Gene R. Safir

Effects of ferulic acid onGlomus fasciculatum and associated effects on phosphorus uptake and growth of asparagus (Asparagus officinalis L.)

The effect of ferulic acid, an allelochemical produced by asparagus, on hyphal elongation and colonization of asparagus byG. fasciculatum was studied. Spore germination in vitro was not affected, but hyphal elongation decreased significantly with increasing ferulic acid concentration. In the greenhouse, mycorrhizal colonization of roots and growth of mycorrhizal asparagus decreased significantly with increasing ferulic acid concentration, while growth of nonmycorrhizal plants was not affected by ferulic acid. Although plant tissue phosphorus levels were not affected by ferulic acid or mycorrhizal status, ferulic acid inhibition of hyphal elongation in vitro and fungal root colonization in vivo suggests that production of ferulic acid by asparagus reduces the symbiotic effectiveness of the fungus and subsequently reduces plant growth.

The Potential Impact of Agricultural Management and Climate Change on Soil Organic Carbon of the North Central Region of the United States

Soil organic carbon (SOC) represents a significant pool of carbon within the biosphere. Climatic shifts in temperature and precipitation have a major influence on the decomposition and amount of SOC stored within an ecosystem. We have linked net primary production algorithms, which include the impact of enhanced atmospheric CO2 on plant growth, to the Soil Organic Carbon Resources And Transformations in EcoSystems (SOCRATES) model to develop a SOC map for the North Central Region of the United States between the years 1850 and 2100 in response to agricultural activity and climate conditions generated by the CSIRO Mk2 Global Circulation Model (GCM) and based on the Intergovernmental Panel for Climate Change (IPCC) IS92a emission scenario. We estimate that the current day (1990) stocks of SOC in the top 10 cm of the North Central Region to be 4692 Mt, and 8090 Mt in the top 20 cm of soil. This is 19% lower than the pre-settlement steady state value predicted by the SOCRATES model. By the year 2100, with temperature and precipitation increasing across the North Central Region by an average of 3.9°C and 8.1 cm, respectively, SOCRATES predicts SOC stores of the North Central Region to decline by 11.5 and 2% (in relation to 1990 values) for conventional and conservation tillage scenarios, respectively.

Plant Growth and Arbuscular Mycorrhizal Fungal Colonization Affected by Exogenously Applied Phenolic Compounds

The effects of the application of 0.25 or 1.0 mM p-coumaric acid, p-hydroxybenzoic acid, or quercetin on growth and colonization of clover (Trifolium repens L. cv. Ladino) and sorghum (Sorghum bicolor L.) roots by the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith were studied. In general, soil application of these compounds at 0.25 mM stimulated plant growth and AM colonization, whereas at 1.0 mM these phenolics were inhibitory to both growth and colonization. Such effects were noted for both clover and sorghum. The results suggest that phenolic compounds, commonly found in many soils, influence the establishment of AM symbioses, and these compounds may have immediate effects on host growth. Studies involving these chemicals and their effects on mycorrhizal associations may provide new insights concerning the importance of the AM symbiosis in agricultural systems. These phenolic compounds may be used as potential soil amendments to enhance AM fungal colonization, and thus, exploit indigenous populations of AM fungi.

Postharvest suppression of potato dry rot (fusarium sambucinum) in prenuclear minitubers by arbuscular mycorrhizal fungal inoculum

Arbuscular mycorrhizae (AM) have been shown to increase plant resistance to root-rotting pathogens. This study was conducted to determine whether a commercial peat-based medium containing the AM fungusGlomus intraradix (Schenck & Smith) could influence postharvest progression of tuber dry rot in prenuclear minitubers of potato (Solanum tuberosum). Minitubers grown in this medium had significantly less tuber dry rot (20–90% reduction) when later inoculated with the dry rot fungusFusarium sambucinum relative to minitubers grown in an identical peat-based medium without the AM fungus. This disease suppression was also demonstrated in a high-input commercial greenhouse, and occurred despite only trace levels of AM colonization of the parent plants, and with no evidence of enhanced plant phosphorus nutrition or differences in minituber mineral content. These results suggest that the AM fungal inoculum has potential for use in suppression of tuber dry rot of potato.

