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Abstract
Clones of ‘Jewel’, ‘Eureka’, ‘Pope’, ‘Oklamex’, ‘Garnet’, L5-19, NC-719, and W-152 sweet potato [Ipomoea batatas (L.) Lam] were tested for 1 to 3 seasons in field plots of coarse-textured sand soils. The soils were infested with Meloidogyne incognita (Kofoid & White) Chitwood and Paratrichodorus minor (Colbran) Siddiqui that included 1,3-dichloropropene fumigated and nonfumigated subplots. ‘Jewel’, followed by ‘Pope’, was the highest-yielding copper-skinned type and the least affected by nematode infection; however, it supported large numbers of M. incognita. Yields of ‘Eureka’ were lowest in nonfumigated plots in the presence of P. minor. Significantly greater P. minor population increase occurred on ‘Eureka’ than on other clones. Yield of red-skinned W-152 was greater than ‘Garnet’ on fumigated plots, but W-152 showed no greater yield when nematode-infected. ‘Oklamex’, L5-19, and NC-719 were discontinued after 1 year because of poor yield or quality. M. incognita resistance in all clones prevented damage to the appearance of sweet potatoes, but plant growth and yield were increased significantly in fumigated plots compared with yields from nonfumigated plots. M. incognita reproduced on all lines, especially when soil temperature was high in 1981.
Abstract
Response of cold-treated ‘Nellie White’ Easter lily bulbs to various degrees of scale removal, ranging from 0 to 100%, showed that scales can perform inhibitory and promotive roles at various times. The scales were not necessary for flower induction, but the number of leaves and flowers initiated was proportional to the number of scales retained. Daughter scale removal accelerated daughter sprouting by increasing internode elongation, but subsequently reduced the rate of organ formation and expansion. Daughter scale removal reduced the number of leaves and flowers initiated and anthesis was delayed because of the reduction in rate at which these organs expanded.
Nematodes impart significant damage to carrot production worldwide. Genetic resistance was studied for Meloidogyne javanica, one of the three major nematodes affecting carrots in warmer climates. F2, F3, and backcross families of `Brasilia' × B6274 were evaluated for resistance in inoculated seedlings. Resistance was conditioned by one, or two linked, dominant loci. Molecular markers were also evaluated with bulked segregant analysis. Three RAPD markers and AFLPs were associated with resistance loci.
Sulfentrazone is a promising new herbicide now under evaluation for use in agronomic and ornamental cropping systems. Sulfentrazone selectively controls yellow nutsedge, morningglories, and other annual grasses and broadleaf weeds. Research was conducted to evaluate the efficacy of sulfentrazone in combination with other labeled products for preemergence weed control in nursery crops. Treatments included sulfentrazone at 0.56 and 1.12 kg a.i./ha and sulfentrazone at 0.37 kg a.i./ha in combination with the following; dithiopyr at 0.37 kg, oxyfluorfen at 0.56 kg, metolachlor at 3.36 kg, isoxaben at 0.56 kg, norfluorazon at 2.64 kg, and isoxaben plus oryzalin at 2.24 kg a.i./ha. Combinations of sulfentrazone with isoxaben or metolachlor provided superior control of morningglory spp., honeyvine milkweed, Carolina horsenettle, and yellow nutsedge. Sulfentrazone plus oxyfluorfen or isoxaben plus oryzalin also provided good control. Poorest overall control was obtained with sulfentrazone plus dithiopyr. Viburnum and deciduous holly were slightly injured 4 WAT with sulfentrazone plus metolachlor. Sulfentrazone plus dithiopyr treatments resulted in serious injury to burning bush 4 WAT and slight injury at 8 WAT.
Potted apple trees were severely (S) or moderately (M) droughted and compared to a well-watered control (C) to determine changes in biogenesis of leaf volatile compounds. Total available water (TAW) of the soil was allowed to decline to near 0% TAW, 20% TAW, and 100% TAW, for S, M and C, respectively, by the end of a two-week drying period. Twenty-nine volatile compounds were identified by GC-MS using headspace sampling of detached leaves. Concentrations of (E)-2-hexenal, (E)-2-hexenyl acetate, l-hexanol, (E)-2-hexen-1-ol and hexyl acetate were 5 to 310 times higher for S than C. It is suggested that the large drought induced increase in C-6 compounds was related to enhanced lipoxygenase activity.
Abstract
Hand- and machine-harvested ‘Stover’ (a white Euvitis hybrid) and ‘Noble’ (a red Vitis rotundofolia cultivar) grapes were either treated with 100 mg SO2/kg (applied as potassium metabisulfite, K2S2O5) or not treated and held at ambient temperature (≈25°C) for 0, 24, and 48 hr after harvest. Raw fruit and wine quality from each treatment were evaluated. ‘Noble’ grapes of all treatments held for 24 hr had developed signs of microbial spoilage, and the machine-harvested grapes held without SO2 had the most. However, only the machine-harvested ‘Stover’ grapes held without SO2 had began to deteriorate during 24 hr. Grapes of both cultivars had deteriorated after 48 hr, but SO2 limited the deterioration of both machine- and hand-harvested grapes. In general, machine-harvested grapes deteriorated to a greater extent than hand-harvested grapes. Wines made from ‘Noble’ grapes that had been held for 0 or 24 hr had similar quality, but machine-harvested ‘Stover’ grapes held for 0 to 24 hr without SO2 produced a poorer wine than the other treatments. Wines from machine-harvested grapes held for 48 hr had poorer quality than wines from hand-harvested grapes. Postharvest additions of SO2 improved the quality of wine from machine-harvested but not hand-harvested fruit held for 48 hr.
