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Ainhoa Martínez-Medina, Antonio Roldán, and Jose A. Pascual

phosphates and micronutrients by the plant-growth promoting and biocontrol fungus Trichoderma harzianum Rifai 1295-22 Appl. Environ. Microbiol. 65 2926 2933 Arnon, D.I. 1949 Copper enzymes in isolated chloroplasts

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Rong Zhang, Zhubing Yan, Yikun Wang, Xuesen Chen, Chengmiao Yin, and Zhiquan Mao

; Shoresh et al., 2010 ; Tucci et al., 2011 ). Trichoderma harzianum has been widely used in various agricultural systems because of its excellent biocontrol characteristics. Continuous cropping constitutes a type of stress for crop roots, which can be

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A.G. Taylor, G.E. Harman, and P.A. Nielsen

This work was partially supported by a grant from Eastman Kodak, Data on compatibility of Trichoderma harzianum with synthetic pesticides was developed by Kodak and Gustafson, Inc. and we acknowledge information provided by T. Stasz and K

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Laura L. Arriola, Mary K. Hausbeck, John Rogers, and Gene R. Safir

Commercially available biocontrol agents Trichoderma harzianum Rifai and the arbuscular mycorrhizal fungus Glomus intraradices Schenck and Smith were tested for their efficacy in controlling fusarium root rot in potted asparagus (Asparagus officinalis L.) seedlings. High and low concentrations of Fusarium oxysporum (Schlect.) emend. Snyd. & Hans. f. sp. asparagi Cohen & Heald (FOA) were combined with G. intraradices and/or T. harzianum treatments. In both experiments included in this study, T. harzianum and G. intraradices alone and in combination effectively reduced root rot caused by FOA when asparagus seedlings were grown in low levels of FOA-infested medium. When seedlings were grown in high levels of FOA-infested medium, the combination of T. harzianum + G. intraradices significantly increased dry shoot mass and limited root rot compared to the control.

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Amy J. MacKenzie, Terri Woods Starman, and Mark T. Windham

Trichoderma harzianum Rifai, a fungus that controls soilborne pathogens, can enhance growth of several vegetable and floriculture crops. Zero, 5, or 25 g of T. harzianum (isolate T-12) peat–bran amendment was added per kilogram medium in an effort to enhance the rooting of four chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] cultivars, two considered easy to root (`Davis' and `White Marble') and two considered hard to root (`Dark Bronze Charm' and `Golden Bounty'). Adding the T. harzianum amendment at both rates tested increased root and shoot fresh weights during 21 days of rooting, relative to the control. Supplementary treated cuttings were transplanted into nontreated growing medium after 21 days. Midway between transplant to flowering, increases in height, shoot dry weight, and root fresh and dry weight were detected in `Dark Bronze Charm' with T-12, relative to the control; increases in height, shoot fresh and dry weight, and number of nodes were detected in `Golden Bounty' with T-12. By this time, there were no detectable differences in `Davis' or `White Marble'.

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Thomas Bjorkman, Gary E. Harman, and Lisa Blanchard

Production of shrunken-2 sweet corn is often limited by poor establishment. Good root development is necessary for establishment, and it can be limited by stress or disease. Trichoderma harzianum strain 1295-22 was developed as a biocontrol fungus with particularly strong root-colonizing ability. In addition to acting as a biocontrol agent, it stimulates root growth. In greenhouse experiments using field soil, root dry weight 21 days after planting was 500 mg, greater compared with 320 mg in uninoculated controls, an average increase of >50%. The thoroughness of soil exploration more than doubled, from 31% (control) to 70% (Trichoderma) of the soil being within 1 cm of a root. The difference in performance was not attributable to disease: no disease symptoms were evident, the occurrence of disease organisms was low, it was the same in both treatments, and it was not associated with smaller plants. Furthermore, the greatest differences were noted in steam-sterilized soil. Colonization of the roots by Trichoderma was related to the age of the root. The oldest part of the radicle had 106 cfu/g root DW. Branched seminal roots had 105.5 cfu/g. Even the rapidly growing tips of the first-whorl roots were well-colonized (104.7 cfu/g). The mechanism of increased root growth has not been identified, but colonized roots acidify about 0.1 pH units more than control roots, which could cause both faster acid-growth and increased ion uptake. Ion leakage into distilled water is about 25% lower in colonized roots.

