Determining empty seed formation and germination rates induced by Leptoglossus occidentalis (Heidemann) in coniferous species in Turkish forests

Abstract

In recent years, low germination rates have been a problem in the seeds of various coniferous species in Turkey, 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 (Heidemann) in coniferous forests, suggesting an investigation of the 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 L. occidentalis in coniferous species in Turkey. Sample cones were collected 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), based on their geographical distribution. The seeds were extracted, and 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 between species. Among the eight species examined, Scots pine (Pinus sylvestris) had the highest germination rate of 37.9%, while fir (Abies spp) had the lowest rate of 0.4%. Further analysis showed variations in germination rates based on aspects, with generally higher rates observed in sunny aspects. The results indicated that L. occidentalis caused a significant decrease in seed germination ranging from 60 to 99% in coniferous species and reductions in 1000-seed weights ranging from 19 to 81% among the species, except for Scots pine. The findings highlight widespread germination issues in the seeds of most coniferous trees in Turkey. It was found that L. occidentalis significantly contributes to the formation of empty seeds and lower germination rates in coniferous forests. Therefore, developing strategies to protect and conserve seed resources is essential to mitigate negative impacts on forest resources.