THE STATE OF THE FEMALE GENERATIVE SPHERE OF SCOTS PINE IN THE ACTIVE FOCUS OF THE ROOT FUNGUS (Heterobasidion annosum (Fr.) Bref.)

Abstract

Evaluation of the manifestation of Scots pine trees reaction to the weakening effect of Heterobasidion annosum (Fr.) Bref. is relevant from the perspective of the potential opportunities for further natural regeneration of the forest. The main reason for the decrease in the biological stability of the pine plantation was the development of the root sponge focus. Over the three-year period 2017-2019 the weighted average tree health category in the sample area increased from 2.21 to 2.52. The morphometric parameters of cones turned out to be more stable in the female generative sphere. Greater variability was noted for full-grain seed yield and the number of sterile apex scales. Relatively high preservation of seed ovules was found in the first and second vegetative periods of development within the boundaries of average values. For trees of different status categories during the whole period of observations it was 70.60-81.77 and 79.07-88.35% respectively, which indicated sufficient quality of pollination and marked compatibility of male and female genotypes against the background of reduced viability of mother trees. Embryo survival in the experiment reached 63.44-81.48%. The sensitivity of the generative sphere of Scots pine to the stress caused by the development of the disease has been proved. A significant decrease in the average length and diameter of mature cones and a relative increase in female reproduction rates were confirmed with the weakening and dying out of pine trees infected with root sponge. The possibility of identifying separate periods of preservation of ovules during gametophytic and embryonic cycles and the annual regularity of seed production allow us to recommend Scots pine for monitoring the state of the female generative sphere and assess the potential of the species to survive the action of aggressive stressors, such as Heterobasidion annosum (Fr.) Bref.