Leaf Surface Chemicals Research Articles

Morpho-physiological traits and leaf surface chemicals as markers conferring resistance to sorghum shoot fly (Atherigona soccata Rondani)

Sorghum shoot fly, Atherigona soccata,causes substantial economic losses in sorghum globally. Cultural practices and host plant resistance are effective measures for mitigating the losses caused by sorghum shoot fly. Therefore, we evaluated 32 sorghum genotypes consisting of a set of 10 restorer lines, 10 CMS (cytoplasmic male-sterile) lines and their respective maintainers exhibiting resistance/susceptibility to shoot fly along with resistant and susceptible checks under field conditions. The traits such as leaf glossiness, leaf sheath pigmentation, percentage plants with shoot fly deadhearts and number of shoot fly eggs per plant were used as morphological markers for selecting genotypes with resistance to shoot fly during the rainy and post rainy seasons of 2016 and 2017. The test material was also subjected to biochemical analysis (total soluble sugars, protein and tannin contents), while the leaf surface chemicals were analysed by GC–MS to identify the compounds associated with resistance/susceptibility to shoot fly. The genotypes differed significantly for all the traits, except percentage plants with shoot fly deadhearts during the 2016 rainy season. The genotypes ICSB 458, ICSA/B 467, ICSA/B 487, ICSA/B 14037, IS 18551 and ICSV 93046 exhibited moderate to high levels of resistance to shoot fly based on number of plants with shoot fly deadhearts, plants with shoot fly eggs and total number of shoot fly eggs. The shoot fly resistant genotypes ICSB 84, ICSA/B 467, ICSB 487, ICSB 14024, and IS 18551 had low shoot fly deadheart incidence, higher amounts of condensed tannins, soluble sugars, phenols and lower protein content as compared to the susceptible genotypes. Thirteen unique compounds were identified from leaf surface extracts by GC–MS which were associated with shoot fly resistance/susceptibility. While HPLC analysis revealed that Protocatechuic and coumaric acids were present in most of the sorghum genotypes, but their amounts were significantly greater in resistant as compared to the susceptible ones. The findings of the study highlight the importance of various morphological and biochemical traits conferring resistance to sorghum shoot fly, and these traits can be used as markers to identify shoot fly resistant genotypes for use in breeding programs.

Species‐specific elicitors induce tea leaf to arrest the endoparasitoid Ascogaster reticulata (Hymenoptera: Braconidae)

AbstractAscogaster reticulata Watanabe (Hymenoptera: Braconidae) is an egg‐larval endoparasitoid of the smaller tea tortrix, Adoxophyes honmai Yasuda. Recent studies have examined tritrophic interactions among Camellia sinensis, A. honmai and A. reticulata, but the effect of non‐host insects on the induction of tea plant that may affect foraging behaviour of A. reticulata remains unclear. In this study, we selected two non‐host insects, Homona magnanima Diakonoff and Ostrinia furnacalis (Guenée), as representative species in our bioassays. Tea leaves were treated with homogenized female reproductive tissues of a non‐host insect in comparison with untreated leaves in a choice test. Residence times of parasitoids on both leaves were recorded. The parasitoids seemed to prefer walking on leaves treated with homogenates of H. magnanima over untreated leaves, but the difference in residence times was not significant. In contrast, its residence time on leaves treated with homogenates of O. furnacalis was significantly shorter than that on untreated leaves. Thus, the induction of tea leaf surface chemicals may differ among moth species, which may produce different types of elicitors. This difference may, in turn, affect the host‐searching behaviour of A. reticulata.

