Downy mildew, a foliar disease caused by the oomycete Pseudoperonospora cubensis (Berk. and Curt.) Rostow. is one of the most destructive pathogens of cucurbits. Resistant cultivars are available but nevertheless yield losses are high in North Carolina and Poland if fungicides are not used. The first objective of this experiment was to test all available plant introduction accessions from the U.S. National Plant Germplasm System of cucumber for downy mildew resistance under field conditions. The 1289 cultigens were tested at Clinton NC, USA, and Skierniewice, Poland during 2005-2007 under natural field epidemics of the disease. Averaged over locations, eighty-one cultigens were classified as highly resistant, 130 as moderately resistant, 406 as intermediate, 408 as moderately susceptible, and 271 as highly susceptible. The 40 most resistant and 10 most susceptible cultigens from these field trials, were further evaluated in replicated field and greenhouse experiments in North Carolina, along with 22 check cultivars. Results from the retest study in North Carolina confirmed the results of the initial screening study, although the range of downy mildew ratings in the North Carolina field retest were much narrower compared with the screening results obtained in the larger study. The most resistant and most susceptible lines in the screening study were also the most resistant and most susceptible lines in the field retest. The most resistant 10 cultigens averaged over both locations were Ames 2353, Ames 2354, PI 197085, PI 197088, PI 234517, PI 321008, PI 330628, PI 432878, PI 605996 and PI 618931. These cultigens originated from India, the United States, Pakistan, P.R. China and Taiwan. Despite the identification of resistant plant introduction accessions, they were not significantly better than the most resistant cultivars currently used in either North Carolina or Poland. The most positive aspect of the screening effort was that resistant plant introductions originated from diverse geographic regions. Because geographic diversity is often associated with genetic diversity in germplasm collections, the newly identified resistant typed may carry unique alleles as compared to commercial material. If so, then the potential exists to develop recombinant types from crosses of commercial by exotic materials which may be more resistant. The second objective of this study was to measure the correlation of four response traits. A low correlation among the four response traits on a diverse array of cucumber cultigens would suggest that the traits are controlled by different genes. Field studies were conducted to measure the response traits of plant stunting, leaf necrosis, chlorosis and sporulation caused by downy mildew infection. Each of the four traits were measured on 67 diverse cucumber cultigens in North Carolina and India. All cucumber cultigens were tested in four replications and two locations under natural field epidemics of the disease. A significant genotype by location interaction was found by analysis of variance and data from the two locations were analyzed separately. In North Carolina, necrosis and chlorosis were highly correlated (r=0.90) while sporulation was moderately correlated with necrosis and chlorosis(r=0.71 and r=0.70, respectively) and not significantly correlated with stunting. Stunting was moderately correlated with necrosis and chlorosis (r=0.43 and r=0.34, respectively). In India, chlorosis and sporulation were highly correlated (r=0.97) while necrosis was moderately correlated with chlorosis, sporulation and stunting (r=0.67 and r=0.0.65 and r=0.76, respectively). Stunting was moderately correlated with chlorosis and sporulation (r=0.55 and r=0.57, respectively). Sporulation or necrosis may be controlled by a different gene(s) but another year of testing is required. Stunting may also be controlled by a different gene(s) but difficulties in differentiating between stunting resulting from genotype and stunting resulting from disease must be resolved. Different degrees of correlation among chlorosis, necrosis and sporulation in North Carolina and India may be due to the presence of different races in the two locations. These differences may also be explained by the variable number and timing of ratings between the two locations. Availability of only one set of data for sporulation in North Carolina may have reduced the correlation between it and necrosis and chlorosis. Sporulation ratings need to be taken on a weekly basis rather than once during the last rating. Therefore, the possibility exists that chlorosis, necrosis and sporulation are response traits controlled by the same genes.

