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United States Department of Agriculture

Agricultural Research Service

Research Project: Alternatives to methyl bromide soil fumigation for vegetable and floriculture production

Location: Subtropical Plant Pathology Research

Title: Trichoderma rot on ‘Fallglo’ Tangerine Fruit

Authors
item Cuifeng, Hu -
item Rosskopf, Erin
item Ritenour, M -

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2011
Publication Date: N/A

Interpretive Summary: In the fall of 2009, ‘Fallglo’ tangerine fruit were harvested and put into storage. After seven weeks of storage, fruit showed symptoms of fruit rot. An experiment was conducted to determine if one of four fungicides could control the observed decay. Fruit were treated with fungicides fourteen days prior to harvest. The control fruit were treated with tap water. Decaying fruit from the control treatment was used to isolate the fungus, which was initially identified as a Trichoderma sp. The isolate was cultured from hyphal tips, axenically cultured, and identified as Trichoderma atroviride based on the fungal morphology using the TrichOKey website. The identification was confirmed using DNA sequence data from two regions. Fruit were wound-inoculated with a suspension of fungal conidia and the symptoms were recreated. This is the first report of this species causing fruit decay, although in the past, T. viride has been identified as the cause of this disease in several citrus production regions. All fungicide treatments, Switch, Topsin-M, HDH Peroxy, and Bravo, were effective at preventing decay.

Technical Abstract: In September 2009, brown rot symptoms were observed on ‘Fallglo’ fruit after 7 weeks of storage. Fourteen days prior to harvest, fruit were treated by dipping into one of four different fungicide solutions. Control fruit were dipped in tap water. After harvest, the fruit were degreened with 5 ppm ethylene for 5 days. Decaying fruit were collected from the control treatment, which had an average of 2.6% decay. The decay area became brown and leathery and was round to elliptical in shape with an average diameter of 4 to 6 cm. A fungus was isolated from the diseased peel of symptomatic fruit. The fungus grew rapidly on potato dextrose agar (PDA) medium and produced white mycelium after one day on PDA at 25°C and filled the Petri dish (100 X 15 mm) after 5 days. The colony turned white to grey after 14 days with scattered green tufts. Green conidia were formed in concentric rings and first observed on PDA at 25°C within 72 hours. Conidiophores were branched with flask-shaped phialides. The fungus was identified as a Trichoderma atroviride based on the morphology, which was confirmed by sequencing of the internal transcribed spacer regions and portions of the gene encoding translocation elongation factor 1-alpha. ‘Fallglo’ fruit developed the same symptoms that were previously observed 4 days after wound-inoculated with a spore suspension (2.1 X107/ml). Fruit dipped in Switch, Topsin-M, HDH Peroxy, and Bravo had 0.0% incidence of decay.

Last Modified: 9/22/2014
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