bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental Regulation of Anther Dehiscence and Pollen Germination in Pecan
Authors: Yates I.E. , Sparks Darrell
Published: January 2019

Detached anthers and pollen of pecan [Carya illinoinensis (Wangenh.) C. Koch] were exposed to a range of relative humidities (RH) and/or temperatures to assess the interaction of these environmental factors on pollen dispersal and germination. Dehiscence of anthers was evaluated at selected time intervals following exposure to ≈56%, 33%, 64%, and 97% RH at 10, 21, 27, and 33C in a factorial experiment. Pollen release increased as RH decreased and temperature increased for detached anthers under laboratory conditions and for attached anthers under field conditions. Inhibition of anther dehiscence by high RH could be overcome or minimized with high temperatures and inhibition by low temperatures, in most cases, with low RH. Temperature effects on specific phases in the pollen germination process were evaluated in a sequence of experiments. First, pollen rehydration temperature was varied (3, 15, 29, 33, and 42C) and incubation temperature during tube development kept constant at 25C. After 2 hours of rehydration, tube formation was maximized at 15C and tube length at 29C. Second, all pollen was rehydrated at a constant temperature (25C) and the incubation temperature during tube development varied (3, 15, 29, 33, and 42C). The temperature for maximum tube formation (15C) was different from that for maximum tube length (33C). Morphology of pollen tubes was normal under all rehydration conditions; but, during incubation for pollen tube development, tubes did not develop at 3C and developed abnormally at 42C. The adverse effect on tube development at 3C, but not at 42C, could be reversed by transferring pollen to 25C.
An Irrigation Scheduling Model for Turnip Greens
Authors: Simonne Eric H. , Smittle Doyle A. , Mills Harry A.
Published: January 2019

An irrigation scheduling model for turnip (Brassica rapa L.) was validated using a line-source irrigation system in a 2-year field trial. The model used a water balance, a variable root length, and a crop factor function of plant age (i). Evapotranspiration was computed daily as class A pan evaporation times a crop factor [CF(i) = 0.365 + 0.0154i-0.00011i2]. Irrigation according to the model maintained soil water tension at <25 kPa at a 30-cm depth. When rainfall amounts were less than water use, leaf yields responded quadratically to irrigation rates, from 0% to 160% of the model rate, and the highest leaf yield with the lowest water applications corresponded to the model rate. Therefore, this model could replace the “feel or see” methods commonly used for scheduling irrigation of leafy vegetables grown in the southeastern United States.
Reversed Greenhouse Temperatures Alter Carbohydrate Status in Lilium longiflorum Thunb. `Nellie White'
Authors: Miller William B. , Hammer P. Allen , Kirk Terri I.
Published: January 2019

Commercial greenhouse operators are increasingly using “negative DIF” temperature regimes to control crop height. A negative DIF exists when greenhouse night temperature is greater than the day temperature. Large negative differences in day and night temperatures strongly suppress stem elongation in many crops. We have explored the effects of negative DIF temperature regimes on leaf, flower, and stem carbohydrate levels in Lilium longiflorum Thunb. `Nellie White'. During two growing seasons, `Nellie White' plants were grown under positive or negative DIF regimes (±5 or 8C) under prevailing daylengths, with temperatures adjusted so that daily temperature averages were equal between regimes. Plants were harvested ≈10 days after visible bud stage and at anthesis. Carbohydrates in stems, leaves, and flowers were analyzed by high-performance liquid chromatography. Compared to plants grown under positive DIF, negative DIF plants showed significantly reduced stem length and leaf and stem dry weights. Negative DIF regimes reduced leaf and stem total soluble carbohydrate (TSC) content by 39% to 46% at visible bud and anthesis, while flower TSC content was reduced by 10% to 13%.
Canopy Nutrient Allocation in Relation to Incident Light in the Tropical Fruit Tree Borojoa patinoi (Cuatr.)
Authors: Lynch Jonathan , González Alonso
Published: January 2019

The relationship of incident photosynthetically active radiation (PAR) and mineral nutrient allocation was evaluated in canopies of Borojoa patinoi (Cuatr.) growing in the Chocó rainforest of Colombia, South America. Allocation of P in the canopy was positively correlated with incident PAR, principally because of increased leaf frequency (number of leaves per unit volume of canopy) brought about by local branching, with a smaller contribution from increased specific leaf weight (SLW, leaf dry weight per unit leaf area). The chemical fractionation of P within leaves did not respond to incident PAR. Canopy N allocation also was positively correlated with incident PAR because of increased leaf frequency and SLW. The N partitioning to soluble protein rather than chlorophyll was positively correlated with incident PAR. The allocation of K, Ca, Mg, S, Mn, and Cu also was positively correlated with incident PAR primarily because of increased leaf frequency and secondarily because of increased SLW. The area of individual leaves and the concentration of nutrients in leaf dry weight were not important in determining nutrient allocation responses to incident PAR. Our observations suggest that leaf frequency caused by local branching, followed by changes in SLW, are the primary determinants of canopy nutrient allocation in this tropical fruit tree.
A Modified Hypothesis on the Role of Conjugated Trienes in Superficial Scald Development on Stored Apples
Authors: Du Zhanyuan , Bramlage William J.
Published: January 2019