Watermelon fruit characters may affect customer acceptance of the watermelon fruit. The qualitative fruit traits, such as flesh color, seed size, seed coat color, rind pattern, fruit shape, exhibit wide ranges of phenotypes. The flesh color can be red, orange, yellow, or white. The seed length of watermelon also varies from 4.4mm to 16.5mm. The seeds can have various coat colors or other decorations. The rind of watermelon fruits can be striped or solid colored, which are further characterized by different stripe widths, stripe colors, backgrounds colors, and additional modifications. The fruit shape can be elongate, oblong, and round. Other fruit traits include shape of fruit blossom end, fruit surface characters, and hollow-hearted flesh. By crossing watermelon cultivars with different phenotypes, we studied the inheritance of the various phenotypes and identified and verified genes responsible for the flesh color, seed size, rind pattern, and fruit shape. In addition, we studied the quantitative traits of the fruit weight and total soluble solids content. The calculated broad-sense and narrow-sense heritability for fruit weight is low to medium, indicating large environmental effect on fruit weight. Medium to high heritability is found for the total soluble solid content, suggesting possible gains from selection.

Despite the high level of interest for growing red raspberries (Rubus ideaus) in the southeastern US, production is limited by the lack of adapted, high quality cultivars. Breeding efforts are underway for increasing cultivar availability for this region, however breeding improvements in Rubus are slow and time-consuming. In order to expedite the slow, but effective, breeding process, more molecular breeding tools should be developed. Cultivars adapted to the southeastern US need to tolerate warm summers, and winters with temperature fluctuations. To address this issue, we have developed a genetic linkage mapping population from a cross that segregates for the tolerance of both conditions, (R. parvifolius à âTulameenâ) à âQualicumâ. This population was used for the construction of a genetic linkage map and for quantitative trait loci (QTL) analysis of heat tolerance, and chilling requirement for tolerance to fluctuating winter temperatures. As expected, seven linkage groups were created and were similar to the already published map. Because heat tolerance is a difficult trait to measure, a protocol was developed using chlorophyll fluorescence to assess heat tolerance. This protocol was used to measure tolerance in the population, and after QTL analysis, 3 QTL explained ~35% of the variation. Chilling requirements in the population were estimated by measuring bud break under greenhouse conditions. Quantitative analysis was performed on these estimates, and 3 QTL were found in two separate season evaluations, and in most cases co-localization occurred in the same region on the map. These regions explained the majority of the variation in the trait (100-64.5%). In summary, this research has established a protocol that measures heat tolerance in red raspberry, without relying on visual assessment, and has mapped important QTL for further molecular studies. Future research should focus on these regions to develop closely linked molecular markers for marker assisted breeding.

Sweetpotato (Ipomoea batatas (L.) Lam) is an extremely diverse and important crop ranking seventh in terms of global production. It is grown throughout the world as a staple crop, and is particularly important in tropical developing countries due to its wide adaptability as well as its enormous potential for preventing malnutrition. The International Potato Center (CIP) in Lima, Peru and the USDA-ARS Plant Genetic Resources Conservation unit (PGRCU) in Griffin, Georgia are the most important sweetpotato gene banks worldwide. Roughly 7,000 and 750 accessions are present in each, respectively. Both collections have been characterized for many phenotypic traits of economic importance, and they are very important in terms of germplasm conservation, as they represent a vital resource for breeders seeking future genetic improvement of sweetpotato. The molecular genetic diversity present in each collection, however, is poorly understood. In this study, 775 accessions from the PGRCU collected from various countries were sampled and fingerprinted using AFLP markers derived from 10 primer pair combinations. A total of 183 polymorphic and clearly scorable bands were generated. Using polymorphisms and phylogenetic software (PAUP and NTSysPC), we were able to clearly distinguish a different banding pattern for each of the 775 accessions. A Neighbor-Joining phylogram was constructed and revealed 6 base clades with no region specificity. Analysis of molecular variance (AMOVA) was carried out using the software program Arlequin. The within-region variation at 97.94% was the major source of molecular variance. Pairwise genetic distances between regions were calculated and the smallest distance was between the Caribbean and Central America and the greatest distance was between the Pacific Islands and South America. Principle coordinate analysis (PCO) was performed by NTSysPC and several clusters of germplasm were noted. This research indicates that there is an abundance of genetic diversity present in sweetpotato.

