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- Author or Editor: William M. Randle x
Sixty onion (Allium cepa L.) entries were evaluated for nonstructural water-soluble carbohydrates (NWSC) under high (4.0 meq·liter-1) and low (0.1 meq·liter-1) S nutrition. Significant differences were detected among entries for sucrose, fructose, glucose, total fructans, total NWSC, and soluble solids content (SSC). Sucrose, total fructans, and SSC were highly correlated with total NWSC although deviant NWSC concentration was detected. Since a significant S × entry interaction was found for all NWSC concentrations tested. selection should be conducted at S concentrations indicative of targeted production areas.
Sulfur fertility influences flavor in onions. To determine how sulfur is utilized by onions over the course of growth and development, five short-day onion (Allium cepa L.) cultivars were grown at high (4.0 mequiv.liter-1) and low (0.1 mequiv. liter-1) sulfur fertility regimes under greenhouse conditions. Plants were measured for foliar sulfur content at 4 week intervals during the course of the growing season and for bulb sulfur and pyruvic acid development at plant maturity. Patterns of sulfur uptake and utilization were similar for all five cultivars but cultivars differed in their magnitude of sulfur accumulation. Foliar sulfur accumulation correlated poorly with bulb sulfur and pyruvic acid development at all sampling dates.
Twenty bulbs from each of 10 onion (AIlium cepa L.) cultivars and one mass population were harvested from two locations and evaluated for three traits associated with flavor quality. Variance components for soluble solids content (SSC), pyruvic acid concentration (PAC), and percent S were calculated, and sampling schemes required to detect specific differences among treatment means were determined. In general, a five-bulb sample and four replications were sufficient to detect desired differences for SSC and PAC, whereas percent S required a larger sample size and more replications.
World-wide, onions are the most important member of the vegetable Alliums. Members of this group are primarily consumed because of their unique flavors and aromas. Allium aroma is dominated by organosulfur compounds arising from the enzymatic decomposition of S-alk(en)yl-L-cysteine S oxide (ACSO) flavor precursors following tissue disruption. Primary products from the decomposition of the four ACSOs are sulfenic acids, including the lachrymator, pyruvate, and ammonia. The sulfenic acids, however, are short-lived and disassociate rapidly into thiosulfinates, which, in turn, are unstable and randomly rearrange or dissociate over time. The thiosulfinates each have unique sensory qualities and are responsible for the flavor notes of fresh cut Alliums, while of the degradation compounds can contribute to off-fl avors and bitterness. ACSO concentration affects ultimate flavor and aroma intensity, while ACSO composition determines among species flavor differences. Controlling sulfur uptake and sulfur metabolism that terminates in ACSO synthesis is one method of controlling ultimate flavor and aroma intensity. Cultivar difference in the ability to absorb and metabolize sulfur have been identified. Sulfur availability, plant growing temperatures, and irrigation intensity also influence sulfur absorption and metabolism, and can be manipulated. Differences in alliinase concentration and the efficiency at which alliinase decompose the ACSO substrates also affect aroma generation. Difficulties, however, exist in controlling alliinase activity. Alliinase has been cloned and anti-sense constructs have been made, but an efficient vectoring system has yet to be developed for the Alliums.
Field-grown `Granex 33' onions were subjected to four preplant calcium (Ca) treatments and evaluated for bulb quality and shelf-life over two seasons. Mature, cured bulbs were analyzed at harvest and after 1, 2, and 3 months of 4C storage. As preplant calcium increased, percentage of seed stems decreased, yield and soluble solids concentration increased, and then decreased, bulb firmness increased. Bulb pungency was unaffected by Ca fertility, except at the highest treatment. Percent bulb rot during storage first decreased with increasing Ca fertility, but then increased at the highest Ca treatment.
An interactive computer-based model has been developed to simulate the effects of precision planting onion on quality and yield. Variables used by the model are seed germination, plant survival, planter efficiency, onion growth potential, maximum onion size, sizing potential and inside-outside bed effects. Data bases obtained from 3 onion cultivars were used in the development of the model. The model shows when germination and plant survival are high, single seed drops by the planter results in high yield and large bulbs. At lower germination and survival values, however, a compromise is needed between maximizing yield and obtaining large bulbs.
