Abstract Background Amaranthus palmeri has emerged as the most widespread weed of agricultural land in large parts of North and South America. Understanding its population dynamics and the influence of meteorological variables becomes important for decision-making in an integrated management context. The hypothesis is that the emergence of A. palmeri is influenced by thermal time and extreme weather events that occurred in the previous 45, 30 or 15 days. Objective The work was aimed to detect the influence of meteorological variables and extreme weather events on the emergence of A. palmeri under field conditions. Methods A field experiment was carried out in order to record seedling emergence of A. palmeri in two growing seasons, 2017/2018 (S1) and 2018/2019 (S2), in Argentina. Associations between weed emergence and thermal time (in growing degree-days GDD), meteorological variables or extreme weather events recorded at 15, 30 and 45 days before to each evaluation time were studied by regression, principal components and multiple correspondence analyses. Results Thermal time was closely associated to the progress of cumulative emergence in both seasons, but the emergence periodicity was conditional with rainfall. The high precipitation during the spring determined a short lag period (121.8 GDD) in S2. Contrarily, the largest lag period (236.6 GDD) was detected in S1 related to a drought that concentrated the emergence in the beginning of the summer when the rainfall increased. Conclusions Thermal time allows the cumulative emergence prediction; however, extreme weather events like drought induce quiescence, concentrating the emergence in a short period.

Abstract Background: Megathyrsus maximus (Jacq.) is a perennial weed that affects many crops. In Argentina, sugarcane is the most affected. Objective: Study effective techniques to break dormancy and the effect of environmental factors on the germination of this weed. Methods: Experiments were carried out in cabinet incubators twice, with five replicates per treatment. The experimental unit was made up for 50 seeds. Results: Seed dormancy was strongly associated with the presence of glumes. Manual extractions of glumes and immersion in sulphuric acid were the most effective techniques for breaking dormancy. Megathyrsus maximus did not depend on light to germinate, and it did so both under a 12 h-light-dark photoperiod and in complete darkness, with maximum mean germination percentages of 73 and 76%, respectively. Mean germination percentage (G) and coefficient of germination (CG: number of germinated seeds per day) showed that this weed responded to a wide range of temperatures, the optimal varied between 25 and 35 °C. Both mean germination percentages and CG decreased as osmotic potential became increasingly negative (0 MPa to -0.6 MPa), and as sodium chloride solution concentrations increased (10 to 130 mmol L-1). No germination was observed at -0.8 MPa and with a 150 mmol L-1 sodium chloride solution. Conclusions: The optimal germination conditions for M. maximus can be found in central sugarcane areas in Argentina, since soils are in ideal conditions and are kept under irrigation. In marginal areas, M. maximus germination would depend on rainfall and certain sodium chloride concentrations in the soil.

Abstract: Background and Aims: Flaveria is an American genus with 23 species; in Argentina it is represented by two of them both native and annual: F. bidentis (which is cited as a weed of agroecosystems) and F. haumanii. The genus is mentioned with a base chromosome number of x=18 and cytogenetic backgrounds for F. bidentis are know, but not so for F. haumanii. The aim of this work was to cytogenetically characterize F. bidentis and F. haumanii through the analysis of mitosis, meiotic behavior and estimation of pollen grain viability. Methods: The material was collected in the province of Santiago del Estero (Argentina). The root tips were pretreated with 8-hydroxyquinoline 0.002 M for eight hours. Inflorescences and root tips were fixed in Farmer and preserved in cold 70% ethyl alcohol. To stain chromosomes 2% propionic hematoxylin was used. The viability of pollen grains was estimated with the Mützing and DAF stain solutions. Key results: Flaveria bidentis and F. haumanii have a sporophytic chromosome number of 2n=36, with a symmetric unimodal karyotype. The meiotic behavior was regular, in diakinesis n=18 bivalent was observed and the estimated viability of the pollen grains was greater than 90%. Conclusions: The sporophytic and gametophytic chromosomal numbers of F. haumanii are mentioned for the first time; in addition, through meiotic analysis the cytogenetic information is completed for F. bidentis. These are the first data related to pollen grain viability.