Three experiments were conducted using `Cortland' and `Delicious' apples (Malus domestica Borkh.). Fruit varying widely in superficial scald susceptibility, because of either endogenous or experimentally induced conditions, were stored for various intervals at 0C and evaluated for scald development at 20C. Samples were extracted periodically in hexane, and ultraviolet absorption spectra of the extracts were used to evaluate α-farnesene and conjugated triene (CT) relationships to scald development. CT concentrations were calculated using each of the three CT absorption maxima (258-290 nm, 269-290 nm, and 281-290 nm) and expressed accordingly as CT258, CT269, and CT281. The poor association of CT281 concentrations with scald development led us to propose that metabolic products of CT281 species are more likely to be associated with scald development than the species themselves.
Source- and Sink-limited Growth Periods of Developing Peach Fruits Indicated by Relative Growth Rate Analysis
Authors: Pavel E.W. , DeJong T.M.
Published: January 2019

Peach [Prunus persica (L.) Batsch] fruit thinning was used to reduce the competition for assimilates among peach fruits and to identify periods of source- and sink-limited growth during development. Individual fruit size, based on diameter or calculated dry matter accumulation, increased in trees with lower crop loads compared to fruits of unthinned trees in three peach cultivars. Relative growth rate analysis indicated that peach fruit growth was apparently limited by the assimilate supply (source-limited) or by its genetic growth potential (sink-limited) during specific growth periods. In stage I and at the beginning of stage III of the double-sigmoid growth curve, periods of source-limited growth occurred in the later-maturing cultivars Flamecrest and Cal Red. Peach fruit growth was apparently sink-limited during stage II of the growth curve when fruit relative growth rates were similar for the thinning treatments. Fruit growth in `Spring Lady', an early maturing cultivar, appeared to be primarily source-limited during the season. Although total fruit dry matter production was reduced by thinning, individual fruit dry weight on thinned trees was higher than that on trees with a heavy crop load. This typical thinning response was apparently caused by the differences in the amount of time that fruits grew under sink-vs. source-limited conditions with different crop loads. Final crop yield depended on fruit count per tree and on the available assimilate supply, and was affected by the individual fruit growth potential.
Nitrogen-induced Changes in the Growth and Metabolism of Cultured Potato Tubers
Authors: Chen Junne-Jih , Liao Yu-Ju
Published: January 2019

The effect of N source on `Kennebec' potato (Solanum tuberosum L.) tuberization was investigated using single-node segments originated from in vitro virus-free plantlets and inoculated on media with two nitrate: ammonia ratios (low, 2:1; high, 5:1). Cell count and size and sugar-use characteristics were measured at intervals of tuber development. Tubers grown on high nitrate-ammonia medium exhibited higher rates of sucrose use and higher dry-matter accumulation than tubers grown on low nitrate-ammonia medium. The median value of tuber fresh weight increased from 0.66 to 1.23 g as a result of increasing nitrate-ammonia. Significant differences in cell size and growth rate were observed between the two N treatments. There was also a high correlation between tuber cell size and dry matter (r = 0.82, P ≤ 0.05). These data demonstrate the importance of the nitrate: ammonium ratio in determining C use, tuber cell size, and tuber weight. Chemical names used: α-naphtylacetic acid (NAA); 6-benzylaminopurine (BA).
Male and Female Fertility of Loosestrife (Lythrum) Cultivars
Authors: Anderson Neil O. , Ascher Peter D.
Published: January 2019

Male and female fertility, seed germination, and progeny fertility were used to determine cultivar fertility in species of Lythrum. One short-, 11 mid-, and six long-styled cultivars were included in this study. Duplicates of several cultivars from different nurseries and three unknown cultivars from Minnesota gardens were also collected. Plants from 17 Minnesota and one Wisconsin population of L. salicaria served as fertile male and/or female testers. Pollen stainability (usually 100%) showed low levels of male gamete abortion. Pollen size within and among anther type varied widely; possible 2n gametes were present in primarily the short- and mid-anther morphs. Seed production per capsule from legitimate cross-pollinations, using cultivars as male parents with Minnesota or Wisconsin female testers, averaged 48 ± 36 across style morphs. Cultivars differed as males, as did anther morphs. With female fertility tests, seed set per capsule ranged from zero to 152 and averaged 54 ± 40 in legitimate pollinations (i.e., pollinations between stamen and styles of the same length). Seed set for other crosses showed similar trends. Only `Morden Gleam' produced no seed with all legitimate pollinations, although illegitimate selfs or interspecific crosses produced seed. Seed from legitimate crosses of L. salicaria × cultivars had 30% to 100% germination. Common male and female parents within each legitimate crossing group were not significantly different. This study showed that the cultivars are highly fertile when used as male or female parents with wild purple loosestrife, native species (L. alatum Pursh.), or other cultivars. Thus, cultivars grown in gardens could serve as pollen or seed sources for the continued spread of purple loosestrife. The implications of cultivar fertility, especially interspecific F1 hybrids, is discussed in relation to the spread of noxious weeds in wetlands.
Contributions of Dent Corn Germplasm to Stalk and Root Quality in Sweet Corn
Authors: Treat C.L. , Tracy W.F.
Published: January 2019

