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Dao-Jing Wang, Jing-Wen Zeng, Wen-Tao Ma, Min Lu, and Hua-Ming An

Trichomes usually root in epidermal cells and present everywhere at all times in many plant families. They exhibit a high level of multiplicity in morphology, cellular structure, and function ( Uphof, 1962 ). Because the morphological and mechanical

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Dalia Taher, Mohamed Rakha, Srinivasan Ramasamy, Svein Solberg, and Roland Schafleitner

insect resistance and trichome types and densities has been reported for many plant species ( Mitchell et al., 2016 ; Tian et al., 2012 ). For the genus Solanum , eight types of trichomes have been identified, of which four (i.e., types I, IV, VI, and

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Qiubin Xiao and J. Brent Loy

Trichomes are epidermal hairs found on the surface of nearly all plants. They are used widely in plant taxonomy. Trichome initiation is an early event in leaf organogenesis first characterized by epidermal cell enlargement and then outgrowth and

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Gretchen Hatch and Albert H. Markhart III

The concentration of active ingredient in a given dry weight of a medicinal herb is important to the consumer and producer of herbal remedies. Feverfew is a commonly used medicinal herb where the active compound has been identified. There is considerable variability in the amount of the active ingredients in different genotypes of feverfew. Important secondary plant compounds are often produced in the trichomes of leaves. The objective of this investigation is to determine if there is a correlation between the number of leaf trichomes and the level of active ingredient in several feverfew genotypes. Rooted cuttings of feverfew (Chrysanthemum parthenium) genotypes previously characterized for parthenolide content were grown under identical conditions in an environmentally controlled greenhouse. Light and scanning electron microscopy were used to describe and quantify the number and type of trichomes on the youngest fully expanded leaf of each plant from each genotype. The relationship between trichome number and parthenolide content will be presented.

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John C. Snyder

Breeding for resistance to insects and other arthropod pests in vegetables has been a difficult endeavor. Greater public awareness of health and environmental issues requires that we as horticultural scientists reexamine why breeding for resistance has been difficult. The literature clearly suggests the potential for a genetic solution, and the literature also reveals some reasons why achievement of genetic resistance to arthropod pests has not been as successful as the achievement of resistance to pathogens. The thesis of my presentation is that the complexity of plant-arthropod interactions often prevents simple genetic approaches to breeding for resistance. Data using Lycopersicon hirsutum and its interaction with spider mites will provide examples of the these complex interactions. L. hirsutum is a wild relative of L. esculentum, the common tomato, and is nearly immune to insect attack. However, there are few or no clear examples of this taxa contributing to the insect resistance of tomato. The complexity of the interaction between mites and trichomes on L. hirsutum will be highlighted as it pertains to environment and genetics of the plant, and the development of the arthropod.

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Ruixiang Yan, Joshua B. Gurtler, James P. Mattheis, and Xuetong Fan

addition, many types of fruit, such as peaches, have a layer of nonsecreting trichomes (fuzz). Commercially, peaches are often wet-brushed to remove the trichomes (fuzz) for consumer appeal ( Taylor and Rushing, 2012 ). The fuzz, which is single

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Renee G. Murray and James E. Simon

Essential oil content of Ocimum basilicum, cv. sweet basil, increases with plant maturity. The increase in essential oil content may correspond to the formation of glandular trichomes during leaf expansion. Greenhouse grown plants were harvested every 2 weeks. Leaves were grouped according to size, examined with a stereo microscope, and trichome densities compared. Results indicate that trichome formation continues throughout leaf expansion. In young basil plants, leaves ranged in size from 2-30cm2 Highest density (416 trichomes/cm2) occurred in leaves 2–6c m2. Prior to open bloom, leaves ranged in size from 2-49cm2. Highest density occurred in leaves 18-24c m2. In flowering plants leaves ranged in size from 2-34cm2, yet there was NSD in trichome density in leaves of different sizes. Analysis of the entire leaf surface of plants at each harvest showed the greatest density of trichomes in plants at full bloom (280 trichomes/c m2). All leaves have visible glandular trichomes. These glandular trichomes are most likely formed both prior to and during leaf expansion.