Comparative studies of leaf surface chemical biosynthesis in different tobacco cultivars

To understand the differences in the biosynthesis of leaf surface chemicals and their influence on aphid preference for different tobacco cultivars (Nicotiana tabacum), we analyzed the secretory characteristics of glandular trichomes of four commercial cultivars, K326 (flue-cured), Beinhart 1000-1 (cigar), Basma YNOTBS1 (oriental), and Dabai 1 (burley), and their parental species, Nicotiana sylvestris and Nicotiana tomentosiformis. Trichome-type observation showed that K326 and N. sylvestris have three kinds of glandular trichomes (non-glandular, long stalked glandular, and short stalked glandular trichomes), whereas Beinhart 1000-1, Basma YNOTBS1, Dabai 1, and N. tomentosiformis had two kinds of glandular trichomes (long and short stalked glandular trichomes). The gas chromatography–mass spectrometry profiles of leaf exudates indicated that N. tomentosiformis synthesized only labdanoids; N. sylvestris, K326 and Dabai 1 synthesized only cembranoids; and Beinhart 1000-1 and Basma YNOTBS1 synthesized cembranoids and labdanoids. Gene expression pattern analysis revealed that the labdanoid synthesis-related genes NtABS and NtCPS2 were expressed in N. tomentosiformis, Beinhart 1000-1, and Basma YNOTBS1, whereas the cembranoid synthesis-related genes NtCYC and NtCYP71D16 were expressed in N. sylvestris and all four commercial cultivars. Evolutionary analysis indicated that NtCYC and NtCYP71D16 might be phylogenetically originated from N. sylvestris, whereas NtABS and NtCPS2 expressed in Basma YNOTBS1 and Beinhart 1000-1 might be derived from N. tomentosiformis. In addition, aphid attraction (number of aphids) was significantly and positively correlated with the total glandular secretion (r2 = 0.9425, P ≤ 0.05), and it was significantly and positively correlated with amount of CBT-diol (r2 = 0.9224; P ≤ 0.05). These results provide new insights into the biosynthesis of diterpenoids and biotic stress resistance in tobacco.

Ultrastructural leave features of grapevine cultivars (<em>Vitis vinifera</em> L. ssp. <em>vinifera</em>)

<p style="text-align: justify;"><strong>Aim</strong>: To investigate and compare of <em>Vitis vinifera</em> Linné subsp. <em>vinifera</em> leaves of cultivars important for the Austrian wine producers in order to learn more about their surface architectures in the microand nanoscale.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Atomic force microscopy, binocular fluorescence microscopy, contact angle measurements, and environmental scanning electron microscopy were employed in order to assess physicochemical features of fresh plant material. Erect and prostrate trichomes are the most characteristic features present on the epidermal surfaces of grapevine leaves. These hairs occur in rather different densities from none to densely covering the whole surface. Contact angels are highly affected by these hairs, resulting in individual cases in values >150° in the presence of a high reclining hair density. On nanoscopic scale blades of the varieties differ with respect to their wax structures, in orientation, shape and size. Cuticular striae and epicuticular waxes, mostly granules and platelets, are the most conspicuous characteristics of grapevine leaf ultrastructure.</p><p style="text-align: justify;"><strong>Conclusion</strong>: The microscopy techniques applied are complementary, enabling morphological analysis at different scales. They are not only efficient tools for descriptive botanics and finding morphological adaptions to the environmental conditions, they provide also an insight into the habitat of leaf colonizing microbes, pathogenic as well as beneficial ones and may add to the understanding of the conditions they find on leaf surfaces.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: Leaf surface structures and chemicals are part of the defence system of the plant. Water-repellency can be advantageous for the plant as it creates unfavourable conditions for the successful colonization of pathogens. The knowledge of wetting properties of leaf surfaces will advance the insight in the interaction with additives, promoting the secure and optimal use of plant protection agents applied by spray deposition, especially under difficult weather conditions. The application of such research will be better contact and or penetration, better adhesion of pesticides and other plant protecting agents but also improved adhesion of plant promoting bacteria in biocontrol applications.</p>