Root or stalk lodging can be a serious problem in sweet corn (Zea mays L.) production. Four dent corn inbreds, crossed to five sweet corn inbreds in a design II mating system, and a half diallel with five sweet corn inbreds were used to 1) determine the effect and potential contribution of dent corn germplasm on stalk and root quality traits in sweet corn, 2) examine the variation for stalk and root quality traits in some sweet corn germplasm, and 3) evaluate the utility of traits used in improving dent corn root and stalk quality in sweet corn improvement. The dent corn germplasm used in this study had a favorable affect on stalk and root quality in the dent × sweet hybrids. Compared to the sweet × sweet hybrids, the dent × sweet hybrids had significantly higher stalk crushing strength and stalk soluble carbohydrates, while having significantly less stalk lodging. The mean stalk lodging for the dent × sweet hybrids was 4.4%, while the sweet × sweet hybrids averaged 18.7%. Within the diallel, effects due to hybrids were highly significant for stalk section weight, rind thickness, and stalk diameter. Percent stalk lodging was negatively correlated with stalk section weight [r = (-0.63), P ≤ 0.05] and crushing strength [r = (-0.64), P ≤ 0.05]. No traits were significantly correlated with root lodging within the sweet corn crosses. Dent corn has potential as a source of improved stalk and root quality in sweet corn.
In Vitro and ex Vitro Adventitious Root Formation in Asian Jasmine (Trachelospermum asiaticum) II. Physiological Comparisons
Authors: Apter R.C. , Davies F.T. , McWilliams E.L.
Published: January 2019

In vitro tissue-cultured (TC) and macropropagated (MACRO) 18-day old adventitious roots of Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai] were compared for their ability to absorb and translocate radiolabelled P from a nutrient solution. Samples were taken at 1, 2, 4, 8, 12, and 24 hours after the initial dosage of the nutrient solution with 7.4 × 10-2 MBq KH 322PO4/liter. TC roots were capable of absorbing P, but at significantly lower levels than MACRO roots. Greater P absorption occurred in MACRO roots within the first hour and continued for the duration of the experiment. However, there was no significant difference in the rate of P translocation from roots to shoots between treatments. Root systems formed in vitro survived acclimation and had developed into well-branched root systems after 13 weeks. Reduced P absorption by TC roots did not limit either P translocation or survivability during and after acclimation.
Economic Analysis of Integrated Crop Management Practices of `Navel' Oranges
Authors: Takele Etaferahu , Menge John A. , Pehrson John E. , Meyer Jewell L. , Coggins Charles W. , Arpaia Mary Lu , Hare J. Daniel , Atkin Darwin R. , Adams Carol
Published: January 2019

The effect of various integrated crop management practices on productivity (fruit yield, grade, and sire) and returns of `Washington Navel' oranges [Citrus sinensis (L.) Osbeck] was determined in the San Joaquin Valley of California. Seventy-two combinations of treatments comprised of three irrigation levels [80%, 100%, and 120% evapotranspiration demand (ETc)], three N fertilizer levels (low, medium, and high based on 2.3%, 2.5%, and 2.7% leaf N, respectively), gibberellic acid (±), miticide (±), and fungicide-nematicide (±) were included in the analysis. Using a partial budgeting procedure, returns after costs were calculated for each treatment combiition. Costs of treatments, harvesting, packing, and processing were subtracted from the value of the crop. The value of the crop was calculated as the sum of returns of crop in each size and grade category. The overall result indicated that returns after costs were higher for the +fungicide-nematicide treatment and also were generally more with increased irrigation. The combination of 120% ETc, +fungicide-nematicide, medium or high N, -miticide, and -gibberellin showed the highest return of all treatment combinations. Second highest returns were obtained with high N or with miticide and gibberellin used together.
Nuclear DNA Content and Ploidy Levels in the Genus Ipomoea
Authors: Ozias-Akins Peggy , Jarret Robert L.
Published: January 2019

The nuclear DNA content of 53 accessions from 24 Ipomoea (Convolvulaceae) species, including four sweetpotato cultivars, was determined by flow cytometry of DAPI-stained nuclei. Ploidy level and DNA content were significantly correlated within the genus, but more highly so within species that contained multiple cytotypes. DNA content of cultivated Z. batatas (L.) Lam. (4.8 to 5.3 pg/2C nucleus) and feral tetraploid I. batatas (3.0 to 3.5 pg/2C nucleus) was estimated from the known DNA content of chicken erythrocytes (2.33 pg), which were used as an internal standard. Tetraploid forms of Z. cordato-triloba Dennstedt also were identified. Ploidy analysis using flow cytometry is rapid and suitable for large-scale experiments such as studying the genetic structure of populations of Z. batatas and related species. Chemical name used: 4′,6-diamidino-2-phenylindole (DAPI).
Cultivar, Ground-cover, and Irrigation Treatments and Their Interactions Affect Long-term Performance of Peach Trees
Authors: Layne Richard E.C. , Tan Chin S. , Hunter David M.
Published: January 2019

