Helianthus petiolaris and H. annuus are exotic invaders that have spread widely in central Argentina in the last 70 years. As other annuals of the same genus, these species are outcrossers bearing a sporophytic self-incompatible mechanism. We investigated the ability to self-pollinate in plants of five accessions of each species, its influence on some reproductive traits, and compared to the cultivated sunflower, in which breeding for self-compatibility has been very successful. Plants were allowed to self-pollinate in bagged heads, manually forced to self-pollinate or allowed to cross-pollinate. Although both invasive species were confirmed as self-incompatible, some plants within most accessions were able to self-pollinate. There was no significant interaction between accessions and pollination type for most traits, except for seed set which was attributed to interspecific introgression. The self-compatibility of some plants was transmitted to their progeny. No significant correlation between self-pollination and spread distance from the proposed entry point for the exotic species was found. The occurrence of self-compatible plants was demonstrated in both species and this fact could in part explain the high invasive ability of annual Helianthus species in Argentina.

Helianthus petiolaris y H. annuus son invasores exóticos que se han extendido en el centro de Argentina en los últimos 70 años. Como otras anuales del mismo género, estas especies son de polinización cruzada y llevan un mecanismo de auto-incompatibilidad esporofítica. Se investigó la capacidad de auto-polinización en plantas de cinco colecciones de cada especie, su influencia sobre algunos aspectos reproductivos y en comparación con el girasol cultivado, en el que el mejoramiento para la auto-compatibilidad ha sido exitoso. Las plantas se auto-polinizaron con los capítulos tapados por bolsas, se auto-polinizaron de manera forzada manualmente o se permitió la polinización cruzada. Aunque ambas especies invasoras fueron confirmadas como auto- incompatibles, algunas plantas dentro de la mayoría de las colecciones fueron capaces de auto-polinizarse. No hubo interacción significativa entre las colecciones y el tipo de polinización para la mayoría de los rasgos, excepto para la producción de semillas que se debió a la introgresión interespecífica. La auto-compatibilidad de algunas plantas se transmitió a su descendencia. No se encontró una correlación significativa entre la auto-polinización y la distancia de propagación desde el punto de entrada propuesto para las especies exóticas. La aparición de las plantas auto-compatibles se demostró en ambas especies y este hecho podría explicar en parte la alta capacidad invasiva de las especies anuales Helianthus en Argentina.

O nabo tornou-se feral, sendo uma preocupação para a agricultura em diversas partes do mundo. Na Argentina, é uma das plantas daninhas mais difundidas e problemáticas das culturas. No Brasil, essa espécie gerou biótipos resistentes aos herbicidas inibidores de AHAS. O objetivo deste estudo foi documentar a presença de nabo-silvestre com resistência na Argentina. Na primavera de 2008, observaram-se plantas de nabo nos últimos estádios de floração em um campo de canola tolerante aos herbicidas do grupo químico das imidazolinonas, que havia recebido uma aplicação de imazethapyr. Testes de rastreio e dose-resposta foram conduzidos por duas gerações sucessivas, os quais provaram o status de biótipo resistente e mostraram alta sobrevivência (entre 50 e 80% de controle) na aplicação de dose dupla de quatro herbicidas inibidores da AHAS (duas famílias químicas diferentes: imidazolinonas e sulfonilureias). Os ensaios de dose-resposta exibiram resistência muito elevada para imazethapyr (LD50 = 2.452,5 g i.a. ha-1, GR50 = 2.926,9 g i.a. ha-1) e intermediária para metsulfuron (LD50 = 3.0 g i.a. ha-1, GR50 = 43.2 g i.a. ha-1). A aquisição de resistência cruzada para famílias de herbicidas diferentes proporcionaria uma vantagem adaptativa e invasiva em ambientes agrícolas para esse biótipo. Devido à rotação do herbicida conduzida no campo, a dispersão desse biótipo foi restringida. Esse é o primeiro relato de resistência em nabo-silvestre para a Argentina.

Radish has developed feral and weedy biotypes, which is a concern for agriculture around the world. In Argentina, it is one of the most widespread and troublesome crop weeds. In Brazil, this species has developed herbicide-resistance to acetohydroxyacid synthase (AHAS) inhibiting herbicides. The objective of this study was to record the presence of herbicide-resistant weedy radish plants in Argentina. In spring 2008, we found a small population of radish at the end of the flowering stage in an imidazolinone-tolerant canola field treated with imazethapyr. Screening and dose-response tests were conducted to two successive generations. They proved the biotype resistant status, and showed extensive survival (between 50 and 80% of control) to the application of a double dose of four AHAS‑inhibiting herbicides from two different chemical families (imidazolinones and sulfonylureas). Dose-response assays exhibited very high resistance for imazethapyr (LD50 = 2452.5 g a.i. ha-1, GR50 = 2926.9 g a.i. ha-1) and intermediate for metsulfuron (LD50 = 3.0 g a.i. ha-1, GR50 = 43.2 g a.i. ha-1). The acquisition of cross-resistance to different herbicide families would confer an adaptive and invasive advantage in agricultural environments to this biotype. Due to the herbicide rotation conducted in the field, the dispersion of this biotype was restricted. This is the first report of resistance in weedy radish in Argentina.

