Search Results

You are looking at 11 - 20 of 31 items for

  • Author or Editor: Patrick J. Conner x
Clear All Modify Search

A detached leaf screening technique was developed for studying specific interactions between pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars and isolates of the pecan scab fungus, Cladosporium caryigenum. Monoconidial isolates were obtained from leaf scab lesions on `Wichita', `Desirable', `Cape Fear', and `Elliot'. Each isolate was then inoculated onto detached leaves of each of the four cultivars and fungal growth was observed under the microscope after eight days. `Wichita', `Desirable', and `Cape Fear' isolates produced subcuticular hyphae at a much higher frequency when inoculated back onto the cultivar from which they were isolated in comparison to the other cultivars. The `Elliot' isolate was able to produce a high frequency of subcuticular hyphae when inoculated onto `Elliot' and `Cape Fear', but not when inoculated onto `Desirable' and `Wichita'. Field inoculations conducted with the `Wichita' and `Desirable' isolates validated the detached leaf protocol. The results obtained indicate that pecan scab is composed of multiple races with a high degree of specificity for host cultivars. A rapid whole-leaf staining system is presented which appears to have wide applicability to assessing fungal growth in leaves.

Free access

The Coastal Plain Experiment Station has been evaluating pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars for over 75 years. Using annual yield data from this program, the alternate bearing intensities (I) of 66 pecan cultivars and numbered U.S. Dept. of Agriculture (USDA) selections were determined. Values ranged from 0.19 to 0.93 in young trees, and from 0.27 to 0.91 in mature trees under high-input production practices. The adoption of fungicides, insecticides, and irrigation during the last 30 years has reduced the average I value from 0.70 to 0.55. I was negatively correlated with both nut yield and nut weight. All but one cultivar recommended for commercial production in Georgia have I values lower than the average of 0.57 for all cultivars in this test. Values calculated early in a tree's productive life cycle were highly correlated with those of mature trees.

Free access

Genetic variation among pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars was studied using randomly amplified polymorphic DNA (RAPD) markers. Using a combination of primers, a unique fingerprint was produced for each of the pecan genotypes studied. The genetic relatedness between 44 cultivars was estimated using more than 100 RAPD markers. Genetic distances based on the simple matching coefficient varied from 0.91 to 0.59. The phenetic dendogram developed from cluster analysis showed relatively weak grouping association. However, cultivars with known pedigrees usually grouped with at least one of the parents and genetic similarity estimates appear to agree with known genetic relationships. Using RAPD information in determining genetic relationships among pecan cultivars with unknown or questionable pedigrees and the integration of that knowledge into the breeding program is discussed.

Free access

Anthocyanin content and composition and CIE 1976 (L*, a*, b*) color space (CIELAB) color coordinates were examined for the skin of 22 muscadine grape (Vitis rotundifolia Michx.) cultivars and Muscadinia Planch germplasm. Analysis of berry skin extracts by high-performance liquid chromatography (HPLC) determined that anthocyanin content varied from less than 100 μg·g−1 in bronze and pink berries to over 5500 μg·g−1 in highly pigmented black berries. The anthocyanins delphinidin, cyanidin, petunidin, pelargonidin, peonidin, and malvidin were detected in their 3,5-diglucosidic forms. Analysis of berry color with a colorimeter revealed chroma (C*) ranged from 2.4 to 22.8 with the highest values occurring in bronze- and red-colored berries. As anthocyanin concentration increased, lightness (L*) decreased to a low of 20 to 23 in black-colored berries. Pink and red skin colors were primarily a result of lower levels of total anthocyanins, although there was also a shift away from delphinidin and petunidin production toward more cyanidin and peonidin. Malvidin, the most important anthocyanin for muscadine wine and juice color stability, was only abundant in a few clones, all of which had V. munsoniana (Simpson ex Munson) Small or V. popenoei (Fennell) Small in their pedigree. The interspecific hybrid ‘Fennell’s 3-way Hybrid’ had the largest proportion of malvidin, contributing ≈58% of the total anthocyanin content. This clone also had low levels of delphinidin and high total levels of anthocyanin, making it a promising source for the improvement of muscadine grape pigment profiles.

Free access

Fifteen pecan (Carya illinoinensis) genotypes were evaluated over a period of 20 years in a test orchard located near Tifton, Ga. Genotypes tested included seedling selections (`Candy', `Maramec', `Melrose', `Moreland', `Sumner', and `Western Schley'), USDA releases (`Creek', `Kanza', `Kiowa', and `Pawnee'), and USDA selections (USDA 41-19-20, USDA 53-11-139, USDA 53-9-1, USDA 57-7-22, and USDA 64-11-17). Actual yields were measured for each tree in the test throughout the test period and the alternate bearing intensity (I) of each cultivar was calculated. Average annual nut production in years 1 to 10 ranged from 19 lb (8.6 kg) in the precocious cultivar `Candy' to 6 lb (2.7 kg) in the nonprecocious cultivar `Melrose'. Although a wide variation was seen in the average yield of clones in years 11 to 20, differences were not significant. A subsample of nuts was taken for each tree annually and percent kernel, nuts/lb, specific gravity, and nut volume were determined. Significant differences were found between clones for each of these traits. Most clones were not acceptable for commercial use in Georgia due to small nut size, poor kernel quality, or excessive alternate bearing. Recommended clones include: `Pawnee', which produced large nuts of excellent quality with an early harvest date, `Sumner', which produced large nuts of moderate quality with a late harvest date, and `Kiowa', a precocious bearer of large, good-quality nuts.