Three cultivars (`Garnet Beauty', `Harbrite', `Canadian Harmony'), two ground covers (temporary cover vs. permanent sod), and no irrigation vs. season-long trickle irrigation were studied in a high-density (633 trees/ha) peach [Prunus persica (L.) Batsch] orchard established on Fox sand in 1980. From 1985 to 1989, soil water content in the top 130 cm was similar in nonirrigated and trickle-irrigated plots except during the growing season (May to September). Total soil water was lowest in nonirrigated plots that had permanent sod strips in the row middles and fell below the-permanent wilting point for ≥11 months in summer but not at depths below 130 cm. Trunk cross-sectional area (TCA) was greater for `Canadian Harmony' and `Harbrite' than `Garnet Beauty', ground-cover treatments had no effect, and irrigated trees were generally larger than those not irrigated. Photosynthetic rate and stomatal conductance differed by cultivar, were unaffected by ground cover, and were enhanced by irrigation. Defoliation differed by cultivar, ground cover had little effect, and irrigation usually delayed defoliation. Flower bud and shoot xylem hardiness differed by cultivar but not by ground cover and were generally enhanced by irrigation. Tree survival was significantly affected by cultivar, being best with `Harbrite' and `Canadian Harmony' and poorest with `Garnet Beauty'. Permanent sod enhanced tree survival while trickle irrigation reduced it. Cumulative marketable yields were affected more by cultivar than by ground cover or irrigation. `Canadian Harmony' had the highest yield, followed by `Harbrite', then `Garnet Beauty'. Yields in sod were slightly higher than in temporary cover and yields with trickle irrigation were slightly higher than without irrigation. The best soil-management system when TCA, marketable yield, and tree survival were considered was a combination of permanent creeping red fescue sod strips in the row middles and trickle irrigation in the tree row. This system is being recommended to commercial growers in southwestern Ontario.
Irrigation Regimes Affect Cabbage Water Use and Yield
Authors: Smittle Doyle A. , Dickens W. Lamar , Stansell James R.
Published: January 2019

Cabbage (Brassica oleracea L.) was grown in drainage lysimeters under controlled soil water regimes during 3 years. Three irrigation regimes were imposed on cabbage grown on two soil types during the spring and fall growing seasons. Irrigation regimes consisted of applying water when the soil water tension at 10 cm exceeded 25, 50, or 75 kPa during crop growth. Yields and water use were highest when irrigation was applied at 25 kPa soil water tension. Regression equations are presented to describe the relationships of water use to plant age and to compute the ratios of daily evapotranspiration to pan evaporation (crop factors) for cabbage grown under the three irrigation regimes.
Regulating Vegetative Growth and Flowering with Gibberellic Acid in Intact Plants and Cultured Phylloclades of `Crimson Giant' Easter Cactus
Authors: Boyle Thomas H. , Marcotrigiano Michael , Hamlin Suzanne M.
Published: January 2019

Investigations were performed to determine the influence of gibberellic acid (GA3) on intact plants and cultured phylloclades of `Crimson Giant' Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran]. Responses of intact plants depended on GA3 concentration, number of spray applications, and application time. Single GA3 applications delayed flowering and reduced the percentage of apical phylloclades flowering and number of flower buds per plant when applied before floral primordia formation [from 20 days before to the start of long days (LDs)], but hastened flowering and did not affect the percentage of apical phylloclades flowering or number of flower buds per plant when applied during floral bud development (20 days after the start of LDs). When sprays were applied at or before the start of LDs, increasing the GA, concentration resulted in fewer plants flowering, longer flowering delays, and further decreases in the number of flower buds per plant. Multiple GA3 applications were more inhibitory to flowering than single applications. Whole plants and cultured phylloclades exhibited similar reactions to GA3, but cultured phylloclades were more responsive to GA3 than intact plants. Intact plants and cultured phylloclades generally produced more new phylloclades as GA3 concentration increased. Spine growth also increased when phylloclades were cultured in a GA3-containing medium. Flowering was accelerated by ≈55 days when GA, was applied to intact plants with 1- to 2-mm-long flower buds. GA, may be horticulturally useful for Easter cactus crop scheduling.
Molecular Confirmation that Sterile Cytoplasm Has Been Introduced into Open-pollinated Grano Onion Cultivars
Authors: Havey M.J. , Bark O.H.
Published: January 2019

Open-pollinated (OP) onion (Allium cepa L.) cultivars are primarily in normal (N) fertile cytoplasm; however, specific cultivars possess both N and sterile (S) cytoplasm or are exclusively in S cytoplasm. It is unclear whether the presence of S cytoplasm in OP cultivars is due to ancient or recent introduction or both. Restriction-enzyme analysis of the chloroplast DNA established that S cytoplasm has been introgressed into OP onion cultivars since its discovery in 1925. `Valencia Grano' (released in 1927), `New Mexico Early Grano' (1931), `Texas Early Grano (TEG) 502' (1947), and `Temprana' (1979) are in N cytoplasm; S cytoplasm was introduced into the population `TEG 502 PRR', and subsequent selections (`NuMex BR1' and `NuMex Sunlite') are in S cytoplasm. The inbred `TEG 951 C' and `Texas Grano 1015Y' possess a mixture of N and S cytoplasm and, because these two onions originated from self-pollinations of single plants, bulb or seed mixtures or both must have occurred.
Inter- and Intraspecific Resistance Variability in Myrobalan Plum, Peach, and Peach-Almond Rootstock Using 22 Root-knot Nematode Populations
Authors: Esmenjaud D. , Minot J.C. , Voisin R. , Pinochet J. , Salesses G.
Published: January 2019