Leaf surface chemistry of sorghum seedlings influencing expression of resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata is one of the serious constraints to sorghum production, and host plant resistance is an important component for controlling this pest. We studied the expression of resistance to A. soccata in a diverse array of sorghum genotypes in relation to composition of leaf surface chemicals during the seedling stage. The sorghum genotypes IS 1054, IS 1057, IS 2146, IS 4664, IS 2312, IS 2205, SFCR 125, SFCR 151, ICSV 700, and IS 18551 exhibited antixenosis for oviposition, and suffered less deadhearts due to sorghum shoot fly, A. soccata. Compounds undecane 5- methyl, decane 4- methyl, hexane 2, 4- methyl, pentadecane 8- hexyl, and dodecane 2, 6, 11- trimethyl, present on the leaf surface of sorghum seedlings, were associated with susceptibility to shoot fly; while 4, 4- dimethyl cyclooctene was associated with resistance to shoot fly. The compounds associated with resistance/susceptibility to shoot fly, can be used as marker traits to select for resistance as well as for diversifying and increasing the levels of resistance to this pest. The role of biochemical compounds for developing sorghum varieties with resistance to shoot fly, A. soccata has been discussed.

Infection by Mycorrhizal Fungi Increases Natural Enemy Abundance on Tobacco (Nicotiana rustica)

The presence of arbuscular mycorrhizal fungi (AMF) influences plant nutrient uptake, growth, and plant defensive chemistry, thereby directly influencing multi-trophic interactions. Different fungal isolates (genotypes of the same fungal species) have been shown to differ in nutrient uptake ability. Plants infected with different AMF genotypes may vary in foliar nutrient or defensive chemical levels, potentially influencing multi-trophic interactions. Using a completely randomized design, we compared the effect of two isolates of the mycorrhizal fungus Glomus etunicatum W. N. Becker & Gerdemann on silver leaf whitefly (Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) and parasitic wasp (Eretmocerus eremicus Rose & Zolnerowich) (Hymenoptera: Aphelinidae) abundance. Whitefly populations were not influenced by AMF infection. Parasite populations were higher on plants infected with the isolate collected from Georgia, even after controlling for whitefly abundance and plant architecture. We propose that AMF indirectly influences parasite abundance and parasitism through a change in leaf surface chemicals that affect parasitic wasps. Because of the ubiquity of and genetic variation in AMF, multi-trophic interactions are likely to be strongly influenced by belowground processes.

HOST AND NON-HOST PLANT VOLATILES ON OVIPOSITION AND ORIENTATION BEHAVIOUR OF TRICHOGRAMMA CHILONIS ISHII.

ABSTRACT In the process of host location and selection several cues associated with host’s play a major role. Volatile compounds emitted by plants as a consequence of herbivore activities are often attractive to insect natural enemies including the Hymenopteran egg parasitoids, Trichogramma species. We studied the plant - parasitoid interactions where the plant surface chemicals act as infochemicals that attract or arrest the parasitoids for egg parasitization and strategically help in preventing the pest infestation. The leaf surface chemicals of R. communis, damaged due to the feeding of the host, Achaea janata (L) (castor semilooper) (Lepidoptera: Noctuiidae), and a non – host, Serpentine leaf miner Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) were evaluated for their influence on host location, host acceptance and ovipositional behavior against the egg parasitoid, T. chilonis in laboratory bioassays. The A. janata damaged leaf emissions had synomonal effects on the parasitoid and induced orientation and oviposition, whereas, the surface chemicals from the plant infested with non-host L. trifolii ceased to produce any such effects. The maximum egg parasitization was observed in A. janata infested castor leaf extracts compared to the leaf miner infested or normal healthy castor leaf extracts. The results are interesting in the context of tritrophic interactions between the pest, parasite and the host plant and are useful in biological control of insect pests.

