Search Results

You are looking at 31 - 40 of 48 items for

  • Author or Editor: John R. Stommel x
Clear All Modify Search

Color observed in plants is due to several pigments, in particular chlorophylls, carotenoids, flavonoids, and betalains. The many hues can be attributed to a number of biochemical factors, inclusive of pigment concentration, pigment combinations and their ratios, and vacuolar pH. Shades of violet to black pigmentation in pepper (Capsicum annuum L.) are attributed to anthocyanin accumulation. The color of unripe pepper fruit varies from green and yellow to ivory, through varying shades of violet and purple to nearly black. Whereas pepper fruit color is important for culinary product quality, foliar pigmentation is also an important aspect of ornamental variety appeal. Foliage and stem color may vary from green to varying shades of green/purple to nearly black. HPLC analysis of violet and black pepper fruit revealed a single anthocyanidin that was identified as delphinidin. Black fruit contained five-fold higher chlorophyll concentrations in comparison to violet fruit, which contained relatively little chlorophyll. Differences in fruit pH were not statistically significant. Similar to fruit, black pepper leaf tissue contained delphinidin as the predominant anthocyanidin, but in higher concentration relative to that found in fruit. The results demonstrate that high concentrations of delphinidin in combination with chlorophyll account for black pigmentation. Real-time PCR analysis of tissues that varied in pigmentation intensity due to varying anthocyanin concentration revealed functional, but differentially expressed, structural genes in the anthocyanin biosynthetic pathway. Analysis of regulatory gene expression identified a MYB transcription factor that was differentially expressed in response to varying anthocyanin concentration.

Free access

Bacterial soft rot of bell pepper (Capsicum annuum L.), caused by Erwinia spp., is a destructive postharvest market disease of this crop. Control is presently limited to chemical treatments. Methods of inoculating pepper fruit were evaluated to develop a reliable technique for soft rot resistance screening. Erwinia carotovora subsp. atroseptica (Eca) was isolated from partially decayed field grown pepper fruit at Beltsville, MD. Fruit were inoculated with suspensions of Eca via: (a) abrasion with Carborundum, (b) hypodermic puncture, or (c) non-wounded tissue. Inoculated fruit were held under high humidity at 21-23C for two to three days prior to scoring. Degree of soft rot decay was determined via fruit weight loss from two replicates of the experiment over the course of the growing season. Significant differences were not evident among varieties or experiment dates for weight loss due to tissue decay. Hypodermic puncture inoculation was superior to other methods for inducing fruit rot.

Free access

Incorporation of genes from wild species has been a major contributor to tomato improvement in recent years. Solanum ochranthum, a woody non-tuber bearing species, is a potential source of resistance against tomato diseases and insect pests but is genetically isolated from tomato. Somatic hybridization methods were developed to facilitate the use of S. ochranthum for tomato germplasm improvement. Leaf mesophyll protoplasts of S. ochranthum and a Lycopersicon esculentum hybrid were chemically fused with polyethylene glycol. The protoplasts were initially cultured in Shepard's CL, a MS based medium, containing 1 mg·1-1 NAA, 0.5 mg·1-1 BAP and 0.5 mg·1-1 2,4-D. Hybrid regenerants and regenerants of the L. esculentum parent were recovered; S. ochranthum did not regenerate. Hybridity was established by morphological characters, peroxidase isozyme and RAPD markers. Use of these somatic hybrids for tomato improvement was evaluated.

Free access

Anthocyanin pigmentation in leaves, flowers, and fruit imparts violet to black color and enhances both ornamental and culinary appeal. Shades of violet to black pigmentation in Capsicum annuum L. are attributed to anthocyanin accumulation. Anthocyanin production is markedly influenced by numerous environmental factors, including temperature and light stress. The objective of this study was to determine the genetic basis for differences in C. annuum anthocyanin content in response to varying environments. Growth experiments conducted under controlled environment conditions demonstrated that anthocyanin concentration was significantly higher in mature leaves in comparison with immature leaves under high light (435 μmol·s−1·m−2) conditions. High (30 °C day/25 °C night) versus low (20 °C day/15 °C night) temperature had no significant effect on anthocyanin concentration regardless of leaf maturity stage. Foliar anthocyanin concentration in plants grown under short days (10 h) with low light intensity (215 μmol·s−1·m−2) was significantly less than under long days (16 h) with low light. Under high light intensity, daylength had no effect on anthocyanin content. Three structural genes [chalcone synthase (Chs), dihydroflavonol reductase (Dfr), anthocyanin synthase (Ans)] and three regulatory genes (Myc, MybA , Wd40) were selected for comparison under inductive and noninductive environmental conditions for anthocyanin accumulation. Expression of Chs, Dfr, and Ans was significantly higher in mature leaves in comparison with younger leaves. Consistent with anthocyanin concentration, temperature had no effect on structural gene expression, whereas light positively influenced expression. Under low light conditions, temperature had no effect on Myc, MybA , and Wd40 expression; whereas under high light conditions, temperature only had an effect on MybA expression. The study of anthocyanin leaf pigmentation in C. annuum under inductive and noninductive environments provides a new approach for elucidating the molecular genetic basis of epistatic gene interactions and the resulting phenotypic plasticity.

