Seedbank persistence and emergence pattern of Argemone mexicana, Rapistrum rugosum and Sonchus oleraceus in the eastern grain region of Australia

A thorough understanding of the emergence pattern and persistence of weed seeds is a prerequisite in framing appropriate weed management options for noxious weeds. In a study conducted at the University of Queensland, Australia, the emergence and seed persistence behavior of three major weeds Sonchus oleraceous, Rapistrum rugosum, and Argemone mexicana were explored with seeds collected from Gatton and St George, Queensland, Australia, with an average annual rainfall of 760 and 470 mm, respectively. Seed persistence was evaluated by placing seeds at the surface layer (0 cm) or buried at 2 and 10 cm depths enclosed in nylon mesh bags and examined their viability for 42 months. In another study, the emergence pattern of four populations, each from these two locations, was evaluated under a rainfed environment in trays. In the mesh-bag study, rapid depletion of seed viability of S. oleraceous from the surface layer (within 18 months) and lack of seed persistence beyond two years from 2 and 10 cm depths were observed. In trays, S. oleraceous germinated 3 months after seeding in response to summer rains and there was progressive germination throughout the winter season reaching cumulative germination ranging from 22 to 29% for all the populations. In the mesh-bag study, it took about 30 months for the viability of seeds of R. rugosum to deplete at the surface layer and a proportion of seeds (5 to 13%) remained viable at 2 and 10 cm depths even at 42 months. Although fresh seeds of R. rugosum exhibit dormancy imposed due to the hard seed coat, a proportion of seeds germinated during the summer months in response to summer rains. Rapid loss of seed viability was observed for A. mexicana from the surface layer; however, more than 30% of the seeds were persistent at 2 and 10 cm depths at 42 months. Notably, poor emergence was observed for A. mexicana in trays and that was mostly confined to the winter season.

Agricultural Weed Assessment Calculator: An Australian Evaluation

Weed risk assessment systems are used to estimate the potential weediness or invasiveness of introduced species in non-agricultural habitats. However, an equivalent system has not been developed for weed species that occur in agronomic cropland. Therefore, the Agricultural Weed Assessment Calculator (AWAC) was developed to quantify the present and potential future adverse impact of a weed species on crop production and profitability (threat analysis), thereby informing or directing research, development, and extension (RDE) investments or activities. AWAC comprises 10 questions related primarily to a weed’s abundance and economic impact. Twenty weed species from across Australia were evaluated by AWAC using existing information and expert opinion, and rated as high, medium, or low for RDE prioritization based on total scores of 70 to 100, 40 to <70, or <40, respectively. Five species were rated as high (e.g., Lolium rigidum Gaud.), eight were rated as medium (e.g., Conyza spp.), and seven were rated as low (e.g., Rapistrum rugosum L.). Scores were consistent with the current state of knowledge of the species’ impact on grain crop production in Australia. AWAC estimated the economic or agronomic threat of 20 major or minor agricultural weeds from across Australia. The next phase of development is the testing of AWAC by weed practitioners (e.g., agronomists, consultants, farmers) to verify its utility and robustness in accurately assessing these and additional weed species.

Effect of emergence time on growth and fecundity of Rapistrum rugosum and Brassica tournefortii in the northern region of Australia

Weeds from Brassicaceae family are a major threat in many crops including canola, chickpea, cotton and wheat. Rapistrum rugosum (L) All. and Brassica tournefortii Gouan. are two troublesome weeds in the northern region of Australia. In order to examine their phenology of these weeds, a pot study was conducted in 2018 at the Research Farm of the University of Queensland, Gatton campus with two populations sourced from high (Gatton) and medium (St George) rainfall areas of the northern grain region of Australia. Planting was carried out monthly from April to September, and the growth, flowering and seed production were evaluated. Maximum growth and seed production were observed in weeds planted in April, compared to other planting dates. Biomass of R. rugosum and B. tournefortii was reduced by 85% and 78%, respectively, as a result of the delay in planting from April to July. R. rugosum and B. tournefortii produced more than 13,000 and 3500 seeds plant−1, respectively, when planted in April and seed production was reduced by > 84% and > 76% when planted in July. No significant differences were observed between populations of both weeds for plant height, number of leaves and biomass, however, the medium rainfall population of R. rugosum produced more seeds than the high rainfall population when planted in April. The results of this study suggest that, although R. rugosum and B. tournefortii were able to emerge in a wider time frame, the growth and seed production were greatest when both weeds were planted in April and there was concomitant reduction in growth attributes when planted in the subsequent months, indicating that management of these weeds early in the cropping season is a prerequisite to population reduction and the mitigation of crop yield losses.

