applied at stages I and II of development (Table 2).…”

Cross-resistance to diquat in glyphosate/paraquat-resistant hairy fleabane (Conyza bonariensis) and horseweed (Conyza canadensis) and confirmation of 2,4-D resistance in Conyza bonariensis

“…Although no attempt was made to study the mechanism of resistance to 2,4-D, none of the plants exhibited the rapidnecrosis phenotype reported in 2,4-D-resistant Sumatran fleabane [C. sumatrensis (Retz.) E. Walter] from Brazil (de Queiroz et al 2020). It is important to note that the GR 50 level of the GPS population was 766.7 g ai ha -1 , which approaches the reference rate.…”