Estéfani Sulzbach

Background: Weedy rice (Oryza spp.) and Echinochloa spp. are the most problematic grass weeds in rice (Oryza sativa L.) production systems due to their high competitiveness, prolific seed production, and widespread herbicide resistance. The adoption of imidazolinone (IMI)-resistant rice enabled selective control; however, gene flow rapidly led to resistant weedy rice populations. More recently, rice cultivars resistant to aryloxyphenoxypropionate (FOP) ACCase-inhibiting herbicides were introduced, providing a new control strategy. Objective: This study aimed to establish the baseline sensitivity of [...] Abstract Background: Weedy rice (Oryza spp.) and Echinochloa spp. are the most problematic grass weeds in rice (Oryza sativa L.) production systems due to their high competitiveness, prolific seed production, and widespread herbicide resistance. The adoption of imidazolinone (IMI)-resistant rice enabled selective control; however, gene flow rapidly led to resistant weedy rice populations. More recently, rice cultivars resistant to aryloxyphenoxypropionate (FOP) ACCase-inhibiting herbicides were introduced, providing a new control strategy. Objective: This study aimed to establish the baseline sensitivity of

Herbicide target site resistance in polyploid species is more complex than in diploids due to potential subgenome interactions. This study characterized mutations in the ALS gene across distinct subgenomes of hexaploid Echinochloa crus‐galli and evaluated the cross‐resistance patterns conferred by each mutation to various ALS‐inhibiting herbicides. E. crus‐galli populations were screened, and dose–response curves were performed with ALS inhibitors from different chemical groups. The ALS gene copies of each subgenome (A, B, and C) were sequenced. Copy number variation, global relative expression, and the specific relative expression of ALS gene from each subgenome were performed. The mutations Ala122Thr, Ala205Asn, and Ser653Asn conferred resistance only to imazethapyr, whereas Trp574Leu to imazethapyr, penoxsulam, bispyribac‐sodium, and nicosulfuron, when considered the label rate. ALS mutations were more frequent in subgenome A, but ALS from subgenome C had the highest expression. Biotypes with the same mutation showed different resistance level to herbicides. The biotype SAOJER‐01 had Trp574Leu mutation in subgenome C and was 22 times more resistant to imazethapyr and penoxsulam than CAMAQ‐01, which had the same Trp574Leu mutation in subgenome A. Both SAOJER‐01 and CAMAQ‐01 biotypes showed CYP450 metabolism mediating penoxsulam resistance in addition to the target site mutation. In conclusion, the mutations Ala122Thr, Ala205Asn, Trp574Leu, and Ser653Asn confer resistance to imazethapyr, but only Trp574Leu confers resistance to the other chemical groups. The herbicides penoxsulam, bispyribac‐sodium, and nicosulfuron are effective in controlling three out of four mutations. CYP450‐mediated metabolism coexists in biotypes carrying the Trp574Leu mutation. The subgenome location of the ALS mutation may result in variable levels of resistance.

Herbicide target site resistance in polyploid species is more complex than diploids due to potential subgenome interactions and gene dosage of mutations. The objective of this study was to identify the level of resistance and cross-resistance patterns of ALS mutations located in the different subgenomes of allohexaploid Echinochloa crus-galli . E. crus-galli populations were screened and dose-response curves were performed with ALS-inhibitors from different chemical groups. The ALS genes of each subgenome (A, B, and C) were sequenced. Copy number variation, global relative expression, and the specific relative expression of ALS gene from each subgenome were performed. Out of 100 populations, 32% were resistant only to imazethapyr, and 48% were cross-resistant to all ALS-inhibitors. The mutations Ala122Thr, Ala205Asn, and Ser653Asn confer resistance only to imazethapyr, while Trp574Leu confers resistance to all four herbicides tested. ALS mutations were most frequent in subgenome A, but ALS from subgenome C had the highest expression. The biotype SAOJER-01 had Trp574Leu mutation in subgenome C and was 22 times more resistant to imazethapyr and penoxsulam than CAMAQ-01, which had the same Trp574Leu mutation in subgenome A with no differences in herbicide metabolism rate. The ALS genes from subgenomes A and C contribute approximately 13% and 50% respectively to the total ALS transcripts. The higher contribution of subgenome C to the total ALS transcripts pool combined with the Trp574Leu resistance mutation makes the biotype SAOJER-01 more resistant to herbicides than CAMAQ-01. This is the first study showing the effect of subgenome gene expression level on the herbicide resistance level in a polyploid weed species. In addition, while imazethapyr did not control any biotype with an ALS mutation, the other ALS-inhibitor herbicides were able to control biotypes carrying Ala122Thr, Ala205Asn, and Ser653Asn, which reinforces the utility of these herbicides in weed and resistance management.

The presence of glyphosate-resistant smooth pigweed (Amaranthus hybridus L.) biotypes has increased in southern Brazil in recent years, presenting the triple amino acid substitution TAP-IVS in 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS) previously found in Argentina. Some of these biotypes have morphological characteristics of A. hybridus and redroot amaranth (Amaranthus retroflexus L.). The present study aimed to identify, through molecular markers, the herbicide-resistant species of Amaranthus from Brazil that have the TAP-IVS substitution and to analyze the occurrence of pollen-mediated gene flow (PMGF) as the source of the TAP-IVS substitution in these biotypes. Six biotypes were evaluated using internal transcribed spacer (ITS) sequences, of which two (AMACHY-S and CAMAQ-R) were molecularly classified as A. hybridus and four (AMACRET-S, AMACVI-S, ARRGR-R, and SAOJER-R) were unclassified. Interestingly, all the glyphosate-resistant biotypes (ARRGR-R, SAOJER-R, and CAMAQ-R) had the TAP-IVS substitution and an increase in EPSPS relative copy number; however, only CAMAQ-R was confirmed as A. hybridus. Although the biotypes ARRGR-R and SAOJER-R are closely related to A. hybridus and green pigweed (Amaranthus powellii S. Watson), their species identity could not be resolved. The biotype SAOJER-R also was resistant to acetolactate synthase (ALS)-inhibiting herbicides due to a tryptophan to leucine substitution at position 574 in ALS. The evaluation of 119,746 seedlings in an intraspecific hybridization study of A. hybridus indicated an outcrossing frequency of 0.09%. In contrast, an absence of interspecific hybridization (A. hybridus × unclassified biotype, AMACVI-S) was found after screening 111,429 offspring. Unclassified biotypes might be derived from one or more ancient hybridization events and subsequently evolved the triple mutation independently. Alternatively, such biotypes could have evolved from recent hybridization events, which occur at a frequency below the level of detection in our study.

Prosopanche cocuccii is described as a new species from Southern Brazil. It resembles P. bonacinae due to the trigonous rhizome and by the general size of the flower organs. Nevertheless, P. cocuccii is distinguished by the main floral morphological characteristics used to differentiate species. In addition, the new species presents some rare characters for the genus, such as a highly branched rhizome and flowers usually grouped in fascicles. We provide a description, illustrations, field photographs, morphological details under the stereomicroscope, and comments on habitat, ecology, distribution, and conservation of the new species, as well as an updated key for the genus Prosopanche. In addition, we identified that P. cocuccii produces a large number of rhizomes and fruits for each single host specimen of tobacco (Nicotiana tabacum), which resulted in a decrease in height and growth of its only known host plant.