Two-species CBC hybrids between Phaseolus vulgaris and P. acutifolius exhibit transgressive segregation for seed color and patterning, root peroxidases, and seed proteins. CBC pedigrees between P. vulgaris and P. coccineus (differing for species-specific traits) were created to test whether variation would be similar or greater than with P. acutifolius. P. vulgaris `Soldier' (Vermont) × 2- and 4-way intraspecific P. coccineus accessions were used as parents. CBC1 through CBC3 were evaluated for segregation of species-specific genes. Hybrid breakdown was evident in all CBC generations, particularly nonflowering dwarf cripples. Transgressive segregants were found as early as CBC2. One individual was found that had crossovers for species traits: a determinate, red-flowered plant with P. coccineus flowers and P. vulgaris introrse stigmas. By CBC3, all of the variation reported for three-species CBC hybrids (P. coccineus × [P. vulgaris × P. acutifolius]) was evident.
Neil O. Anderson, Peter D. Ascher and Emily E. Hoover
Catherine Nicolle, Gérard Simon, Edmond Rock, Pierre Amouroux and Christian Rémésy
Carrot (Daucus carota L.) is ranked among vegetables as the most consumed and the best provitamin A provider. Moreover, carrot also contains vitamins, phenolic compounds, and other antioxidant micronutrients. The influence of carrot genetic background on the content of several micronutrients was investigated. Carotenoids and vitamins (C and E) were analyzed by HPLC in 20 varieties of carrot, and antioxidant activity of carrots was investigated with colorimetric methods (ORAC and Folin-Ciocalteu). There were large differences among cultivars in carotenoid content (0.32 to 17 mg/100 g of fresh weight). In yellow and purple carrots, lutein represents nearly half of the total carotenoids. By contrast, in orange carrots, β-carotene represents the major carotenoid (65%). The concentration of vitamin E ranged from 191 to 703 μg/100 g of fresh weight, whereas the concentration in ascorbic acid ranged from 1.4 to 5.8 mg/100 g. For all these components, dark-orange carrots exhibited the highest values. Significant differences among these 20 varieties were also recorded for mineral and total phenolic compound concentrations. Purple and dark-orange carrots could be preferred to usual carrot varieties to benefit from their specific micronutrients (anthocyanins, carotenoids, or vitamin E). ORAC is a complex reflection of phytomicronutrients but is not tightly linked to vitamin C levels, as shown for white carrots, which are rich in this vitamin.
Arambage Abesinghe and James O. Garner
Storage roots of `Beauregard' and `Centennial' were used to identify varietal differences in fatty acid composition in plasmalemma lipids during storage conditions. Total plasmalemma fatty acid composition of glycolipids and phospholipids in storage roots of `Beauregard' and `Centennial' did not differ. The fatty acid composition of MGDG and DGDG in storage root plasmalemma was >50% unsaturated fatty acids in `Beauregard'. The high percentage of 18:2 (65.44%) fatty acid compared to `Centennial' (19.70%) and 79.35% total unsaturated fatty acid content in MGDG may contribute to low temperature tolerance in `Beauregard'. The higher percentages of 16:1 and 22:1 fatty acids in `Centennial' compared to `Beauregard' contributed to MGDG fatty acid unsaturation. However, these fatty acids have not been related to chilling tolerance.
Maria M. Jenderek and Yayeh Zewdie
Until recently, there has been no large-scale production of true seeds in garlic (A. sativum L. and A. longicuspis L.). The recent discovery of male fertile garlic accessions stimulated research on the genetics and breeding of garlic. However, there is no information regarding the phenotypic characteristics of garlic populations generated from true seeds. We evaluated the first generation of sexually derived families of garlic for bulb and clove weight, number of cloves per bulb, flower stalk height, number of leaves, plant height, and days required to achieve bulb maturity. Significant variations were observed within and among families for these important traits.
