Inheritance of resistance in <Emphasis Type="Italic">Solanum nigrum</Emphasis> to <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

Solanum nigrum, black nightshade, is a wild non-tuber bearing hexaploid species with a high level of resistance to Phytophthora infestans (Colon et al. 1993), the causal agent of potato late blight, the most devastating disease in potato production. However, the genetic mode of resistance in S. nigrum is still poorly understood. In the present study, two S. nigrum accessions, 984750019 (N19) and #13, resistant (R) and susceptible (S), respectively, to three different isolates of P. infestans, were sexually crossed. The various kinds of progeny including F1, F2, F3, and backcross populations (BC₁; F1 × S), as well as two populations produced by self-pollinating the R parent and S parent, were each screened for susceptibility to P. infestans isolate MP 324 using detached leaf assays. Fifty seedling plant individuals of the F1 progeny were each resistant to this specific isolate, similarly to the seedling plants resulting from self-pollination of the resistant R parent. Thirty seedling plants obtained from self-pollination of the S parent were susceptible. Among a total of 180 F2 plants, the segregation ratio between resistant and susceptible plants was approximately 3: 1. Among the 66 seedling plants of the BC₁ progeny originating from crossing an F1 plant with the susceptible S parent, there were 26 susceptible and 40 resistant plants to P. infestans. The segregation patterns obtained indicated monogenic dominant inheritance of resistance to P. infestans isolate MP 324 in S. nigrum acc. 984750019. This gene, conferring resistance to P. infestans, may be useful for the transformation of potato cultivars susceptible to late blight.     

A new aqueous suspension concentrate formulation of cis‐permethrin and its insecticidal activity

Isomers of pyrethroids usually have different insecticidal activities. Permethrin, a non‐cyano pyrethroid, is not an exception and cis‐permethrin is much more active than the trans‐isomer against Triatoma infestans, vector of Chagas' Disease in Argentina. The large‐scale separation of cis‐ and trans‐permethrin was performed by successive recrystallizations from ethanol‐water mixtures. An aqueous suspension concentrate (flowable) formulation of pure crystalline cis‐permethrin was prepared and assayed for its insecticidal activity on wood and ceramic surfaces against nymph V of T infestans. This formulation was at least three times more effective than deltamethrin, with LC₅₀ values on ceramic of 0.11 µg cm⁻² and 0.33 µg cm⁻² respectively. On wood surfaces, the LC₅₀ value was 0.57 µg cm⁻² compared with 3.20 µg cm⁻² for deltamethrin. Against other insect species such as Periplaneta americana, Aedes aegypti and Culex quinquefasciatus, the suspension concentrate formulation of cis‐permethrin was, however, less effective than similar formulations of deltamethrin or β‐cypermethrin. © 2000 Society of Chemical Industry     

The role of aggressiveness and competition in the selection of Phytophthora infestans populations

Selection within populations of Phytophthora infestans was investigated by comparing the aggressiveness of single‐lesion isolates on detached leaflets of four potato cultivars with differing levels of race‐nonspecific resistance to P. infestans. The isolates included 23 representative of Northern Ireland genotypes from the early 2000s, used to inoculate previously reported field trials on competitive selection (2003–2005), plus 12 isolates recovered from the 2003 trial. The cultivars were those planted in the previous trials: Atlantic (blight‐susceptible) and Santé, Milagro and Stirling (partially resistant). Very highly significant variation for latent period, infection frequency and lesion area was found between genotypes and cultivars; differences between genotypes were more marked on the more resistant cultivars, but no one genotype was the most aggressive across all. Detached leaflets were also inoculated with mixtures of isolates from each genotype group at three sporangial concentrations: differences in aggressiveness between genotypes were more apparent at lower concentrations and on the more resistant cultivars. Genotype groups that were the most aggressive on the more resistant cultivars tended to be those selected by the same cultivars in the field. A mixture of all isolates of all genotypes was used to inoculate detached leaflets of the same cultivars. With one exception, single spore isolates recovered from any one leaflet belonged to a single genotype, but different genotypes were recovered from different cultivars. Phytophthora infestans isolates from Northern Ireland showed significant variation for foliar aggressiveness, and pathogen genotypes exhibited differential aggressiveness to partially resistant cultivars and interacted competitively in genotype selection.     

