Susceptible Clones Research Articles

Development of somatic hybrids Solanum × michoacanum Bitter. (Rydb.) (+) S. tuberosum L. and autofused 4x S. × michoacanum plants as potential sources of late blight resistance for potato breeding

Key message Phytophthora infestans resistant somatic hybrids of S. × michoacanum (+) S. tuberosum and autofused 4 x S. × michoacanum were obtained. Our material is promising to introgress resistance from S. × michoacanum into cultivated potato background. Solanum × michoacanum (Bitter.) Rydb. (mch) is a wild diploid (2n = 2x = 24) potato species derived from spontaneous cross of S. bulbocastanum and S. pinnatisectum. This hybrid is a 1 EBN (endosperm balance number) species and can cross effectively only with other 1 EBN species. Plants of mch are resistant to Phytophthora infestans (Mont) de Bary. To introgress late blight resistance genes from mch into S. tuberosum (tbr), genepool somatic hybridization between mch and susceptible diploid potato clones (2n = 2x = 24) or potato cultivar Rywal (2n = 4x = 48) was performed. In total 18,775 calli were obtained from postfusion products from which 1,482 formed shoots. The Simple Sequence Repeat (SSR), Cleaved Amplified Polymorphic Sequences (CAPS) and Random Amplified Polymorphic DNA (RAPD) analyses confirmed hybrid nature of 228 plants and 116 autofused 4x mch. After evaluation of morphological features, flowering, pollen stainability, tuberization and ploidy level, 118 somatic hybrids and 116 autofused 4x mch were tested for late blight resistance using the detached leaf assay. After two seasons of testing three somatic hybrids and 109 4x mch were resistant. Resistant forms have adequate pollen stainability for use in crossing programme and are a promising material useful for introgression resistance from mch into the cultivated potato background.

Barley yellow dwarf virus transmission and feeding behaviour of Rhopalosiphum padi on Hordeum bulbosum clones

AbstractA Hordeum bulbosum L. (Poaceae) clone A17 was identified, which showed complete resistance to Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV). It was not possible to infect plants of A17 with BYDV‐PAV, ‐MAV, or with CYDV‐RPV by the aphid vectors Rhopalosiphum padi (L.) or Sitobion avenae (Fabricius) (both Hemiptera: Aphididae). Plants of the A17 clone and of the BYDV‐susceptible H. bulbosum clone A21 revealed some resistance to R. padi compared to the susceptible winter barley cultivar Rubina [Hordeum vulgare L. (Poaceae)]. The development time to the imago was longer and the number of nymphs was reduced on both clones compared with cv. Rubina. The probing and feeding behaviour of R. padi on plants of the H. bulbosum clones was studied over 12 h and compared with that on plants of the barley cv. Rubina. Principal component analysis of the results of the feeding behaviour revealed a clear separation of the H. bulbosum genotypes from Rubina. On H. bulbosum the number of penetrations was higher but total feeding time was shorter. Significant differences were mainly found in the phloem feeding parameters for plants of both clones in comparison to Rubina, with the virus resistant A17 clone having the strongest effect and the susceptible A21 clone being intermediate. Most significant differences were found in parameters of the phloem salivation phase. On A17, an average of less than one (0.9) E1 phase per plant was observed (3.3 on A21 and 5.7 on Rubina) and its duration was reduced to less than 1 min (0.9 min) in comparison to 2.4 min on A21 and 5.7 min on Rubina. Also, the phloem feeding (E2) phase was clearly reduced on A17 plants with 0.5 E2 phases per test and a mean duration of 1.1 min in contrast with 2.9 and 3.5 E2 phases per test and 34.1 and 421.3 min for A21 and Rubina, respectively. These results point towards a phloem‐localized factor for aphid resistance in H. bulbosum, i.e., on A17 plants the phloem salivation time is too short for a successful infection by BYDV leading to vector resistance.