The purpose of this research was to adapt the PourThru nutrient extraction technique, which is the displacement of the bulk solution from the production container without a destructive harvest, to commercial greenhouse crop production. PourThru is a quick and easy nutrient sampling technique that is not laboratory oriented and can help prevent costly nutritional problems for greenhouse crop producers. Additionally, time domain reflectometry (TDR) was evaluated as an experimental tool to measure substrate moisture content, which may affect PourThru extraction. Time domain reflectometry is quick, non-destructive and has potential for use in automation of moisture content determination in greenhouse production. Previous PourThru research had focused on techniques for use on large nursery containers (≈ 3800 cm3) versus the smaller floriculture containers (≈ 1500 cm3) and no exact calibration of PourThru nutrient values to saturated media extract (SME) values, the current standard for nutrient testing, had been completed. Therefore, studies were implemented to examine the relationship of PourThru to SME, evaluate irrigation systems and timing effect on PourThru results as well as develop recommended influent and leachate volumes to ensure an unadulterated sample. Calibration curves were developed between PourThru and SME values and r2 values ranged from 0.91 to 0.99 for linear relationships. Irrigation systems did affect electrical conductivity (EC) values and alternative interpretive standard values were developed dependent upon irrigation system. Timing of the PourThru was important to ensure adequate leachate was collected for sample analysis and the amount of influent affected EC values and the amount of leachate collected. The use of TDR was effective in small containers (980.6 and 2177.5 cm3); however, care should be taken to match probe size to container size to ensure representative sampling. The largest limitation to TDR use was the bulk density of the substrate being analyzed. Approximately a 50 to 75% underestimation occurred when substrate bulk densities were below 1.2 g.cm-3, but material specific calibration improved TDR accuracy to within 4%.

Several field, greenhouse, and laboratory studies were conducted to evaluate the effects of vermicomposted (VC) hog manure amended to pine bark (PB) on substrate physical properties, plant growth and flower production, water use efficiency of productivity (WUEP), effluent nitrogen and phosphorus content, substrate solution pH, macronutrient release rate characteristics, and the ability of VC to replace conventional fertilizer nutrient inputs. Nitrogen and phosphorus budgets were determined, and nutrient use efficiencies of nitrogen (NUEN) and phosphorus (NUEP) were calculated. Container capacity and available water increased linearly and air space decreased linearly with increasing rate of VC. Growth of several species increased linearly with increasing VC rate with no traditional amendments of limestone and micronutrients; and 20% VC resulted in greater plant dry weights than the PB control (amended with limestone and micronutrients). However, there were species where growth decreased linearly with increased VC rate, while the 20% VC maintained equivalent dry weights to the PB control. The WUEP of several species were improved compared to the control. Liming effects of 5% VC were equivalent to the control receiving limestone, whereas VC rates >10% had greater liming effects compared to the respective control. Twenty percent VC provided sufficient quantities of P, Ca, Mg, S, and micronutrients such that an additional supply of these nutrients need not be applied. Although 20% VC did not supply K in quantities comparable to traditional inputs, the reduction of K did not affect growth or flower bud production of hibiscus. Macronutrient release rates (determined on a volume basis) of N and S from VC followed a first-order model, Ca and Mg followed a two pool first/zero-order model, and P followed a zero-order model. The tissue nutrient content of N, Ca, Mg, and S increased with increasing VC rate while P decreased with decreasing VC rate. Vermicompost in the substrate increased N and P effluent content, but reducing the leaching fraction decreased nutrient contents. The NUEN ranged from 9% to 20% with no major differences between substrate or leaching fraction treatments. However, the NUEP was improved when VC was amended to the substrate.

