The Effect of Pseudomonas fluorescens and Fusarium oxysporum f.sp. cubense on Induction of Defense Enzymes and Phenolics in Banana

The effect of Pseudomonas fluorescens treatment and Fusarium oxysporum f. sp. cubense inoculation on induction of phenylalanine ammonia-lyase (PAL), peroxidase (POX), chitinase, -1,3-glucanase and accumulation of phenolics in banana (Musa sp.) was studied. When banana roots were treated with P. fluorescens strain Pf10, a two-fold increase in phenolic content in leaf tissues was recorded 3 – 6 d after treatment. Challenge inoculation with F. oxysporum, the wilt pathogen, steeply increased the phenolic content in P. fluorescens-treated banana plants. Significant increase in POX activity was detected 6 – 9 d after P. fluorescens treatment. PAL, chitinase and -1,3-glucanase activities increased significantly from 3 d after P. fluorescens treatment and reached the maximum 6 d after treatment. Challenge inoculation with F. oxysporum further increased the enzyme activities. These results suggest that the enhanced activities of defense enzymes and elevated content of phenolics may contribute to bioprotection of banana plants against F. oxysporum.     

Production of potato monohaploids (2n=x=12) through prickle pollination

Summary Data are presented on the potential of gynogenesis for the production of monohaploids and on factors affecting their frequency and relative vigour. Diploid Solanum tuberosum L. and S. tuberosumxS. phureja Juz et Buk hybrids were used as maternal parents and selected S. phureja clones as prickle pollinators with embryo-spot and nodal band as dominant seed and plant marker. About 2 million seeds were screened for absence of embryo-spot. After raising plants from phenotypically spotless seeds, further screening for absence of nodal bands and for ploidy level was carried out. Finally more than 500 monohaploid plants from three genetically different groups of maternal parents were obtained. Frequency and vigour of the monohaploids were clearly dependent on their maternal genotypes. The data also indicated an effect of the pollinator genotype, the physiological stage of the maternal plant and the environment on monohaploid frequency. On the basis of these results the possibility of breeding for a higher monohaploid production rate and for more stable and vigorous monohaploids is discussed. Furthermore, gynogenesis and androgenesis are compared. It is suggested that both should be used in order to obtain monohaploids from sufficiently various diploid breeding material.     

Is the increased vigour of invasive weeds explained by a trade-off between growth and herbivore resistance?

Blossey and Nötzold (1995) recently hypothesised that the increased vigour of certain invasive plant species has been at the expense of defences against natural enemies. A prediction of their evolution of increased competitive ability (EICA) hypothesis is that invasive genotypes are relatively poorly defended. We tested this prediction with herbivore bioassays and with direct quantification of plant secondary metabolites comparing non-indigenous genotypes of Lythrum salicaria L. (purple loosestrife) with indigenous forms. The herbivore bioassays revealed no significant intra-specific variation in herbivore resistance between indigenous and non-indigenous hosts. The phenolic content of L. salicaria leaves was significantly higher in indigenous genotypes, as predicted by the EICA hypothesis. The average phenolic content of leaves (regardless of their origin) was, however, low, implying that the role of plant phenolics in purple loosestrife anti-herbivore defence is probably limited. It is suggested that the EICA hypothesis, as tested in the current study, does not explain the increased vigour of L. salicaria in non-indigenous habitats.     

