Comparison of Molecularly Identified Resistant and Susceptible Johnsongrass ( L.) Populations at Gene, in the Absence and Presence of Field Crops.

Background/objectives: Johnsongrass () is an erect tetraploid, perennial, C4 grass weed species categorized among the world's most noxious weeds due to its high competitive ability against crops and the increased number of field-evolved herbicide-resistant populations. The aim of the present study was to assess the growth rate and performance of resistant (R) johnsongrass genotypes hosting Trp574Leu target-site cross-resistance at gene, inhibiting various herbicides, compared to susceptible (S) conspecific weeds, in the absence and presence of corn or sunflower antagonism.

Methods: The aboveground biomass, tiller, and rhizome production ability of one S and one R johnsongrass population with a Trp574-Leu substitution conferring cross-resistance to ALS-inhibiting herbicides were compared under non-competitive conditions.

Transmission of Moroccan watermelon mosaic virus (MWMV) by Aphids in Greece.

The aphid-transmitted Moroccan watermelon mosaic virus (MWMV; Potyvirus, Potyviridae) is an emerging pathogen in cucurbit crops in the Mediterranean basin but information on its transmitting vector species is limited. This study aimed to record the competence of 22 species of the Greek aphid fauna to vector MWMV. Timed-probe transmission experiments and arena tests were performed using laboratory colonies of aphid species abundant in field surveys; less common species were tested as apterous individuals collected directly from field plants in mass-inoculation (nonpersistent) tests.

ACCase mutations in Avena sterilis populations and their impact on plant fitness.

Avena sterilis (sterile oat) populations originating from wheat-growing regions of Greece, developed resistance to fenoxaprop, clodinafop and other herbicides. The partial ACCase gene sequence revealed six point mutations (Ile-1781-Leu, Trp-1999-Cys, Trp-2027-Cys, Ile-2041-Asn, Asp-2078-Gly, and Cys-2088-Arg) in 24 out of the 26 resistant (R) populations, confirming the molecular mechanism of resistance to ACCase-inhibiting herbicides. However, DNA sequence of two R populations did not reveal any known ACCase mutations, suggesting possible presence of unknown mutation or metabolism-based mechanism of resistance.