Histological and histochemical detection of defence responses in pine embryos challenged in vitro with Heterobasidion annosum

Abstract

Embryos of Pinus sylvestris, Pinus nigra var. maritima and Pinus contorta were inoculated in vitro with Heterobasidion annosum and the histology and histochemistry of the host response determined. Three days after challenge, intercellular penetration of hyphae through the epidermis and into the cortex of the host species had occurred. In cells close to the invading hyphae, cell walls became thickened in all three pine species. Lignification and suberization of cell walls in the cortex was detectable in P. nigra var. maritima and P. contorta, but not in P. sylvestris. Moreover, cells in the cortex of P. nigra var. maritima and P. contorta became occluded with dense deposits staining positively for phenolic and lipidic materials. Starch grains had accumulated in host cells close to sites of penetration by day 3, and levels appeared to increase by day 6, except for tissues where heavy mvasion by H. annosum had occurred. Host responses intensified between 3 and 6 days after challenge. By day 6, however, the pathogen had penetrated as far as the stele and into the developing xylem vessels. Nine days after challenge, host tissues contained abundant intra-and inter-cellular hyphae, causing severe disruption and disintegration of all tissues. The utility of such in vitro systems in studies on the resistance responses of conifers to challenge with fungal pathogens is discussed.

Soluble carbohydrates, radial growth and vigour of fertilized Norway spruce after inoculation with blue-stain fungus, Ceratocystis polonica

“…Most soluble sugars are withdrawn from or utilized around the attack-invasion site within 48 h (Cook and Hain 1987). Thus, the fungus is first confined by the consumption of essential nutrients from the entry site (Wong and Berryman 1977;Nsolomo and Woodward 1997) and only secondarily by resinosis (Raffa and Berryman 1982;Christiansen and Ericsson 1986).…”

Interactions between callus cultures of Pinus sylvestris and pine fungi with different trophic properties

“…Pathogenicity of different fungal species and growth responses of embryogenic or non‐embryogenic callus tissue was tested in the past (Hŕib et al. , see also Spanos and Woodward ), demonstrating that there is a network of growth correlations between cells, tissues and organs during organogenesis in plants, which is similar to defence systems in fully differentiated plants (Woodward ; Nsolomo and Woodward ; Glazebrook ). Tests carried out in dual cultures, therefore, not only provide the basis for the assessment of pathogenicity and the degree of risk from a pathogen, but may also enable, in some cases, selection of plant genotypes showing greater resistance to the pathogen (Nawrot‐Chorabik ).…”