Clone-specific responses in leaf phenolics of willows exposed to enhanced UVB radiation and drought stress

The effects of enhanced UVB radiation and drought stress on willow secondary phenolics were studied using the leaves of 8‐week‐old micropropagated plantlets from interspecific hybrids (Salix myrsinites L. ×S. myrsinifolia Salisb.) and pure species (S. myrsinifolia). The plantlets were subjected for 4 weeks to two levels of UVB radiation (ambient, enhanced) and two levels of watering (well‐watered, drought‐stressed) according to a 2 × 2 factorial design. Enhanced UVB radiation increased the total concentration of flavonoids and phenolic acids in all plantlets, while the total concentration of salicylates remained unaffected. Drought stress reduced the total concentration of salicylates and phenolic acids in S. myrsinifolia plantlets, while in hybrids only phenolic acids were affected. The response of phenolic acids to enhanced UVB in drought‐stressed plantlets was different from that in well‐watered ones, indicating that drought stress limited the accumulation of phenolic acids under enhanced UVB radiation. Flavonoids increased in response to enhanced UVB radiation in drought‐stressed plantlets, although drought caused serious physiological stress on growth. There were significant differences between hybrid and S. myrsinifolia plantlets with respect to the composition of phenolics and between families and clones with respect to their concentration. In addition, the response of salicylates, flavonoids and phenolic acids to enhanced UVB and drought stress was clone‐specific, which may indicate that climatic changes will alter the genetic composition of northern forests.     

Genetic fingerprinting for determining the mode of reproduction in Paspalum notatum, a subtropical apomictic forage grass

 Paspalum is an important genus of the family Gramineae that includes several valuable forage grasses. Many of the species are polyploid and either obligate or facultative apomicts. Cyto-embryological observations of several tetraploid genotypes of P. notatum were performed to determine their mode of reproduction. Afterwards, selfed progenies of the genotypes F131, Q3664 and Q4117 were analysed using RFLP and RAPD genetic fingerprints to identify maternal and non-maternal (aberrant) plants, and to establish the degree of apomictic reproduction. Five maize clones and six primers were used for detecting genetic deviations from the maternal profile. Maize clones umc379, umc384 and umc318 and primers OPG10 and OPI4 were the most informative for discriminating between maternal and aberrant individuals within the progenies of F131 and Q3664. The combined results of three RFLP clones or 4–6 RAPD primers were necessary to ascertain the mode of reproduction in plants F131 and Q3664. The results obtained with the RFLP and RAPD markers were in agreement with the cyto-embryological studies in ascertaining the mode and degree of apomictic reproduction. Plant F131 showed a completely sexual reproductive behaviour, Q3664 an elevated expression of sexuality, while Q4117 was highly apomictic. A fingerprint analysis of an outcrossing population, aimed at the identification of hybrid plants, was also performed. Maize clones um318 and umc379 and primers OPC2 and OPC9 were used. The presence of specific bands belonging to the male parent permitted a rapid and easy detection of hybrids. The methodology described here can be applied both for the characterisation of P. notatum populations and to identify hybrid progenies in Paspalum breeding programs. Received: 5 March 1997 / Accepted: 13 May 1997     

Willow genotype, but not drought treatment, affects foliar phenolic concentrations and leaf-beetle resistance

In a greenhouse experiment we examined the effect of willow genotype and irrigation regime (moderate drought and well‐watered) on plant growth parameters, foliar nitrogen, and phenolic concentrations, as well as on the preference and performance of the blue leaf beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae). The 10 vegetatively propagated willow genotypes in the experiments were F2 full‐sibling hybrids, originated from a cross between Salix viminalis (L.) (Salicaceae) (high in condensed tannins) and Salix dasyclados (L.) (Salicaceae) (rich in phenolic glycosides). Insect bioassays were conducted on detached leaves in Petri dishes as well as with free‐living insects on intact potted plants. The 10‐week long irrigation treatments caused statistically significant phenotypic differences in the potted willow saplings. Total biomass was somewhat higher in the well‐watered treatment. The root to total biomass ratio was higher in the drought‐treatment plants. There was significant genotypic variation in foliar nitrogen concentrations, and they were higher in the drought‐treatment plants. There was also a strong genotypic variation in each of the phenolic substances analyzed. Condensed tannins, which accounted for the greatest proportion of total phenolic mass, were higher in the well‐watered treatment. There was, however, no difference in levels of the other phenolics (salicylates, cinnamic acid, flavonoids, and chlorogenic acid) between irrigation treatments. The sum of these phenolics was higher in the well‐watered treatment. There was a strong variation in P. vulgatissima larval development on different willow genotypes, and larval performance was negatively correlated with levels of salicylates and cinnamic acid. There was, however, no effect of irrigation treatment on larval performance. Phratora vulgatissima preferred to feed on well‐watered plants, and we found a preference for oviposition there, but neither feeding nor oviposition site preference was affected by willow genotype. Adult feeding and oviposition preferences were not correlated with larval performance.     