Insecticide resistance status of Aedes aegypti (L.) from Colombia

BACKGROUND: To evaluate the insecticide susceptibility status of Aedes aegypti (L.) in Colombia, and as part of the National Network of Insecticide Resistance Surveillance, 12 mosquito populations were assessed for resistance to pyrethroids, organophosphates and DDT. Bioassays were performed using WHO and CDC methodologies. The underlying resistance mechanisms were investigated through biochemical assays and RT‐PCR. RESULTS: All mosquito populations were susceptible to malathion, deltamethrin and cyfluthrin, and highly resistant to DDT and etofenprox. Resistance to lambda‐cyhalothrin, permethrin and fenitrothion ranged from moderate to high in some populations from Chocó and Putumayo states. In Antioquia state, the Santa Fe population was resistant to fenitrothion. Biochemical assays showed high levels of both cytochrome P450 monooxygenases (CYP) and non‐specific esterases (NSE) in some of the fenitrothion‐ and pyrethroid‐resistant populations. All populations showed high levels of glutathione‐S‐transferase (GST) activity. GSTe2 gene was found overexpressed in DDT‐resistant populations compared with Rockefeller susceptible strain. CONCLUSIONS: Differences in insecticide resistance status were observed between insecticides and localities. Although the biochemical assay results suggest that CYP and NSE could play an important role in the pyrethroid and fenitrothion resistance detected, other mechanisms remain to be investigated, including knockdown resistance. Resistance to DDT was high in all populations, and GST activity is probably the main enzymatic mechanism associated with this resistance. The results of this study provide baseline data on insecticide resistance in Colombian A. aegypti populations, and will allow comparison of changes in susceptibility status in this vector over time. Copyright © 2011 Society of Chemical Industry     

Activation of defence responses to Phytophthora infestans in potato by BABA

Late blight caused by Phytophthora infestans is one of the most devastating diseases of the potato crop. Resistance breeding and current fungicides are unable to control the rapidly evolving P. infestans and new control strategies are urgently needed. This study examined mechanisms of dl ‐β‐aminobutyric acid (BABA)‐induced resistance (IR) in the potato–P. infestans system. Leaves from two cultivars that differ in their degree of resistance, Bintje and Ovatio, were analysed after foliar treatment with BABA. Rapid activation of various defence responses and a significant reduction in P. infestans growth were observed in leaves treated with BABA. In the more resistant cultivar, Ovatio, the activation was both faster and stronger than in Bintje. Microscopic analysis of leaves treated with BABA revealed induction of small hypersensitive response (HR)‐like lesions surrounded by callose, as well as production of hydrogen peroxide (H₂O₂). Molecular and chemical analyses revealed soluble phenols such as arbutin and chlorogenic acid and activation of PR‐1. These results show a direct activation of defence responses in potato, rather than priming as reported for other plant species. They also show that the efficiency of BABA‐IR differs between cultivars, which highlights the importance of taking all aspects into consideration when establishing new methods for disease management.     

Evaluation and QTL mapping of resistance to powdery mildew in lettuce

Lettuce (Lactuca sativa) is the major leafy vegetable that is susceptible to powdery mildew disease under greenhouse and field conditions. Quantitative trait loci (QTLs) for resistance to powdery mildew under greenhouse conditions were mapped in an interspecific population derived from a cross between susceptible L. sativa cultivar Salinas and the highly susceptible L. serriola accession UC96US23. Four significant QTLs were detected on linkage groups LG 1 (pm‐1.1), LG 2 (pm‐2.1 and pm‐2.2) and LG 7 (pm‐7.1), each explaining between 35 to 42% of the phenotypic variation. The four QTLs are not located in the documented hotspots of lettuce resistance genes. Alleles for the disease resistance at the four QTLs originated from both parents (two from each), demonstrating that even highly susceptible accessions may provide alleles for resistance to powdery mildew. These QTLs appeared to operate during limited periods of time. Results of the field trials with F_2:3 and F_3:4 families derived from a Soraya (moderately resistant) × Salinas cross demonstrated effective transfer of resistance to powdery mildew in this material. An integrated rating approach was used to estimate relative levels of resistance in 80 cultivars and accessions tested in a total of 23 field and greenhouse experiments. Generally, very low resistance was observed in crisphead‐type lettuces, while the highest relative resistance was recorded in leaf and butterhead types. Comparison of two disease assessment methods (percentage rating and the area under the disease progress steps, AUDPS) for detection of QTLs shows that the two approaches complement each other.     