Bastard Cabbage (Rapistrum rugosum L.) Resistance to Tribenuron-Methyl and Iodosulfuron-Methyl-Sodium in Spain and Alternative Herbicides for Its Control

Complaints about the lack of control of Rapistrum rugosum with tribenuron-methyl and iodosulfuron-methyl-sodium in winter cereals in Northeastern Spain motivated this study. During 2015–2018, greenhouse trials were conducted to test the responses of two possibly resistant (R1 and R2) and two susceptible populations to both active ingredients to determine the response of these populations to alternative herbicides. In the first trial that was repeated twice, populations were treated with both active ingredients (three rates, six replicates), and the lack of control confirmed resistance both times. The second trial was conducted on the self-pollinated progeny of the initial populations (13 rates, 6 replicates) to confirm the heritable character of resistance and to determine the resistance factors related to survival and biomass. Resistance factors based on biomass were 188 and 253 for tribenuron-methyl and 42 and 26 for iodosulfuron-methyl-sodium for R1 and R2, respectively, confirming the strong resistance of the progeny. In the third trial, nine active ingredients (a.i.) registered for broadleaved weed control in winter cereals were tested on the four populations (two rates, four replicates). All the alternative herbicides, except florasulam, results in important phytotoxicity to all tested populations, with 100% efficacy for several a.i. This work is the first report of R. rugosum that is resistant to iodosulfuron-methyl-sodium and the first report in Europe of R. rugosum that is resistant to tribenuron-methyl.

Interference of turnipweed (Rapistrum rugosum) and Mexican pricklepoppy (Argemone mexicana) in wheat

Turnipweed [Rapistrum rugosum (L.) All.] and Mexican pricklepoppy (Argemone mexicana L.) are increasingly prevalent in the northern cropping regions of Australia. The effect of different densities of these two weeds was examined for their potential to cause yield loss in wheat (Triticum aestivum L.) through field studies in 2016 and 2017. There was 72% to 78% yield reduction in wheat due to competition from R. rugosum. Based on the exponential decay model, 18.2 and 24.3 plants m−2 caused a yield reduction of 50% in 2016 and 2017, respectively. Rapistrum rugosum produced a maximum of 32,042 and 29,761 seeds m−2 in 2016 and 2017, respectively. There was 100% weed seed retention at crop harvest. Competition from A. mexicana resulted in a yield loss of 17% and 22% in 2016 and 2017, respectively; however, plants failed to set seeds due to intense competition from wheat. Among the yield components, panicles per square meter and grains per panicle were affected by weed competition. The studies indicate a superior competitiveness of R. rugosum in wheat and a suppressive effect of wheat on A. mexicana. The results indicate that a wheat crop can be included in crop rotation programs where crop fields are infested with A. mexicana. High seed retention in R. rugosum indicates the possibility to manage this weed through seed catching and harvest weed seed destruction.

Μελέτη ανθεκτικών και ευαίσθητων πληθυσμών Sinapis arvensis και Rapistrum rugosum σε ζιζανιοκτόνα αναστολείς του ενζύμου ALS