Combining the environmentally sound practices of reduced tillage and cover crop use with organic vegetable production systems requires management choices that are tailored to specific climate and crop combinations. In the southeastern U.S. summer cover crops can be grown through the fall until desiccation by frost. At this time a cash crop such as bulb onions (Allium cepa L.) can be grown using reduced tillage for over winter production. Field experiments were conducted on first year transitional (non-organic) land in 2006-07 and 2007-08. Cover crops of foxtail millet âGerman Strain Râ [Setaria italica (L.) Beauv.] and cowpea âIron & Clayâ [Vigna unguiculata (L.) Walp.] were grown as monocrops (MIL, COW) and biculture mixtures and compared to a bare ground control (BG). Mixtures of cowpea and millet consisted of seeding rates aimed at producing 70%, 50%, and 30% millet per total biculture biomass (MIX-70, MIX-50, MIX-30). Cover crop residue treatments were evaluated for weed suppression and N contribution to no-till organic onion production. Supplemental N in the form of surface applied soybean meal [Glycine max (L.) Merrill] was applied to cover crop treatment subplots at three rates: 0, 105, and 210 kg Nâha-1. Onion yields increased linearly from 0 to 210 kg Nâha-1 rates of soybean meal. Cover crop treatments COW and BG had the greatest total marketable onion yield and were statistically equivalent both years. Losses in marketable yield were primarily due to mortality in MIL and MIX in 2006-07 and bolting across all cover crop treatments, which averaged 28% in 2006-07 and 72% in 2007-08. Onion mortality was over 50% in MIL and MIX treatments in 2006-07 and was attributed to physical properties of thick surface mulch. Onion mortality in 2007-08 was highest on MIL compared to all other cover crop treatments but remained below 20%. Weed interference during onion production was highest in COW and lowest in treatments with millet (MIL, MIX) in 2006-07. Nitrogen rates of 105 and 210 kg Nâha-1 increased soil mineral N (NO3- and NH4+) on BG plots two weeks after surface application of soybean meal at the end of November each year but generally ceased to have an effect on soil mineral N by February or March. The 105 kg Nâha-1 soybean meal rate appeared to be more than sufficient for use as a starter fertilizer. Split applications of soybean meal could be an important improvement in N management to avoid N leaching and better meet increased N uptake demand during bulb initiation and growth in the spring. Overall, this study shows that cowpea cover crops grown preceding an over-wintered no-till allium crop is feasible with appropriate management, and provides onion yield comparable to bare ground production.

Stokesia laevis (J. Hill) Greene is a herbaceous perennial with blue, lavender, violet, albescent, pale yellow or pale pink flowers. All cultivars are diploid (2n=2x=14) except for ?Omega Skyrocket, a tetraploid (2n=4x=28) cultivar selected from a wild population. Anthocyanidin and copigment aglycones extracted from floral tissue were characterized using high-performance liquid chromatography. Results indicated that blue, lavender, violet and albescent flowers contained petunidin, though albescent flowers contained a substantially smaller amount. Pale pink flowers were found to contain only cyanidin. Anthocyanidins and carotenoids were not present in pale yellow flowers. All flowers contained the flavone luteolin. Genetic analyses suggested that at least three genes (A, P, Y) each with two alleles control flower color: A permits normal synthesis of anthocyanins and other flavonoids, a reduces synthesis and/or prevents the accumulation of anthocyanins and other flavonoids; Y permits normal synthesis of anthocyanins, y completely blocks synthesis of anthocyanins; P produces petunidin, p produces cyanidin. All three genes are completely dominant, and yy is epistatic to A and P. We provide a model for flavonoid biosynthesis in Stokesia. Study of karyotypes and meiotic behavior of diploid cultivars and ?Omega Skyrocket? suggest that ?Omega Skyrocket? is an autotetraploid form of Stokesia. The karyotype of ?Omega Skyrocket? was almost indistinguishable from the average diploid karyotype. Meiotic pairing in diploids was normal (i.e. 100% bivalents); no meiotic irregularities such as laggards/bridges were observed and disjunction was equal (7:7). Meiotic pairing in ?Omega Skyrocket? demonstrated a high frequency (60%) of quadrivalent formation, though later stages of meiosis were regular with balanced disjunction (14:14). Meiosis in synthetic autotetraploids and triploids from crosses of diploid cultivars × ?Omega Skyrocket? included univalents, bivalents, trivalents, quadrivalents, 5-valents; abnormalities (i.e. laggards, unequal and/or premature disjunction, chromosome bridging, chromosome stickiness) were observed. Nuclear 2C DNA content for diploids and synthetic tetraploids was 20.3 pg and 39.9 pg. Nuclear 2C DNA content for ?Omega Skyrocket? was 37.3 pg (i.e. 8.2% less than twice the 2C DNA content of diploids), indicating that genomic downsizing has likely occurred in this cultivar. Differences