Resistance variability was evaluated for five rootstock: three Myrobalan plum (Prunus cerasifera Ehr.) genotypes (P.1079, P.2175, and P.2032) grown from in vitro plantlets, one peach (P. persica (L.) Batsch `GF 305') grown from seeds, and one peach-almond hybrid (P. persica × P. amygdalus Batsch `GF 557') grown from rooted cuttings. Twenty-two root-knot nematode populations from different origins were used: Meloidogyne arenaria (Neal) Chitwood (six populations), M. incognita (Kofoid and White) Chitwood (eight populations), M.javanica (Treub) (four populations), M. hispanica Hirschmann (one population), M. hapla Chitwood (two populations), and an unclassified root-knot species (one population). The study was conducted under greenhouse conditions for 1 and 2 months. No galling or nematode reproduction was observed in P.1079 and P.2175, which should be considered immune; P.2032 showed the highest galling and nematode counts when inoculated with M. hispanica and M. javanica. In P.2032, a high proportion of males was recovered in populations that had a limited development. Because the populations of the first four Meloidogyne species reproduce by obligatory mitotic parthenogenesis, high sex ratio maybe the expression of a late form of resistance. Host suitability of `GF 305' was highly variable among M. arenaria and M. incognita populations. A lower relative variation was observed in M. javanica. `GF 557' was resistant to M. arenaria and M. incognita except for one population of M. arenaria that was weakly aggressive and susceptible to M. javanica. Consequently, resistances specific to the genus Meloidogyne for the Myrobalan plum genotypes P.1079 and P.2175, specific to the nematode species for `GF 557', and specific to the nematode population for `GF 305', were evidenced. This study indicates that, in rootstock selection procedures, it is important to test resistance to several populations within the same nematode species.
Potential Evapotranspiration as a Means of Predicting Irrigation Timing in Greenhouse Tomatoes Grown in Peat Bags
Authors: Norrie J. , Graham M.E.D. , Gosselin A.
Published: January 2019

The use of potential evapotranspiration (PET) estimates to identify irrigation timing for greenhouse tomatoes (Lycopersicon esculentum Mill.) grown in peat-based substrate was evaluated for a spring and fall crop. PET (using the Penman equation) was calculated from leaf, wet and dry bulb temperatures, and incident and reflected photosynthetic photon flux. Substrate matric potential (SMP) was monitored continuously using electronic tensiometers. Two irrigation starting setpoints (-4.5 and -6.5 kPa SMP) and two nutrient solution electrical conductivity (EC) treatments (1.5 and 3.0 dS·m-1) were factorially combined in a completely randomized design. Irrigation frequency was greater in treatments irrigated at -4.5 than at -6.5 kPa. The integral of calculated PET values was correlated with SMP for both experiments. Accumulated PET values were higher at the start of irrigation in the -6.5-kPa treatments for spring and fall crops. Nutrient solution EC did not influence irrigation frequency. Leaf pressure potential (LPP) was correlated to PET-predicted LPP (r2 > 0.56) in plants subjected to high EC, low (-6.5 kPa) matric potential setpoint, or both treatments. PET and electronic tensiometer technology can be used jointly to improve irrigation management for tomatoes grown in peat-based substrates by more accurately responding to crop needs for water and nutrients.
Orchard Groundcover Management Impacts on Apple Tree Growth and Yield, and Nutrient Availability and Uptake
Authors: Merwin Ian A. , Stiles Warren C.
Published: January 2019

This study compared various conventional and alternative orchard groundcover management systems (GMSs)—including a crownvetch “living mulch” (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of postemergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during 6 years in a newly established apple (Malus domestica Borkh.) planting. Trunk cross-sectional area and fruit yield were higher in STMCH, GLY, and NDPQT, intermediate in tilled, and lower in GRSOD, MWSOD, and CNVCH treatments after 5 years. Despite N and K fertilizer applications, extractable soil N and leaf N concentrations were reduced under MWSOD and GRSOD, and soil K, P, and B concentrations were greater under STMCH. Leaf K concentrations were usually highest in STMCH trees, even when heavily cropped; leaf K declined below the sufficiency range in GLY, NDPQT, and tilled trees as they began to bear fruit. Leaf Ca was marginally deficient in all trees and was unaffected by GMS. Foliar Mn, Zn, and B concentrations declined rapidly in all treatments during 2 years without micronutrient fertilizers. Leaf Cu was higher in herbicide and tilled treatments where seasonal soil water content was intermediate (22% to 27%) and lower where soil was very wet or dry for most of the 1988 growing season. Multiple regression analysis indicated that leaf N and B and soil organic matter in 1990, and mean soil water content during the unusually dry Summer 1988, were the best predictors of fruit yield in 1990. Phytophthora root rot and meadow vole depredation were serious problems in STMCH and CNVCH trees. GMSs greatly affected tree establishment, nutrition, and yield; each system involves tradeoffs among important short- and long-term impacts on the orchard agroecosystem.
Responses of Young Peach Trees to Root Confinement
Authors: Rieger Mark , Marra Francesco
Published: January 2019