Molecular analysis of pyrethroid resistance conferred by target insensitivity and increased metabolic detoxification in Plutella xylostella

BACKGROUND: The pyrethroid resistance of the diamondback moth Plutella xylostella (L.) is conferred by increased gene expression of cytochrome P450 to detoxify the insecticide and/or through gene mutation of the sodium channel, which makes the individual insensitive to pyrethroids. However, no information is available about the correlation between the increased metabolic detoxification and the target insensitivity in pyrethroid resistance. RESULTS: Frequencies of pyrethroid‐resistant alleles (L1014F, T929I and M918I) and two resistance‐related mutations (A1101T and P1879S) at the sodium channel and expression levels of the cytochrome P450 gene CYP6BG1 were examined individually using laboratory and field strains of P. xylostella. Real‐time quantitative PCR analysis using the laboratory strains revealed that levels of larval expression of the resistant strain, homozygous for the pyrethroid‐resistant alleles other than the M918I, are significantly higher than those of the susceptible strain. In the field strains, the expression levels in insects having the same resistant alleles as those of the resistant strains varied greatly among individuals. The expression levels were not significantly higher than those in the heterozygotes. CONCLUSION: Significant correlation between the target insensitivity and the increased metabolic detoxification in pyrethroid resistance of P. xylostella was observed in the laboratory but not in the field. Copyright © 2010 Society of Chemical Industry     

Efficacy of insecticide mixtures against pyrethroid‐ and organophosphate‐resistant populations of Spodoptera litura (Lepidoptera: Noctuidae)

BACKGROUND: Spodoptera litura (F.) is an important pest worldwide, with over 112 host plants, and is exposed to insecticides throughout the year, resulting in the rapid development of resistance. Insecticide mixtures can delay the development of resistance more effectively than sequences or rotations. Cypermethrin, deltamethrin, profenofos, chlorpyrifos and fipronil were assessed separately and in mixtures against laboratory susceptible S. litura and two field‐collected populations. RESULTS: The field‐collected population from Khanewal (KWL) was significantly more resistant to cypermethrin, deltamethrin, chlorpyrifos and profenofos than one collected from Muzaffar Garh (MGH). Mixtures of cypermethrin + chlorpyrifos or profenofos and of deltamethrin + chlorpyrifos or profenofos at 1:1, 1:10 and 1:20 ratios significantly increased (P < 0.01) toxicity to cypermethrin and deltamethrin in field populations. The combination indices of cypermethrin + chlorpyrifos at 1:1 and 1:10 ratios and cypermethrin + fipronil at 1:1, 1:10 and 1:20 ratios for the KWL strain and of cypermethrin + profenofos or fipronil at 1:1, 1:10 and 1:20 ratios for MGH were significantly below 1, suggesting synergistic interactions. The inhibitors DEF and PBO largely overcame resistance to deltamethrin, cypermethrin and profenofos, suggesting that resistance to the insecticides was associated with esterase and monooxygenase detoxification respectively. CONCLUSION: Chlorpyrifos, profenofos and fipronil could be used in mixtures to restore cypermethrin and deltamethrin susceptibility. These findings may have considerable practical implications for S. litura resistance management. Copyright © 2008 Society of Chemical Industry     

High-throughput approach to detection of knockdown resistance (kdr) mutation in mosquitoes, Culex quinquefasciatus, based on real-time PCR using single-labelled hybridisation probe/melting curve analysis

