Degree Type

Thesis

Date of Award

2013

Degree Name

Master of Science

Department

Plant Pathology and Microbiology

First Advisor

Xiao Bing Yang

Abstract

Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, is an important root disease that can cause root rot and express foliar symptoms leading to premature defoliation and yield reduction. Earlier reports suggested that the germination of F. virguliforme macroconidia and penetration of their germination tube may differ among the sites along the root system of soybean plants. Glyphosate [N-(phosphonomethyl) glycine] is a post-emergent broad spectrum non-selective herbicide that is largely used in soybean production systems. Previous study shows that infection does not always lead to disease in this host-pathogen interaction as the fungus can reach high level of infection of colonization and remain asymptomatic. Expression of foliar symptoms is critical to the occurrence of SDS. The objectives of this study were (1) to assess effects of different root inoculation sites on foliar symptom expression and the effect of mechanical injury of seedling tap roots on foliar symptoms expression of SDS and (2) to evaluate the effect of glyphosate application on SDS foliar symptom development two greenhouse experimentsWe evaluated three different sites of infection: root tip, middle root portion and upper root. After inoculation, seedlings were transplanted to cones filled with sterile potting mixture. Rhizosphere temperature was controlled by using a water bath (20°C). Plants were evaluated three weeks after transplanting for incidence and severity of SDS. Root sites were not significant for incidence of SDS. Higher incidence was observed when root tips were wounded, probably because tissue wound increased xylem infections. A field survey was done to compare disease levels for plants grown in greenhouse to plants in the fields. Adjacent symptomatic and asymptomatic plants were collect from three fields naturally infested with F. virguliforme. Our results suggested that F. virguliforme can infect plants and remain asymptomatic at a high incidence level. To evaluate the effect of glyphosate application on SDS foliar symptom development two greenhouse experiments were conducted using 4 glyphosate-tolerant soybean cultivars, P92Y51, P93Y13, P93Y13, and P93Y13, that were planted in soil inoculated with F. virguliforme and sprayed with 4 different application rates of glyphosate 0, 1.2, 1.6, and 2.4 L ha-1 of Roundup Ultra ®, plants were sprayed 2 weeks after planting. Incidence and severity of foliar symptoms were evaluated as well as plant height. Our results show that specific cultivars and rates of glyphosate can increase incidence and severity of SDS foliar symptoms.

Copyright Owner

Marcio Leizer Zaccaron

Language

en

File Format

application/pdf

File Size

70 pages

Included in

Agriculture Commons

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