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This study was designed to investigate the genetic diversity and relationships between yield and related traits in oily sunflower lines. 152 sunflower lines collected from different parts of the world were investigated at completely randomized design with nine replications on Urmia University in 1391 under pot conditions. 14 agro-morphological traits including plant height, stem diameter, number of leaves, leaf length, leaf width, petiole length, head diameter, 100 seed weight, head dry weight, , seed yield per plant, number of days from planting to flowering, and number of days from planting to maturity, dehulled kernel to whole kernel and harvest index were measured. Analysis of variance revealed significant differences among genotypes for all studied traits. Among the traits, the highest coefficient of phenotypic variation was observed for seed yield per plant (56.30), harvest index (44.4) and head dry weight (35.44). The results of correlation analysis showed that there is significant and positive correlation between seed yield per plant with most of the studied traits. Results of sequential path analysis revealed that the variables such as number of leaves, dehulled kernel to whole kernel, head diameter, and plant height were arranged as the first-order variables. Cluster analysis subdivided the genotypes into 4 groups. The maximum distance were observed between the genotype from groups 3 and 4 (28.30).

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Basal stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is one of the most important diseases of sunflower. Quantitative trait loci (QTL) implicated in partial resistance to two isolates of S. sclerotiorum (SSU107 and SSKH41) were investigated using F₉ recombinant inbred lines (RILs) from the cross between sunflower parental lines PAC2 and RHA266. Experiments were conducted in completely randomized design with 3-6 replications under controlled conditions. The reaction of genotypes to basal stem rot disease was evaluated by measuring the percentage of necrosis area three days after inoculation. Combined analysis of experiments showed significant interactions between sunflower genotypes and S. sclerotiorum isolates suggesting that partial resistance to S. sclerotiorum should be isolate-specific in sunflower. QTLs were mapped using an updated high-density SSR and SNP linkage map. The map consisted of 210 SSRs and 11 gene-derived markers placed in 17 linkage groups (LGs). The total map length was 1,653.1 cM with a mean density of 1 marker per 7.44 cM. A total of 14 QTLs were detected for partial resistance to two isolates. The phenotypic variance explained by QTLs (R²) ranged from 0.10 to 9.85. The sign of additive gene effects showed that favorable alleles for partial resistance to isolates came from both parents. Six QTLs were common between two isolates on LGs 1, 8 and 17, whereas the others were specific for each isolate. Co-localized QTLs on LG 1 were linked to the glutathione S-transferase gene (GST). The co-localized QTLs for partial resistance to basal stem rot isolates could be good candidates for marker assisted selection (MAS).

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The sunflower caterpillar Chlosyne lacinia saundersii (Lepidoptera: Nymphalidae) is considered a major pest in sunflower, causing severe defoliation and, thus, threatening production of oilseed. Chemical control remains the most widely used method for the management of this defoliator. To manage insect pests, there is a need to use substances of low toxicity that are able to stimulate the plant to use its own defense mechanisms. Therefore, in this study, we evaluated the induction of resistance by silicon (Si) and acibenzolar-S-methyl (ASM) against C. lacinia saundersii in sunflower plants. The bioassay was conducted in a completely randomized design using 4 treatments and 10 replicates. The treatments were: (1) Si; (2) ASM; (3) Si+ASM, and (4) the control. The biological parameters of the caterpillar and the accumulation of Si and lignin in plants were evaluated. The application of resistance inducers reduced weight of the caterpillars 10 and 15 days of age. The use of Si alone or Si+ASM promoted the accumulation of this element; however, only ASM increased lignin content in plants. Negative correlations between the silicon content and larval weight and between the silicon content and lignin content were observed. Therefore, the application of silicic acid or ASM can inhibit the development of C. lacinia saundersii, conferring a resistance in plants attributable to the accumulation of silicon and lignin, thus serving as an alternative approach that may potentially be integrated into the management of this key pest in sunflower crops.