Food Conditioning Affects Expression of Insect Resistance in Diploid Willows (<i>Salix</i> spp.)

The high energy quota and versatility of use make willows (Salix spp.) attractive as bioenergy crops. Insect defoliation constitutes a threat to the profitability of willow growers. Hitherto, the breeding for resistance against the main insect pests has been hampered by the fact that all known resistant willow clones are polyploids, and existing molecular breeding tools work most effectively for diploids. Here, we firstly report diploid willows highly resistant to the main insect defoliator, the leaf beetle (Phratora vulgatissima), offering new opportunities for breeding resistance. Leaf beetles exposed to three resistant clones (two S. purpurea one S. eriocephala) laid three to 27 times fewer eggs than females on a susceptible S. viminalis clone. Secondly, we show that beetles laid significantly more eggs on resistant clones if they were fed the susceptible clone prior to the oviposition monitoring test compared to when they prefed on resistant clones. Nevertheless, the differences observed between resistant and susceptible clones were pronounced in all cases. The food conditioning effect means that small differences in resistance among clones may be undetected.

Varying Tolerance to Glyphosate in a Population of Palmer Amaranth with Low EPSPS Gene Copy Number

A Palmer amaranth population (seeds collected in the year 2000; Washington Co., MS) suspected to be susceptible to glyphosate was examined as a population and as individual plants and found to exhibit varying tolerance or resistance to glyphosate. Whole plant spraying of glyphosate (0.84 kg·ha?1) to the population revealed that approximately 40% of this population were resistant to glyphosate and an LD50 of 0.75 kg·ha?1 was determined. Spray application of glyphosate indicated that some plants displayed varying degrees of resistance 14 days after treatment. Initial tests using leaf disc bioassays on 10 individual plants selected randomly from the population, allowed characterization of glyphosate resistance using both visual ratings of injury and quantitative measurement via chlorophyll content analysis. After initial bioassays and spray application, five plants with a range of tolerance to glyphosate were selected for cloning so that further studies could be accomplished on these individuals. Q-PCR analysis of these clones showed that resistance was not due to elevated EPSPS gene copy number. Shikimate levels were lower in the resistant and higher in the susceptible clones which correlated with varying degrees of resistance demonstrated in bioassays and spray application of glyphosate of these clones. Results demonstrate that individuals in a population can vary widely with respect to herbicide resistance and suggest that uptake, translocation, sequestration, metabolism or altered target site may contribute to the resistance in some individuals of this population.

Construction and Analysis of SSH-cDNA Library from Leaves of Susceptible Rubber Clone Resistant to Powdery Mildew Induced by BTH

To understand the mechanism of benzothiadiazole (BTH)-induced susceptible rubber clone resistance to powdery mildew on gene level, a differentially expressed cDNA library was constructed by suppression subtractive hybridization (SSH) with rubber Reyan 7-33-97 clone. The constructed cDNA library was high integrity through detection of the critical processes of SSH, such as efficiency of adaptor connection, subtraction and conversion, as well as the type of recombinant genes. The positive rate was 99% after identification with random 400 white spots. The size of the cDNA clone inserted fragments was various but most in 400 bp - 1000 bp. There were 23 cDNA sequences matching the function of energy and basic metabolism, signal transduction, membrane and transport, secondary metabolism and so on after detection of the 42 positive clone sequences selected randomly from the cDNA library and comparison on nucleic acid sequences in Genbank. 7 ESTs were logged in Genbank and accession numbers were GW873071 and GW874604- GW874610. The results implicated that BTH could effectively induced rubber tree resistance to powdery mildew through increasing expresses of defense-related genes in leaves of rubber tree susceptible clone. It should provide a new approach for rubber disease management.

