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ABSTRACT Partridge, Darcy Erin. Potential for Management of Sclerotinia Blight of Peanut (Arachis hypogaea L.) caused by Sclerotinia minor with the Biological Control Agent Coniothyrium minitans. (Under the direction of Drs. Turner B. Sutton and David L. Jordan.) Sclerotinia blight of peanut (Arachis hypogaea L.), caused by Sclerotinia minor (Jagger) Kohn, is an important disease in North Carolina and Virginia. Sclerotia are the main overwintering propagules of S. minor and serve as the primary source of inoculum for Sclerotinia blight. The effectiveness of the fungal mycoparasite Coniothyrium minitans, which is capable of colonizing sclerotia of Sclerotinia spp., was evaluated in a 5-year field study and in eight short-term field studies in northeastern North Carolina. Control of Sclerotinia blight was highest when C. minitans was applied for 3 consecutive years. However, application of C. minitans for 1 or 2 years also reduced disease in the long-term study. A single application of C. minitans was less effective when applied 4 to 6 months prior to planting and sclerotia numbers were only reduced in two of the eight short-term field studies. Sclerotia used as baits placed in the long-term field study as well as the sclerotia isolated from soil were infected by C. minitans, and the number of sclerotia was reduced where C. minitans was applied. Moderate resistance in the cultivar Perry and application of the fungicide fluazinam provided adequate control of Sclerotinia blight in all plots. The integration of C. minitans with current peanut management practices is needed for successful biological control of Sclerotinia blight. Laboratory experiments evaluated the effects of nine pesticides commonly used in peanut production on mycelial growth, conidia germination, and mycoparasitic activity of C. minitans on sclerotia of S. minor. The commercial formulations of the fungicides azoxystrobin, chlorothalonil, fluazinam, pyraclostrobin, and tebuconazole, and the herbicide flumioxazin reduced mycelial growth and conidia germination of C. minitans. Eight of nine pesticides, azoxystrobin, chlorothalonil, fluazinam, pyraclostrobin, tebuconazole, diclosulam, flumioxazin, and pendimethalin applied to soil plates reduced but did not inhibit the mycoparasitic activity of C. minitans on sclerotia of S. minor. Temperature and moisture effects on mycoparasitism were also evaluated to determine optimum conditions for infection of sclerotia of S. minor by C. minitans. Optimum temperatures for infection of sclerotia of S. minor by C. minitans ranged from 14 to 22º C and soil moisture –0.33 to –1 kPa x 102. These results indicate that C. minitans should remain active throughout most of the year in North Carolina, except during the hot summer months of June, July and August. Soil fauna such as collembola may aid in the reduction of sclerotia through direct predation and the movement of inocula of mycoparasites from infected to noninfected sclerotia. Collembola diversity and abundance were compared in four peanut fields. The most prevalent collembola families were Isotomidae, Smithurididae, Poduridae, and Hypogastruridae, with Isotomidae isolated most frequently from all sites. Abundance and diversity of collembola increased from August to October with sampling date and location having the greatest effect on the composition of the population. Determining the abundance and diversity of collembola in the field can help increase our understanding of the soil community structure. These studies show that C. minitans is able to persist and infect sclerotia of S. minor in peanut fields of North Carolina when applied in the fall or early winter across crop residue and incorporated into the top layers of the soil. C. minitans will not eradicate infestations by S. minor, but over time has the potential to reduce inoculum levels and ultimately decrease the incidence of the disease. POTENTIAL FOR MANAGEMENT OF SCLEROTINIA BLIGHT OF PEANUT (ARACHIS HYPOGAEA L.) CAUSED BY SCLEROTINIA MINOR WITH THE BIOLOGICAL CONTROL AGENT CONIOTHYRIUM MINITANS by DARCY ERIN PARTRIDGE A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy PLANT PATHOLOGY and CROP SCIENCE Raleigh 2005 APPROVED BY: _____________________________________ ____________________________________ Dr. Barbara Shew Dr. Marc Cubeta _____________________________________ ____________________________________ Dr. Turner B. Sutton Dr. David L. Jordan Co-chair of Advisory Committee Co-chair of Advisory Committee DEDICATION Jack E. Bailey (September 16, 1951- April 12, 2002) I am dedicating my dissertation to Dr. Jack E. Bailey. Dr. Bailey, a long-time Professor and Extension Specialist in the Department of Plant Pathology, at North Carolina State