Management of Phytophthora Capsici on Summer Squash and Age-Related
Total Page：16
File Type：pdf, Size：1020Kb
MANAGEMENT OF PHYTOPHTHORA CAPSICI ON SUMMER SQUASH AND AGE- RELATED RESISTANCE ON PROCESSING PUMPKIN AND WINTER SQUASH FRUITS BY Michael D. Meyer A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Plant Pathology 2012 ABSTRACT MANAGEMENT OF PHYTOPHTHORA CAPSICI ON SUMMER SQUASH AND AGE- RELATED RESISTANCE ON PROCESSING PUMPKIN AND WINTER SQUASH FRUITS BY Michael D. Meyer Phytophthora blight, caused by Phytophthora capsici Leonian, is an economically important disease of cucurbit crops (Cucurbita spp.). Michigan accounts for 20% of the squash produced in the U.S., with total cash receipts of $12 million in 2009. Field and greenhouse trials were conducted to compare soil drenches and foliar sprays of eleven fungicides for control of Phytophthora crown and root rot on summer squash. Soil drenches were more effective than foliar sprays at limiting plant death caused by P. capsici. Mean plant death 42 days post inoculation (dpi) was 41% for soil drenches and 92% for foliar sprays. Drenches of fluopicolide, mandipropamid or dimethomorph limited plant death to ≤10%, and prevented yield loss associated with crown and root rot. Similarly, disease progress was slower and crown rot was less severe following soil drenches compared to foliar sprays in greenhouse trials. Most fungicide treatments were more effective on the cultivar ‘Leopard’ than ‘Cougar’, which is more susceptible to P. capsici. A laboratory study evaluated age-related resistance to Phytophthora fruit rot in ‘Dickenson Field’ processing pumpkin and ‘Golden Delicious’ winter squash. Hand-pollinated fruits were harvested 3, 7, 10, 14, 21, 28, 42, or 56 days post pollination (dpp) and inoculated with P. capsici. Susceptibility to Phytophthora fruit rot decreased with fruit age in ‘Dickenson Field’ processing pumpkin, whereas ‘Golden Delicious’ winter squash remained susceptible to fruit rot even as fruit reached full maturity. Lesion diameter and pathogen growth were generally greater on younger fruit than older fruit. Less than 15% of ‘Dickenson Field’ fruit 21 dpp or older became diseased. Conversely, about 80% of ‘Golden Delicious’ fruit 21 dpp or older became diseased. Several morphological and physiological changes were observed as fruit matured. Soluble solids content and exocarp firmness of both cultivars increased with fruit age, and were negatively correlated (ρ = -0.29 to -0.73) with lesion diameter and pathogen growth density. Field trials were conducted to evaluate the effects of bed height, mulches, dried poultry litter, and cultivars on Phytophthora crown and root rot of summer squash. Differences in cultivar susceptibility to P. capsici accounted for most of the variation in the observed disease levels. Mean incidence of plant death 35 dpi was 87% for ‘Payroll’ and 99% for ‘Cougar’. Plant death of ‘Payroll’ was greater in flat beds than raised beds. Disease was not affected by bed height, mulches, or rates of dried poultry litter application. Crown rot severity differed significantly among thirty-two summer squash cultivars and ten cucurbit germplasm accessions in a separate greenhouse trial. Mean crown rot ratings were 4.3 on commercial cultivars and 2.2 on germplasm accessions. Crown rot was least severe on the cultivar ‘Spineless Beauty’. No disease developed on four accessions of Cucurbita moschata (PI 442262, PI 442266, PI 458740, and PI 634693) previously reported to be crown rot resistant. ACKNOWLEDGEMENTS I would like to thank my advisor Dr. Mary Hausbeck for accepting me into her program, and encouraging me to seek opportunities I had not previously considered. I would also like to thank my graduate committee members Drs. Ray Hammerschmidt, Mathieu Ngouajio, and Jianjun Hao for their support as I finish my graduate program in an expeditious manner. In addition, I would like to thank Brian Cortright for technical assistance. I learned a tremendous amount of practical knowledge about vegetable production and chemical disease control while accompanying him to research sites around the state. I would also like to thank Dr. Leah Granke for critically reviewing portions of this dissertation. Finally, I would like to thank my wife Katie Meyer for her tremendous patience and support while preparing this dissertation and studying for my comprehensive exams. iv TABLE OF CONTENTS LIST OF TABLES ......................................................................................................................... vi LIST OF FIGURES ...................................................................................................................... vii LITERATURE REVIEW Cucurbit Production ....................................................................................................................1 Phytophthora Blight ....................................................................................................................2 Phytophthora Blight Management ..............................................................................................3 Literature Cited .........................................................................................................................10 CHAPTER I: Using soil-applied fungicides to manage Phytophthora crown and root rot on summer squash Abstract .....................................................................................................................................16 Introduction ...............................................................................................................................17 Materials and Methods ..............................................................................................................19 Results .......................................................................................................................................24 Discussion .................................................................................................................................35 Acknowledgements ...................................................................................................................38 Literature Cited .........................................................................................................................40 CHAPTER II: Age-related resistance to Phytophthora fruit rot in ‘Dickenson Field’ processing pumpkin and ‘Golden Delicious’ winter squash fruits Abstract .....................................................................................................................................44 Introduction ...............................................................................................................................45 Materials and Methods ..............................................................................................................47 Results .......................................................................................................................................50 Discussion .................................................................................................................................60 Acknowledgements ...................................................................................................................62 Literature Cited .........................................................................................................................64 CHAPTER III: Using cultural practices and cultivar resistance to manage Phytophthora crown and root rot on summer squash Abstract .....................................................................................................................................66 Introduction ...............................................................................................................................67 Materials and Methods ..............................................................................................................69 Results .......................................................................................................................................72 Discussion .................................................................................................................................81 Acknowledgements ...................................................................................................................82 Literature Cited .........................................................................................................................85 CHAPTER IV: Conclusion ............................................................................................................88 v LIST OF TABLES Table 1.1. Fungicides and rates of application evaluated for managing Phytophthora crown and root rot caused by Phytophthora capsici on summer squash in field and greenhouse trials .........21 Table 1.2. Area under the disease progress curve (AUDPC) values for plant death on summer squash ‘Cougar’ grown in field trials evaluating fungicides applied as a foliar spray or soil drench to control Phytophthora crown and root rot caused by Phytophthora capsici ...................28 Table 1.3. Yield of summer squash ‘Cougar’ expressed as a percentage of the uninoculated control yield in field trials evaluating foliar spray and soil drench applications of eleven fungicides for managing Phytophthora crown and root rot caused by Phytophthora capsici ............................................................................................................................................30