Softening to a normal melting flesh texture in peaches involves a combined participation between polymers located in the middle lamella and primary cell wall. Pectins located in the primary cell wall polysaccharide matrix which cosolubilize when hemicellulose is extracted with KOH have received less attention than the chelator or sodium carbonate soluble pectin likely to be associated with the middle lamella. We conducted a series of extractions for cell walls prepared from softening peach fruit (47, 30, and 15 N firmness) using 0.5 m imidazole, sodium carbonate and a graded series of KOH. Hemicellulose-associated pectin was a substantial proportion of most KOH extracts (30 to 50 mole percent) and fractionated on size exclusion chromatography as a high apparent molecular weight peak which became more prominent as fruit softened and could be separated from two lower apparent molecular weight peaks by anion exchange chromatography. The nature of a hemicellulose-pectin interaction in peach was apparently by physical entrapment, versus covalent cross-linking. Softening related changes in hemicellulose-associated pectin will be addressed.
Supreetha Hegde and Niels O. Maness
Supreetha Hegde and Niels O. Maness
Changes in cell wall polysaccharides associated with peach fruit softening were characterized over two harvest seasons. Enzymically inactive cell walls were prepared from mesocarp tissues of peach fruit harvested at three stages of softening. Pectin-associated and hemicellulose-associated polysaccharides were extracted from the cell walls sequentially, and glycosyl residue compositions were determined by GLC. Pectin extracts from both years were richest in galacturonosyl, arabinosyl, and rhamnosyl residues. Hemicellulose extracted with 1 m potassium hydroxide contained a high mole percentage of xylosyl, glucosyl, and fucosyl residues. Hemicellulose extracted with 4 m potassium hydroxide contained a substantial amount of pectin-associated sugar residues in addition to hemicellulose-associated sugar residues. During softening in both years, sugar compositions for cell walls, aqueous phenol-soluble polysaccharides, and imidazole extracts reflected a decrease in galacturonosyl residues and a concomitant increase in arabinosyl residues on a mole percent basis. The degree of change for galacturonosyl residues in these fractions depended on season, with greater variation exhibited from fruit at earlier stages of softening. With the notable exception of the seasonal variation exhibited for galacturonosyl residues in cell walls, the relative stability of other glycosyl compositional changes over seasons indicates conserved changes for pectins and hemicelluloses occur during peach fruit softening.
Supreetha Hegde and Niels O. Maness
Pectin and hemicellulose were solubilized from cell walls of peach [Prunus persica (L.) Batsch] fruit differing in firmness by extraction with imidazole and sodium carbonate (pectin extracts), followed by a graded series of potassium hydroxide (hemicellulose extracts). The extracts were subjected to size exclusion chromatography. In imidazole extracts, as fruit softened, there was an increase in proportion of a large apparent molecular mass peak, with a galacturonosyl to rhamnosyl residue ratio resembling a rhamnogalacturonan-like polymer. A smaller apparent molecular mass peak was enriched in galacturonic acid and probably represented a broad polydisperse peak derived from more homogalacturonan-like polymers. In sodium carbonate extracts, a homogalacturonan-like polymer appeared to elute primarily as a higher apparent molecular mass constituent, which increased in quantity relative to other constituents as fruit softened. In cold 1 mol·L-1 KOH extracts three peaks predominated. A xyloglucan-like polymer appeared to elute predominantly in the second peak and fucose was strongly associated with it. In 4 mol·L-1 KOH extracts (tightly bound hemicellulose) the higher apparent molecular mass peak was predominantly acidic and presumably of pectic origin. The smaller apparent molecular mass peaks were composed primarily of neutral sugars, the second peak became smaller and the third peak larger as fruit softened. The ability to separate pectin and xyloglucan-like polymer as two separate fractions based on charge suggests that the nature of any pectin-hemicellulose interaction in this fraction is probably one of physical entrapment of pectin fractions by hemicellulose and not principally by covalent crosslinking between the two polysaccharide classes in peach. Flesh firmness serves as an important determinant of quality in peaches. Our results indicate that apparent molecular mass of both pectins and hemicelluloses changed as peaches softened, resulting in alteration of cell wall structure and associated with decreased tissue cohesion.
