Dr.Sci.Biol. Arefjev Y.F.

Voronezh State Academy of Forestry Engineering, Russia

ECOLOGICAL-GENETIC ASPECT OF SUPPRESSION OF THE PATHOGENIC FUNGI POPULATIONS IN FOREST ECOSYSTEMS

Introduction

The urgency of the given work is defined by necessary to radical restriction the application of fungicides, and selective trees cutting of the infected and died trees for protection of plantings against pathogenic fungi. The purpose of these researches is to prove efficiency of the ecological-genetic approach in radical preliminary protection of forest plants against pathogenic fungi. It was established that survival rate of the wildlings dropped with reduction gap size in forests. On the basis of results of long-term researches in oak and pine forests of Central Russian forest-steppe preventive measures on restriction of injuriousness of Oak Powdery Mildew and a Annosus Root Rot are offered.

Materials and methods

The research was conducted in oak and pine forests of the Central Russian forest-steppe and in forest cultures of educational-experiences forest enterprise of Voronezh State Academy of Forestry Engineering. Oak stands (age of 65 years) except an oak (Quercus robur) included an ash (Fraxinus excelsior) – 20-50 %. Pine stands (age of 35-40 years) except a pine (Pinus sylvestris) included an oak (Q. robur) – 20-50 %. Mixed forest cultures included pine (30-50 %), oak (30-50 %), birch (Betulae pendulae).

Response of Erisiphe alphitoides Griff & Maubl and Heterobasidion annosum L. populations on isolation was studied in an mixed oak-pine and pine-oak-birch forest. Quantitativ wildlings were estimated on 5 mark scale (Table 1).

Table 1. Estimation of wildlings placing on points

Points	Average number of individuals on 1 m^2	Indexes of occurrrnce
4	> 5	Plentiful
3	3 – 5	Average
2	2 – 3	Rare
1	< 2	Individual
0	0	Absence

Viability of trees and plantings was estimated on 5 mark scale (Table 2).

Table 2. Estimation of trees and plantings viability

Points	State of tree health (on a crone and trunk condition), %	Indexes of viability
4	100	Total
3	> 50, ср. 75	Heavy
2	10 – 50, ср. 30	Moderate
1	< 10, ср. 5	Llight
0	0	Zero

The basic test test object was the representative of an Ascomycota the Erisiphe alphitoides Griffon & Maublanc, infecting oak with powdery mildew. The additional test object was – representative of a Basidiomycota the Heterobasidion annosum L., infecting pine with infecting pine.

Development illness rate was defined under the following formula:

,

where

D – disease development, %; N – total of the considered plants; B – the highest point on the accepted scale; n – number of plants of a certain point; b – a certain point.

Statistical analyses

Quantitative data examined by the one-way analysis of variance. Development of Powdery mildew mycelium on the oak leaves was analyzed by means of χ². The significance level used was P 0,05, unless otherwise mentioned. The minimum necessary number (n) of concrete estimations was defined under the formula:

_,

where

s_{x %} – Variation factor, t – Criterion of Stjudents, k – accuracy of experience.

Результаты исследований и их анализ

It was established that survival rate of the wildlings dropped with reduction gap size in forests. With respect to wildlings survival and technologies of forest cultures creation the size of the open areas equal ≈ 0,25 hectare is optimum.

Response of wildling on ecological isolation occurs through distinctions in development of Oak Powdery Mildew (Table 3).

Table 3. Development of the Powdery mildew on oak in the conditions of opened and ecologically isolated oak plantings

Conditions of oak growth	Development of the Powdery mildew, % D ±	Variability of an diseases development index, V %
Open sites of oak plantings	78,3±4,7	21,4
Ecologically isolated sites of oak plantings	16,7±2,3	8,2

As appears from the table 4, ecological isolation of sites of oak plantings by a pine, ash and birch-tree on sites ≈ 0,25 hectares causes decrease in pathogen development on the average in 4,7 times. Key parametres of generative developments the E. alphitoides in the conditions of isolation and open plantings of an oak are presented in table 4.

Table 4. Key parametres of generative organs of the E. alphitoides in the conditions of isolation and open plantings of an oak

Conditions of oak growth	Frequency of fruit bodies placing, n/cm^2	Average diameter of a fruit body, µm	Average length of conidien, µm	Average width of conidien, µm
Free infection	64,3 ± 3,2	99,5 ± 5,3	32,7 ± 2,9	18,1 ± 0,9
Reproductive isolation	8,7 ± 0,6	74,4 ± 3,1	24,8 ± 1,6	13,7 ± 0,8

As appears from the table 5, average values of key parametres of generative organs of E. alphitoides by reproductive isolation is much less, than by free infection. This fact testifies to easing of pathogen subpopulations in the conditions of reproductive isolation on rather small spaces. It is effect of inbreeding depression. In this aspect, the analysis of development of forest cultures in the forest cultures of the Voronezh State Academy of Foresry Engineering is of interest.

In second half of 20-century, the representative of basidiomycetes (H. annosum) has intensively extended in pine cultures of Central Russian forest-steppe. It was a great epiphytotic. Constant cutting down of the sick and died trees upset the infected off H. annosum the pine cultures even more. On the cut down sites of pine plantings there was a high infectious background of the pathogen. It creates the big threat for the subsequent pine cultures. With a view of overcoming of this threat in 1936 on the area of Voronezh State Academy of Foresry Engineering, infected of pathogen, the mixed wood cultures in so-called ”chess order” have been created. Since 1992 phytopathologic researches in these mixed cultures and surrounding pure plantings of a pineare regularly conducted. The short characteristic of investigated mixed forest culture is presented in table 5.

Table 5. The characteristic of investigated forest culture

Growth conditions	Sandy dry soil
Plantings surrounding object	Сосновые насаждения с высоким инфекционным фоном патогена H. annosum
Structure of plantings	In total 27 rectangular platforms have been put. The size of each platform was 40 × 50 m (0,2 hectares). Pine platforms were adjoined directly by oak platforms. Oak platforms were adjoined directly by pine and birch platforms. Placing of trees in platforms was linear, uniform. The sizes of row-spacings of 2 m, in rows - 0,5 m.
The characteristic of plantings during the investigations	Pine had bonitet I, completeness 0,7; birch had bonitet I, completeness 0,6; oak had bonitet III, completeness 0,6.
Economic actions	Intermediate cuttings down were carried out regularly according to the ten year plans

At inspections, in the mixed pine-oak-birch plantings it was not revealed symptoms of H. annosum development, in oak subpopulations E. alphitoides has been developed almost slightly. The surrounding pure plantings of a pine and oak were strongly damaged.

Conclusions

1. Ecological isolation of forest species on rather small areas of causes effect of inbreeding depressions in subpopulations of pathogenic fungi.

2. Ecological barriers as ecosystem membranes in the conditions of Central Russian forest-steppe are effective at width of 200-250 m.

3. The problem of the future researches consists in, that for other conditions to optimise width of ecosystem membranes.