Determining Empty Seed Formation and Germination Rates Induced by Leptoglossus occidentalis (Heidemann) in Coniferous Species in Turkiye Forests

Abstract

In recent years, low germination rates have been a problem in the seeds of various coniferous species in Turkiye, particularly Turkish red pine (Pinus brutia) and black pine (Pinus nigra), which are commonly used species for afforestation activities. The increase in low germination rates corresponds to the spread of Leptoglossus occidentalis in coniferous forests, suggesting an investigation of potential correlation between the spread of this insect and the empty seed formation and germination rates. This study aimed to investigate the main causes of empty seeds and low germination rates induced by Leptoglossus occidentalis (Heidemann) in coniferous species in Turkiye. In the study, sample cones from various coniferous species including Fir (Abies spp.), Stone pine (Pinus pinea), Turkish red pine (Pinus brutia), Spruce (Picea orientalis), Cedar (Cedrus libani), Maritime pine (Pinus pinaster), Black pine (Pinus nigra) and Scots pine (Pinus sylvestris) were collected based on their geographical distribution, and then their seeds were extracted. The 1000-seed weights were determined for each species, followed by germination tests conducted under controlled conditions. Statistical analysis revealed significant variations in germination rates among species. Among the eight species examined, Scots pine (Pinus sylvestris) had the highest germination rate at 37.9%, while fir (Abies spp) had the lowest rate at 0.4%. Further statistical analysis revealed variations in germination rates based on aspects, with generally higher rates observed in sunny aspects. The results indicated that Leptoglossus occidentalis caused a significant decrease in seed germination ranging from 60–99% in coniferous species. Additionally, reductions in 1000-seed weights ranging from 19–81% were observed in the species, except Scots pine. The findings highlight widespread germination issues in seeds of majority of the coniferous tree in Turkiye. As a result, it was found that L. occidentalis significantly contributes to empty seed formation and lower germination rates in coniferous forests. Therefore, it is essential to develop strategies to protect and conserve seed resources to mitigate any negative impacts on forest resources.