Induction of Defence Responses in Roots and Mesocotyls of Sorghum Seedlings by Inoculation with Fusarium thapsinum and F. proliferatum, Wounding and Light

The defence reactions of sorghum seedlings 7 days after inoculation with Fusarium thapsinum and F. proliferatum, and interactions with wounding and exposure to light were studied to determine whether responses to these fungi differed from those to abiotic stresses. In non‐wounded plants, inoculation with both fungi increased concentrations of anthocyanins and soluble phenolics and activities of peroxidase (POX), chitinase and β‐1,3‐glucanase in the roots, and increased β‐1,3‐glucanase activity in the mesocotyls. There was no effect of inoculation on phenylalanine ammonia‐lyase (PAL) activity. Wounding by itself increased anthocyanin content of mesocotyls. Wounding also had a variety of interactions with inoculation. Exposure to light had very little effect on any defence response measured. A time course experiment showed that induction of chitinase and β‐1,3‐glucanase occurred in less than 24 h after inoculation. POX activity increased 2 days after inoculation, followed by a transient increase in PAL activity. The content of anthocyanins and soluble phenolics in roots of inoculated seedlings increased gradually compared with controls over 6 days. The responses of sorghum seedlings to inoculation with F. thapsinum and F. proliferatum were similar to those found by other workers following challenge by necrotrophic pathogens and were different from those induced by wounding and exposure to light.     

The role of phenolics in goldenrod ball gall resistance and formation

Some genotypes of Solidago altissima have been shown to exhibit a hypersensitive response to the tephritid ball gallmaker Eurosta solidaginis. When the gallmaker attempts to stimulate gall formation in these genotypes, necrotic tissue surrounds the larva and apparently causes larval death [Anderson, S. S., et al. (1989) Ecology 70, 1048]. Other genotypes have varying degrees of resistance or susceptibility [McCrea, K. D. and Abrahamson, W. G. (1987) Ecology 68, 822]. Studies of other host plants have shown that phenolic compounds can play an important role in this defensive reaction. To determine the role of phenolics in the resistance of S. altissima to ball gallmakers, weekly tissue samples were collected from two resistant and two susceptible clones, both with and without Eurosta attack. These samples were analysed for total phenolics using the Folin-Ciocalteau procedure. Phenolic content increased over time in all clones. In unattacked ramets, phenolic levels were higher in susceptible clones than in resistant clones. No evidence of an increase in phenolics was seen with a hypersensitive response, but a significantly higher concentration was found in plants that had initiated normal gall development. A second study of rapidly growing galls in three additional susceptible clones confirmed this increase in phenolics, demontrated that the higher phenolic concentrations were restricted to gall tissue, and showed that phenolic levels increase as much as five-fold in galls near their peak growth period. Increases in total phenolic levels were clearly not responsible for the hypersensitive reaction for resistance, but phenols could potentially play a role in gall formation by influencing the hormonal control of growth and/or in protection of the gallmaker from its natural enemies.     

