The use of biostimulants is one of the recognized strategies for mitigating the adverse effects of drought on crops. In a greenhouse tomato experiment, the effect of two biostimulants in combination with three levels of drought was investigated. Specifically, the doses of 150 mL and 1000 g ha⁻¹ of a plant-derived polyhydroxy acids extract (B1) and a Sargassum seaweed extract (B2), respectively, were studied in combination with drought levels of 85, 63.75, and 42.5% of field capacity. Four applications were performed during key growth stages. The effects were comprehensively investigated by assessing agronomic and physiological traits of the plants at three defined time points during the experimental period. Furthermore, organoleptic characteristics, bioactive compounds, antioxidant activity in the fruits, and overall yield components were evaluated. Drought stress provoked a consistent negative impact on several physiological traits, such as stomatal conductance (up to −58.3%), net photosynthesis (up to −47.9%), and quantum yield. A comparable impact was observed on agronomic traits, such as plant height, stem thickness, and number of leaves, with reductions of up to 13.6%. Both biostimulants’ applications enhanced certain physiological features across all irrigation levels, including net photosynthesis by up to 44.3% and chlorophyll content index by up to 33.4%, while B2 further increased intrinsic water use efficiency by up to 42.9% compared to the respective controls. However, this trend was not reflected in the evaluated post-harvest parameters, such as fruit yield, fruit number, fruit weight, and quality indices. These findings suggest that biostimulants may have a supporting role in physiological responses under drought stress but have limited effects on fruit production. Future research should focus on optimizing the formulation, dosage, and timing of biostimulant applications, as these factors may be critical to enhancing plant tolerance to drought stress and improving fruit yield responses.

Three perennial ryegrass (Lolium perenne) populations (R1, R2, and R3) with suspected resistance (R) to acetolactate synthase (ALS) or acetyl-CoA carboxylase (ACCase) herbicides were collected from wheat (Triticum aestivum) fields in northwestern Greece to study the underlying mechanisms of resistance and their impact on growth rate and competitive ability against wheat. Preemergence and postemergence plant dose–response assays showed that the R1 population was cross-resistant to the ALS inhibitors chlorsulfuron, mesosulfuron + iodosulfuron, and pyroxsulam, but susceptible (S) to imazamox. However, all populations were susceptible to the ACCase inhibitors clodinafop-propargyl, clethodim, diclofop-methyl, and pinoxaden. The analysis of the ALS gene sequence revealed a substitution of Pro197 by His or Leu in the ALS enzyme in L. perenne, which is reported for the first time in this weed and indicates a potential mechanism of target site-mediated resistance. The R1 population grown in the absence or presence of wheat competition displayed similar aboveground biomass and tiller number trends, and therefore similar estimated growth rates. In addition, the aboveground biomass of wheat was similarly reduced by both the R1 and S populations, supporting the evidence of their similar competitive ability against wheat. In general, these findings indicate that there is no clear evidence for the fitness advantage of R1 over the S population.

Background/Objectives: Johnsongrass (Sorghum halepense) 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 ALS 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. Furthermore, the competitive ability of these two johnsongrass populations against corn or sunflower was determined in a target-neighborhood design. Results: The S and R johnsongrass populations displayed similar growth rates concerning aboveground biomass and tiller number, whereas the R population displayed a slightly greater growth rate for rhizome production compared to the S population. Both populations grown with corn produced more aboveground biomass than the ones grown with sunflowers. The aboveground biomass of corn was reduced to a greater extent than sunflower by the presence of both johnsongrass populations, while both crops were affected more by the S than by the R population. Conclusions: Although the inheritance and the genetic background of plant materls were not addressed, the findings of this study indicate clearly that the growth rate and competitive ability of the ALS-resistant johnsongrass population are not associated with the resistance mechanism involved.