Mechanism of resistance in Australian sugarcane parent clones to smut and the effect of hot water treatment

Resistance of sugarcane plants to smut is believed to be manifested by two mechanisms, (i) external resistance, governed by structural barrier of bud scale and/or chemical secretion from the bud, and (ii) internal resistance, regulated by interaction of plants and fungus within the plant tissue. Hot water treatments are routinely used to treat seed cane to eliminate a range of diseases including smut. It is believed that hot water treatment predisposes sugarcane plant to smut. This study was conducted to determine the resistance mechanisms of some important Australian parent clones, and their response to hot water treatment in relation to smut infection. Twenty-one clones, used regularly in the Australian sugarcane breeding program, were evaluated. Results showed that ~47% of clones had external and 33% had internal resistance mechanisms, indicating that parent clones selected for this study possessed diverse mechanism of resistance. There is a possibility some or all clones with internal resistance mechanisms could also possess external resistance mechanism. Except one highly susceptible clone (Q205) in one trial, none of the clones subject to hot water treatment became more susceptible to smut. Although some clones showed increased resistance after hot water treatment. These findings will benefit breeders in selecting parent materials in their crossing programs to develop smut-resistant cultivars.

Utilization of a major brown rust resistance gene in sugarcane breeding

Brown rust, caused by Puccinia melano- cephala, has had devastating effects on sugarcane (Saccharum spp.) breeding programs and commercial production. The discovery of Bru1, a major gene conferring resistance to brown rust, represented a substantial breakthrough. Markers for Bru1 are the first available for sugarcane molecular breeding. The contribution of Bru1 towards brown rust resistance in the Canal Point (CP) sugarcane breeding program was determined as a means of directing future breeding strategies. Bru1 was detected in 285 of 1,072 (27 %) clones used for crossing; this germplasm represents the genetic base for cultivar development in Florida. The frequency of Bru1 was greatest in CP clones (42 %) and lowest among Louisiana clones (6 %). Bru1 was not detected in clones with year assignments before 1953. However, Bru1 frequency increased from 15 % (assignments 1975-1985) to 47 % in the current decade. The increase coincided with the introduction of brown rust to Florida. Bru1 was detected in 155 (32 %) of 485 parental clones tested for brown rust susceptibility at two field locations. Of clones classed resistant to brown rust, 154 (59 %) contained Bru1, yet none of 100 susceptible clones contained the gene. Bru1 was detected in 667 (44 %) clones in the second clonal stage of selection, 87 % of which were free of brown rust symptoms. Bru1 is the predominant source of resistance in the Florida sugarcane genetic base. Efforts to identify and integrate new brown rust resistance genes must be pursued to minimize risks associated with a future breakdown in major gene resistance provided by Bru1.

Geno- and phenotypic correlates of virologic response to the attachment inhibitor BMS-626529 in an 8-day monotherapy study of its prodrug BMS-663068