Leaf surface factors of transgenic Bt cotton associated with the feeding behaviors of cotton aphids: A case study on non-target effects

The present paper reports case study results of the risk assessment of transgenic Bt cotton on a non-target pest, cotton aphid, Aphis gossypii. Several types of techniques, i.e., electrical penetration graph (EPG), light and electron microscopy, bioassays and chemical analysis, were applied to investigate physical and chemical leaf factors of 2 transgenic Bt cotton lines (GK12 and GK19) and their parental non-Bt cotton line (Simian3) associated with searching and feeding behaviors of cotton aphids on leaves or leaf extracts of cotton plants. EPG results showed that there were some differences among behaviors of cotton aphids on 2 Bt cotton and 1 non-Bt cotton lines. Cotton aphids performed similarly to leaf surface extracts from 3 cotton lines; and leaf surface chemicals, mainly volatiles and waxes, were almost identical in the components and concentrations among the cotton lines. However, three cotton lines were quite different from each other in the densities of certain kinds of covering trichomes. Therefore, the relationships between the physical characteristics and the searching behaviors of cotton aphids on the three cotton lines were constructed as the regression equations. Glandular trichomes and covering trichomes with 5 branches influenced the cotton aphids' searching behaviors effectively; and other trichomes with other branches affected aphids in varying ways. These results demonstrated that leaf surface physical factors of transgenic Bt cotton lines different from their parental non-Bt line could affect the penetration behaviors of non-target cotton aphids. Cotton aphids penetrate and feed more easily on two Bt cotton lines than on the non-Bt cotton line.

Behavioural responses of the Colorado potato beetle to trichomes and leaf surface chemicals of Solanum tarijense

AbstractWild Solanum species constitute a source of resistance to several pests and diseases of potato. Several species of wild tuber‐bearing potato have been identified as resistant to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), including Solanum tarijense Hawkes (Solanaceae). Our objective was to determine the mechanism of resistance of S. tarijense to the Colorado potato beetle and, because the resistance is limited to the adult stage of the insect, to study the host selection behaviour on resistant plants.In the field, Colorado potato beetles demonstrated a unique behaviour when in contact with S. tarijense, abandoning the plant by falling to the ground after a few minutes. The abundant trichomes on the leaves of S. tarijense induced the falling behaviour. However, on S. tarijense feeding remained low even after the trichomes were mechanically removed. Observations demonstrated that the normal sequence of behaviour leading to feeding was interrupted before adult beetles fed on S. tarijense leaves. Feeding experiments using volatile and non‐volatile fractions of leaf surface extracts identified a phagodeterrent effect of the volatile fraction. Our results contrast with a similar evaluation of the mode of resistance of Solanum berthaultii Hawkes, a close relative of S. tarijense, on which some feeding occurred and adults did not show falling behaviour. This study presents information on S. tarijense as a new source of resistance to the Colorado potato beetle that can be used for potato breeding.

Oviposition‐induced plant cues: do they arrest Trichogramma wasps during host location?

AbstractPlants can defend themselves against herbivorous insects before the larvae hatch from eggs and start feeding. One of these preventive defence strategies is to produce plant volatiles, in response to egg deposition, which attract egg parasitoids that subsequently kill the herbivore eggs. Here, we studied whether egg deposition by Pieris brassicae L. (Lepidoptera: Pieridae) induces Brussels sprouts plants to produce cues that attract or arrest Trichogramma brassicae Bezdeko (Hymenoptera: Trichogrammatidae). Olfactometer bioassays revealed that odours from plants with eggs did not attract or arrest parasitoids. However, contact bioassays showed that T. brassicae females were arrested on egg‐free leaf squares excised from leaves with 72 h‐old egg masses, which are highly suitable for parasitisation. We tested the hypothesis that this arresting activity is due to scales and chemicals deposited by the butterflies during oviposition and which are thus present on the leaf surface in the vicinity of the eggs. Indeed, leaf squares excised from egg‐free leaves, but contaminated with butterfly deposits, arrested the wasps when the squares were tested 1 day after contamination. However, squares from egg‐free leaves with 72 h‐old butterfly deposits had no arresting activity. Thus, we exclude that the arresting activity of the leaf area near 72 h‐old egg masses was elicited by cues from scales and other butterfly deposits. We suggest that egg deposition of P. brassicae induces a change in the leaf surface chemicals in leaves with egg masses. A systemic induction extending to an egg‐free leaf neighbouring an egg‐carrying leaf could not be detected. Our data suggest that a local, oviposition‐induced change of leaf surface chemicals arrests T. brassicae in the vicinity of host eggs.