Effect of phenolic compounds on asparagus mycorrhiza

Asparagus (Aspurugus o@iic~nulis L.) produces several cinnamic acid derivatives known to be allelochemicals (Young. 1984: Young and Chou. 1985; Hartung ef ul.. 1990). It has been suggested that these allelochemicals may either be directly involved in asparagus decline by affecting plant vigor (Young. 1984; Young and Chou, 198s) or indirectly through chemical-mediated changes in the microbial community (iiartung and Stephens. lYX3). which in turn aflcct plant growth. Wacker CI cl/. (199Ob) have shown that ferulic acid, an allclochcmical found in asparagus roots, decreases root colonization by vesicular arbuscular mycorrhirae (VAM) and the growth ol’ mycorrhiznl asparagus. Wackcr (*I ul. (IYYOc) I‘ound a change in the composition of the VAM fungal community in asparagus fields with increasing age up IO 20 yr. Root colonization by VAM fungi and spore density in the soil also c Wackcr cr ul.. IYYOa) plant health may be adversely alTected if the nutritional contribution to asparagus by native VAM fungal species decreases with plant age. Because available P decreased with increasing number of years cropped in asparagus, soil P may not be the factor responsible for the reduction in root colonization by VAM fungi and the change in the composition of the VAM fungal community observed by Wacker (1990~). Accumulation of phcnolic allclochcmicals produced by asparagus could be a mechanism by which asparagus monocropping alters the species composition of the VAM fungal community. WC report the etfrcts of’ fcrulic. catTcic and methylencdioxycinnamic (MDC) acids and also those of soil extracts from an asparagus field soil and an adjacent non-cultivated soil on VAM formation and growth of asparagus. To examine the etTccts of three phenolic acids on VAM formation in asparagus. asparagus seeds (cv. “Mary Washington”) were surface-sterilized (Elmer and Stephens, 1988). germinated and sown into plastic cell-pack units (2 x 2) with 8Og of washed sand per cell. A 9.0cm dia Petri dish base was used under each J-cell unit to avoid chemical cross-contamination. A VAM fungus resembling G/r~nlus/ct.vcicu/urunr (Thaxtcr) Gerd. and Trappc emend. Walker and Koske was multiplied in pot cultures with sorghum (.Sorlral seedlings. Alier transplanting, plants were watcrcd weekly with IO ml of 0.1 strength

VA-mycorrhizae and mycorrhiza stimulating isoflavonoid compounds reduce plant herbicide injury

Imazaquin, imazethapyr and pendimethalin showed high toxicity to sorghum plants grown in a greenhouse soil mix. However, mycorrhizal sorghum plants were less affected by herbicide toxicity than non-mycorrhizal ones, at low to moderate herbicide concentrations. VAM herbicide safening effects were more evident on imazaquin-treated plants, than for those treated with the other two herbicides. Applications of imazethapyr and pendimethalin at the two highest concentrations, but not imazaquin, reduced VAM colonization rates in sorghum. Applications of the VAM stimulating isoflavonoids, biochanin A and formononetin, at 5 ppm solutions to a field soil sample containing toxic levels of imazaquin (13 ppb) and indigenous VAM fungi, reduced herbicide-induced injury in corn and sorghum under growth chamber conditions. The benefits of isoflavonoids were reduced when additional propagules of Glomus intraradix were added into field-soil samples, and were eliminated when VAM fungi were inactivated by autoclaving. This indicates that herbicide safening effects of biochanin A, and formononetin are VAM-mediated and also suggests the potential use of these isoflavonoids as herbicide safeners.