Background : Administered as monotherapy for 8 days, BMS-663068, the prodrug of the attachment inhibitor BMS-626529, demonstrated significant reductions in plasma HIV-1 RNA. Although baseline IC 50 >100 nM to BMS 626529 correlated with a poor virologic response, BMS-663068 did not appear to select for BMS-626529 resistance on population sequencing or phenotyping. Methods : Genotypic population analyses of baseline samples from non-responders identified amino acid changes that could potentially encode for reduced susceptibility to BMS-626529. Reverse genetics of functional envelope clones confirmed changes responsible for this in phenotypic assays. Additional genotypic, phenotypic and reverse genetic assays were performed on samples from responders to probe the context dependence of the identified substitutions. Results : The gp120 M426L substitution was the major change associated with reduced virologic response (present in 5 of 6 non-responders) and high BMS-626529 IC 50 (present in virus from 6 of 7 subjects with IC 50 >100 nM). The remaining non-responder virus sample contained a S375M substitution that encoded reduced susceptibility. However, the M426L substitution was also identified in two responders, one with reduced susceptibility (IC 50 6300 nM) and another with low IC 50 (38 nM). A series of functional clones from 4 samples (including 2 responders with resistance mutations on population genotyping) were analyzed for susceptibility to BMS-626529. Variability of susceptibility of clones (37-246 fold) was higher than variability observed with other entry inhibitors (enfuvirtide, 6-9 fold; maraviroc, 3-9 fold). In the responder subject with M246L, all functional clones contained M426L and susceptibility varied by 246-fold, suggesting that susceptibility is highly context dependent. One of the responders contained viruses of either tropism. Clones of R5- or X4-tropic viruses from this individual exhibited the same variable range of susceptibility to BMS-626529. Conclusions : gp120 substitutions M426L and S375M were found to be strongly, albeit not exclusively, associated with low susceptibility to BMS-626529 and a lack of virologic response to its prodrug, BMS-663068. Functional clones derived from single individuals exhibited 2-3 log 10 variability in susceptibility to the agent, regardless of tropism, suggesting that susceptibility can be highly context-dependent. (Published: 11 November 2012) Citation: Abstracts of the Eleventh International Congress on Drug Therapy in HIV Infection Zhou N et al. Journal of the International AIDS Society 2012, 15 (Suppl 4):18270 http://www.jiasociety.org/index.php/jias/article/view/18270 | http://dx.doi.org/10.7448/IAS.15.6.18270

Ovipositional preference and larval performance of poplar defoliator, Clostera restitura on different poplar clones in north-western India

We evaluated ten poplar clones (G-3, G-48, L-50/88, L-154/84, L-156/89, S7C8, S7C15, WSL-22, WSL-29 and Uday) for ovipositional preference and larval performance of Clostera restitura. Female moths did not show any preference with respect to clones for oviposition. Significant differences were observed for number of eggs laid on different plant parts. C. restitura laid eggs in clusters, preferably on upper surface of leaf and size of the egg cluster varied from 15 to 167 eggs. Clones varied for their relative resistance and susceptibility to C. restitura. L-50/88; L-156/89 were identified as most resistant clone based on minimum leaf consumption, whereas S7C15 was found to be most susceptible clone to C. restitura. In multiple choice experiments, no feeding preference by C. restitura larvae was detected amongst different poplar clones. After initial settlement of larvae on a particular clone, the larvae remained confined to that clone and negligible inter-clonal movement was noticed subsequently. The fresh pupal weight was correlated negatively (r = −0.37) with percentage surface leaf area eaten and positively (r = 0.47) with length of larval period, measured on different clones. Relationship between percentage leaf area eaten and length of larval period was negative (r = −0.23). Owing to relative resistance of L-50/88 and L-156/89 against C. restitura, these clones can be recommended for plantation in defoliator prone areas in north-western India.

Effetti diretti e indiretti di trattamenti chimici contro le ruggini del pioppo

Abstract: Some quantitative consequences of poplar rust attacks (Melampsora larici-populina and M. allii-populina) were analysed, both in absence and in presence of some preventive chemical treatments. Their effectiveness was previously assessed only partially and without evaluations of plant behaviour in the following vegetative season. Three IBS systemic triazoles (tebuconazole, cyproconazole and epoxyconazole), the translaminar cytotropic mandipropamid and a mixture of cyproconazole and azoxystrobin (methoxyacrilate similar to strobilurines) were tested on one-year plantlets of the susceptible clone ’Neva’ (Populus ×canadensis). The products were sprayed twice in August 2010, the second treatment twenty days after the first one. The leaf area covered by uredinia was assessed in several dates from the beginning of August until the end of September, as well as the percentage of still living leaves on the plant (last ten days of October). In May 2011, the average leaf surface of side shoots close to the top of the crown and the Chlorophyll Content Index (CCI) were measured. The tested fungicides dramatically reduced the infections, except mandipropamid which showed no effectiveness. Tebuconazole and cyproconazole, either alone or in mixture with azoxystrobin, have offered the best performance (at the end of September, less than 10% of leaf surface covered by uredinia vs. over 50% of the control and mandipropamid treatment), followed by epoxyconazole that is anyway satisfying (about 15% of surface covered by uredinia). The systemic properties of these fungicides allowed a preventive action on leaves sprouted after both of the treatments as well, thus uredinium eruption was limited to 20% of leaf surface instead 40% on the test thesis. The same effectiveness ranking was reiterated for the percentage of still living leaves on the plant at the end of October (about 45% vs. 4% of the control test) and, during the following season, for the average leaf surface of side shoots (over 800 cm2 vs. less than 400 cm2 of the test) and for the CCI parameter (over 21 vs. 16). Thus, the phylloptosis induced by rusts involves a seriously impaired leaf sprouting during the season following the attacks, both as regards tissue amount and its photosynthetic efficiency.