Rooted cuttings of Nemaguard peach [Prunus persica (L.) Batsch.] were grown in 0.18-, 0.36-, 0.90-, and 2.40-liter containers for 16 weeks to study the influence of root confinement on growth, gas exchange, water uptake, and leaf carbohydrate and nutrient content. An automatic nutrient-solution dispensing system was used to ensure uniform fertility among treatments and to prevent drought stress. Leaf area and stem length were reduced by root confinement 6 to 7 weeks after transplanting, and differences among treatments increased throughout the experiment. Final tree dry weights were reduced by 51% over a 13-fold reduction in rooting volume, but dry weight partitioning was largely unaffected. A temporary limitation to CO2 assimilation (A) and leaf conductance (g) was observed just after budbreak, but consistent reductions in A and g for confined trees did not occur until after week 11. Sorbitol and starch accumulated earlier in leaves of trees in smaller containers than larger containers. Despite similar fertility, concentrations of all nutrients except N and Cu were reduced ≈2-fold for trees in 0.18-liter containers compared to other treatments. However, characteristics of nutrient deficiency were not observed on any trees, and growth reduction with no change in leaf nutrient content was observed in other treatments. It was concluded that the initial mechanisms limiting growth were not gas exchange rates, levels of nonstructural carbohydrates, or drought stress, although nutrient deficiency may have contributed to growth limitation in trees with severely confined root systems.
Heat Tolerance of Five Taxa of Birch (Betula): Physiological Responses to Supraoptimal Leaf Temperatures
Authors: Ranney Thomas G. , Peet Mary M.
Published: January 2019

Leaf gas-exchange and chlorophyll fluorescence measurements were used as indexes for evaluating heat tolerance among five taxa of birch: paper (Betula papyrifera Marsh.), European (B. pendula Roth.), Japanese (B. platyphylla var. japonica Hara. cv. Whitespire), Himalayan (B. jacquemontii Spach.), and river (B. nigra L. cv. Heritage). Gas-exchange measurements were conducted on individual leaves at temperatures ranging from 25 to 40C. River birch maintained the highest net photosynthetic rates (Pn) at high temperatures, while Pn of paper birch was reduced the most. Further study of river and paper birch indicated that the reduced Pn at high temperatures and the differential sensitivity between taxa resulted from several factors. Inhibition of Pn at higher temperatures was due largely to nonstomatal limitations for both taxa. Increases in respiration rates, decreases in maximal photochemical efficiency of photosystem (PS) II (FV/FM), and possible reductions in light energy directed to PS II (F0 quenching) were apparent for both taxa. The capacity of river birch to maintain greater Pn at higher temperatures seemed to result from a lower Q10 for dark respiration and possibly greater thermotolerance of the Calvin cycle as indicated by a lack of nonphotochemical fluorescence quenching with increasing temperatures. Thermal injury, as indicated by a rapid increase in minimal, dark-acclimated (F0) fluorescence, was not evident for either paper or river birch until temperatures reached ≈49C and was similar for both taxa.
Variation in the Onset of Flowering of Summer Squash as a Function of Days and Heat Units
Authors: NeSmith D.S. , Hoogenboom G.
Published: January 2019

The time from sowing to flowering and maturity of summer squash (Cucurbita pepo L.) varies depending on environment. Research was conducted over a 2-year period to assess flowering time of five squash cultivars grown at different locations and times in Georgia representing varying thermal regimes. Heat units (HUs) were calculated using a single equation to determine if this approach could account for a significant proportion of the variability in the time to onset of flowering observed over this range of environments. Depending on the cultivar and flower sex, the number of days to flowering varied as much as 20 days. There were no cultivar differences in overall mean days to first staminate flower; however, there were differences in mean days to first pistillate flower. There were cultivar differences in HUs required for staminate and pistillate flowers. The use of HUs significantly affected the variability in time to flowering as indicated by regression analyses and mean absolute differences between predicted and observed days to flowering.
Predicting Tomato Seedling Morphology by X-ray Analysis of Seeds
Authors: van der Burg W.J. , Aartse J.W. , van Zwol R.A , Jalink H. , Bino R.J.
Published: January 2019

