Development of genetic stocks of sunflower with resistance to sunflower chlorotic mottle virus / Conformación de recursos genéticos de girasol con resistencia al virus del moteado clorótico del girasol

ABSTRACT The common race of sunflower chlorotic mottle virus (SCMoV-C) can cause severe yield losses in susceptible genotypes of sunflowers if infection occurs at early plant stages. In Argentina, SCMoV-C is widespread in sunflower production fields and even if its incidence is generally low, in some cases it can reach up to 95%. To date, no complete resistance to SCMoV-C has been detected in commercial cultivars. In the search for resistant germplasm, wild sunflower (Helianthus annuus L.) populations from Argentina were tested, as they were exposed to natural selective pressure during their naturalization. After artificial inoculation with SCMoV-C, symptom-free plants were selected and grown for controlled self-pollination, sibling crosses and crosses with inbred lines. Recurrent selection for non-symptomatic plants and self-fertility significantly increased the frequency of asymptomatic individuals after SCMoV-C inoculation in the development germplasm. After eight generations of recurrent selection and controlled crosses, four genetic stocks with complete SCMoV-C resistance were developed. These genetic stocks could be used for breeding programs and genetic studies. The genetic stocks were registered in the Active Sunflower Germplasm Bank of the National Institute of Agricultural Technology (INTA, EEA-Manfredi), for maintenance and public distribution.

RESUMEN En los genotipos susceptibles de girasol, la cepa común del Virus del moteado clorótico del girasol (SCMoV-C) puede causar graves pérdidas de rendimiento si la infección ocurre en las primeras etapas del desarrollo de la planta. En Argentina, el SCMoV-C está muy extendido en los campos de producción de girasol y aunque su incidencia es generalmente baja, en algunos casos puede llegar hasta el 95%. Hasta ahora, no se ha detectado resistencia completa a SCMoV-C en cultivares comerciales. En la búsqueda de germoplasma resistente, poblaciones de girasol silvestre (Helianthus annuus L.) de Argentina fueron testeadas, ya que durante su naturalización estuvieron expuestas a presión selectiva natural. Después de la inoculación artificial con SCMoV-C, se seleccionaron y cultivaron plantas libres de síntomas y se realizaron cruzamientos controlados, entre hermanos, con líneas endogámicas y autofecundaciones. La selección recurrente de plantas asintomáticas y autofértiles aumentaron considerablemente la frecuencia de individuos asintomáticos después de la inoculación con SCMoV-C en el germoplasma en desarrollo. Después de ocho generaciones de selección recurrente y cruces controlados, se desarrollaron cuatro stocks genéticos con resistencia completa a SCMoV-C. Este germoplasma podría utilizarse para programas de mejoramiento y estudios genéticos. Los stocks genéticos fueron registrados en el Banco de Germoplasma Activo de Girasol del Instituto Nacional de Tecnología Agropecuaria (INTA, EEA-Manfredi), para su mantenimiento y distribución pública.

IMI resistance associated to crop-weed hybridization in a natural Brassica rapa population: characterization and fate.

Wild turnip (Brassica rapa) is a common weed and a close relative to oilseed rape (Brassica napus). The Clearfield® production system is a highly adopted tool which provides an alternative solution for weed management, but its efficiency is threatened by gene transfer from crop to weed relatives. Crop-weed hybrids with herbicide resistance were found in the progeny of a B. rapa population gathered from a weedy stand on the borders of an oilseed rape (B. napus) imidazolinone (IMI)-resistant crop. Interspecific hybrids were confirmed by morphological traits in the greenhouse and experimental field, survival after imazethapyr applications, DNA content through flow cytometry, and pollen viability. The transference of herbicide resistance was demonstrated even in a particular situation of pollen competition between both an herbicide-resistant crop and a non-resistant crop. However, IMI resistance was not found in further generations collected at the same location. These results verify gene transmission from oilseed rape to B. rapa in the main crop area in Argentina where resistant and susceptible varieties are found and seed loss and crop volunteers are common. Hybridization, introgression, and herbicide selection would be associated with the loss of effectiveness of IMI technology.

Persistence of sunflower crop traits and fitness in Helianthus petiolaris populations.

Transgenic plants have increased interest in the study of crop gene introgression in wild populations. Genes (or transgenes) conferring adaptive advantages persist in introgressed populations, enhancing competitiveness of wild or weedy plants. This represents an ecological risk that could increase problems of weed control. Introgression of cultivar alleles into wild plant populations via crop-wild hybridisations is primarily governed by their fitness effect. To evaluate this, we studied the second generation of seven wild-crop interspecific hybrids between weedy Helianthus petiolaris and cultivated sunflower, H. annuus var. macrocarpus. The second generation comprised open-pollinated progeny and backcrosses to the wild parent, mimicking crosses that occur in natural situations. We compared a number of morphological, life history and fitness traits. Multivariate analysis showed that the parental species H. annuus and H. petiolaris differed in a number of morphological traits, while the second hybrid generation between them was intermediate. Sunflower crop introgression lowered fitness of interspecific hybrids, but fitness parameters tended to recover in the following generation. Relative frequency of wild/weedy and introgressed plants was estimated through four generations, based on male and female parent fitness. In spite of several negative selection coefficients observed in the second generation, introgressed plants could be detected in stands of <100 weedy H. petiolaris populations. The rapid recovery of fecundity parameters leads to prediction that any trait conferring an ecological advantage will diffuse into the wild or weedy population, even if F1 hybrids have low fitness.