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Roger L. Vallejo, Wanda W. Collins, and Robert H. Moll

Glandular trichomes from some Solanum species have suppressed infestation by insects including green peach aphid, which is a main vector of potato virus Y (PVY) and potato leaf roll virus (PLRV), both of which contribute to a serious loss in potato production. Eight Solanum phureja Juz. et Buk.-S. stenotomum Juz. (Phu-Stn), three S. berthaultii Hawkes (Ber), nine F1 [(Phu-Stn) × Ber], fifteen backcross (BC) [(Phu-Stn) × F1], and seventeen reciprocal BC (BCR) [F1 × (Phu-Stn)] families were evaluated to determine the genetic variability and heritability of A and B glandular trichome density and polyphenol oxidase (PPO) activity. Experiments were carried out in completely randomized and randomized complete-block designs in the greenhouse. Genetic analysis was done using half-sib family and parent-offspring regression analysis. Phu-Stn showed a higher density of A trichomes than Ber and F1, while the BC and BCR had densities of A trichomes similar to Phu-Stn. B trichomes were not observed in Phu-Stn. Ber showed a high B trichome density, which was transmitted to the F1. In the BC, B trichomes were almost absent, but, in the BCR, the density of B trichomes was higher than that of BC. Ber and F1 had similar or higher PPO activity than Phu-Stn. PPO activity decreased in the BC, but, in the BCR, it was high and similar to Ber and F1. Broad-sense heritability estimates for A and B trichome density and PPO activity were from medium to high (0.48 to 0.77) in Phu-Stn, Ber, and F1. Narrow-sense heritability estimates for A and B trichome density and PPO activity were very low (0.04 to 0.24) in BC and BCR. In the BC families, additive genetic variance was very low for A and B trichome density and PPO activity. Half-sib family selection based on progeny testing and combined with BCs to Phu-Stn in subsequent generations would be a suggested breeding procedure to improve these traits. Phenotypic correlations between A and B trichome densities were 0.26 (F1) and 0.44 (BCR), between A trichome density and PPO activity 0.20 (F1) and 0.31 (BCR), and between B trichome density and PPO activity 0.04 (F1) and 0.27(BCR. Positive associations found between traits might facilitate simultaneous improvement for high levels of A and B trichome density and PPO activity.

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Jacqueline A. Ricotta and John B. Masiunas

In the past few years, leaf trichomes of tomato (Lycopersicon esculentum) and related wild species have received considerable attention due to their potential role in insect resistance. However, the last complete characterization of all 7 trichome types was by Luckwill in 1943, before the advent of scanning electron microscopy (SEM). Since that time, the taxonomic designations of the genus have been modified, expanding from 6 species to 9. The purpose of this work was to use SEM to observe and record trichome types from the presently accepted Lycopersicon species, and determin etheir species specific distribution. Studies have shown variation within trichome type due to number of cells per trichome, and base and surface characteristics.

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Roger L. Vallejo, Wanda W. Collins, and Rocco Schiavone

A hybrid diploid potato population (Solanum phureja x Solanum stenotomum) with superior horticultural traits has been developed for breeding purposes. Because this highly advanced population has no resistance to potato virus Y (PVY), and because PVY pressure is very high in North Carolina, glandular trichomes from another diploid species, Solanum berthaultii, were introduced as a defense against aphids, the PVY vector. Two types of glandular trichomes, A and B, were transferred. Preliminary results show that genetic diversity and broad-sense heritability are adequate to transfer these traits; however, non-additive gene action was indicated in narrow-sense heritability estimates. Spearman's coefficients of rank correlation showed a low level of association between A and B trichomes; density of both types is postulated to be under the control of a Small number of genes.