University, was passionate about teaching and mentoring students. He first made contact with me back in 2001 when he relentlessly pursued and convinced me that his lab was the place for me to start my PhD graduate research. Upon my arrival in Raleigh, Jack eagerly welcomed me and instantly sparked my interest in diseases of peanut. He was involved in both applied and basic research aimed at solving disease problems for growers. He was a man with many dreams and not enough time to complete them. He loved to debate philosophical ideas and opened his home to students regularly for discussions and socials. His friendship and guidance is greatly missed. I hope that in the future I may show as much passion and dedication in my research as Jack had in all his accomplishments. ii BIOGRAPHY Darcy Erin Partridge was born on June 17, 1977, in Batavia, New York. Agriculture and plant sciences were introduced to her as a child growing up on a dairy farm and working in her parents’ vegetable stand. In 1999, Darcy obtained her Bachelor of Science in Plant Biology with a concentration in Botany from Cornell University in Ithaca, NY. She then received her Master of Science degree in Plant, Soil and General Agriculture in 2002 from Southern Illinois University, Carbondale, IL under the guidance of Dr. John S. Russin. Her master’s thesis research involved studying the effects of two soilborne fungi, Fusarium solani f.sp. glycines and Macrophomina phaseolina, on soybean nodulation and nitrogen fixation. In the summer of 2001 she began work on her degree of Doctor of Philosophy in Plant Pathology and Crop Science at North Carolina State University under the direction of Drs. Jack E. Bailey and David L. Jordan. Dr. Turner B. Sutton graciously joined her committee as Co-chair upon the sudden death of Dr. Bailey. Darcy completed her degree studying the potential for management of Sclerotinia blight of peanut (Arachis hypogaea L.) caused by Sclerotinia minor with the biological control agent Coniothyrium minitans in the spring of 2005 under the direction of Drs. Turner B. Sutton and David L. Jordan. iii ACKNOWLEDGEMENTS I would like to sincerely thank my graduate advisors Drs. Turner B. Sutton and David L. Jordan for their instruction, patience, friendship, dedication, and their confidence in me and Drs. Barbara B. Shew and Marc Cubeta for graciously serving on my graduate advisory committee. Dr. Osama Anas for his generous support and friendship. Virginia Curtis, for her vital support in my field research, making sure I was never lost between the cracks, and being a wonderful friend over these last four years. Joyce Hollowell, Damon Smith, and Gabriela Alandia Robles for their friendship and assistance in the laboratory and field. Dewayne Johnson, Carl Murphy, and Brenda Perry for helping with peanut planting and harvest. The NC Peanut Grower’s Association, Inc., National Peanut Board, IR-4 Project, and NSF-IPM for research funding and farm cooperators and county agents for their vital assistance. Nikki Charlton, Kimberly Schwartzburg, and Andrea Lamay for their friendship and sharing coffee or running through the woods with me. My family, for their continuous love and support of me even when I’m far from home and finally Dominic Telenko, for his love, friendship, support, and dedication to protecting our freedom, so that I may pursue my dreams. iv TABLE OF CONTENTS Page LIST OF TABLES ………………………………………………………………………….vii LIST OF FIGURES…………………………………………………………………………..ix INTRODUCTION…………………………………………………………………………….1 Biology of Sclerotinia minor and disease cycle on peanut……………………………2 Biology of Coniothyrium minitans and potential as a mycoparasite of sclerotia……..6 Literature cited……………………………………………………………………….11 CHAPTER 1. MANAGEMENT OF SCLEROTINIA BLIGHT IN PEANUT FIELDS WITH THE BIOLOGICAL CONTROL AGENT CONIOTHYRIUM MINITANS………….22 Abstract………………………………………………………………………………23 Introduction…………………………………………………………………………..24 Materials and methods ...……………….……………………………………………26 Results………………………………………………………………………………..30 Discussion……………………………………………………………………………34 Literature cited……………………………………………………………………….38 CHAPTER 2. SENSITIVITY OF CONIOTHYRIUM MINITANS MYCELIAL GROWTH, CONIDIA GERMINATION, AND MYCOPARASITIC ACTIVITY ON SCLEROTIA OF SCLEROTINIA MINOR TO PESTICIDES COMMONLY USED IN PEANUT PRODUCTION………………………………………………………………………………60 Abstract………………………………………………………………………………61 Introduction…………………………………………………………………………..62 Materials and methods……………………………………………………………….64 Results………………………………………………………………………………..67 Discussion……………………………………………………………………………69 Literature cited……………………………………………………………………….72 CHAPTER 3. EFFECT OF TEMPERATURE AND MOISTURE ON THE MYCOPARASITISM OF SCLEROTIA OF SCLEROTINIA MINOR BY CONIOTHYRIUM
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