Studies based on X-ray photographs were conducted to predict the morphology of tomato (Lycopersicon esculentum Mill.) seedlings at transplanting stage. Currently, seed-lot quality of tomato seeds for growing commercial transplants is determined with grow-out tests in the greenhouse because the standard germination test fails to predict the percentage of normal or usable transplants (UTs). These grow-out tests, however, are difficult to standardize. An X-ray evaluation procedure is presented as an alternative. X-ray images nondestructively provide information on embryo size and morphology and the amount of endosperm and the area of free space. These parameters correlate well with the morphology of 14-day old seedlings. Cotyledon morphology has the highest correlation with the percentage of UTs. A test based on the evaluation of X-ray images, classifying the cotyledon morphology and seed free space, predicts the percentage of UTs more accurately than the currently used germination test. A second method based on an equation that uses the probabilities of all X-ray categories proportionally predicts the percentage of UTs of primed seeds more accurately than the first method. Selecting individual seeds based on X-ray images has the potential to raise the percentage of UTs of seed lots. On the average, the percentage of UTs of control seeds was 22% higher after hand selection based on X-ray evaluation. Primed seeds gave 12% higher results. Hence, X-ray analysis can predict seedling performance and enable the selection of high-quality seeds.
A Role for Ethylene in the Yellowing of Broccoli after Harvest
Authors: Tian M.S. , Downs C.G. , Lill R.E. , King G.A.
Published: January 2019

Ethylene production from florets of `Shogun' harvested broccoli (Brassica oleracea L.var. italica) held at 20C in darkness increased as the sepal tissues yellowed. The pattern of respiration rate and ethylene production from branchlets or entire heads was similar, although the magnitude of ethylene and carbon dioxide production appeared to be diluted by the other fleshy stem tissues. The reproductive structures, stamens and pistil, may have a role in determining the rate of sepal degreening, since removing them from florets reduced the yellowing rate. The pistil and stamens also had 7-fold higher levels of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity and more than double the ethylene production of other tissues within the floret. Stamen ACC oxidase activity was high on the first day after harvest, before yellowing became obvious. Changes in ACC oxidase activity of the pistil and stamens mirrored changes in ACC content in these tissues. The climacteric status of harvested broccoli was confirmed by exposure to 0.5% propylene. Propylene stimulated respiration and ethylene production and accelerated yellowing (measured as chlorophyll and hue-angle decline). Broccoli tissues did not respond to propylene immediately after harvest. In tissues aged in air before treatment, the time for response to propylene was shorter, a result suggesting a change in tissue sensitivity. Ethylene exposure induced a dose-dependent decline in hue angle, with 1 ppm ethylene giving the maximum response.
Respiratory Metabolism of Pear Fruit and Cultured Cells Exposed to Hypoxic Atmospheres: Associated Change in Activities of Key Enzymes
Authors: Nanos George D. , Romani Roger J. , Kader Adel A.
Published: January 2019

`Bartlett' pears (Pyrus communis L.) at two physiological stages, climacteric minimum or approaching the climacteric peak as achieved via storage for 2 or 8 weeks in air at 0C, respectively, were either ripened at 20C in air immediately or after exposure to 0.25% 02 for 4 days at 20C. Fruit stored for 2 weeks had relatively stable phosphofructokinase (PFK), pyrophosphate: fru-6-P phosphotransferase (PFP), and pyruvate kinase (PK) activities but decreasing succinate dehydrogenase (SDH) activities during ripening in air. Similar fruit treated with 0.25% O2 had slightly increased PFK, PFP, and SDH activities and decreased PK activity. Fruit stored for 8 weeks exhibited higher levels of PFK and PFP activity upon transfer to 20C, in accordance with their more advanced physiological state. In general, the enzymic changes in these fruit upon exposure to 0.25% O2 and subsequent ripening in air were similar to those observed in the less-mature counterparts, most notable being an increase in mitochondrial SDH. Exposure of suspension-cultured pear fruit cells to hypoxia resulted in an accentuated rise in phosphoenolpyruvate carboxykinase activity and a dramatic rise in SDH activity upon transfer to air. Taken in concert, the enzymic analysis supports the hypothesis that the rise in succinate levels observed in hypoxic fruit tissues is the result of a partial reductive tricarboxylic acid cycle. Cytochrome oxidase activity did not change during hypoxia whereas soluble peroxidase decreased somewhat, perhaps a reflection of their Michaelis constants for O2.
Variability in Sorbitol: Sucrose Ratios in Mature Leaves of Different Peach Cultivars
Authors: Escobar-Gutiérrez Abraham J. , Gaudillére Jean-Pierre
Published: January 2019

The aim of this study was to investigate variability in the sorbitol: sucrose ratio (SSR) in source leaves of different peach [Prunus persica (L.) Batsch] cultivars. Four- and 5-year-old trees of 58 cultivars were examined. Mature leaves were sampled on three dates in middle to late summer and analyzed for neutral soluble sugars using high-performance liquid chromatography. Differences in SSRs were observed. In most cultivars, the sorbitol content was at least twice that of sucrose. The maximal range of SSR occurred on the third date and ranged from 1.5 to 4.3. There was a date × genotype interaction (P < 0.01). When cultivars were grouped by country of origin, the mean ratios of the Japanese group were lower than those of the Italian and American groups for all three sampling dates. The SSRs of nectarines were higher than those of peach and canning clingstone-type cultivars. In general, variations in SSR were due mostly to differences in sucrose content. The SSR was negatively correlated with flowering date. These results indicate variability in SSR in peach germplasm, variability that seems to be related to the geographical origin of the cultivars.
Pumpkin Growth, Flowering, and Fruiting Response to Nitrogen and Potassium Sprinkler Fertigation in Sandy Soil
Authors: Swiader John M. , Sipp Stanley K. , Brown Ronald E.
Published: January 2019