Effect of leaf surface extraction on palatability of romaine lettuce to Diabrotica balteata

Abstract The leaf surface of a plant, especially its chemical components, constitutes the first line of resistance to herbivores and other pests. Our previous research indicated that ‘Valmaine’ (Val) romaine lettuce, Lactuca sativa L., was highly resistant to feeding by adult banded cucumber beetle, Diabrotica balteata LeConte, while ‘Tall Guzmaine’ (TG) was highly susceptible. We investigated the leaf surface chemistry of these two cultivars for its possible role in their resistance to D. balteata. Three solvents with different polarity (hexane, methylene chloride, and methanol) were tested to remove leaf surface chemicals, but only methylene chloride and methanol extracts were used in feeding bioassays. Adult D. balteata consumed much more of the leaf tissue of Val and TG when their surface chemicals were removed with methylene chloride, but not methanol, compared to nonextracted leaf tissue, leading us to hypothesize that methylene‐chloride extractable leaf surface chemicals may have a role in the expression of lettuce resistance. However, leaf surface chemicals extracted from Val with methylene chloride were not a deterrent to adult D. balteata when applied to palatable lima bean leaf surfaces at various concentrations in dual‐choice tests. Furthermore, the application of surface extracts from TG did not stimulate beetle feeding in similar choice tests. In a no‐choice feeding test, there was no significant difference in leaf area consumption on lima bean leaves sprayed with extracts of Val or TG. These results suggest that leaf surface chemicals in romaine lettuce do not explain the resistance of Val to adult D. balteata, and that factors inside the leaf may play a role in resistance. We discuss the possibility that the solvent may have increased the palatability of lettuce leaves to D. balteata by causing enzymatic browning and cellular damage, which is likely to have degraded internal feeding deterrents and impaired the plant's ability to emit latex.

Resistance in Lettuce toDiabrotica balteata(Coleoptera: Chrysomelidae): The Roles of Latex and Inducible Defense

Abstract A previous study showed that feeding of adult banded cucumber beetle, Diabrotica balteata LeConte, and development of the female reproductive system were strongly inhibited by a diet of fresh Valmaine (Val) romaine lettuce, Lactuca sativa L., relative to Tall Guzmaine (TG). Leaf surface chemicals have been shown not to be involved in the resistance of Val. In this study, leaves of TG and Val were freeze-dried and incorporated into an artificial diet to evaluate whether the chemicals within the lettuce leaves were responsible for resistance to D. balteata feeding. The amount consumed and mature eggs produced were not significantly different when adults were given either a choice or no choice of TG or Val diets. However, latex from TG and Val strongly inhibited D. balteata feeding on a favorite food, lima bean leaves, when applied to leaf surfaces. Latex from Val turned brown faster than that from TG, and flowed for a longer period of time before ceasing. Localized induced resistance to feeding was...

Insect Feeding Stimulants from the Leaf Surface of Populus

Leaf surface chemicals from a beetle-preferred poplar clone, Eugenei (Populus deltoides × Populus nigra), induce feeding in adult cottonwood leaf beetles, Chrysomela scripta. The feeding stimulants were isolated and identified as n-beheryl alcohol (C22), n-lignoceryl alcohol (C24), n-hexacosanol (C26), n-octacosanol (C28), n-triacontanol (C30), and α-tocopherylquinone [2-(3-hydroxy-3,7,11,15-tetramethyl-hexadecyl)-3,5,6-trimethyl-2,5 cyclo-hexadiene-1,4-dione] (α-TQ). It is the first time that α-TQ has been reported as a feeding stimulant for an insect. Fatty alcohols or α-TQ alone do not induce beetle feeding significantly, but a mixture of alcohols and α-TQ synergistically stimulates beetle feeding. The role of these feeding stimulants in insect feeding behaviors and possible use in a pest management program is discussed.