Correlations between Accumulation of Dianthramides, Dianthalexin and Unknown Compounds, and Partial Resistance to Fusarium oxysporum f. sp. dianthi in Eleven Carnation Cultivars

The accumulation of dianthramides, dianthalexin and other phenolic compounds in carnation cells at different times before and after inoculation of plants with Fusarium oxysporum f. sp. dianthi, and the development of wilt symptoms were compared for eleven carnation cultivars. Untreated and water-treated controls contained only a little acetone-extractable phenolics. Upon inoculation with F. oxysporum f. sp dianthi, all cultivars accumulated the same range of phenolic compounds, including several dianthramides and dianthalexin, but in different proportions. The total amount of accumulated phenolic compounds per fresh material weight of the extracted stem segments could not be related to the disease resistance level of the different cultivars. However, the accumulation of dianthramides and dianthalexin in the cultivars was positively correlated to resistance, while the accumulation of two other, as yet unidentified, compounds was inversely related to resistance.     

Does nitrogen fertilization have an impact on the trade-off between willow growth and defensive secondary metabolism?

The effect of nitrogen fertilization on the phytomass production, shoot length and leaf secondary phenolics in nine Salix myrsinifolia clones was investigated. Cuttings taken from 1-year-old and 2-year-old shoot parts of field cultivated clones were grown at three concentrations of nitrogen (7, 150 and 300 ppm) in a greenhouse for one growing season. The willow clones differed significantly in phytomass yield and secondary phenolics content. Nitrogen fertilization affected significantly the growth and secondary metabolism of willow clones. In most clones, the addition of nitrogen from a sub-optimum concentration (7 ppm) to an optimum concentration (150 ppm) appeared to reduce the amounts of salicortin, chlorogenic acid and unknown salicylate and increased shoot phytomass, but a supraoptimum nitrogen concentration (300 ppm) resulted in highly variable growth and secondary phenolic responses. A significantly negative correlation between leaf phytomass and amount of total phenolics at sub-optimum and optimum N-treatments indicates trade-off between growth and secondary metabolism in willow clones at these treatments. However, the leaf phytomass:total amount of phenolics ratio varied significantly among clones, and in all clones it was not significantly lower at sub-optimum N-treatment than at optimum N-treatment.     

Effect of cucumber mosaic virus infection on morphology,yield and phenolic contents of tomato

Ten tomato genotypes were screened for their resistance against cucumber mosaic virus (CMV) and its vector Myzus persicae under natural infection in field, using aphids M. persicae under net-house and mechanical inoculation under greenhouse. Large differences were observed among genotypes for infection percentage (IP) and severity index (SI) among the testing methods used. All genotypes showing tolerance to CMV in the field or through aphid inoculation, however, become susceptible and highly susceptible after mechanical inoculation. All the test genotypes also showed susceptibility to the aphid M. persicae population. Plants inoculated with CMV showed substantial decrease in yield and yield-contributing parameters which varied with cultivars that probably depended upon its genetic make up. All the test genotypes exhibited 0.97–30.19% decrease in plant height, 11.47–52.65% decrease in root length, 46.56–95.56% decrease in fresh plant weight, 65.78–92.84% decrease in root fresh weight, 19.97–87.65% decrease in the dry weight of plants, 75.63–95.43% decrease in dry root weight, 69.51–95.65% reduction in the number of fruits and 89.04–99.89% decrease in yield per plants. After 15 days of inoculation, the quantitative analysis using double beam spectrophotometer showed an increase in total phenolics in CMV-inoculated plants as compared to un-inoculated plants among genotypes. Similarly the thin layer chromatography (TLC) on silica gel G indicated that the number of phenolic compounds was increased in most of the inoculated genotypes while in others they were either decreased or remained same.     

