DEVELOPMENT OF EXTERNAL HYPHAE BY DIFFERENT ISOLATES OF MYCORRHIZAL GLOMUS SPP. IN RELATION TO ROOT COLONIZATION AND GROWTH OF TROYER CITRANGE

Abstract

SUMMARYThe hypothesis was tested that the amount of external hyphae of a vesicular-arbuscular mycorrhizal (VAM) fungus extending from roots out into soil is not always proportional to the extent of colonization of the root cortex. Growth enhancement and amount of external hyphae were compared for eight isolates of five Glomus spp. that differed in their geographic origin and capacity to enhance growth of Troyer citrange, but were similar in their capacity to extensively colonize Troyer citrange roots. In general, isolates from California increased growth in a P-deficient (9-8 mg kg"^) California soil more than did non-native isolates from Florida soils. The difference between the capacity of California and Florida isolates to enhance growth was not a function of the degree to which they colonized the roots since all had colonized over 95 % of the root length by the time of harvest. Differences in growth enhancement did appear, however, to be a function of the amount of external hyphae that had developed as estimated by the weight of soil they had bound into aggregates. This study suggests that isolates of VA mycorrhizal fungi may differ in their capacity to develop an external hyphal system independent of their capacity to colonize the root cortex, and that we cannot assume that high levels of colonization will necessarily nnean the fungus has also developed the mycelium in the soil necessary to transport nutrients responsible for plant growth enhancement.

Desempenho de fungos micorrízicos arbusculares na produção de mudas de maracujazeiro-amarelo, em diferentes substratos

“…Neste trabalho, esse efeito inibidor não foi observado para G. clarum e G. etunicatum, que apresentaram praticamente a mesma porcentagem de colonização radicular nos dois substratos (Quadro 1). Nesse caso, a colonização micorrízica deve ter sido controlada por fatores genéticos que podem ser originários da planta e/ou do isolado de fungo empregado (GRAHAM et al, 1982).…”

Absorção e translocação de manganês por plantas de soja micorrizadas, sob doses crescentes deste nutriente

“…A espécie de FMA com maior percentagem de colonização foi G. margarita, cerca de 8 %, diferindo significativamente das demais (P < 0,01), que, por sua vez não diferiram entre si e apresentaram colonização média de 4,5 %. Verificase que nem sempre existe relação direta entre a percentagem de colonização radicular e a eficiência micorrízica (Graham et al, 1982), conforme foi demonstrado para a produção de biomassa (Figura 1a e 1c) Com relação ao conteúdo, não houve efeito da micorrização. O P geralmente tem seu teor aumentado nas plantas micorrizadas, mas esse efeito não foi constatado nesse experimento.…”

Interactions between mycophagous nematodes, mycorrhizal and other soil fungi

“…Sanders & Tinker (1973) found that this may lead to an increase of the inflow of phosphorus to the roots which was subsequently found to be proportional to the amount of external mycelium (Sanders et al 1977). Taking the matter further, Graham, Linderman & Menge (1982) suggested that lack of growth enhancement could reflect limited production of external hyphae rather than limited root colonization.…”

“…The correlation between the length of active external hyphae and root colonization was significant whereas that between the length of total external hyphae and root colonization was not. Graham, Linderman & Menge (1982) found that internal root colonization could exceed 95% without a proportional development of external mycelium and attributed this to restrictive soil factors.…”

“…Quantification of the external mycelium is often difficult because this involves its extraction from soil and separation from debris and other non-mycorrhizal mycelia (see Sanders et al 1977;Graham, Linderman & Menge 1982;Sylvia 1988 (Phillips & Hayman 1970;Giovannetti & Mosse 1980). Although frequently used as a measure of the extent of VAM infection, percentage infection should be treated with caution since it is not directly related to fungal biomass (Kucey & Paul 1982).…”