BACKGROUND: Knockdown resistance (kdr) mutation (L1014F) is a well‐defined mechanism of resistance to pyrethroids and DDT in many insect species. Sensitive detection of the mutations associated with resistance is a prerequisite for resistance management strategies. The authors have developed a new real‐time molecular diagnostic assay based on SimpleProbe^®/melting curve analysis for large‐scale kdr genotyping in the wild population of Culex quinquefasciatus Say, the principal vector of bancroftian filariasis. Melting curve analysis is based on the thermal stability difference between matched and mismatched DNA duplexes. The application of SimpleProbe^® chemistry in insects described here is novel in entomology research. RESULTS: The mosquitoes homozygous for knockdown‐resistant and knockdown‐susceptible allele showed melting peaks at 60.45 °C ( ± 0.25) and 64.09 °C ( ± 0.24) respectively. The heterozygous mosquitoes yielded both peaks at approximately 60.5 °C ( ± 0.2) and 64.20 °C ( ± 0.23). Among the 92 samples genotyped, 16 were found to be homozygous resistant, 44 homozygous susceptible and 32 heterozygous. Comparative assessments were made of all the reported methods for kdr genotyping. CONCLUSION: The present method is cheaper, faster, more reliable and versatile than other alternatives proposed in detecting correct kdr genotypes in mosquitoes. This is the first report using a single‐labelled hybridisation probe to detect point mutations in insect populations. Copyright © 2010 Society of Chemical Industry     

Imidacloprid‐susceptible Nilaparvata lugens individuals exceeded resistant individuals in a mixture population with density pressure

BACKGROUND

Fitness costs associated with insecticide resistance in pest insects have mainly been studied under optimal laboratory conditions. However, resistant insects face more stressors than just insecticides in the field, and how the resistant population reacts to these stressors is of practical importance for the control of pest insects such as the brown planthopper Nilaparvata lugens. The aim of the present study was to explore the impact of population density on the competitiveness of resistant and susceptible individuals.

RESULTS

Two isogenic N. lugens populations, a highly imidacloprid‐resistant population (HZ‐R) with a resistance ratio (RR) of 227.10 and a relatively susceptible population (HZ‐S) with an RR of 2.99, were created from a field‐resistant population (HZ; RR 62.51). The high resistance levels of HZ‐R and HZ were mainly attributable to the overexpression of multiple cytochrome P450 (CYP) genes such as CYP6ER1, CYP6AY1, CYP6CW1 and CYP4CE1 compared with HZ‐S, this being supported by piperonyl butoxide synergism. HZ‐R was observed to be more resistant to thiacloprid and etofenprox compared with HZ and HZ‐S. Most interestingly, in high population density treatments, HZ‐S individuals were much more competitive than HZ‐R individuals.

CONCLUSION

Imidacloprid‐resistant individuals of N. lugens are less competitive than their susceptible counterparts under density pressure. © 2017 Society of Chemical Industry     

Differences in the responses of melon accessions to fusarium root and stem rot and their colonization by Fusarium oxysporum f. sp. radicis‐cucumerinum

Fusarium root and stem rot caused by the fungus Fusarium oxysporum f. sp. radicis‐cucumerinum is a major disease in greenhouse cucumbers. Over the past decade, the disease has been documented in melon greenhouses in Greece, and recently it has been sporadically recorded in greenhouse melons in Israel. Variations in disease response were found among 41 melon accessions artificially inoculated with the pathogen: 10 accessions were highly susceptible (90–100% mortality), 23 exhibited an intermediate response (20–86%) and eight were resistant (0–4%). Two melon accessions – HEM (highly resistant) and TAD (partially resistant) – were crossed with the susceptible accession DUL. The responses of the three accessions and F₁ crosses between the resistant and susceptible parents were evaluated. HEM contributed higher resistance to the F₁ hybrid than TAD. Roots of susceptible and resistant accessions were 100 and 79% colonized, respectively, following artificial inoculation. However, only susceptible plants showed colonization of the upper plant tissues. Microscopic evaluation of cross sections taken from the crown region of the susceptible DUL revealed profuse fungal growth in the intercellular spaces of the parenchyma and in xylem vessels. In the resistant cultivar HEM, very little fungal growth was detected in the intercellular spaces of the parenchyma, and none in the xylem or any other vascular tissue. Finding resistant accessions may create an opportunity to study the genetics of resistance inheritance and to develop molecular markers that will facilitate breeding resistant melon cultivars.     