Free access

Solanum ochranthum, a woody non-tuber bearing species, may possess genes for insect and disease resistance which could be useful in solanaceous crop improvement. Methods for tissue and protoplast culture of S. ochranthum were developed as part of an ongoing project to improve tomato and potato using wild relatives and in vitro techniques such as somatic hybridization. For protoplast experiments, axenic shoot tip cuttings were propagated on medium containing MS salts, Staba vitamins, 100 mg·l-1 casein, 3% sucrose and 0.6% activated charcoal (OM) or medium containing MS salts and vitamins, 100 mg·l-1 casein and 2% sucrose (TPM). Plants grown on OM were significantly taller, had higher root dry weight and gave protoplasts with higher average plating efficiency than plants grown on TPM. Leaf protoplasts from 5 week old plants cultured in medium with high Ca2+ and myoinositol generally had higher percent viability and plating efficiency than protoplasts grown in a modified Kao and Michayluk 8p medium.

Free access

Gene silencing is one of the ways in which gene expression is controlled. The authors have developed a model system to study anthocyanin gene silencing using a recessive mutation in Petunia Juss. (Star mutation) and the ability of certain viruses to reverse the gene silencing mutation. In healthy plants, the star pattern was enhanced (increase in level of gene silencing) under high temperature or light growing conditions. Virus infection did not significantly influence the star pattern when plants were grown under either low-light or low-temperature conditions. Under high-light and -temperature conditions, virus infection reverses silencing, leading to a change in the star pattern. These changes in the star pattern corresponded to changes in gene expression. Viral infection had a greater affect on regulatory gene (Wd40, Myc, and Myb) expression than on structural gene expression (Chs and Ans).

Free access

Viral satellite RNA associated with cucumber mosaic virus (CMV) is know to modulate CMV symptomology. Virulent CMV associated RNA 5 (CARNA 5) satellites may intensify crop disease. Naturally occurring variants of these satellites, however, attenuate CMV symptoms. Satellite transgenic tomato plants expressing the S-CARNA 5 or 1-CARNA 5 ameliorating forms of the satellite were evaluated under simulated CMV epidemic conditions in USDA–APHIS approved field trials. Trials conducted at Beltsville, Md., in 1994 and 1995 demonstrated that CMV can be effectively controlled under field conditions in satellite transgenic plants. Yields of transgenic lines infected with CMV were 50%–65% greater than that of non-transgenic infected controls. Yields of noninfected transgenic lines ranged from 5% greater than, to 33% less than, noninfected nontransgenic controls. Expression of CARNA 5 in inoculated transgenic plants greatly reduced CMV foliar symptoms and virus titers when compared to inoculated control plants. Levels of CARNA 5 were detected at varying levels in infected transgenic plants throughout the growing season. Virus or satellite was not detected in samples collected from tomato border plants and weeds growing inside and outside a nonhost crop border surrounding the test plot. Field tests conducted in 1996 will evaluate transgenic tomato plants with a double construct coding for the CMV coat protein gene and 1-CARNA 5 satellite.

Free access

In the floriculture trade, cut pepper (Capsicum annuum) stems are typically grown for their fruit to add color contrast to the foliage and blossoms of conventional floral arrangements. Stems are commonly stripped of foliage because leaves wilt rapidly. Three divergent plant types and commercial hydration protection spray products were evaluated to identify effective vase life treatments and new pepper lines that combine both fruit and foliar interest with an acceptable postharvest cut stem life. Three inbred US Department of Agriculture pepper breeding lines with a tall vigorous growth habit and black foliage were selected for evaluation as cut stems. Line 190-2 produced upright, tabasco-like fruit; 191-1 produced upright, clustered, round fruit; and 196-1 was fruitless. Three commercial spray treatments Crowning Glory (FLCG), Finishing Touch, and Aqua Finish Clear (AFC) were evaluated on treated cut stems stored at 10 and 23 °C. The pepper breeding line had the greatest influence on cut stem foliage and fruit vase life. The fruitless line, 196-1 exhibited an extended vase life in comparison with fruited lines. Cold storage extended the vase life of cut stems. FLCG reduced foliage vase life at 23 °C, and AFC extended foliage vase life of the fruitless line 196-1. Relative to foliage, fruit exhibited greater resistance to desiccation, with glossier fruit of 191-1 desiccating more rapidly than fruit of 190-2. Similar trends were noted when cut stems were stored at 10 °C for 7 days and moved to 23 °C. However, in 2022 trials, the vase life of 190-2 was shortened, and those of 191-1 and 196-1 were extended, highlighting the influence of preharvest factors on vase life. The results demonstrate that cut stems of new pepper lines with vigorous upright growth habits and black-pigmented foliage, together with diverse fruit morphology, provide innovative possibilities for stunning cut flower arrangements.

Open Access