Susceptibility and effectiveness of vesicular-arbuscular mycorrhizae in wheat cultivars under different growing conditions

Summary Wheat cultivars assumed to be non-susceptible to vesicular-arbuscular (VA) mycorrhizae became colonized, and this effect persisted under different growth conditions. Colonization of all cultivars was similar regardless of the amount of inoculum and the time interval of inoculation. Different plant growth temperatures and the support given by the culture media, inoculation with different endophytes, and inoculation with sterilized and unsterilized spores affected VA colonization levels, although the level of colonization reached in cv. Champlein was similar to that reached in cv. 7-Cerros under each condition. VA mycorrhizal colonization was also affected by different plant growth conditions. After VA reinoculation, the plant dry weight of Castan and 7-Cerros increased, but not Negrillo and Champlein cultivars. VA mycorrhizae increased the shoot dry weight of 7-Cerros only, but not of Champlein, when grown at 35/24°C, and had no effect on the dry weight of either cultivar grown at 18/12°C and 42/24°C. Inoculation with Glomus mosseae increased the dry weight of the cultivars more than inoculation with G. fasciculatum or G. agregatum. The effect on the plant dry weight was greater in plants grown in soil than in sand/vermiculite pots. Inoculation with sterilized and unsterilized spores of G. mosseae, either in soil pots or in sand/vermiculite tubes, did not increase the plant dry weight. Our results indicate that there was no close relationship between the level of root colonization and the effect on plant growth. The effects of accompanying microorganisms in the VA inoculum on VA mycorrhizal symbiosis are discussed.     

Shoot‐produced,light‐dependent factors are partially involved in the expression of the arbuscular mycorrhizal (AM) status of AM host and non‐host plants

Arbuscular mycorrhizal (AM) colonization and hyphal attachment to the roots of a host plant, bean, and a non‐host plant, lupin, were compared when grown either with light or in the dark with the AM fungus Glomus mosseae. When grown with light, bean roots were heavily colonized whereas lupin roots showed no signs of colonization, no formation of appressoria and only scarce hyphal attachment to the roots. In contrast to roots of plants grown with light, to living roots of beans and lupins grown in the dark many hyphae were attached and appressoria were formed. The role of shoot produced, light‐dependent factors in the expression of the AM mycotrophic status of AM host and non‐host plants is discussed.<?show $6#>     

The bioprotective effect of AM root colonization against the soil-borne fungal pathogen Gaeumannomyces graminis var. tritici in barley depends on the barley variety

The systemic effect of root colonization by the arbuscular mycorrhizal fungus (AMF) Glomus mosseae on the susceptibility of old and modern barley varieties to the soil-borne fungal pathogen Gaeumannomyces graminis var. tritici (Ggt) was studied in a split-root system. Plants were precolonized on one side of the split-root system with the AMF and thereafter the other side of the split-root system was inoculated with the pathogen. At the end of the experiment the level of bioprotection was estimated by quantifying lesioned roots and the determination of the root fresh weight. AM root colonization provided protection in some of the barley genotypes tested, but not in others. This protective effect seemed to vary in the oldest and the most modern barley variety tested.     

Effect of Glomus mosseae on concentrations of rosmarinic and caffeic acids and essential oil compounds in basil inoculated with Fusarium oxysporum f.sp. basilici