Detection of Hevea brasilensis clones yield potential and susceptibility to tapping panel dryness in Côte d’Ivoire using the 32 and 35 KDa lutoidic proteins

This study was carried out to identify protein markers with yield potential and susceptibility to tapping panel dryness (TPD). To achieve this goal, 11 clones, stimulated and non stimulated, yield and susceptibility to TPD were compared. Their lutoid fraction polypeptides were analysed using one and two-dimensional electrophoresis. Susceptibility to TPD appeared as a clonal trait which is not related to yield potential. TPD can occur either in stimulated or non stimulated clones but, overstimulation increase TPD symptoms. Clones PB 235, PB 260 and IRCA 130 are highly susceptible to TPD, whereas IRCA 41, PB 217, AF 261, AVROS 2037 and GT 1 are less susceptible. Productive and less susceptible clones to TPD are characterized by abundant quantity of 35 KDa polypeptide and absence or very small amount of 32 KDa polypeptide. Contrarily, clone susceptible to TPD are characterized by abundant quantity of 32 KDa polypeptide. In unproductive clones (RO 38, TJR 1), 32 KDa protein was more abundant than 35 KDa. Overstimulation induces a decrease of 35 KDa protein intensity. Thus, 32 and 35 KDa polypeptides could be used for identification of Hevea clones yielding potential and susceptibility to TPD. Keywords: Hevea brasiliensis , lutoid, protein, rubber, tapping panel dryness, yield

Differentially expressed genes and proteins upon drought acclimation in tolerant and sensitive genotypes of Coffea canephora

The aim of this study was to investigate the molecular mechanisms underlying drought acclimation in coffee plants by the identification of candidate genes (CGs) using different approaches. The first approach used the data generated during the Brazilian Coffee expressed sequence tag (EST) project to select 13 CGs by an in silico analysis (electronic northern). The second approach was based on screening macroarrays spotted with plasmid DNA (coffee ESTs) with separate hybridizations using leaf cDNA probes from drought-tolerant and susceptible clones of Coffea canephora var. Conilon, grown under different water regimes. This allowed the isolation of seven additional CGs. The third approach used two-dimensional gel electrophoresis to identify proteins displaying differential accumulation in leaves of drought-tolerant and susceptible clones of C. canephora. Six of them were characterized by MALDI-TOF-MS/MS (matrix-assisted laser desorption-time of flight-tandem mass spectrometry) and the corresponding proteins were identified. Finally, additional CGs were selected from the literature, and quantitative real-time polymerase chain reaction (qPCR) was performed to analyse the expression of all identified CGs. Altogether, >40 genes presenting differential gene expression during drought acclimation were identified, some of them showing different expression profiles between drought-tolerant and susceptible clones. Based on the obtained results, it can be concluded that factors involved a complex network of responses probably involving the abscisic signalling pathway and nitric oxide are major molecular determinants that might explain the better efficiency in controlling stomata closure and transpiration displayed by drought-tolerant clones of C. canephora.