Fumigant toxicity of lemon eucalyptus oil constituents to acaricide-susceptible and acaricide-resistant Tetranychus urticae

BACKGROUND: This study was aimed at assessing the fumigant toxicity of 14 essential oil constituents from lemon eucalyptus, Eucalyptus citriodora Hook, and another ten known compounds to females of acaricide‐susceptible, chlorfenapyr‐resistant, fenpropathrin‐resistant, pyridaben‐resistant and abamectin‐resistant strains of Tetranychus urticae Koch. RESULTS: Menthol (LC₅₀, 12.9 µg cm^?3) was the most toxic compound, followed by citronellyl acetate (16.8 µg cm^?3), against the susceptible females. High toxicity was also produced by β‐citronellol, citral, geranyl acetate and eugenol (LC₅₀, 21.7–24.6 µg cm^?3). The fumigant toxicity of these compounds was almost identical against females from either of the susceptible and resistant strains, indicating that the compounds and acaricides do not share a common mode of action or elicit cross‐resistance. CONCLUSION: Global efforts to reduce the level of highly toxic synthetic acaricides in the agricultural environment justify further studies on materials derived from lemon eucalyptus oil, particularly menthol and citronellyl acetate, as potential acaricides for the control of acaricide‐resistant T. urticae as fumigants with contact action. Copyright © 2011 Society of Chemical Industry     

Field-evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India

BACKGROUND: The pink bollworm is one of the most destructive pests of cotton. Transgenic cotton producing Bt toxin Cry1Ac or a combination of Cry1Ac and Cry2Ab2 has been used effectively against this pest. However, some other insects have evolved resistance to Bt toxins in the field. During the 2007–2008 and 2008–2009 seasons, pink bollworm populations in India were surveyed to evaluate their responses to Cry1Ac and seed powder containing Cry1Ac and Cry2Ab2. RESULTS: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non‐Bt cotton in the Amreli district of Gujarat in western India. The median lethal concentration of Cry1Ac for five‐day‐old larvae (LC₅₀) was significantly higher for insects derived in 2008 from Amreli than for any of the other field populations tested from four locations in India. For Cry1Ac, the mean LC₅₀ for the strain derived from Amreli in 2008 was 44 times higher than for the most susceptible population. However, for seed powder of Bollgard II containing primarily Cry2Ab2, the 2008 Amreli population was only slightly less susceptible than the most susceptible population. CONCLUSIONS: The data reported here constitute the first evidence of field‐evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009–2010 growing season, which confirmed field‐evolved resistance to Cry1Ac in Amreli. The lack of cross‐resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac. Copyright © 2011 Society of Chemical Industry     

Molecular basis of resistance to acetolactate synthase-inhibiting herbicides in Sisymbrium orientale and Brassica tournefortii

Three Australian Sisymbrium orientale and one Brassica tournefortii biotypes are resistant to acetolactate synthase (ALS)-inhibiting herbicides due to their possession of an ALS enzyme with decreased sensitivity to these herbicides. Enzyme kinetic studies revealed no interbiotypic differences within species in K_m (pyruvate) (the substrate concentration at which the reaction rate is half maximal) but a greater V_max (the rate when the enzyme is fully saturated with substrate) for two of the resistant S orientale biotypes over susceptible levels. F₁ hybrids from reciprocal crosses between resistant and susceptible biotypes of S orientale showed an intermediate response to chlorsulfuron compared to the parental plants. ALS herbicide resistance in S orientale segregated in a 3:1 (resistant:susceptible) ratio in F₂ plants with a single rate of chlorsulfuron, indicating that resistance is inherited as a single, incompletely dominant nuclear gene. Two regions of the ALS structural gene known to vary in ALS-resistant biotypes were amplified and sequenced. Resistant S orientale biotypes NS01 and SS03 contained a single nucleotide substitution in Domain B, predicting a Trp (in susceptible) to Leu (in resistant) amino acid change. Two adjacent nucleotide substitutions (CC T to AT T) predicting a Pro (in susceptible) to Ile (in resistant) change in the primary amino acid sequence were identified in Domain A of resistant S orientale biotype SS01. Likewise, a single nucleotide substitution at the same site in the resistant B tournefortii biotype predicts a Pro (in susceptible) to Ala (in resistant) substitution. No other interbiotypic nucleotide differences predicted amino acid changes in the sequenced regions, suggesting that the amino acid substitutions reported above are responsible for resistance to ALS-inhibiting herbicides in the respective biotypes. © 1999 Society of Chemical Industry     

