Search

The tree pathogenic fungi Heterobasidion annosum s.s. and Heterobasidion parviporum cause root and butt rot in Norway spruce (Picea abies) and produce serious economic losses to the forest sector in Europe. We experimentally studied inter- and intraspecific differences between H. parviporum and H. annosum s.s. in the way they infect stumps and spread into neighbouring trees. Eleven H. parviporum and nine H. annosum s.s. isolates were artificially inoculated on stumps of two spruce stands after first thinning. After 15 years, the same isolates were reisolated from neighbouring trees. Heterobasidion parviporum spread more frequently from the inoculated stumps to the neighbouring trees than H. annosum s.s. The surroundings of H. annosum s.s. stumps that did not spread were often colonized by H. parviporum. Heterobasidion annosum s.s. spread was restricted mainly to the areas of the plot where no other Heterobasidion genotypes had been inoculated. In such cases, H. annosum s.s. tended to develop into bigger genets than H. parviporum. The probability of stump-to-tree spread of H. parviporum depended on the diameter of the stumps, suggesting that H. parviporum spread may relate to the presence of heartwood. Both H. parviporum and H. annosum s.s. proved to be strong pathogens on Norway spruce; however, when competing for the same trees, H. parviporum seemed capable of excluding H. annosum s.s. from the stand.

Stump protection using chemical or biological agents is the main control measure against root and butt rot caused by Heterobasidion annosum s.l. in northern and temperate conifer forests. Long-term effects of urea treatment of stumps are poorly known and here we describe a 15-year study of urea treatment on the rot incidence on Norway spruce (Picea abies). We also tested the effect of urea protection on tree growth and on the resistance of stands against strong winds. Four treatments were made in two replications in two first-rotation P. abies stands in southern Sweden; after first-thinning stumps were (i) treated with urea 35% (w/v), (ii) artificially infected with H. annosum conidia, (iii) half urea treated and half artificially conidia infected, (iv) untreated, therefore naturally infected. After 15 years, the trees were sampled at 20 cm above ground using an increment borer and observed for presence of rot and, following incubation, presence of H. annosum conidia. Tree growth was calculated by measuring the diameter before and after the treatment. Urea treated plots showed the lowest incidence of rot (3%) as well as of H. annosum incidence (0%). Conidia treatment showed the highest incidence of rot (68%), its incidence was higher than that observed in natural infection treatment (43%), but did not differ from that of the 50% conidia treatment (47%). On about 30% of the rotted trees we observed conspicuous H. annosum fruiting. We did not observe growth reduction associated with tree rot. H. annosum was the only fungus observed associated with rotted trees which suggest that it was responsible for most of the rot observed in the investigated plots. Urea treated plots showed the lowest incidence of windthrown trees, and 59% of the windthrown tree incidence among the plots was explained by the incidence of H. annosum. Urea can be regarded as a reliable long-term protection method against root and butt rot of Norway spruce.

The effects of clear-cutting and thinning as well as heartwood and sapwood moisture content on spore infection by Heterobasidion annosum (Fr.) Bref. were investigated in summer cuttings in southern and central Sweden. At five sites, 20-100 stumps in clear-cut, thinned, and precommercially thinned stands of Norway spruce (Picea abies (L.) Karst.) were created and left for natural spore infection. An additional 20 stumps per stump type and site were artificially inoculated with conidiospores of H. annosum. The probability of natural infection was 0.73 and 0.53 for stumps in thinned and clear-cut stands, respectively. Almost all (95%) of the artificially inoculated stumps in thinned and clear-cut stands became colonized, and no differences due to stump type were found. The probability of infection of stumps in precommercially thinned stands was lower than for the other stump types of both naturally and artificially inoculated stumps. The proportion of colonized sapwood was reduced with increasing moisture content. Stump colonization seemed unaffected by temperature, even though stump temperatures exceeded 40°C for 2 h at one site.

Les auteurs ont compare la croissance de paires d'epiceas communs (Picea abies (L.) Karst.) sains et infectes par Heterobasidion annosum (Fr.) Bref. dans deux peuplements installes sur des terres qui avaient deja ete cultivees dans le sud de la Suede. La croissance en diametre a hauteur de poitrine, a 3 et 5 m, ainsi que la croissance en hauteur et en volume, ont ete reconstruites dans les deux peuplements sur respectivement 12 et 20 ans. Aucune reduction de croissance n'a ete detectee dans le premier peuplement ou le champignon etait present depuis 8 ans. Dans le deuxieme peuplement, ou H. annosum a probablement ete introduit lors de la premiere eclaircie il y a 17 ans, les arbres infectes avaient perdu 9,9 mm (5%) de croissance en diametre a hauteur de poitrine et 10% de croissance en volume pendant la periode de 20 ans. L'ajustement de courbes polynomiales orthogonales indiquait que les reductions de croissance augmentaient avec le temps chez les arbres infectes. Au cours des 5 dernieres annees, les pertes de croissance en diametre a hauteur de poitrine atteignaient en moyenne 20% tandis que la croissance en hauteur, le diametre a 5 m et le volume avaient respectivement subi une reduction de 25, 20 et 23%. L'impact de l'etendue de la carie sur la croissance des arbres a ete investigue mais aucune difference significative n'a ete observee. La position des arbres sains dans le peuplement a ete cartographiee et l'effet potentiellement different, selon que les arbres voisins etaient sains ou infectes, a ete investigue. L'etat de sante des arbres voisins ne semblait pas avoir d'effet sur la croissance des arbres sains.

The long-term effect of butt rot on the diameter increment of Norway spruce, Picea abies Karst., was studied by analysing data collected by the Swedish National Forest Inventory. The 15 698 Norway spruce trees were classified as healthy or infected based on bore cores taken at breast height. Healthy and infected trees, similar in terms of age, diameter at breast height in 1954, increment from 1954 to 1963, and from sites of the same productivity class in the same region were paired. Owing to restrictive criteria used, only 329 pairs were chosen for further analysis. These trees were analysed groupwise as well as pairwise. In the period 1954–1958, trees classified as infected grew faster than the healthy controls; however, within 5 years the relationship had reversed. The degree to which the growth of infected trees was suppressed increased with time, and was 8.9% and 8.2% respectively during the last two 5 year periods. Differences in growth between healthy and infected trees within pairs were highly significant. The diameter growth of the infected trees was reduced by an average of 1.4 mm, or 9.4%, during the last 5 years, corresponding to a 9.6% reduction in the basal area growth.