Characterization and Expression Analysis of a Retinoblastoma-Related Gene from Chinese Wild Vitis pseudoreticulata

Retinoblastoma-related (RBR) genes, a conserved gene family in higher eukaryotes, play important roles in cell differentiation, development, and mammalian cell death; however, little is known of their function in plants. In this study, a RBR gene was isolated from the Chinese wild grape, Vitis pseudoreticulata W. T. Wang clone “Baihe-35-1”, and designated as VpRBR. The cDNA sequence of VpRBR was 3,030 bp and contained an open reading frame of 3,024 bp. Conceptual translation of this gene indicated a composition of 1,007 amino acids with a predicted molecular mass of 117.3 kDa. The predicted protein showed a retinoblastoma-associated protein domain A from amino acid residues 416 to 579, and domain B from residues 726 to 855. The result of expression analysis indicated that VpRBR was expressed in tissues, leaves, stem, tendrils, flower, and grape skin at different expression levels. Further quantitative reverse transcription-PCR (qRT-PCR) data indicated that VpRBR levels were higher in Erysiphe necator-treated “Baihe-35-1” and “Baihe-13-1”, two resistant clones of Chinese wild V. pseudoreticulata, than in E. necator-treated “Hunan-1”, a susceptible clone of V. pseudoreticulata. Furthermore, the expression of VpRBR in response to salicylic acid (SA), methyl jasmonate (MeJA), and ethylene (Eth) in grape leaves was also investigated. Taken together, these data indicate that VpRBR may contribute to some aspect of powdery mildew resistance in grape.

Leaf thickness and structure of <em>Vitis vinifera</em> L. cv. Albariño clones and its possible relation with susceptibility to downy mildew (<em>Plasmopara viticola</em>) infection

<p style="text-align: justify;"><strong>Aims</strong>: The grapevine (<em>Vitis vinifera</em> L.) cultivar Albariño is currently the most economically important in Galicia (northwestern Spain). Earlier works assessing the natural susceptibility to downy mildew leaf infection (both in the laboratory and in the field), carried out in the collection of Albariño clones at the Misión Biológica de Galicia (CSIC), showed great differences among the clones (Boso <em>et al.</em>, 2004b, 2005b, 2006; Boso and Kassemeyer, 2008). The aim of the present work is to highlight the histological differences in leaves, in particular thickness and structure, among the 11 different Albariño clones and to find out their possible relation with their natural susceptibility to <em>Plasmopara viticola</em>.</p><p style="text-align: justify;"><strong>Methods and Results</strong>: Transverse sections of adult leaves where prepared and observed under light microscope. The area corresponding to the different leaf layers was measured. The results showed significant differences between the clones regarding the thickness of the spongy mesophyll. The clones CSIC-4 and CSIC-1 had the thickest spongy mesophyll (average mean = 14316.8 μm<sup>2</sup>) whereas CSIC-3 showed the thinnest one (11548.1 μm<sup>2</sup>).</p><p style="text-align: justify;"><strong>Conclusion</strong>: The CSIC-3 clone, one of the least susceptible clones to <em>P. viticola</em> in previous studies, showed the thinnest and most compact spongy mesophyll. On the contrary, the CSIC-1 clone had the thickest spongy mesophyll and was also one of the most susceptible to this pathogen. Therefore, it could be possible to relate their histological leaf characteristics with their different levels of natural susceptibility to <em>P. viticola</em>.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This work contributes to the understanding of the link between histological characteristics of leaf layers and mesophyll cells and the different natural susceptibility of grapevines to downy mildew. This may become in the future a valid tool to be used during clonal selections in grapevine breeding programs.</p>

Local and systemic defense response in Aspen clones: contrasting defense response to biotrophic and necrotrophic pathogens