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Thomas Björkman, Lisa M. Blanchard, and Gary E. Harman

Sweet corn (Zea mays L.) varieties carrying the sh2 gene are in high demand, but such varieties have poor stress tolerance, especially during plant establishment. Trichoderma harzianum Rifai strain 1295-22 is a biocontrol fungus developed to provide season-long colonization of crop roots. It has the potential to reduce root rot and increase root growth. In the absence of detectable disease, colonization by Trichoderma increased root and shoot growth by an average of 66%. The enhancement was not uniform among the plants. Low- and intermediate-vigor plants were larger in the presence of Trichoderma, but high-vigor plants were not further enhanced by the fungus. Seeds that were subjected to oxidative stress with 0.05% NaOCI had much-reduced vigor; subsequent treatment with Trichoderma fully restored vigor. This result indicates that the damage caused by hypochlorite is specifically repaired by Trichoderma. Treatment of imbibed but unemerged seeds with cold (5/10 °C night/day) for varying periods reduced subsequent growth. Plants with Trichoderma-colonized roots were 70% larger at all durations of cold treatment. The absence of interation indicates the growth reduction due to cold and the growth enhancement due to Trichoderma are by different mechanisms. Allelopathic reduction in root growth by rye was mimicked by applying benzoxazolinone to the soil. Trichoderma-colonized roots grew faster, but the characteristic shortening of the radicle still occurred. There was no interaction between Trichoderma and allelopathy, indicating that these two treatments affect growth by independent mechanisms. The different ways that growth was enhanced by Trichoderma lead us to propose that this fungus acts, in part, by reversing injurious oxidation of lipids and membrane proteins. Root growth is markedly enhanced by colonization with Trichoderma harzianum. This enhancement can restore some stress-induced growth reduction and may directly reverse oxidative injury.

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Amy J. MacKenzie, Terri W. Starman, and Mark T. Windham

Trichoderma harzianum is a well-documented biocontrol agent that has been shown to enhance rooting of chrysanthemum `White Marble'. The objective of this research was to determine if T. harzianum would enhance rooting of hard-to-root chrysanthemum cuttings. Two hard-to-root cultivars (`Dark Bronze Charm' and `Golden Bounty') and two easy-to-root cultivars (`Davis' and `White Marble') were propagated in a 1:1 peat-perlite medium amended with T. harzianum at a rate of 0, 5, or 25g/kg medium. Measurements were taken 7, 14, and 21 days after insertion of the cuttings into the medium. Interactions occurred between rate of amendment and day of measurement for some variables measured. However, overall there was increased root fresh and dry weight of all cultivars when T. harzionum rates were 5 or 25 g/kg medium. Increased root fresh and dry weight occurred on days 14 and 21 for most cultivars. Root fresh and dry weight increased with increasing rate of amendment on day 14 but there was no difference between the 5 and 25 g/kg rates on day 21. Shoot fresh weight was increased with 5 or 25 g/kg each measurement day for all cultivar except `White Marble' and shoot length was increased with 25g/kg for all cultivars.

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Leonor F.S. Leandro, Lisa M. Ferguson, Frank J. Louws, and Gina E. Fernandez

-management practices applied to field soil. There is a need to develop transplant production systems that reduce the risk of introducing root pathogens into fields and that ensure plant vigor and productivity. Root dips with Trichoderma harzianum strain T22 (T22

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Glenn A. Hardebeck, Ronald F. Turco, Richard Latin, and Zachary J. Reicher

Pseudomonas aureofaciens strain Tx-1 is suggested as a biological control for Sclerotinia homoeocarpa (F.T. Bennett) and brown patch (Rhizoctonia solani Kuhn) on golf courses. To overcome application difficulties, a field bioreactor is used to grow Tx-1 daily and then inject into nightly irrigation on the golf course. Though Tx-1 shows some promise for disease control in vitro, it is relatively untested under field conditions. We conducted three field experiments to 1) evaluate the efficacy Tx-1 when applied through an irrigation system for the control of dollar spot and brown patch; 2) determine if there is an interaction between nitrogen fertility or fungicides on efficacy of Tx-1; and 3) determine if Tx-1 can extend the duration of dollar spot control by a single application of fungicide. Nightly applications of Tx-1 through irrigation did not affect brown patch on `Astoria' colonial bentgrass (Agrostis capillaris Sibth.) during the 2 years of our study. Tx-1 reduced dollar spot in `Crenshaw' creeping bentgrass (Agrostis palustris Huds.) by 37% in 1998 compared to non-Tx-1 treatments, but Tx-1 had no effect on dollar spot in 1999. Under low disease pressure, Tx-1 increased the dollar spot control of fungicides by 32% and increased the duration of control by 2.6 days. However, Tx-1 had no effect on fungicide efficacy or duration of control later in the summer when dollar spot pressure was high. Fungicides did not negatively affect Tx-1's control of brown patch or dollar spot, nor did fertilizer regime affect brown patch or dollar spot control by Tx-1. Although delivery of Tx-1 in our studies was optimized, disease control was marginal and occurred only under low disease pressure. Therefore, we conclude Tx-1 has limited practical value for turfgrass disease control on golf courses.