Increased accumulation of phenolic metabolites in groundnut (Arachis hypogaea L.) genotypes contribute to defense against Sclerotium rolfsii infection

Abstract

Fungal infections cause several metabolic changes to the plants, which can affect its physiology and survival in various ways. In the present study, we have analysed various phenolic compounds and activity of oxidative enzymes in healthy and Sclerotium rolfsii-infected groundnut genotypes. Increased phenolics content and higher activity of oxidative enzymes was observed in the tolerant genotype (CS 19, GG 16) followed by susceptible genotype (GG 20, TG 37A). Among the phenolic compounds tested, chlorogenic acid content has increased greatly in leaf, stem and root of infected tolerant genotypes compared to the respective controls. In vitro growth of S. rolfsii showed significant inhibition at concentrations 500 and 1000 µg/mL of phenolic compounds in the radial growth inhibition assay. These results have strongly suggested that, higher accumulation of chlorogenic acid could be an important factor in imparting resistance and protecting groundnut against S. rolfsii infection in tolerant genotypes.     

Phenolic compounds of Sorghum vulgare in response to Sclerotium rolfsii infection

Abstract

Identification of individual phenolic acids of Sorghum vulgare Pers. cv. M.P. after interaction with Sclerotium rolfsii Sacc. using high performance liquid chromatograph (HPLC) showed the presence of phenolics namely tannic, gallic, ferulic, chlorogenic and cinnamic acids in varying amounts. After 72 h inoculation with S. rolfsii, a maximum amount of ferulic acid (166.6 µg g^?1 fresh wt) was present in the collar of inoculated plants, followed by leaves and roots and its level decreased gradually with time. Similarly, the presence of chlorogenic acid was traced after 48 h, while that of cinnamic acid was traced after 72 h of inoculation. Reddish-brown pigmentation at the collar region of inoculated plants was also observed along with the high content of tannic acid. Among other phenolics, the presence of gallic acid was recorded consistently and maximum accumulation (139.3 µg g^?1 fresh wt) was noticed at the zone of interaction (collar region) after 72 h of inoculation. In contrast, maximum lignin deposition was observed at collar region after 96 h of inoculation. Induction of phenolic acids in S. vulgare along with the lignin deposition and red pigmentation at collar region is considered a key biomarker in the non-host-pathogen interaction in the S. valgare–S. rolfsii pathosystem.     

Composition of cell wall phenolics and polysaccharides of the potential bioenergy crop –Miscanthus

The composition and concentrations of cell wall polysaccharides and phenolic compounds were analyzed in mature stems of several Miscanthus genotypes, in comparison with switchgrass and reed (Arundo donax), and biomass characteristics were correlated with cell wall saccharification efficiency. The highest cellulose content was found in cell walls of M. sinensis‘Grosse Fontaine’ (55%) and in A. donax (47%) and lowest (about 32%) in M. sinensis‘Adagio’. There was little variation in lignin contents across M. sinensis samples (all about 22–24% of cell wall), however, Miscanthus×giganteus (M × g) cell walls contained about 28% lignin, reed – 23% and switchgrass – 26%. The highest ratios of cellulose/lignin and cellulose/xylan were in M. sinensis‘Grosse Fontaine’ across all samples tested. About the same total content of ester‐bound phenolics was found in different Miscanthus genotypes (23–27 μg/mg cell wall), while reed cell walls contained 17 μg/mg cell wall and switchgrass contained a lower amount of ester‐bound phenolics, about 15 μg/mg cell wall. Coumaric acid was a major phenolic compound ester‐bound to cell walls in plants analyzed and the ratio of coumaric acid/ferulic acid varied from 2.1 to 4.3, with the highest ratio being in M × g samples. Concentration of ether‐bound hydroxycinnamic acids varied greatly (about two‐three‐fold) within Miscanthus genotypes and was also the highest in M × g cell walls, but at a concentration lower than ester‐bound hydroxycinnamic acids. We identified four different forms of diferulic acid esters bound to Miscanthus cell walls and their concentration and proportion varied in genotypes analyzed with the 5‐5‐coupled dimer being the predominant type of diferulate in most samples tested. The contents of lignin and ether‐bound phenolics in the cell wall were the major determinants of the biomass degradation caused by enzymatic hydrolysis.     