Trees are exposed to a variety of pathogenic fungi. The defense response toward a biotroph may require a different strategy that toward a necrotroph. To understand the key processes of defense responses toward pathogenic fungi in aspen (Populus tremulae) at the transcript level we inoculated clones of this species with a foliar rust on the leaves and a necrotroph in the bark. Leaf samples were collected from above the inoculation site to examine the long distance (systemic) defense responses and bark tissue around the site of inoculation examined for the local response as early as day1 post treatments. We performed microarray experiments on the biotrophic and necrotrophic interaction and between healthy controls of two SwAsp clones. Selected candidate genes were also examined in more detail by qRT-PCR and chemical analysis for phenols and tannins was also performed. We found that the two clones respond in a very different in fashion at the transcriptional level to both the biotrophic and necrotrophic pathogen. The more resistant clone responded systemically within 24 hours while little response at the transcriptional level was detected in the more susceptible clone in response to the biotroph, while indications of suppression in response to the necrotroph was found.

Greenhouse Assessment of Differences in Clomazone Tolerance among Sweetpotato Cultivars

Differences in clomazone tolerance among sweetpotato cultivars were first observed in April 2007 after use of the herbicide for weed control in fields containing the sweetpotato breeding project at the U.S. Vegetable Laboratory. Susceptible cultivars and experimental clones exhibited severe foliar chlorosis and reduced growth, whereas the most tolerant were not injured. Twelve cultivars and experimental clones were included in a greenhouse experiment to quantify the differences in clomazone tolerance. In the greenhouse, the clomazone concentration that caused moderate injury or reduction in shoot growth to the most tolerant clones was approximately 10 times the concentration that caused a similar response in the most susceptible clones. Two older cultivars, Excel and Sumor, that were developed before the registration of clomazone for use in sweetpotato were susceptible. Clomazone is an important component in sweetpotato weed management, and susceptibility is an undesirable trait that should be avoided in new sweetpotato cultivars.

Combining Ability Analysis of Resistance in White Clover to Southern Root‐Knot Nematode

White clover (Trifolium repens L.) is an important forage crop worldwide and also in the southeastern United States. Root‐knot nematodes (RKN; Meloidogyne spp.) can be a major factor limiting white clover production and persistence. This study was conducted to determine the genetic basis of resistance to M. incognita race 4 in white clover. Eight parents composed of three resistant, two intermediate, and three susceptible clones were crossed in a partial diallel design, and progeny of those 28 crosses were evaluated for egg mass score, gall score, eggs per gram of dry root weight, eggs per plant, shoot weight, and root weight. Progeny were arranged in a randomized complete block design with five replications each consisting of 14 individual plants. Two weeks after germination, plants were inoculated with approximately 500 M. incognita race 4 eggs. To serve as a noninoculated control, cross progeny were arranged in another randomized complete block design with three replications each consisting of seven plants. The analysis of egg mass score, gall score, eggs per gram dry root weight, and eggs per plant showed that both general combining ability (GCA) and specific combining ability (SCA) were significant in the expression of those variables. The GCA effects were related with previously classified resistance reaction to the southern RKN.

The resistance of cocoa hybrids to vascular-streak dieback

Breeding for VSD resistance on cocoa was carried out by inter-crossing the selected clones of TSH 858, KW 162, KW 163, KW 165, KEE 2, ICS 13 and NIC 7 which were selected based on the criteria of VSD resistance, productivity and cross-compatibility. This research has objective to evaluate hybrids of the crossess for VSD resistance, inheritance of the resistance and selecting the most valuable parental-clones for further crossess. Fourteen hybrids and one control were tested 14 in the randomized-completely block design with 4 blocks where in each plot 16 trees planted at Kaliwining Experimental Station in Jember. The resistance was evaluated in the field by scoring the symptoms in the range of 0—6 at 7 year after planting. The scores were varied significantly among the hybrids in the range of 2.19—4.53. Hybrids which were generated from the crosses of resistant clones performed lower number of the score than the hybrids generated from crosses between two susceptible clones (TSH 858 x NIC 7) which performed highest score. The hybrids classified as resistant were TSH 858 x KW 162 (F1 and reciprocal), KW 162 x KEE 2 (F1 and reciprocal), KW 162 x ICS 13, KW 165 x KEE 2. Of the parental clones, KW 162 is the most promising parent as lower score obtained when used it as male or female compared to KEE 2 which performed quite similar of the score with TSH 858 as susceptible parent. Therefore, it could be supposed that KW 162 has better combining ability than KEE 2 where these resistant-clones showed different segregation of their resistance. The resistance was segregated by KW 162 in term of ratio 15 resistant : 1 susceptible while KEE 2 the ratio 1 resistant: 1 susceptible.Key words: Theobroma cocoa L., hybrid, resistance, vascular-streak dieback.