in chromosome symmetry between the diploid and tetraploid karyotypes and the reduction in nuclear DNA content observed in ?Omega Skyrocket? both suggest that some divergence has occurred between ?Omega Skyrocket? and its diploid progenitor. A crossability study was conducted to determine the ploidy level and the frequency of progeny produced by interploid and intraploid crosses of Stokesia. A high percentage (70%) of progeny were aneuploids (i.e. 2x-1 to 6x+3) with the total percentage of aneuploids ranging from 92% to 94% in 2x × 3x, 3x × 2x, 3x × 3x, 3x × 4x and 4x × 3x crosses. Progeny (94%) from 2x × 2x crosses were diploids, and progeny (81%) from 2x × 4x and 4x × 2x crosses were triploids and 3x±1 aneuploids. Progeny from crosses of synthetic tetraploids were mostly tetraploids (16%) and tetraploid aneuploids (69%). Unreduced gamete production was estimated to be 0.7% to 1.4%. Reciprocal crosses of identical 2x and 4x parents produced viable progeny, demonstrating that a triploid block is not present in this species. Triploid fertility was higher than expected; crosses using triploids produced seed 38% of the time with an average seed set of ~2 seeds/inflorescence. Fertility of synthetic tetraploids was reduced relative to their progenitor diploids; pollen viability was reduced by 36% and the percentage of inflorescences producing seed and average seed set/inflorescence were reduced by ~50%. Pollen size was positively correlated with ploidy level (i.e. DNA content).

North Carolina is the fifth largest producer of blueberries (Vaccinium spp.) in the U.S. with approximately 5,000 acres harvested in 2006. A study was conducted to determine if a positive correlation exists between the weed populations in field drainage ditches and weed populations in the field interior, and to inventory the weed species present in the ditches and the field interiors. Sixty-six species were inventoried over a two year period. A second study was conducted to define the seed biology of Rhexia mariana L., an aggressive perennial weed in blueberry, by determining temperature effects on germination, average seed number per capsule, seed number in the seed bank, and seed dormancy. Maximum seed germination was observed at day/night temperatures of 20/35C. Seed germination ranged from 47 to 86% and dormancy ranged from 14 to 53%. The number of seed capsules produced per infested area was different among locations and ranged from 500 to 1125 capsules/m2. Across locations, seed capsules produced an average of 74 seeds each. On average, 27 R. mariana seeds were present in each 273cm2 sample of soil. A single m2 of R. mariana infestation has the potential to produced 12,375 seed capsules and 915,750 seeds. Of those seeds, roughly 604,395 would be viable, 519,779 could germinate as freshly mature seeds, and an additional 84,615 seeds would be dormant. An estimated 1000 R. mariana seeds could germinate from 1m2 of the soil seed bank. A third study was conducted to determine the efficacy of flumioxazin on R. mariana and the tolerance of blueberry to flumioxazin. The data indicate that flumioxazin does not injure blueberry when applied PRE. Flumioxazin applied PRE in a single or a sequential application does not have a negative effect on blueberry yield, even at rates that exceed the registered rate. Control of R. mariana with a single application of flumioxazin at the registered rate of 0.42 kg ai/ha ranged from 83 to 100% at 60 days after treatment (DAT). Sequential applications of flumioxazin at 0.21 kg ai/ha per application resulted in control greater than 96% 30 d after the last of two applications. The data indicates that flumioxazin applied PRE at the registered rate of 0.42 kg ai/ha in a single application or 0.21 kg ai/ha in a sequential application in a 12 month period would give effective control of R. mariana. A final study was conducted in which a grower survey was used to determine the current weed management practices employed by blueberry growers in North Carolina. A 41-question survey was mailed to 241 blueberry growers in February 2008. A total of 58 valid responses were returned and were entered into the data set. Respondents represent 24% of the survey population. Thirty-eight percent of the survey population grows a combination of rabbiteye and highbush blueberry types. The highbush variety âCroatanâ was the most frequently planted variety in total hectacreage, and the rabbiteye variety âPremierâ was the most common variety of that blueberry type. Growers use a combination of mechanical cultivation, hand removal, and herbicides to control weeds in blueberry. Greenbriar species (Smilax spp.) were reported as those species that are increasing in severity, are the hardest to manage, and that interfere most with harvest. Sethoxydim and hexazinone are the most common herbicides used in non-bearing and bearing blueberries, respectively. Growers indicated that their greatest concern in weed management is crop safety to herbicides. Results from all four studies will aid in the development of a comprehensive weed management plan to address the specific needs of North Carolina blueberry producers.