Leaf-Surface Chemicals of Orchardgrass (Dactylis glomerata L.) Varieties with Different Palatabilities

Leaf-Surface Chemicals of Orchardgrass (Dactylis glomerata L.) Varieties with Different Palatabilities

Epicuticular Wax Chemicals in Zea mays Influence Oviposition in Ostrinia nubilalis

The chemical basis of oviposition elicitation in a generalist herbivore was determined by examination of oviposition responses in Ostrinia nubilalis to corn (Zea mays) chemicals in two-choice laboratory bioassays. A pentane extract of corn leaves stimulated oviposition and the activity persisted for three days, indicating that oviposition in O. nubilalis is elicited by low-volatility chemicals. Chemicals in the extract were fractionated by column chromatography on Florisil, using a sequence of solvents of increasing polarity. Bioassays of Florisil fractions indicated that the stimulants were eluted with nonpolar solvents. Positive bioassay results with an extract prepared by dipping corn leaves in pentane for 20 sec for extraction of leaf surface chemicals suggested that some of the active material was present in the leaf epicuticle. Gas chromatographic analyses and comparisons with retention times of standards suggested the presence of several n-alkanes in the dip extract. Five n-alkanes—hexacosane, heptacosane, octacosane, nonacosane, and tritriacontane—known to be present in the epicuticle of corn leaves were bioassayed, and all five elicited oviposition responses. These results suggest that oviposition elicitation in O. nubilalis is influenced by the presence of n-alkanes in the host plant epicuticle.

Leaf Surface Compounds and Oviposition Preference of Turnip Root Fly Delia floralis: The Role of Glucosinolate and Nonglucosinolate Compounds

The role of leaf surface compounds influencing the oviposition of the turnip root fly, Delia floralis, was investigated using bioassays and fractionation of leaf surface extracts from four Brassica genotypes. Polar leaf surface extracts contained between 65 and 175 nM/g leaf equivalent of glucosinolates. However, following fractionation it was found that nonglucosinolates were the major stimuli for D. floralis oviposition. Electrophysiological studies of leaf surface extracts and their fractions were performed by using D. radicum, the cabbage root fly, as an analytical tool. The most behaviorally active fractions contained stimulatory compound(s) that had an activity profile identical to that previously described for recently discovered nonglucosinolate compounds. The role of leaf surface chemicals in influencing antixenotic resistance to D. floralis is discussed.

Influence of tobacco leaf surface chemicals on germination ofPeronospora tabacina adam sporangia

Chromatographic procedures were utilized to isolate and purify components of tobacco cuticular extracts and leaf surface chemicals.In vitro microbial bioassays determined the influence of these leaf surface compounds on germination and germ tube morphology ofP. tabacina sporangia, the tobacco blue mold pathogen, and to a lesser extentAlternaria alternata, the tobacco brown spot pathogen. Exposure to 10 μg/cm(2) of α- and β-duvatrienemonols, sucrose esters, or hydrocarbons did not inhibit germination, whereas germination was significantly decreased bycis-abienol.cis-Abienol did not inhibit sporangial germination when combined with sucrose esters or hydrocarbons at a combined 10 μg/cm(2). Germination of sporangia was completely inhibited by α- and β-duvatrienediols. In contrast to a previous report, α-DVT-diol was more inhibitory than the β isomer. Toxic effects of the DVT-diols were not altered by pH. Diluting the DVT-diols to less than 0.1 μg/cm(2) resulted in a small but significant stimulation of germination. Previously, the DVT-diols had been identified only as inhibitory toP. tabacina. None of the leaf surface chemicals affected germination ofA. alternata conidia.