Mild onion consumption is increasing in the U.S. The ability to produce mild onions depends on selecting proper cultivars and growing them in an appropriate environment. A major decision in producing onions with mild flavor is determining when to stop applying sulfate to the crop. While adequate sulfur is necessary for good early onion growth, high levels of sulfur increase bulb pungency. A study was conducted where sulfate was eliminated from the fertility program at biweekly intervals during onion growth and development. Mature bulbs were then analyzed for flavor precursors and their biosynthetic intermediates, and pungency. Pungency linearly increased from 3.7 to 5.1 μmols pyruvic acid from the earliest cut-off date to the latest cut-off date, respectively. While total milligrams of flavor precursors did not significantly change in response to sulfate elimination, the methyl cysteine sulfoxide: 1-propenyl cysteine sulfoxide ratio did. Methyl cysteine sulfoxide concentration decreased in a quadratic manner while 1-propenyl cysteine sulfoxide linearly increased as sulfate fertility was extended in the growing season. Changes in individual precursors will significantly affect flavor perception as well as flavor intensity.
Short-day (SD) and long-day (LD) cultivars of onion (Allium cepa L.) representing various storage and flavor characteristics were greenhouse-grown to maturity. Bulbs were harvested and cured, then stored at 4C and evaluated monthly for pyruvic acid concentration (EPY), soluble solids content (SCC), and weight loss (WL). The EPY of `Dehydrator #3' (SD) decreased linearly with storage while EPY of `Granex 33' (SD) increased linearly. The EPY of `Zenith' (LD) had a quadratic response, decreasing then increasing during storage, while EPY of `Sweet Sandwich' (LD) increased then decreased quadratically during storage. Cultivar SSC generally decreased, while WL increased during storage.
A factorial mating design, using three male-sterile F1 lines in testcrosses with a sample of open-pollinated (OP) onion populations, was used to estimate combining abilities and heterosis for bulb yield, size, storage ability, pungency, soluble solids content (SSC), and water loss after 3 months in storage. Samples of testcross bulbs were flowered and scored for fertility to estimate frequencies of the nuclear allele maintaining cytoplasmic male sterility. General combining ability (GCA) estimates for OP populations (males) were significant (P < 0.05) for yield, SSC, and proportion of bulbs with diameters >7.5 cm. GCA estimates for female testers were significant for storage ability and proportion of bulbs with diameters <5.0 cm. Male × female interactions (specific combining ability estimates) were significant for SSC and storage ability. Our analyses did not reveal any storage population from which inbreds would likely yield significantly better with the male-sterile tester lines. Spanish OP populations tended to produce testcrosses with larger bulbs, lower pungency and SSC, and poorer storage ability. Heterosis estimates were most often significant for yield and SSC; less often for pungency, storage ability, and bulb size; and not significant for water loss in storage. Overall, significant GCA estimates indicate that superior onion inbreds and populations may be developed using recurrent-selection strategies that increase the frequency of desirable alleles with additive effects.
Although Petunia hybrida Vilm., a major bedding plant, is susceptible to many diseases, no formal disease resistance studies have been conducted. Botrytis cinerea Pers. ex Fr. is a ubiquitous pathogen, causing great damage to greenhouse-grown ornamental crops, including petunia. In this study, a screening procedure for B. cinerea resistance in petunia was developed and 48 diverse petunia phenotypes were screened for resistance to B. cinerea in two seasons, spring and fall. The range of variability for resistance to B. cinerea in petunia was wide and continuous. Spearman's rank correlation coefficients between seasons were significant and moderate. While the majority of phenotypes displayed less than a 10% difference in mean percent infection in spring vs. fall seasons, several phenotypes displayed large differences that require further testing. One cultivar, `Pink Sensation Improved', exhibited low and consistent mean percent infection in both spring and fall and, therefore, may be a useful source of resistance to B. cinerea in petunia.