Variation in mating competence and random amplified polymorphic DNA in Laccaria bicolor (Agaricales) associated with three tree host species

We examined the population genetic structure of the ectomycorrhizal fungus Laccaria bicolor (Maire) Orton using single spore homokaryotic cultures from 33 basidiomes collected in northern Minnesota in association with red pine (Pinus resinosa Ait.), jack pine (Pinus banksiana Lamb.), and trembling aspen (Populus tremuloides Michx.) of three age-classes (0–20 years, 21–40 years, and \u3e 41 years). Mating competence between cultures of isolates, as determined by the presence of clamp connections, revealed the presence of two subpopulations that were not freely interbreeding, one composed of 29 dikaryons, the other of 3 dikaryons. Phenetic cluster analysis using random amplified polymorphic DNA markers did not reveal differentiation between these subpopulations. Clustering failed to reveal genetically distinct groups based on incompatibility group, tree host species, or geographic origin of isolates. Key words: heterogenic incompatibility, RAPD, population genetics

In vitro ectomycorrhiza formation by monokaryotic and dikaryotic isolates of Pisolithus microcarpus in Eucalyptus grandis Formação de ectomicorrizas in vitro por isolados monocarióticos e dicarióticos de Pisolithus microcarpus em Eucalyptus grandis

The formation of ectomycorrhizas by monokaryotic and dikaryotic isolates of Pisolithus microcarpus (Cooke & Massee) G. Cunn. in Eucalyptus grandis W. Hill ex Maid. was studied by in vitro synthesis in Petri dishes. The formation of ectomycorrhizas was observed for all strains tested. Ectomycorrhizas formed by the monokaryotic strains presented a sheath of hyphae around the roots and a Hartig net limited to the epidermis layer, typical of the angiosperm ectomycorrhizas. Colonization rates, a measure of the number of ectomycorrhizas in relation to the total number of lateral root tips, varied from 23 to 62%. Some monokaryotic strains stimulated the formation of lateral roots, promoting increases of up to 109% above the control. The presence of some of the isolates in the in vitro synthesis medium stimulated the production of thicker lateral root tips. The dimensions of the lateral roots tips and ectomycorrhizas varied from one isolate to the next, indicating a variation in their capacity to provoke morphological changes in the host plant roots. The dikaryotic strain M5M11 presented higher values for lateral root yield, number of ectomycorrhizas, and colonization percentage than the corresponding monokaryotic strains, M5 and M11. This indicated the possibility of selecting compatible performing monokaryotic isolates for the yield of superior dikaryotic strains. The set of monokaryotic strains tested varied greatly in their ability to colonize E. grandis roots and cause secondary metabolism-related morphological changes in roots, providing a wealth of model systems for the study of genetic, physiological, and morphogenetic processes involved in Pisolithus-Eucalyptus ectomycorrhiza formation.<br>A formação de ectomicorrizas por isolados monocarióticos e dicarióticos de Pisolithus microcarpus (Cooke & Massee) G. Cunn. em Eucalyptus grandis W. Hill ex Maid. foi estudada usando-se o método de síntese in vitro em placas de Petri. A formação de ectomicorrizas foi observada para todas as linhagens testadas. Ectomicorrizas formadas pelas linhagens monocarióticas apresentaram manto de hifas circundando a raiz e rede de Hartig limitada à camada da epiderme, típica de ectomicorrizas de angiospermas. As percentagens de colonização, correspondendo ao número de ectomicorrizas em relação ao total de raízes laterais curtas, variaram de 23 a 62%. Algumas linhagens monocarióticas estimularam a formação de raízes laterais curtas, promovendo aumentos médios de 109% em comparação com o controle. A presença de alguns dos isolados no meio de síntese in vitro estimulou a produção de raízes laterais de maior diâmetro. As dimensões das raízes laterais e das ectomicorrizas variaram com o isolado inoculado, indicando variações dentro da população testada na capacidade de provocar mudanças morfológicas nas raízes da planta hospedeira. O dicário M5M11 apresentou maiores valores para produção de raízes laterais, número de ectomicorrizas e percentagem de colonização em comparação com os isolados monocarióticos correspondentes, M5 e M11, indicando a possibilidade de se selecionar isolados compatíveis eficientes para a produção de dicários superiores. O conjunto de isolados monocarióticos testado variou quanto à capacidade de colonização das raízes de E. grandis e de causar mudanças morfológicas nas raízes relacionadas ao metabolismo secundário, constituindo sistema-modelo para o estudo da genética, da fisiologia e dos processos morfogenéticos envolvidos na formação de ectomicorriza entre Pisolithus e Eucalyptus

Pines

Pinus is the most important genus within the Family Pinaceae and also within the gymnosperms by the number of species (109 species recognized by Farjon 2001) and by its contribution to forest ecosystems. All pine species are evergreen trees or shrubs. They are widely distributed in the northern hemisphere, from tropical areas to northern areas in America and Eurasia. Their natural range reaches the equator only in Southeast Asia. In Africa, natural occurrences are confined to the Mediterranean basin. Pines grow at various elevations from sea level (not usual in tropical areas) to highlands. Two main regions of diversity are recorded, the most important one in Central America (43 species found in Mexico) and a secondary one in China. Some species have a very wide natural range (e.g., P. ponderosa, P. sylvestris). Pines are adapted to a wide range of ecological conditions: from tropical (e.g., P. merkusii, P. kesiya, P. tropicalis), temperate (e.g., P. pungens, P. thunbergii), and subalpine (e.g., P. albicaulis, P. cembra) to boreal (e.g., P. pumila) climates (Richardson and Rundel 1998, Burdon 2002). They can grow in quite pure stands or in mixed forest with other conifers or broadleaved trees. Some species are especially adapted to forest fires, e.g., P. banksiana, in which fire is virtually essential for cone opening and seed dispersal. They can grow in arid conditions, on alluvial plain soils, on sandy soils, on rocky soils, or on marsh soils. Trees of some species can have a very long life as in P. longaeva (more than 3,000 years)