<p> The goal of this research was to develop and assess the effectiveness of the press extraction method (PEM) for nutritional analysis of bedding plant plug substrates. Conventional testing methods for soilless substrates are either unsuited for plug production or interpretive standards have not been published for pH, soluble salts, or specific nutrients. With the PEM, the rooting substrate is irrigated to container capacity and after a period of one hour the plug surface is pressed with a finger or thumb to expel the solution. The first series of experiments examined potential variation in pH, electrical conductivity (EC), and extractable nutrients (NO3-N, NH4+-N, P, K, Ca, Mg, Na, B, Cu, Fe, Mn, and Zn) associated with differing extraction forces. A press modified from a fruit penetrometer was designed to apply a range of force (similar to what could be exerted manually) to a 35 g sample of soilless substrate. Testing done on a peat-based substrate fertilized with a single fertilizer rate (20N-4.3P-16.6K at 75 mg.L-1 N) and then fertilized with a range of rates (75, 125, and 175 mg.L-1 N). A coir-based substrate was also tested at one rate (125 ppm mg.L-1 N). For all experiments, the range of extraction forces within a fertilizer rate did not affect chemical properties. When testing included a range of fertilizer rates, the method's ability to detect changes in pH and EC was demonstrated. The second study compared the PEM to the saturated media extract (SME) and the 2:1 water : substrate (v/v) suspension method (2:1). The extraction methods were used on plug trays of a peat-based germination mix treated with 20N-4.3P-16.6K at 50, 100, 150, and 200 mg.L-1 N. Sample sizes of 20 and 60 plugs were used to determine if similar results could be obtained with the smaller, less destructive sample size.. Values for pH were similar among the three methods. The PEM method resulted in the highest EC, NH4+-N, NO3--N, K, Ca, and Mg. Testing 20 plugs was sufficient since sample size accounted for little variation in the results. In a second experiment comparing peat- and coir-based substrates, the coir extract pH averaged 1.5 units higher with much higher levels of K and Na regardless of extraction method when compared to the peat. Solution from the peat substrate was higher in NH4+-N, NO3--N, P, Ca, and Mg. Within each substrate, pH, EC, and nutrients tested were similar between the PEM and SME. The similarity between the PEM and SME nutrient analysis in the second experiment suggested existing SME interpretation standards may be used for the PEM but further investigation was needed. The third study was designed to provide the necessary correlations between the methods to allow for development of pH, EC, and nutrient interpretive ranges for actively growing plugs. First, a wide range of bedding plant plugs grown at various commercial greenhouses were collected and the substrate solution extracted with the PEM, SME, and 2:1 methods. This quickly and inexpensively provided the varied population necessary to establish relative comparisons and correlations between the methods when performed on actively growing plugs. A second experiment provided comparisons of the three extraction methods performed on plugs grown at low, medium, and high fertility rates with a variety of bedding plant species; celosia (Celosia argentea L. var. cristata (L.) Kuntze Plumosa Group), impatiens (Impatiens wallerana Hook. f.), marigold (Tagetes erecta L.), petunia (Petunia × hybrida Hort. Vilm.-Andr.), and salvia (Salvia splendens F. Sellow ex Roem.& Schult.) Thirty days after planting (DAP), shoots were harvested and the solution extraction methods were performed on each flat. For both experiments, the PEM EC was consistently higher and the pH equal to or lower than the SME. The pH with the 2:1 method was similar to that for the PEM, however EC was consistently low ith this method due to the dilution effect. Solution NO3--N, P, and K were well-correlated between the PEM and SME. However, between the two experiments, there were anomalous results for most nutrients extracted by the PEM and SME methods. As found in previous studies, Ca and Mg levels were consistently higher in the PEM extracted solution. The pH and EC relationships between the three extraction methods remained consistent throughout the study. As a result, quantitative interpretation ranges for these two analyses were calculated between the PEM and SME. Plug growers can now use the PEM for on-site pH and EC testing and compare their results with the previously published sufficiency ranges for the SME.<P>