The parasitic weed Orobanche cumana Wallr. (broomrape) is one of the major limiting factors in worldwide sunflower production. However, it is absent in the centre of origin and in the sunflower crop areas of América. It has not yet been elucidated if O. cumana naturalization in sunflower habitats in Argentina is restricted as a result of either abiotic constraints or resistance in grown commercial cultivars. The aim of the present study was to assess the degree of resistance of commercial sunflower cultivars grown in Argentina to O. cumana. More than 95% of the tested sunflower cultivars were, in general, susceptible to broomrape attack. Although three cultivars were found to evidence an acceptable response to broomrape attack, only one of them showed complete resistance to O. cumana. This disregards genetic resistance of grown cultivars as being the reason for the absence of broomrape in Argentina. In view of this, future studies should focus on other biotic and abiotic factors affecting broomrape growth and development which could be potentially responsible for the absence of O. cumana in Argentina.

La planta parásita Orobanche cumana Wallr. (jopo) es una de las mayores limitantes de la producción de girasol en los principales países productores del mundo. Sin embargo, está ausente en el centro de origen y en las áreas de cultivo de girasol en América. No ha quedado claro aún si la naturalización de O. cumana en los hábitats de girasol de Argentina está limitada por restricciones abióticas o por la resistencia de los cultivares comerciales. El objetivo de este estudio fue investigar la resistencia a O. cumana de los cultivares comerciales de girasol en Argentina. En general, más del 95% de los cultivares probados fue susceptible al ataque de jopo; solamente uno de ellos mostró completa resistencia a O. cumana. Esto descarta la posibilidad de considerar a la resistencia genética de los cultivares utilizados como la causa de la ausencia de jopo en Argentina. Por lo tanto, los estudios futuros deberían focalizarse en otros factores bióticos y abióticos que, por afectar el crecimiento y desarrollo del jopo, podrían ser responsables potenciales de la ausencia de este parásito en Argentina.

Cultivated sunflower Helianthus annuus and the wild exotic H. petiolaris are sympatric species in an extensive region of central Argentina. Both species are sexually compatible, they overlap their flowering time and share pollinators in the region. Although there are important barriers to introgression between them, interspecific hybrids are occasionally found in contact zones. We present evidences of crop introgression in H. petiolaris populations under natural conditions and controlled and semi-controlled crosses in the experimental field using morphological traits. If crop genes persist in subsequent generations after hybridization, it could then be possible to find crop morphological traits and molecular markers in hybrid offsprings. Plants of H. petiolaris, sunflower and plants of intermediate morphology (IMP) were characterized in their natural habitats, and progenies of IMPs were grown in a common garden and compared to progenies of interspecific hybrids obtained by open pollination and backcrosses to H. petiolaris. Variability of IMPs in the wild was comparable to variability under experimental conditions, thus confirming introgression from sunflower in H. petiolaris populations. Molecular markers confirmed introgression. This has implications on the usage of herbicide tolerant sunflower varieties and the likely release of genetic modified varieties in agro-ecological regions invaded by H. petiolaris populations.

El girasol cultivado Helianthus annuus y la especie silvestre exótica H. petiolaris son simpátricos en una extensa región central de Argentina. Ambas especies son sexualmente compatibles, superponen su floración y comparten polinizadores en las condiciones locales. Aunque hay importantes barreras a la introgresión entre ellas, en las zonas de contacto se encuentran ocasionalmente híbridos interespecíficos. En este estudio presentamos evidencias de la introgresión del cultivo en las poblaciones naturales de H. petiolaris y cruzamientos controlados y semi-controlados producidos en el campo experimental, utilizando caracteres morfológicos. Si los genes del cultivo persisten en las generaciones posteriores a la hibridación, sería posible encontrar rasgos morfológicos y marcadores moleculares del cultivo en la descendencia de los híbridos. Se caracterizaron plantas de H. petiolaris, girasol y plantas de morfología intermedia (IMP) en sus sitios naturales. Se criaron las progenies de las IMPs en un jardín común y se compararon con progenies de híbridos interespecíficos y sus retrocruzas con H. petiolaris producidas bajo condiciones controladas. La variabilidad fenotípica de las IMPs en el hábitat natural fue similar a la observada en la progenie de cruzas interespecíficas criadas bajo condiciones experimentales, lo cual confirma la introgresión del girasol en H. petiolaris. Los marcadores moleculares también confirmaron la introgresión. Este hallazgo tiene implicancias sobre el uso de variedades de girasol tolerantes a herbicida y la posible liberación de variedades genéticamente modificadas en regiones agro-ecológicas invadidas por poblaciones de H. petiolaris.

Eight isozyme systems were used in this study: acid phosphatase (ACP), alcohol dehydrogenase (ADH), esterase (EST), glutamate dehydrogenase (GDH), malate dehydrogenase (MDH), phosphoglucoisomerase (PGI), 6-phosphogluconate dehydrogenase (PGD), and phosphoglucomutase (PGM). The polymorphism of these enzyme systems was studied in 25 elite inbred lines. A total of 19 loci were identified, but only eight of them were polymorphic in the germplasm tested. The polymorphic index for the eight informative markers ranged from 0.08 to 0.57, with a mean value of 0.36. Five isozyme loci were mapped in F2:3 populations with existing RFLP data. Est-1, Gdh-2 and Pgi-2 were mapped to linkage groups 3, 14 and 9, respectively. As in previous reports, an ACP locus and a PGD locus were found to be linked, both located in linkage group 2 of the public sunflower map.