Genetic resistance to Hymenoscyphus pseudoalbidus limits fungal growth and symptom occurrence in Fraxinus excelsior

SummaryThe European common ash (Fraxinus excelsior) is currently threatened by a pathogenic fungus, Hymenoscyphus pseudoalbidus, which seems to enter the trees through the leaves. Continuous assessments of 39 clones in Danish field trials have shown that there are significant differences in the susceptibility of clones to the new disease. Interestingly, clones that showed early leaf senescence in the autumn were in general less susceptible to the disease than late‐senescing clones. Thus, variation in susceptibility could be owing to phenological differences associated with the infection biology. To test whether differences in susceptibility are driven by genetically based factors other than phenology, we compared inoculations with H. pseudoalbidus on four highly susceptible clones with those of four less susceptible clones. Development of necrosis was hereafter followed regularly. The growth of the fungus in the inner bark was further detected with species‐specific PCR primers. The severity of the response to infection shows significant differentiation among clones and significant correlation with clone susceptibility, as assessed from natural infections in field trials. The fungus was detected in tissues immediately surrounding the necrosis but showed some signs of endophytic growth. The results suggest that healthier clones are able to limit the growth and spread of the fungus and thereby minimize the occurrence of symptoms. This gives hope for the future preservation of F. excelsior in Europe through selection and breeding.

Mutation of a nicotinic acetylcholine receptor β subunit is associated with resistance to neonicotinoid insecticides in the aphid Myzus persicae

BackgroundMyzus persicae is a globally important aphid pest with a history of developing resistance to insecticides. Unusually, neonicotinoids have remained highly effective as control agents despite nearly two decades of steadily increasing use. In this study, a clone of M. persicae collected from southern France was found, for the first time, to exhibit sufficiently strong resistance to result in loss of the field effectiveness of neonicotinoids.ResultsBioassays, metabolism and gene expression studies implied the presence of two resistance mechanisms in the resistant clone, one based on enhanced detoxification by cytochrome P450 monooxygenases, and another unaffected by a synergist that inhibits detoxifying enzymes. Binding of radiolabeled imidacloprid (a neonicotinoid) to whole body membrane preparations showed that the high affinity [3H]-imidacloprid binding site present in susceptible M. persicae is lost in the resistant clone and the remaining lower affinity site is altered compared to susceptible clones. This confers a significant overall reduction in binding affinity to the neonicotinoid target: the nicotinic acetylcholine receptor (nAChR). Comparison of the nucleotide sequence of six nAChR subunit (Mpα1-5 and Mpβ1) genes from resistant and susceptible aphid clones revealed a single point mutation in the loop D region of the nAChR β1 subunit of the resistant clone, causing an arginine to threonine substitution (R81T).ConclusionPrevious studies have shown that the amino acid at this position within loop D is a key determinant of neonicotinoid binding to nAChRs and this amino acid change confers a vertebrate-like character to the insect nAChR receptor and results in reduced sensitivity to neonicotinoids. The discovery of the mutation at this position and its association with the reduced affinity of the nAChR for imidacloprid is the first example of field-evolved target-site resistance to neonicotinoid insecticides and also provides further validation of exisiting models of neonicotinoid binding and selectivity for insect nAChRs.