Expression of isoenzymes altered by both Glomus intraradices colonization and formononetin application in corn (Zea mays L.) roots

Abstract We searched for and found alterations in isoenzymes that were characteristic of the establishment of the Zea mays-Glomus intraradices symbiosis. Isoenzyme activities for NAD-dependent malate dehydrogenase, esterase, and total peroxidase were examined in corn (Zea mays L. cv. Great Lakes-hybrid 582) roots or mycorrhizas during the first 3 weeks of growth. Soil was either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus intraradices Schenck and Smith or was left uninoculated. Plants were also grown in the presence or absence of formononetin. At 2 weeks of growth, there was an 80% relative increase in colonization in plants that received both formononetin and Glomus as compared to plants inoculated with the mycorrhizal fungus alone. One of the malate dehydrogenase isozyme was differentially expressed in VAM roots at 3 weeks. The activity of this isozyme was further enhanced in the presence of formononetin. At 2 and 3 weeks, four esterase isozymes showed higher activity in mycorrhizas than in non-mycorrhizal roots. Formononetin enhanced the activities of these four esterases following fungal colonization. At 2 weeks of growth, mycorrhizal roots had the highest total peroxidase activity compared to formononetin-treated or control roots. In the presence of formononetin, peroxidase activity was reduced below the amounts of untreated controls. According to these results, the differential expression of certain malate dehydrogenase and esterase isozymes, and the change in total peroxidase activity indicate very early physiological alterations in roots during the establishment of a VAM symbiosis. Furthermore, by examining the shifts in isoenzyme activity, the effect of exogenously-applied formononetin on root colonization could be detected at the earliest stages of the Zea-Glomus symbiosis.

Reduction of transpiration from wheat caused by germinating conidia of Erysiphe graminis f. sp. tritici

Abstract Detached wheat leaves, 1 to 6 h after inoculation with viable conidia of Erysiphe graminis f. sp. trici , took up 25 and 20% less 32 P and 35 S, respectively, than did non-inoculated leaves. The transpiration rate of inoculated leaves was 25% less than non-inoculated leaves. Reduced transpiration occurred with both compatible and incompatible parasite/host genotypes. Relative diffusion resistances were higher for inoculated plants than for non-inoculated plants. U.V.-killed spores, chalk dust, carborundum, Puccinia recondita uredospores, and Helminthosporium victoriae conidia heavily dusted onto leaves did not reduce 32 P uptake. Under conditions of these experiments, the uredospores of P. recondita and the conidia of H. victoriae did not germinate.

Growth of asparagus in a commercial peat mix containing vesicular-arbuscular mycorrhizal (VAM) fungi and the effects of applied phosphorus

Commercially prepared, peat-based mycorrhizal inocula were studied for growth effects on asparagus grown under greenhouse and field (fumigated) conditions. The fungi tested were Glomus clarum (GC), G. intraradix (GI), G. monosporum (GM), G. versifomre (GVR) and G. vesiculiferum (GVS). GI significantly increased plant dry weight in the greenhouse and the field. Survival of mycorrhizal tissue-cultured transplants after 14 months in the field was increased by twofold over the control. In a second experiment asparagus was grown from seed in the greenhouse in peat inoculated with a G. fasciculatum-like fungus (GF), GI and GVR with applied P levels of 0, 50, 100 and 150 ppm and harvested after 13 and 17 weeks. Total dry weights of GI and GVR plants were significantly increased over those of the control and GF. Dry weight in this second experiment was positively correlated with root colonization. Root colonization at week 13 was slightly reduced with increasing levels of applied P, but not at week 17. The data suggest that the increased growth of mycorrhizal plants was not related to an increase in tissue P concentration, since there was no growth response to applied P and tissue P concentration in the mycorrhizal plants was lower than in the non-mycorrhizal plants.

Persistence of Isoflavones Formononetin and Biochanin A in Soil and Their Effects on Soil Microbe Populations

Persistence of the isoflavones formononetin and biochanin A in soil was investigated by HPLC analysis. Biochanin A disappeared more rapidly than formononetin in nonsterile soil. In soil planted with corn seedlings, the disappearance was dramamtic for both isoflavones. The results suggested that soil microbial populations were able to metabolize these isoflavones. The response of several microbial populations to isoflavone amendments was measured in soil samples obtained from Michigan potato fields. Results suggested that the isoflavones formononetin and biochanin A were able to stimulate the growth of soil microorganisms.