The cross-resistance to pyrethrins and eight synthetic pyrethroids,of an organophosphorus-resistant strain of the rust-red flour beetle Tribolium castaneum (herbst)

Comparisons with standard susceptible insects showed that a strain of Tribolium castaneum, with a specific resistance to malathion and its carboxylic ester analogues, had no cross-resistance to topical applications of natural pyrethrins. Another strain of T. castaneum, showing resistance to many organophosphorus (OP) insecticides, was cross-resistant to pyrethrins ( × 34) and eight synthetic pyrethroids also applied topically; least cross-resistance occurred with resmethrin ( × 2.2), bioresmethrin ( × 3.3) and phenothrin ( × 4.0). Generally larger resistance factors were recorded with formulations synergised by piperonyl butoxide (PB). The greatest cross-resistance encountered was with unsynergised tetramethrin ( × 338). Apart from tetramethrin, factors of synergism did not exceed 5.7 with either the susceptible or multi-OP resistant strains. PB antagonised six of the nine pyrethroids against the multi-OP resistant strain. Antagonism also occurred with two of these six, permethrin (cis: trans ratio 1:3) and 5-prop-2-ynylfurfuryl ( 1RS)-cis,trans-chrysanthemate (‘Prothrin’), against the susceptible strain. Considering only formulations without the synergist, the most effective compounds against the susceptible strain, relative to pyrethrins, were bioresmethrin (2.7) and permethrin (2.4). Similarly with the multi-OP resistant strain the most effective compounds were bioresmethrin (28), resmethrin (14) and permethrin (6.6). Thus the LD₅₀ (the dose required to kill 50% of the test species) for bioresmethrin against the resistant strain (0.14 μg) only slightly exceeded the LD₅₀ for pyrethrins against the susceptible strain (0.12 μg).     

Functional imaging of biophoton responses of plants to fungal infection

Each living cell of a plant produces photons in certain conditions. Under normal physiological conditions, cell photon emission is stationary and minimal. Disturbance in the oxidative homeostasis by biotic stress is manifested by increased ‘biophoton’ production. Such biophoton responses of plants may be used as an integral indicator of the degree of oxidative homeostasis misbalance. Our results demonstrate that biophoton generation has been much higher in a resistant potato variety than in a susceptible one till 10 h after Phytophthora infestans inoculation. In contrast, ultra-weak luminescence from detached susceptible potato and moderately resistant pelargonium leaves increased from 1–4 to 4–5 days after inoculation with Phytophthora infestans or Botrytis cinerea, respectively. Pre-treatment of susceptible potato leaves with a defence inducer, arachidonic acid, resulted in a transient burst of light in response to P. infestans lasting for 30–45 h post inoculation (hpi). This study presents the potential adaptation of functional imaging of ultra-weak luminescence to monitor time-dependent free radical processes during disease development and its application to draw conclusions on plant resistance to pathogens of different lifestyle. Moreover, it has been shown that imaging of temporal biophoton generation from potato leaves treated with arachidonic acid might be a helpful marker in mapping oxidative changes leading to systemic acquired resistance (SAR).     