William L. Bauerle, Jerry B. Dudley and Lawrence W. Grimes
Cultivars of red (Acer rubrum L.) and Freeman maple (Acer ×freemanii E. Murray) are popular ornamental plants which are commonly placed in a variety of landscapes. To date, little information quantifies the capacity to tolerate and recover from drought among cultivars of red and Freeman maple. The objective of this study was to compare the effects of water stress on the physiology of five different maple cultivars of marketable size including four red maple genotypes, `Summer Red', `October Glory' (October Glory), `Autumn Flame', and `Franksred' (Red Sunset), as well as one hybridized Freeman maple genotype, `Jeffersred' (Autumn Blaze). Two-year-old cloned genotypes of red and Freeman maple were subjected to two treatments: irrigated daily to container capacity or irrigation withheld for one drought and recovery cycle. Light absorption, gas exchange, and chlorophyll fluorescence measurements were conducted under well-watered and drought stress conditions that approached 0.070 m3·m-3. Compared to well-watered conditions, drought stress conditions of 0.090 m3·m-3 had a significant main effect that reduced the amount of light absorption in four of the five genotypes. Additionally, absorption among genotypes was different under both well-watered and water stress conditions. Over the course of drought stress and a recovery phase, net photosynthesis and stomatal conductance were different among genotypes. Maximum photosystem II (PSII) efficiency of dark-adapted leaves (Fv/Fm) was lowered by the water stress condition. The efficiency of excitation capture by open PSII reaction centers (Fv`/Fm') was variable among genotypes. Photochemical quenching was higher in Autumn Blaze, October Glory, and `Summer Red' under drought conditions, which corresponded with a low degree of closure of PSII centers. Additionally, the fraction of excess excitation energy was also lower. Lastly, water deficit caused an increase in PSII efficiency in all genotypes except Autumn Blaze. This research demonstrated physiological variation among commercially available red and Freeman maple genotypes that may be selected for drought tolerance based on site moisture characteristics.
Linda Wessel-Beaver and J.W. Scott
Heritabilities (h2) and genetic correlations between percent fruit set, yield, and fruit weight were estimated from one summer planting each in Florida and Puerto Rico of 100 S, tomato (Lycopersicon esculentum Mill.) families from a synthetic population. Single-location h2 was high for all traits. Across-locations h2 was low for yield, intermediate for fruit set, and high for fruit weight. Genotype × environment interaction (G × E) was 1) the only significant component of variance for yield, 2) somewhat important for fruit set, and 3) not an important variance component for fruit weight. The greater importance of genetic variance compared to G × E variance explains why across-location heritabilities for fruit weight and fruit set were high. Genetic correlations between fruit set and weight were strongly negative, while those between yield and set were large and positive. Yields under high temperatures may increase with selection for fruit set, but a reduction in fruit weight would be expected in this population and those with similar genetic correlations.
Mark K. Ehlenfeldt, Vickie Brewster and Allan W. Stretch
Potted plants of 53 highbush and half-high blueberry cultivars were screened for resistance to the blighting phase of mummyberry, Monilinia vaccini-corymbosii under controlled nursery conditions over an 18 day infection period. Significant differences were observed in the susceptibility of different cultivars, with `Bluehaven', `Bluegold', and `Blueray' being among the most susceptible, and `Bluejay', `Jersey', and `Duke' being among the most resistant. Differences were also observed in the latent periods and rate of disease progress which may have a bearing on the severity of the secondary fruit infection phase. Preliminary observations suggest that shoot blighting and fruit infection frequencies are not strongly correlated under high inoculum conditions.
Paul W. Foote, J. Scott Cameron, Chuhe Chen and Stephen F. Klauer
Gas exchange rates were measured in the field on middle leaflets of Fragaria chiloensis (L.) trifoliates which were then used for Rubisco quantity and activity assays. Side leaflets of the same leaf were utilized for fourth-derivative spectroscopy, chlorophyll extraction, and specific leaf weight data. Differences of CO2 assimilation (A) rates were highly significant between genotypes ranging from 16.2 to 27.6 μmol CO2·s·m. Chlorophyll a and b, and total chlorophyll per unit area were positively correlated to A (r = 0.48**, 0.45**, and 0.49**, respectively). Total chlorophyll per unit dry weight had a correlation coefficient with A of 0.6**.