Resumen: Antecedentes y Objetivos: Flaveria es un género americano integrado por 23 especies y representado en Argentina por dos de ellas, ambas nativas y anuales: F. bidentis (la cual es considerada maleza de agroecosistemas) y F. haumanii. El género tiene un número cromosómico básico de x=18 y los antecedentes citológicos son referidos a F. bidentis, pero no así para F. haumanii. El objetivo de este trabajo fue caracterizar citogenéticamente a F. bidentis y F. haumanii a través del análisis cariotípico, el comportamiento meiótico y la estimación de la viabilidad de los granos de polen. Métodos: El material fue recolectado en la provincia de Santiago del Estero (Argentina). Las raíces fueron pretratadas con 8-hidroxiquinoleina 0.002 M durante ocho horas. Inflorescencias y raíces fueron fijadas en Farmer y conservadas en alcohol etílico al 70% en frío. Para la tinción de los cromo somas se utilizó hematoxilina propiónica al 2%. La viabilidad de los granos de polen se estimó mediante las soluciones colorantes de Mützing y DAF. Resultados clave: Flaveria bidentis y F. haumanii poseen como número cromosómico esporofítico 2n=36, con un cariotipo unimodal simétrico. El comportamiento meiótico es regular y en diacinesis se observó n=18 bivalentes; la viabilidad estimada de los granos de polen fue superior a 90%. Conclusiones: Se mencionan por primera vez los números cromosómicos esporofíticos y gametofíticos de F. haumanii; además, se completa la información citogenética para F. bidentis a través del análisis de la meiosis. Estos son los primeros datos relacionados con la viabilidad de los granos de polen.

Abstract: Background and Aims: Flaveria is an American genus; two species occur in Argentina, F. bidentis and F. haumanii. Anatomical antecedents are scarce for these species and for F. bidentis the presence of uniseriate trichomes, epicuticular waxes, crystals and Kranz structure are reported. Chemically these species have diverse flavonoids of the sulphated group. The aims of this work were to characterize the leaf and cauline anatomy, and quantify the foliar phenolic components for F. bidentis and F. haumanii. Methods: The material was collected in the province of Santiago del Estero (Argentina) and subsequently fixed in FAA; conventional anatomical and phytochemical techniques were used for subsequent analysis. Key results: Both taxa presented entire leaf blade and trinervate, acrodromous primary venation. In paradermal view, both species have polyhedral epidermal cells at both surfaces, which are amphistomatic and with a striate cuticle. Presence of anomocytic, hemiparacytic, brachiparacytic, and polocytic stomata, as well as multicellular glandular trichomes. In cross section, the blade is dorsiventral with collateral vascular bundle and Kranz structure. The growing primary stem showed subepidermal angular collenchymas and amyloid sheath in the inner part of the cortex. Secondary growth included continuous xylem and phloem due to cambium activity. Parenchymal medulla was partially lignified. The presence of secretory schizogenic ducts in both blade and stem was observed. The phytochemical analysis showed higher total content of phenols, flavonoids and hydroxycinnamic acid in F. haumanii than in F. bidentis; only the total content of the ortho-dihydroxyphenols was slightly higher in the latter species. Conclusions: Flaveria bidentis and F. haumanii may be differentiated through stomata and trichome density and size and location of trichomes in the blade; whereas in both species the quantity of vascular bundles and secretory ducts of the stem are different. Quantification of phenolic compounds allowed us to establish a chemical profile for both species having scarce differences.

Resumen: Antecedentes y Objetivos: Flaveria es un género americano; en Argentina presenta dos especies, F. bidentis y F. haumanii. Los antecedentes anatómicos para las especies son escasos y para F. bidentis son referidos a la presencia de tricomas uniseriados, ceras epicuticulares, cristales y estructura Kranz. Químicamente estas especies poseen diversos flavonoides del grupo sulfatado. Los objetivos del presente trabajo fueron caracterizar la anatomía foliar y caulinar, así como cuantificar los componentes fenólicos de las hojas de F. bidentis y F. haumanii. Métodos: El material fue recolectado en la provincia de Santiago del Estero (Argentina), fijado en FAA y posteriormente se emplearon técnicas anatómicas y fitoquímicas convencionales para su análisis. Resultados clave: Ambos taxones presentaron lámina foliar entera, venación primaria trinervada, acródroma. En vista paradermal, en ambas especies las células epidérmicas de la lámina fueron poliédricas en ambas superficies, anfiestomáticas y de cutícula estriada. Se observaron estomas anomocíticos, hemiparacíticos, braquiparacíticos, polocíticos y tricomas glandulares pluricelulares. En corte transversal, la lámina fue dorsiventral con haz vascular colateral y estructura Kranz. El tallo en crecimiento primario presentó colénquima angular subepidérmico y vaina amilífera en la parte interna de la corteza. El crecimiento secundario temprano presentó xilema y floema continuos por la actividad del cambium. Médula parenquimática parcialmente lignificada. Se observó la presencia de conductos secretores esquizógenos en lámina y tallo. Los análisis fitoquímicos mostraron mayor contenido total de fenoles, flavonoides y ácidos hidroxicinámicos en F. haumanii comparados con F. bidentis, donde solo el contenido total de orto-dihidroxifenoles fue ligeramente superior. Conclusiones: Flaveria bidentis y F. haumanii pueden diferenciarse por la densidad de estomas y de tricomas, así como por el tamaño y ubicación de estos últimos en la lámina; mientras que en el tallo existen diferencias en la cantidad de haces vasculares y de conductos secretores. La cuantificación de compuestos fenólicos permitió establecer un perfil químico para ambas especies con escasas diferencias.