Field studies were conducted in 1987 and 1988 to determine the effect of various sprinkler-applied N-K fertigation treatments and 196N-280K (kg·ha-1) dry-blend application on pumpkin (Cucurbita moschata Poir.) flower development, fruit set, vine growth, and marketable yield response in a Plainfield sand. The number of male and female flowers that reached anthesis by 72 days after seeding (DAS) was highest with either 112N-112K or 112N-224K fertigation. Fertigation using either 56N-112K or 168N-224K delayed the start of flowering and reduced the total number of male and female flowers produced by 72 DAS. Fruit set decreased at the low N-K fertigation rate (56N-112K), but otherwise was unaffected by N-K fertility regime. Vine dry weight and stem elongation increased as the N fertigation rate increased, with relatively little effect from fertigated K. There was no field indication of excessive vegetative growth in any of the fertigation treatments. Highest yields of early set marketable fruit (pumpkins that set before 65 DAS), and total marketable yields were obtained with fertigation of 112N, in combination with either 112 or 224 kg·ha-1 fertigated K. Usable green and cull fruit production increased with increasing N-K fertigation rate. Dry-blend application of 196N-280K decreased early and total yields significantly. The results showed that sprinkler-applied 112N-112K split into five fertigations during the growing season (supplemented with a preplant dry-blend application of 28N-56K) produced high yields without compromising early fruit maturity.
Evapotranspiration and Growth Response of Three Woody Ornamental Species Placed under Varying Irrigation Regimes
Authors: Devitt D.A. , Morris R.L. , Neuman D.S.
Published: January 2019

A 2-year study was conducted to quantify the actual evapotranspiration (ETa) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ETa/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ETa was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ETa were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ETa. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.
Salinity Effects on Root Growth and Senescence in Tomato and the Consequences for Severity of Phytophthora Root Rot Infection
Authors: Snapp S.S. , Shennan C.
Published: January 2019

Roots respond first to edaphic stresses, yet little is known about root response to stress in mature, soil-grown plants. We investigated the effects of salinity and phytophthora root rot on root growth and senescence in tomato (Lycopersicon esculentum Mill.). Using minirhizotron- and rhizotron-based methodologies, we quantified intraspecific differences in root-system response to salinity and inoculation. Genotype susceptibility to salt-induced disease was related to root vulnerability to salt. `UC82B' was vulnerable to infection by Phytophthora parasitica when subjected to salt stress and produced thinner roots and ≈50% higher root-senescence rates compared to the phytophthora root rot-resistant `CX8303'. Root growth at the peripheral regions of the `CX8303' root system was inhibited by salinity, but otherwise root dynamics were not affected by salinity or inoculation. Overall, roots from the central root system and roots from the periphery responded differently to salt stress. Monitoring the diameters of new initiated roots indicated the vulnerability of a stressed root system to disease and early senescence.
Production of Methanol from Heat-stressed Pepper and Corn Leaf Disks
Authors: Anderson Jeffrey A.
Published: January 2019

`Early Calwonder' pepper (Capsicum annuum L.) and `Jubilee' corn (Zea mays L.) leaf disks exposed to high temperature stress produced ethylene, ethane, methanol, acetaldehyde, and ethanol based on comparison of retention times during gas chromatography to authentic standards. Methanol, ethanol, and acetaldehyde were also identified by mass spectroscopy. Corn leaf disks produced lower levels of ethylene, ethane, and methanol, but more acetaldehyde and ethanol than pepper. Production of ethane, a by-product of lipid peroxidation, coincided with an increase in electrolyte leakage (EL) in pepper but not in corn. Compared with controls, pepper leaf disks infiltrated with linolenic acid evolved significantly greater amounts of ethane, acetaldehyde, and methanol and similar levels of ethanol. EL and volatile hydrocarbon production were not affected by fatty acid infiltration in corn. Infiltration of pepper leaves with buffers increasing in pH from 5.5 to 9.5 increased methanol production.
Paclobutrazol Reduces Photosynthetic Carbon Dioxide Uptake Rate in Grapevines
Authors: Hunter David M. , Proctor John T.A.
Published: January 2019

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Effect of Bacteria on Scape Bending in Cut Gerbera jamesonii Flowers
Authors: van Doorn Wouter G. , de Witte Yke
Published: January 2019

Including bacteria in the vase water of cut Gerbera jamesonii Bolus flowers resulted in an increase in scape curvature depending on the concentration of bacteria in the water, cultivar, and season. In the summer, a strain of Pseudomonas aeruginosa or a mixed population of bacterial species, all isolated from the vase water of cut gerbera flowers, resulted in curvature of >90° in `Liesbeth' at 108 cfu/ml and in `Mickey' at 1010 cfu/ml. In winter, the lowest bacterial concentrations that resulted in such bending were 106 and 108 cfu/ml, respectively. `Mickey' showed bending at a lower water potential than `Liesbeth'. Comparison between these results and the bacterial counts in vase water and water at retail shops indicates that frequently observed scape bending is at least partly due to bacteria.