Brian A. Kahn and Niels O. Maness
Factorial combinations of two row arrangements on 1.8-m-wide beds (either four rows, each 30 cm apart, or eight rows, each 15 cm apart) and two in-row seeding rates (either 48 or 96 seeds per 30 cm of row) were compared on ‘Santo’ cilantro (Coriandrum sativum L.) in five experiments at Bixby, OK. Plots were harvested once per experiment by cutting at a height of ≈7 cm with a small-plot greens harvester, and fresh weight yields were taken. Treatments minimally affected canopy height at harvest. Eight rows resulted in higher yields than four rows in three of five experiments. Main effects of seeding rate or interactions of row number and seeding rate on yield were rare. Of the four combinations tested, the eight-row arrangement sown at 48 seeds per 30 cm would be recommended. This arrangement was used in three other experiments to test effects of a single preharvest spray application of gibberellic acid (GA). Treatments were a water control and GA at either 10 or 20 g·ha−1. Treatment with GA increased bolting in a 17 Apr. planting and increased canopy height at harvest in two of three experiments. However, GA treatments did not affect yield. Treatment with GA would not be recommended for a spring cilantro crop and may have limited impact on increasing machine recovery of raw product in a fall crop.
Niels O. Maness, Donna Chrz and Joseph C. Goffreda
The `Stony Hard' gene of peach conferred a unique ability to manipulate softening and textural properties of the fruit by controlling the concentration and duration of exposure to ethylene. Fruit ripened in ethylene-free air softened very slowly. Exposure of fruit to 1 ppm ethylene continuously for 48 h, or discontinuously at 100 ppm over the same time period, significantly accelerated softening—to a normal texture. Exposure of fruit to 100 ppm ethylene continuously for 48 h induced softening to the same level, but to a mealy texture. We have prepared cell walls and conducted sequential chemical extractions from fruit exposed to the ethylene treatments above. Galacturonic acid content of chelator soluble pectin fractions decreased for mealy fruit, compared to fruit with normal texture, indicating that selective pectin degradation was associated with mealiness. Other differences in polysaccharide sugar composition and apparent molecular size associated with slow, accelerated, and abnormal softening in peach fruit will be addressed.
Jeffrey A. Anderson, Niels O. Maness and Robert E. Stall
Bell pepper (Capsicum anuum L.) leaves inoculated with Race 1 of Xanthomonas campestris pv. vesicatoria (XCV) produced more ethylene and methanol than water-infiltrated controls in studies with leaves attached or detached during inoculation and dissipation of water-soaking. `Early Calwonder 20R'. a pepper genotype resistant to Race 1 of XCV, evolved more ethylene and methanol than `Early Calwonder 10R' (susceptible) following syringe inoculation of detached leaves with ≈ 7 × 107 cells/ml. A light intensity of ≈ 500 μmol· m-2·s-1 during dissipation of water-soaking of attached leaves triggered more ethylene and methanol than covering inoculated leaves with aluminum foil. Volatile hydrocarbon production from leaves infiltrated with distilled water was not significantly affected by light intensity during dissipation of water-soaking. The lipid peroxidation products, ethane and pentane, were not detected by headspace sampling following bacterial inoculation.
Niels O. Maness, Gerald H. Brusewitz and T. Gregory McCollum
Variability in mesocarp firmness for peach (Prunus persica L. Batsch) fruit halves cut either parallel or perpendicular to the suture was determined for three cultivars (Halehaven, Ranger, and Topaz). Firmness evaluations were conducted using an Instron Universal testing instrument with a 3.2-mm rounded tip probe. Firmness of the inner, middle, and outer regions of the mesocarp at four angular positions around each peach half was determined at four maturity stages. Average mesocarp firmness declined with advanced stages of fruit maturity. Inner mesocarp was firmest for fruit from all three cultivars. Internal variation in firmness for the middle and outer regions of the mesocarp was highly cultivar dependent. Firmness decreased longitudinally from the stem end to the blossom end and latitudinally from the suture to the cheeks.