Σε πειράµατα φυτοδοχείων αξιολογήθηκαν αρχικώς 21 πληθυσµοί άγριου σιναπιού (Sinapis arvensis L.) από καλλιέργειες χειµερινών σιτηρών των Νομών Φθιώτιδας, Πιερίας, Χαλκιδικής, Λάρισας και Θεσσαλονίκης για πιθανή εξέλιξη διασταυρωτής ανθεκτικότητας στα ζιζανιοκτόνα tribenuron και imazamox. Οι 18 από τους 21 πληθυσμούς ήταν ανθεκτικοί στο ζιζανιοκτόνο tribenuron, ενώ οι 15 είχαν διασταυρωτή ανθεκτικότητα στα ζιζανιοκτόνα tribenuron και imazamox. Σε τέσσερις πληθυσμούς διαπιστώθηκε ανθεκτικότητα σε εξελισσόμενη μορφή (στάδιο) στα δύο ζιζανιοκτόνα. Όλοι οι πληθυσμοί ήταν ευαίσθητοι στη συνιστώμενη δόση του ζιζανιοκτόνου MCPA. Οι υπολογισθείσες GR50 τιμές (η δόση του ζιζανιοκτόνου που απαιτείται για µείωση του χλωρού βάρους των ανθεκτικών φυτών κατά 50%) από τα πειράµατα έντασης της ανθεκτικότητας για τους 18 ανθεκτικούς πληθυσμούς στο tribenuron κυμάνθηκαν από 2,92 έως 59,47 g δ.ο./στρ, ενώ το αντίστοιχο εύρος των GR50 τιμών για τους 15 ανθεκτικούς πληθυσμούς στο imazamox ήταν 4,13-90,04 g δ.ο./στρ. Η GR50 τιμή tribenuron για τους ευαίσθητους πληθυσμούς δεν εκτιμήθηκε διότι η χαμηλότερη δόση του μείωσε το νωπό βάρος τους κατά >50%, ενώ η αντίστοιχη GR50 τιμή για το imazamox ήταν 0,05-0,43 g δ.ο./στρ. Η αλληλούχηση του γονιδίου als αποκάλυψε σημειακή μετάλλαξη που οδήγησε στην αντικατάσταση του αμινοξέος Trp574 από Leu στο ένζυμο ALS, η οποία επιβεβαιώθηκε και με την HRM ανάλυση. Η in vitro δράση του ενζύμου ALS έδειξε I50 τιμές (συγκέντρωση ζιζανιοκτόνου που απαιτείται για 50% μείωση της δράσης του ενζύμου ALS) που κυμάνθηκαν από 19,11 έως 217,45 μΜ για το tribenuron, ενώ η αντίστοιχη τιμή για τον ευαίσθητο πληθυσμό ήταν 0,98-1,17 μΜ. Τα αποτελέσματα αυτά τεκμαίρουν ότι η διασταυρωτή ανθεκτικότητα των πληθυσμών S. arvensis οφειλόταν σε σημειακή μετάλλαξη του γονιδίου als που είχε ως συνέπεια την κωδικοποίηση λιγότερο ευαίσθητου ενζύμου ALS στα ζιζανιοκτόνα tribenuron και imazamox.Τα πειράματα διερεύνησης του ρυθμού ανάπτυξης πέντε πληθυσμών S. arvensis (4 ανθεκτικοί και ένας ευαίσθητος) από διαφορετικές περιοχές της Ελλάδος έδειξαν ότι το νωπό βάρος και η παραγωγή σπόρου των ανθεκτικών πληθυσμών δεν διέφερε σημαντικά από εκείνα του ευαίσθητου πληθυσμού. Η μελέτη της γενετικής σύστασης των πέντε πληθυσμών με ανάλυση μοριακών δεικτών ISSR επιβεβαίωσε τη διαφοροποίηση των πληθυσμών ως προς τον τόπο προέλευσης, ανθεκτικότητας. Με βάση τα πειράματα μελέτης δέκα δυνητικώς ανθεκτικών και δύο ευαίσθητων πληθυσμών ράπιστρου (Rapistrum rugosum) για ανθεκτικότητα στα ζιζανιοκτόνα tribenuron και imazamox διαπιστώθηκε ότι ένας από τους 10 δυνητικώς ανθεκτικούς πληθυσμούς εμφάνισε διασταυρωτή ανθεκτικότητα στα δύο ζιζανιοκτόνα, ενώ ένας άλλος πληθυσμός ήταν ανθεκτικός μόνο στο tribenuron και όχι στο imazamox. Όλοι οι πληθυσμοί ήταν ευαίσθητοι στη συνιστώμενη δόση του MCPA. Η αλληλούχηση τμήματος του γονιδίου als στον ένα πληθυσμό, αποκάλυψε σημειακή μετάλλαξη στο κωδικόνιο Pro197 που προσδίδει ανθεκτικότητα στο tribenuron, ενώ στον άλλο διαπιστώθηκε σημειακή μετάλλαξη στο κωδικόνιο Trp574 που προσδίδει διασταυρωτή ανθεκτικότητα στο tribenuron και το imazamox. Οι Ι50 τιμές του ενζύμου ALS στην παρουσία του tribenuron κυμάνθηκαν για τους ανθεκτικούς πληθυσμούς από 66,68 έως 137,01 μΜ, ενώ η αντίστοιχη τιμή για τους ευαίσθητους πληθυσμούς κυμάνθηκε από 0,29 έως 0,54 μΜ. Τα αποτελέσματα αυτά δείχνουν ότι δύο πληθυσμοί R. rugosum εξέλιξαν ανθεκτικότητα σε δύο ζιζανιοκτόνα αναστολείς της δράσης του ενζύμου ALS εξαιτίας διαφορετικών σημειακών μεταλλάξεων στο γονίδιο als.