This study investigated the potential of the arbuscular mycorrhizal (AM) fungus Glomus mosseae to protect basil (Ocimum basilicum) against Fusarium oxysporum f.sp. basilici (Fob). It was hypothesised that G. mosseae could confer a bioprotective effect against Fob as a result of increases in leaf rosmarinic (RA) and caffeic acids (CA) or essential oil concentrations. Glomus mosseae conferred a bioprotective effect against Fob by reducing plant mortality to 20% compared to 33% in non‐mycorrhizal (NM) plants. This bioprotective effect was not related to improved phosphorus (P) nutrition, as AM and NM plants treated with Fob had similar shoot P concentrations (6 and 8 mg g^?1 dry weight (DW), respectively). Both AM and NM plants treated with Fob had similar leaf and root RA and CA concentrations. Furthermore, phenolic (40–70 mg CA g^?1 DW) or essential oil concentrations (0·1–0·6 mg g^?1 DW) were not increased in plants treated with the AM fungus and Fob. Therefore, the bioprotective effect conferred by G. mosseae was not a result of increases in the phytochemicals tested in this study. However, under the AM symbiosis, basil plants treated with Fob had lower methyleugenol concentrations in their leaves (0·1 mg g^?1 DW) than NM plants treated with the pathogen (0·6 mg g^?1 DW).     

A modified procedure for staining arbuscular mycorrhizal fungi in roots

Roots were cleared by boiling in 10% KOH and rinsed several times with tap water. Thereafter roots were boiled in the staining solutions. The staining solutions consisted in different dyes (trypban blue (0.05%), anilin blue (0.05%) and acid fuchsin (0.01%)) which were dissolved in usual household vinegar (5% acetic acid). For best contrast, tryphan and anilin blue stained roots were destained with tap water, whereas acid fuchsin stained roots were destained with vinegar. All fungal structures were stained and clearly visible.     

Glycosidation of apigenin results in a loss of its activity on different growth parameters of arbuscular mycorrhizal fungi from the genus Glomus and Gigaspora

The effect of different concentrations (0.5, 2 and 8 μM) of apigenin and its glycosidated form 5,7,4′-hydroxy flavone glycoside on arbuscular mycorrhizal (AM) fungal spore germination, hyphal growth, hyphal branching, the formation of entry points and root colonization of Gigaspora. rosea, Gi. margarita, Glomus mosseae and G. intraradices was tested. The lowest apigenin concentration (0.5 μM) nearly doubled hyphal branching, the formation of entry points and root colonization of all four tested fungi, whereas higher concentrations (2 and 8 μM) nearly doubled the hyphal growth of Gi. margarita, G. mosseae and G. intraradices. In none of the treatments with the apigenin-glycoside any effect on AM fungi could be observed. Our data show that apigenin exhibits an AM fungal genus and even species activity and we provide strong evidence that glycosidation results in a loss of its activity towards AM fungi.     

The arbuscular mycorrhizal host status of plants can not be linked with the Striga seed-germination-activity of plant root exudates

Journal of Plant Diseases and Protection - Root exudates from sorghum, a Striga and arbuscular mycorrhizal fungal (AMF) host plant, and a number of Striga non-host plants which are AM host or AM...     

Germination of Fusarium oxysporum in root exudates from tomato plants challenged with different Fusarium oxysporum strains

The response of microconidia from pathogenic and non-pathogenic Fusarium oxysporum to root exudates from tomato plants inoculated with different pathogenic and non-pathogenic F. oxysporum strains was studied. Root exudates from non-inoculated tomatoes highly stimulated the microconidial germination of the two tomato pathogens, F. oxysporum f.sp. lycopersici strain Fol 007 and F. oxysporum f.sp. radicis-lycopersici strain Forl 101587. In root exudates from tomato plants challenged with the pathogen Fol 007 the microconidial germination of Fol 007 was increased, whereas in root exudates from plants challenged with Forl 101587 the microconidial germination of Fol 007 was reduced. Root exudates of tomato plants challenged with the non-pathogenic unspecific F. oxysporum strain Fo 135 and the biocontrol strain Fo 47 clearly reduced microconidial germination of the pathogenic strain Forl 101587. Moreover, the microconidial germination rate of the biocontrol strain Fo 47 was increased in the presence of root exudates of tomato plants challenged with the tomato wilt pathogen Fol 007. These results indicate that pathogenic and non-pathogenic F. oxysporum strains alter the root exudation of tomato plants differently and consequently the fungal propagation of pathogenic and non-pathogenic F. oxysporum strains in the rhizosphere is affected differently.