Full access

To facilitate the breeding of scab-resistant pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars, more information is needed about the pathogenic variation of the causal organism, Cladosporium caryigenum (Ell. et Lang.) Gottwald (1982). This study examined the virulence patterns resulting from the field inoculations of 19 pecan cultivars with 12 monoconidial isolates from 8 pecan cultivars at 7 locations. The virulence pattern was different for each of the fungal isolates. Each isolate was virulent on some cultivars and avirulent on others. Most isolates were most virulent on the cultivar of their origin and one or a few other cultivars. Several cultivars were resistant to most of the tested isolates. The results indicate a large pool of differential and ephemeral resistance to scab resides in the pecan germplasm. Microscopic examination of developing lesions suggests that resistance is mediated by the speed of plant cell wall modifications that limit the growth of subcuticular hyphae. This information will be useful in the selection of cultivars with functionally different resistance genes for use in designing cultivar mixtures or in breeding programs.

Free access

Native muscadines (Vitis rotundifolia Michx.) are dioecious, but muscadine vineyards are usually planted with a mixture of female plants and hermaphroditic pollenizers. Hermaphroditic cultivars are derived from either of two separate sources original hermaphroditic plants, H1 or H2. Nine hermaphroditic and two female cultivars were studied to determine their potential as pollenizers. Inflorescences of each cultivar were collected in the field to evaluate the number of anthers per flower, the number of pollen grains per anther, and pollen viability and germination in the main and secondary flowering periods. The number of flower clusters per shoot ranged from one to four with most producing two or three flower clusters per shoot. The number of anthers per flower varied by cultivar and cluster position, but in general was between six and eight anthers per flower. ‘Noble’ showed the highest pollen grains production per anther and per flower, reaching 5777 and 39,860, respectively, in the first cluster and ‘Carlos’ produced the least amount of pollen. All cultivars that had secondary flowering showed lower pollen production per anther and per flower as compared with the main flowering period. Optimal muscadine pollen germination media contained 50 mg·L−1 boric acid, 145 mg·L−1 calcium nitrate, 188 g·L−1 sucrose, 10 g·L−1 agar, and 10 mm 2-(N-morpholino)ethanesulfonic acid (MES) pH 6.0. The pollen grain viability of hermaphroditic and female cultivars was high, but pollen grain germination was low in hermaphroditic cultivars and absent in female cultivars. H1-derived cultivars produced more flower buds per cluster and higher germination rates than H2-derived cultivars, indicating they may be better pollenizers. Chemical names used: 2-(N-morpholino)ethanesulfonic acid (MES).

Free access

Genetic variation among pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars was studied using randomly amplified polymorphic DNA (RAPD) markers. Using a combination of primers, a unique fingerprint is presented for each of the pecan genotypes studied. The genetic relatedness between 43 cultivars was estimated using 100 RAPD markers. Genetic distances, based on the similarity coefficient of Nei & Li, varied from 0.91 to 0.46, with an average value of 0.66 among all cultivars. The phenetic dendrogram developed from cluster analysis showed relatively weak grouping association. However, cultivars with known pedigrees usually grouped with at least one of the parents and genetic similarity estimates appear to agree with known genetic relationships.

Free access

Rooting hardwood cuttings from muscadine (Vitis rotundifolia Michx. syn. Muscadinia rotundifolia) vines has traditionally been considered an exceptionally difficult task. Many previous studies observed almost no root formation, leading to a general consensus that muscadines should either be propagated by softwood cuttings or vegetative layering. However, the University of Arkansas System Division of Agriculture Fruit Breeding Program has been using a hardwood rooting protocol for muscadines with moderate success for the past 10 years. The application of this protocol to meet the modest propagation needs of the breeding program has significantly shortened the time required to advance selections. The goal of this research was to more adequately describe the factors affecting the rooting ability of hardwood muscadine cuttings. This research investigated the effects of cultivar, bottom heat, cold storage, vineyard location, and cutting collection date on the outcome of muscadine hardwood cuttings. The study was conducted during the dormant seasons of 2019–20 and 2020–21, and an overall rooting percentage of 16% was observed. There were multiple higher-order interactions affecting rooting efficacy. Cuttings taken in November generally rooted at higher rates, although interactions with vineyard location and cultivar played a significant role in those results. The Ocilla, GA, location performed exceptionally well in November with rooting percentages greater than 40%. The effects of supplying bottom heat and/or a cold storage treatment on rooting success declined as the dormant season progressed. Other variables such as increased cutting length and diameter were associated with increased rooting success. A second statistical analysis using only data from November showed that when cuttings were not given a cold storage treatment that rooting percentages were greater than 27%. Ultimately, this research shows that institutions with modest muscadine propagation needs can successfully propagate plants from hardwood cuttings.

Open Access