Powdery mildew (PM) occurs worldwide and is prevalent on susceptible cultivars wherever pears are grown, causing economic losses due to russeted fruit and an increased need for fungicides. A core subset of the Pyrus germplasm collection at the USDA National Clonal Germplasm Repository in Corvallis, Ore., was evaluated for resistance to Podosphaera leucotricha, the causal agent of PM, using greenhouse and field inoculations of potted trees. The core collection consists of about 200 cultivars and species selections, representing most of the genetic diversity of pears and includes 31 Asian cultivars (ASN), 122 European cultivars (EUR), 9 EUR × ASN hybrids and 46 pear species selections. Three trees of each core accession were grafted on seedling rootstocks. In 2001–02, trees were artificially inoculated in a greenhouse, grown under conditions conducive for PM, and evaluated for symptoms. The same trees were subsequently evaluated for PM symptoms from natural field infections during 2003 and 2004. In the greenhouse, 95% of EUR and 38% of ASN were infected with PM. Average PM incidence (percent of leaves infected) in the greenhouse (8% for ASN and 30% for EUR) was much higher than incidence in the field (2% for ASN and 5% for EUR) during 2003. Symptoms were also more severe in the greenhouse, with 46% of ASN and 83% of EUR with PM symptoms having a mean PM incidence of >10%. In the field, 42% and 22% of EUR and 23% and 13% of ASN were infected with P. leucotricha in 2003 and 2004, respectively. Field infection was very low during both years, with percentage leaves infected in ASN and species selections significantly different from EUR. In the field, 6% of ASN with PM symptoms had a mean PM incidence >10% during both years, while 15% and 2% of EUR accessions with PM symptoms had a mean PM incidence >10% in 2003 and 2004 respectively. These results should be very useful to pear breeding programs to develop improved PM resistant cultivars in the future, by using accessions with consistent low PM ratings.
Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.
Hydration and elemental absorption of two commercially-available polyacrylamide gels (A and B) were studied in response to a 24-hr soak time in Hoagland's solution concentrations of either 2X, 1X, 0.5X, 0.25X, 0.125X or 0X (deionized water). Elemental absorption of gel specimens was observed and analyzed within the gel matrix on a Philips CM12S STEM equipped with an EDAX 9800 plus EDS unit for micro x-ray analysis. Thick sections were cut on dry glass knives using an RMC MT6000 ultramicrotome. Surface analysis of bulk specimens was made with an AMR 1000A SEM plus PGT1000 EDS unit. Overall, gel hydration decreased quadratically as solution concentration increased linearly; however, hydration for gel A was generally greater than for gel B. Surface analysis of gel samples revealed the presence Ca, K, P, S, Fe, and Zn for both gels. An analysis within the matrix of gel B revealed the presence of Ca, K, P, S, Fe, and Zn; however, an analysis within the matrix of gel A revealed the presence of Zn, and Fe only. The increased absorptive capacity of gel A appeared to be coupled to reduced migration of salts into the gel matrix.
Low and high tunnels and root-zone heating systems are proven tools in horticultural production. However, impacts of their separate and combined application on crop yield, composition, and microclimates are underreported. We addressed these gaps in the literature by exposing lettuce (Lactuca sativa) to four microclimates established with low and high tunnels and root-zone heating during the spring and fall of 2 years in Wooster, OH. Red-leaved romaine lettuce cultivars Outredgeous and Flagship were direct-seeded into raised beds in both outdoor and high-tunnel settings in early October and late March and harvested multiple times over 4 weeks. Half of all plots in each setting were underlain by electric heating cables, and half were covered with 0.8-mil, clear, vented, low tunnels. A growing medium consisting of peat moss, compost, soil, and red clover (Trifolium pratense) hay was used, and all plots were overhead-irrigated. Soil and air temperatures were monitored throughout the experiments, which were repeated four times (2 seasons/year × 2 years). Here, we report primarily on treatment effects on crop yield and related variables. Root- and shoot-zone conditions and cultivar significantly affected leaf biomass in both settings (outdoor, high tunnel), while population was more often affected in the outdoor experiments. Microclimate main effects were more prevalent than cultivar effects or interactions. Leaf yield was greater in low-tunnel-covered and bottom-heated plots than in uncovered and unheated plots. We take these data as further evidence of the potential to alter lettuce yield through root- and shoot-zone microclimate modification, particularly in regions prone to dynamic seasonal and within-season temperature and light conditions. The data also suggest that the relative performance of low and high tunnels in the production of short-statured, quick-cycling crops during fall and spring be more thoroughly evaluated.