Different response of two reindeer forage plants to enhanced UV-B radiation: modification of the phenolic composition

The long-term effects of enhanced UV-B radiation on the content and composition of leaf phenolics in Epilobium angustifolium L. and Eriophorum russeolum Fries ex Hartman were studied in northern Finland (68°N) using two UV-B enhancement experiments, both simulating UV-B_CIE radiation and corresponding to a 20% loss of ozone layer. High proportions of hydrolyzable tannins (69%) and condensed tannins (66%) characterized both Epilobium and Eriophorum leaves, respectively. No UV treatment effect was detected in the content or composition of Epilobium leaf soluble phenolics, whereas significant UV effects were detected in Eriophorum leaves in a developmental-specific manner. At the end of the growing season, the proportion of total soluble phenolics was higher in leaves exposed to enhanced UV-A and UV-B radiation than in the control leaves, but the phenolic composition was not significantly modified. This study introduces a new example on plants’ phenolic response to UV radiation being species-specific and detectable only at certain developmental stages. Possible consequences of increased phenolic content in forage plants for selection and digestibility by reindeer are, however, not yet known.     

Growth Enhancement,Amino Acid Synthesis and Reduction in Susceptibility Towards Phytophthora megakarya by Arbuscular Mycorrhizal Fungi Inoculation in Cocoa Plants

The effects of some selected arbuscular mycorrhizal (AM) fungi, Gigaspora margarita and Glomus mossae on the growth and the role of soluble amino acids of two contrasting cocoa cultivars (ICS84 tolerant and SNK10 sensitive) against black pod disease caused by Phytophthora megakarya were investigated. Root colonization by AM fungi is between 50 and 70% 18 weeks after planting. Tested AM fungi significantly increased all the plant growth parameters (height, number of leaves, shoot and root matter) and P uptake as compared to non‐inoculated plants in pot experiments. AM fungi inoculated cocoa reduced the disease severity. Compared to the control, the soluble amino acid levels increased with inoculation of the AM fungi strains in the necrotic stems of disease on inoculated cocoa plants. Significant relationships between amino acids and disease severity observed for two cocoa cultivars imply that the induction of specific amino acids synthesized by leaves, such as arginine, cysteine and glutamic acid, may represent potential candidate molecules for adaptation of such cultivars to P. megakarya disease. Inoculating seedlings with AMF in nurseries could enhance the development of cocoa plants protected against P. megakarya.     

Variation and inheritance of peroxidase activity and phenol and saccharide content in cacao in relation to susceptibility to black pod disease

The relationship between susceptibility to black pod disease and activity of peroxidases in crude extracts and soluble phenols and saccharides contents was studied in the pod cortex and in the seeds of three cacao clones: SNK413 (lowly susceptible), SNK10 (highly susceptible) and ICS95 (mildly susceptible) and in the F1 (SNK413×SNK10) and the F′1 (SNK10×SNK413) progeny. Phenol content and peroxidase activity in seeds increased as the pods matured; they were not the same in the proximal, middle and distal parts within the same pod at maturity. This variation could be correlated to the stage of development of the seeds. Total soluble saccharides and ketohexoses in the pod cortex did not vary significantly from one clone to another and could not be related to the susceptibility of the pods. Nevertheless, their contents were 2 to 4 times less in the F1 and F′1 progeny. Total soluble phenols, flavanol and hydroxycinnamic derivatives in the pod cortex were higher in the SNK413 clone. Hydroxycinnamic derivatives were not detected in the SNK10 clone and this character was transmitted to the progeny when SNK10 was male (F1 progeny). Phenolic cornpounds decreased in the F1 and F′1 progeny. These results suggest that phenolic compounds and peroxidase activity could be correlated to the susceptibility of cacao clones to black pod disease and that crossing two clones of different susceptibility produces hybrids with lower phenols and saccharides contents which may be responsible for their poor tolerance to black pod disease.     

Rhizobium-Mediated Induction of Phenolics and Plant Growth Promotion in Rice (Oryza sativa L.)