Mutations in the mitochondrial cytochrome b of Tetranychus urticae Koch (Acari: Tetranychidae) confer cross‐resistance between bifenazate and acequinocyl

BACKGROUND: Resistance of Tetranychus urticae Koch to bifenazate was recently linked with mutations in the mitochondrial cytochrome b Q_o pocket, suggesting that bifenazate acts as a Q_o inhibitor (Q_oI). Since these mutations might cause cross‐resistance to the known acaricidal Q_oI acequinocyl and fluacrypyrim, resistance levels and inheritance patterns were investigated in several bifenazate‐susceptible and bifenazate‐resistant strains with different mutations in the cd1 and ef helices aligning the Q_o pocket. RESULTS: Cross‐resistance to acequinocyl in two bifenazate‐resistant strains was shown to be maternally inherited and caused by the combination of two specific mutations in the cytochrome b Q_o pocket. Although most investigated strains were resistant to fluacrypyrim, resistance was not inherited maternally, but as a monogenic autosomal highly dominant trait. As a consequence, there was no correlation between cytochrome b genotype and fluacrypyrim resistance. CONCLUSIONS: Although there is no absolute cross‐resistance between bifenazate, acequinocyl and fluacrypyrim, some bifenazate resistance mutations confer cross‐resistance to acequinocyl. In the light of resistance development and management, high prudence is called for when alternating bifenazate and acequinocyl in the same crop. Maternally inherited cross‐resistance between bifenazate and acequinocyl reinforces the likelihood of bifenazate acting as a mitochondrial complex III inhibitor at the Q_o site. Copyright © 2009 Society of Chemical Industry     

EPSPS gene amplification in glyphosate-resistant Italian ryegrass (Lolium perenne ssp. multiflorum) from Arkansas

BACKGROUND: Resistance to glyphosate in weed species is a major challenge for the sustainability of glyphosate use in crop and non‐crop systems. A glyphosate‐resistant Italian ryegrass population has been identified in Arkansas. This research was conducted to elucidate its resistance mechanism. RESULTS: The investigation was conducted on resistant and susceptible plants from a population in Desha County, Arkansas (Des03). The amounts of glyphosate that caused 50% overall visual injury were 7 to 13 times greater than those for susceptible plants from the same population. The EPSPS gene did not contain any point mutation that has previously been associated with resistance to glyphosate, nor were there any other mutations on the EPSPS gene unique to the Des03 resistant plants. The resistant plants had 6‐fold higher basal EPSPS enzyme activities than the susceptible plants, but their I₅₀ values in response to glyphosate were similar. The resistant plants contained up to 25 more copies of EPSPS gene than the susceptible plants. The level of resistance to glyphosate correlated with increases in EPSPS enzyme activity and EPSPS copy number. CONCLUSION: Increased EPSPS gene amplification and EPSPS enzyme activity confer resistance to glyphosate in the Des03 population. This is the first report of EPSPS gene amplification in glyphosate‐resistant Italian ryegrass. Other resistance mechanism(s) may also be involved. Copyright © 2012 Society of Chemical Industry     

Identification and characterization of RB-orthologous genes from the late blight resistant wild potato species Solanum verrucosum

Late blight, caused by the oomycete pathogen, Phytophthora infestans, is a devastating disease of potatoes and tomatoes. A key long-term management strategy for combating this disease is to develop potato cultivars with high levels of durable resistance through identification and integration of major resistance genes. The RBgene, cloned from the Mexican diploid potato species Solanum bulbocastanum, confers broad-spectrum resistance to potato late blight. Here, we have determined the late blight resistance phenotypes of eight accessions of Solanum verrucosum, another wild diploid potato species, using greenhouse inoculations and discovered variability among the accessions. While most accessions were resistant, one accession was notably more susceptible. Transcribed orthologs of the RB gene from the eight S. verrucosum accessions were cloned using a homology-based PCR approach. Sequence analysis revealed that the RB^ver orthologs share up to 83.5% nucleotide identity with RB^blb. Stable introduction of the RB ortholog from late blight resistant S. verrucosum PI275260 into susceptible S. tuberosum confers resistance to P. infestans. Interestingly, this functional RB^ver ortholog contains an insertion of a complete leucine rich repeat when compared to RB^blb, and differs from the RB^ver ortholog from a susceptible accession at only four amino acid residues.