Charles T. Rohla, Michael W. Smith and Niels O. Maness
Whole fruit clusters of `Pawnee' pecan [Carya illinoinensis (Wang.) C. Koch.] were collected from three shoot types: terminal and lateral shoots without a secondary growth flush and shoots that had an early-season secondary growth flush. Fruit per cluster were counted and nuts were individually harvested, weighed, shelled and graded. Bloom the following year was determined for the same shoots where clusters were collected. Wafers (cotyledons that failed to develop) were not associated with cluster size or shoot type. When wafers were included in the data, nut weight, kernel percentage and return bloom were not affected by cluster size or shoot type. However, when wafers were excluded from the data there were significant relationships of cluster size and shoot type with the dependent variables. Cluster size on lateral shoots was negatively related to nut weight and kernel percentage. Cluster size on terminal shoots without a secondary growth flush was inversely related to kernel percentage, but not related to nut weight. When shoots had a secondary growth flush, cluster size was not related to kernel percentage or nut weight. There was a positive linear relationship between cluster size and total kernel weight for the three shoot types. Return bloom of terminal shoots without a secondary growth flush was negatively related to cluster size, but cluster size did not affect return bloom of the other shoot types. The number of shoots that developed the following year was positively related to cluster size for terminal and lateral shoots, but not for shoots with a secondary growth flush. Shoots with a secondary growth flush produced substantially more shoots with larger fruit clusters the next year than the other shoot types.
Brian A. Kahn, James E. Motes and Niels O. Maness
Mechanical harvest of paprika pepper (Capsicum annuum L.) produces a mixture of marketable and unmarketable fruit. Our objective was to increase the percentage of marketable red fruit in a once-over harvest by using ethephon to remove late-developing flower buds, blooms, and green fruit. Three experiments were conducted on field-grown plants in southwestern Oklahoma. We tested ethephon solutions of 0, 1000, 2000, 3000, and 4000 μL·L-1 as a one-time foliar application on various dates in September and October. Total dry mass of harvested fruit decreased linearly as ethephon rate increased in all experiments. Marketable fruit, as a percentage of total harvested fruit mass, increased linearly with ethephon rate in two of three experiments. Ethephon decreased the percent of total harvested fruit mass due to green fruit in all experiments. We recommend a single application of ethephon at about 2000 to 3000 μL·L-1 as a controlled abscission agent to increase the percentage of harvested red fruit in paprika pepper. The precise timing of the application will vary with the situation, but the last 10 days in September seemed an appropriate interval for southwestern Oklahoma. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).
Charles T. Rohla, Michael W. Smith and Niels O. Maness
Alternate bearing pecan trees [Carya illinoinensis (Wangenh.) C. Koch] were hand-thinned annually to 1, ≤2, or ≤3 fruit/cluster or not thinned when the ovule was about one-half expanded. Return bloom was monitored on (1) vegetative shoots, (2) bearing shoots without a second growth flush in the terminal position on 1-year-old branches, (3) bearing shoots without a second growth flush in the lateral position on 1-year-old branches, and (4) bearing shoots with a second growth flush that were primarily in the terminal position. Yield and nut quality were determined in addition to nonstructural carbohydrate, organically bound nitrogen (N), and potassium (K) concentrations in the roots and shoots during January. Fruit thinning improved return bloom but had little effect on weight/nut, kernel percent, or kernel grade. Fruit thinning had either a modest or no effect on nonstructural carbohydrates, organically bound N, and K concentrations. Vegetative shoots and bearing terminal shoots produced a similar number of flowers/1-year-old branch and percentage of flowering current-season shoots. Bearing lateral shoots produced fewer flowers than vegetative shoots most years and fewer flowering current-season shoots during one year. Shoots with a second growth flush produced more flowers/1-year-old branch and a larger percentage of flowering current-season shoots than did vegetative shoots 2 of 3 years. These data indicate fruit thinning of overloaded trees improved return bloom, but the lack of interactions between thinning treatment and shoot type suggests that the number of fruit/cluster was less important than total crop load in determining nut quality and return bloom. Thus removal of entire fruit clusters appears as effective as thinning fruit within a cluster to maintain adequate nut quality and promote return bloom. Nonstructural carbohydrates, organically bound N, and K were not limiting factors in bearing consistency because they were not depressed in unthinned trees. Nonstructural carbohydrates, organically bound N, and K concentrations were not closely linked to alternate bearing because return bloom was enhanced by thinning, but thinning did not affect their concentrations.