Qualitative and quantitative estimation of phenolic compounds was done through reverse phase–high performance liquid chromatography (RP-HPLC) from different parts (leaf, stem, and root) of rice plants after inoculation with two rhizobial strains, RRE6 (Rhizobium leguminosarum bv. phaseoli) and ANU 843 (R. leguminosarum bv. trifolii) and infection by Rhizoctonia solani. On the basis of their retention time, the major phenolic acids detected in HPLC analysis were gallic, tannic, ferulic, and cinnamic acids. Furthermore, in all Rhizobium-inoculated rice plants, synthesis of phenolic compounds was more consistently enhanced than in control (uninoculated plants), where the maximum accumulation of phenolic compounds was observed in plants inoculated with RRE6 and infection with R. solani. Under pathogenic stress, RRE6 performed better because a relatively higher amount of phenolics was induced as compared with plants treated with ANU 843. Phenolic acids mediate induced systemic resistance and provide bioprotection to plants during pathogenic stresses. In addition, both rhizobial strains promote growth and productivity of rice plants in greenhouse conditions. This report on Rhizobium-mediated defense responses and growth promotion of nonlegume (such as rice) provides a novel paradigm of symbiotic plant–microbe interaction.     

Host preferences of the cocoa pod borer,Conopomorpha cramerella,the main threat to cocoa production in Southeast Asia

Insects ensure the survival of their offspring by depositing their eggs in suitable environments. Even generalist egg-laying insects often show preferences for specific host plants. The cocoa pod borer (CPB), Conopomorpha cramerella (Snellen) (Lepidoptera: Gracillariidae), successfully infests and reproduces on relatively few host plants, but has a major economic impact only on cocoa, Theobroma cacao L. (Malvaceae). Choice tests were performed in the laboratory to compare the frequency of insect visits, the duration of the visits, and the number of eggs laid on the fruits for each combination of host plants tested – that is, cocoa clones or fruits of rambutan (Nephelium lappaceum L.), Fijian longan (Pometia pinnata JR Forst & G Forst, both Sapindaceae), and langsat (Lansium domesticum Corrêa, Malvaceae). Our laboratory study showed that, when given the choice, CPB significantly favored cocoa pods over other host fruits (rambutan, langsat, or Fijian longan). Females also deposited more eggs on unripe fruits than on ripe fruits of similar size. The preference to lay eggs on specific cocoa clones in the bioassays did not reflect the level of the clone resistance to CPB damage reported from the field. Consequently, oviposition preference of female CPB does not seem to be the main factor explaining field resistance of some cocoa clones to CPB infestation.     

Asexual and sexual hybrids between Fundulus diaphanus and F. heteroclitus in the Canadian Atlantic region

Levels and origins of clonal diversity in asexual hybrid animals are critical to understanding how they can coexist with their sexual progenitor species. In this study, asexual gynogenetic hybrids between Fundulus diaphanus and Fundulus heteroclitus known from two sites in Nova Scotia (Canada) were characterized using discriminant morphological traits, eight microsatellite loci, and mitochondrial DNA. Fifteen clonal genotypes were uncovered, all bearing the same F. diaphanus maternal haplotye. Each site harboured a different dominant clone along with several rarer clones that all appear to be of recent origin. Unexpectedly, highly introgressed sexually reproducing hybrids (0.25 > q > 0.75) were also detected. Sexual hybrids with maternal ascendance in either species were also found at three other sites in the Atlantic region. Based on a single meristic trait (scale counts), it is shown that asexual clones can be significantly more variable than populations of sexual parental species. Also, species are morphologically more alike when living in sympatry, suggesting that introgression may occur via sexual hybrids. Altogether, these results confirm and refine the available knowledge on this hybrid system, and indicate that hybridization is probably a more widespread phenomenon than suspected, with implications for the phenotypic variability of a widely used model species, F. heteroclitus.