Responses and relationships among Fusarium species, sweet corn, and western spotted cucumber beetles

45 Introduction . 46 Materials and Methods . 49 Results . 56 Discussion. 71 References. 78 Chapter 4. Sweet corn seedlings grown from Fusarium-infested kernels and feeding damage by adult western spotted cucumber beetles . 82 Abstract. 82 Introduction. 83 Materials and Methods. 88 Results. 95. 82 Introduction. 83 Materials and Methods. 88 Results. 95 TABLE OF CONTENTS (Continued) Page Discussion . 102 References. 108 Chapter 5. General Conclusions . 112 Bibliography. 116 LIST OF FIGURES Figure Page 1-1 Average yield of sweet corn fields in the Willamette Valley based on data from three different sources . 2 2-1 Longitudinal cross section of sweet corn plants showing a plant with healthy (left) and diseased (right) crown and stalk nodes . 8 2-2 Examples of sweet corn crown images (inset) and ImageJ grayscale histogram output of the crown region . 12 2-3 Examples of sweet corn stalk node images and ImageJ grayscale histogram output of the node region . 16 2-4 The best-fitting mixed regression model based on Bayesian Information Criteria model selection . 18 2-5 Grayscale means of sweet corn crowns versus mean ear weight by field sites . 23 2-6 Relationships between mean sweet corn ear weight and disease parameters measured other than crown grayscale . 25 2-7 Relationships between sweet corn mean crown grayscale and other explanatory variables by site . 29 2-8 Best-fitting model based on Bayesian Information Criterion model selection . 36 3-1 Longitudinal cross section of sweet corn plants showing a plant with healthy (left) and diseased (right) crown and stalk nodes . 46 3-2 Mean crown grayscale (A), mean stalk node grayscale (B), and ear weights (C, D) of sweet corn plants sampled from commercial fields in the Willamette Valley when Fusarium species were detected or absent . 59 3-3 Mean crown grayscale (A), and ear weight (B) of sweet corn plants grown from various kernel treatments in 2004 and 2005 field pathogenicity studies . 60 3-4 Recovery (percentage) of Fusarium oxysporum (Foxy), F. verticillioides (Fvert), and F. proliferatum (Fpro) from crowns and nodes of sweet corn plants grown from variously treated kernels in field pathogenicity experiments by year . 63 LIST OF FIGURES (Continued) Figure Page 3-5 Mean crown grayscale (A) and node grayscale (B) of sweet corn plants from 2004 (04) and 2005 (05) field pathogenicity studies from which Fusarium oxysporum (Foxy), F. verticillioides (Fvert), or F. proliferatum (Fpro) was isolated (black bars) or not recovered (gray bars) regardless of kernel treatment. 64 3-6 2004 and 2005 mean crown grayscale (A) and node grayscale (B) of sweet corn plants grown from kernels infested with F. oxysporum var. redolens (Foxy), F. verticillioides (Fvert), F. proliferatum (Fpro), all three Fusarium species combined (Mix), or surface disinfested with 3% H2O2 (Disinf) and the same Fusarium species used in inoculations was/were recovered from crowns or the first stalk node lacking rooted brace roots in field pathogenicity studies . 66 3-7 Mean crown grayscale (A) and ear weight (B) of sweet corn plants grown from various kernel treatments in two greenhouse pathogenicity tests . 67 3-8 Recovery (percentage) in two greenhouse pathogenicity experiments of Fusarium oxysporum (Foxy), F. verticillioides (Fvert), and F. proliferatum (Fpro) from crowns and nodes of sweet corn plants grown from treated seed kernels . 69 3-9 Mean crown (A) and node (B) grayscales of sweet corn plants in greenhouse pathogenicity studies from which Fusarium oxysporum (Foxy), F. verticillioides (Fvert), or F. proliferatum (Fpro) was recovered (black bars) or absent (gray bars), regardless of kernel treatment . 70 4-1 Mean proportion (transformed arcsine√y) of sweet corn plants with leaf feeding injury from WSCB adults. Plants were grown from kernels infested with F. oxysporum var. redolens (Foxy), F. verticillioides (Fvert), F. proliferatum (Fpro), all three Fusarium species combined (Mix), nontreated (Nontrt), or surface disinfested with 3% H2O2 (Disinf) . 96 4-2 Mean severity rating of root worm damage on sweet corn plants sampled at maturity. 98 4-3 Mean number of WSCB leaf feeding regions and mean severity rating of leaf injury to laboratory grown sweet corn seedlings . 100 LIST OF TABLES Table Page 2-1 Varieties, site locations, and sampling dates of commercial sweet corn plants in the Willamette Valley used for symptom-yield association study . 10 2-2 Varieties, commercial site locations by county, sampling dates, and the number of sweet corn plants evaluated for xylem conductance . 14 2-3 Bayesian Information Criterion selection of best-fitting models to explain variation in mean plant ear weight per transect based on 10 plants/transect in 10 transects for each of 10 commercial sweet corn fields in the Willamette Valley of Oregon . 19 2-4 Percent reduction of ear weight of sweet corn plants based on predicted values generated with parallel lines regression model with site and crown grayscale as explanatory variables . 24 2-5 Pearson correlation coefficients and associated P-values of explanatory variables used for model testing to determine the association between specific disease symptoms and ear yield of sweet corn plants in the Willamette Valley . 27 2-6 Relationships between sweet corn crown grayscale and other explanatory variables when a separate slope and intercept is estimated for each field site . 28 2-7 Bayesian Information Criterion selection of best-fitting models (with fields 1-3 removed) to explain variation in mean ear weight per transect based on 10 plants/transect in 10 transects for each of seven commercial sweet corn fields examined in the Willamette Valley of Oregon . 31 2-8 Bayesian Information Criterion (BIC) model selection for flow rates through a 30-cm lower stalk section of 18 to 26 sweet corn plants from each of five commercial field sites . 36 2-9 Percent reduction of fluid movement through xylem of a 30-cm lower stalk section of 18 to 26 sweet corn plants from each of five commercial field sites based on predicted values generated with a parallel lines regression model with site and node mean grayscale as explanatory variables . 37 3-1 Varieties, site locations, and sampling dates of commercial sweet corn plants in the Willamette Valley sampled for Fusarium populations . 50 LIST OF TABLES (Continued) Table Page 3-2 Fusarium isolates used for sweet corn pathogenicity studies . 52 3-3 Concentrations of Fusarium inoculum for each inoculum treatment used for infesting sweet corn kernels in pathogenicity studies . 52 3-4 Percentage of plants from which Fusarium cultures were recovered from 305 plants sampled in commercial sweet corn fields . 57 3-5 Mean germination and disease severity ratings of sweet corn plants grown from various kernel treatments in 2004 and 2005 field pathogenicity studies . 61 3-6 Mean disease severity ratings of plants by kernel treatment in greenhouse p