Fourth-derivative analysis of in vivo leaf attenuance spectra showed a positive correlation between A and Ca693 peak amplitude and a negative correlation of A and Ca677 peak amplitude. Peak amplitude of Ca693 was also correlated with chlorophyll content.
Activity per unit Rubisco was not a significant factor influencing A, but Rubisco quantity on either a leaf area or a dry weight basis was positively linked to A (r = 0.40** and 0.44**, respectively).
C.M. Ronning, S.P. Kowalski, L.L. Sanford and J.R. Stommel
The Colorado potato beetle is a serious pest of the cultivated potato. Natural resistance has been found in a few wild species, including Solanum chacoense Bitter, in which resistance is attributed to the presence of foliar specific leptine glycoalkaloids. Production and accumulation of these compounds within S. chacoense varies widely and appears to be inherited in a quantitative fashion, but high leptine producing clones occur rarely. In the present study, 15 different accessions from various locations and altitudes of origination were analyzed for foliar glycoalkaloid content in order to determine the frequency and distribution of genes for leptine production/accumulation, and to see if we could find a center, or core, of leptine production. Leptines were detected in eight of the 15 accessions, and the amounts within each accession varied widely, but none of the individuals produced high amounts of leptine (defined as greater than 62% of total glycoalkaloids). All of the leptine-containing accessions originated from western Argentina. There was no relationship between elevational level and leptine, but there was a negative trend with total glycoalkaloids and elevation; this was due to levels of solanine and chaconine decreasing with increasing elevation. In addition, nine unidentified glycoalkaloids were detected, in very high proportions in some individuals and accessions. AFLP marker frequency and diversity were used to compare subpopulations of these accessions. AFLP markers revealed substantial diversity among clones. The relationship of marker distribution to glycoalkaloid content is discussed. The results raise interesting questions about glycoalkaloid biosynthesis and inheritance, and point the direction for new avenues of leptine and glycoalkaloid research.
Swee-Suak Ko, Woo-Nang Chang, Jaw-Fen Wang, Shin-Jiun Cherng and S. Shanmugasundaram
In the tropics, onion (Allium cepa L.) bulbs are usually stored in shelters under ambient conditions resulting in severe storage losses. This study was aimed at determining whether variation in bulb storability exists among short-day onion cultivars and whether the trait can be improved through conventional breeding. Twelve onion cultivars with different degrees of storability were selected from preliminary experiments. Bulbs of selected cultivars were grown and stored for 3 months under ambient conditions. Observations were made on disease incidence at harvest, percentage diseased bulbs, and storage disease incidence of bacterial soft rot [BR (Pseudomonas gladioli pv. alliicola Burkholder)], black mold [BM (Aspergillus niger Tiegh.)], and fusarium basal rot (Fusarium oxysporum Schlechtend.:Fr. f. sp. cepae) after 3 months of storage. Data on bulb characteristics such as bulb fresh weight (FW), dry matter (DM) content, total soluble solids (TSS), and pyruvic acid content were recorded at harvest. Mean storage losses of cultivars ranged from 21% to 99% over 3 years. Diseases were the major causes of storage losses, with BR and BM being the most predominant. Performance of most traits (including storage losses) was significantly influenced by year (Y), cultivar (G), and Y × G interaction. Heavy rainfall during bulb development in 1997 may have contributed to higher disease incidence at harvest, higher percentage of diseased bulbs during storage, and lower DM, and TSS of the cultivars. Cultivars with good storability, such as `Red Pinoy' and `Serrana', were less sensitive to stressful environments and high disease pressure. Incidence of storage diseases was significantly correlated with DM (r = -0.65 to -0.84) and TSS (r = -0.66 to -0.87), as well as incidence of BR (r = 0.57 to 0.94) in each year. Thus, they could be good indicators for evaluating storability. Cultivars with good storability tended to have small bulbs, as average bulb FW was positively correlated with incidence of storage diseases. Disease incidences on `Red Pinoy' and `Serrana', both in the field and in storage, were significantly lower than in the other cultivars, indicating they are tolerant to major storage diseases and that they could be used as donor parents for genetic improvement of onion storability.