A cohort-based stochastic model of the population dynamic and long-term management of Conyza bonariensis in fruiting tree crops

Conyza bonariensis is currently a frequent and abundant weed in fruiting tree crops associated with non-tillage in Mediterranean climate areas, such as citrus groves and olive orchards. Because of the mild winters characteristic of this climate, an extended season of seedling emergence, from early autumn to early spring, is often found for this species, this leading to multiple annual cohorts. In this work, a cohort-based stochastic model of C. bonariensis population dynamics was developed and used to simulate the behaviour of the seed bank in Mediterranean fruiting tree crops under ten contrasting management strategies, including single or integrated herbicide and non chemical control measures. The demographic impact of tillage system (ploughing vs. no-till), the use of cover, and timing of herbicide applications was simulated. The model was parameterized with information taken from the literature. In the absence of any control and under no-tillage the modelled seed bank reached an average equilibrium density of 378,092 ± 10,865 seeds m⁻². The most effective management strategy integrated no-till, the use of cover and early and late applications of herbicides, which reduced the equilibrium densities of the seed bank by 78.7%. A sensitivity analysis indicated that C. bonariensis populations in Mediterranean fruiting tree crops are particularly sensitive to small changes in the demographic parameters associated with the earlier cohort and to the efficacy of early herbicide treatments. A diversified, integrated approach including different interventions of chemical and cultural nature appears to be the most successful strategy at the field level for controlling C. bonariensis in Mediterranean fruiting tree crops.     

Growth stage,temperature, and time of year affects the control of glyphosate-resistant and glyphosate-paraquat resistant Conyza bonariensis with saflufenacil

Conyza bonariensis (L.) Cronq. is a problematic weed in crop and non-crop areas of California. This problem has been further aggravated by the discovery of herbicide-resistant biotypes. Experiments were conducted in 2012 and 2013 in fall and spring, respectively, to determine the efficacy of glyphosate, saflufenacil, and a tank-mixture of saflufenacil + glyphosate on glyphosate-susceptible (GS), glyphosate-resistant (GR), and glyphosate-paraquat-resistant (GPR) biotypes of C. bonariensis. Efficacy of the herbicides were evaluated at three growth stages (5- to 8-leaf seedling, rosette, and bolting); and three day/night temperature regimes (15/10 °C, 25/20 °C, 35/30 °C). Results differed between experiments conducted in the fall and spring. Saflufenacil-alone was more effective in the fall than in spring. All the GS, GR and GPR plants were controlled by saflufenacil-alone at the 5-to 8-leaf stage and rosette stage, but level of control declined at the bolting stage. Better control with saflufenacil-alone and glyphosate-alone was obtained at the 15/10 °C and 25/20 °C than at the 35/30 °C temperature regime. However, a tank-mixture of saflufenacil + glyphosate provided good control of the plants at 35/30 °C. Efficacy of saflufenacil-alone was inconsistent in spring and varied between the biotypes, but the control with saflufenacil + glyphosate was excellent and consistent between seasons. Glyphosate-alone provided good control of all three biotypes at the 5- to 8-leaf stage in the fall, but the control was poor in spring. Therefore, saflufenacil-alone can provide excellent control of C. bonariensis plants prior to the bolting stage in the fall; but in spring, it will be more effective when applied with glyphosate.     

高粱EPSPS基因的克隆、修饰及在玉米中的功能验证

针对草甘膦结合位点,对高粱5-烯醇式丙酮酰莽草酸-3-磷酸合酶（EPSPS）基因进行4种定点修饰,将修饰后的基因分别导入到玉米中。通过对转化体的抗性鉴定,确定将高粱EPSPS基因106位的脯氨酸变为丝氨酸（P106S）能够赋予转基因玉米草甘膦抗性。在喷施4倍的草甘膦时抗性事件CL38-1不产生药害。Southern杂交结果表明,目标基因在该转化事件中稳定遗传,转化其余3种EPSPS基因的植株对草甘膦没有足够的抗性。     

Flaxleaf fleabane (Conyza bonariensis) populations have developed glyphosate resistance in north-east Australian cropping fields

In recent years flaxleaf fleabane has become a widespread and difficult-to-control weed in no-tilled fallowed fields, where weeds are controlled by applications of glyphosate, in annual cropping systems of north-east Australia. Fifty-two populations, collected in a national survey from agricultural and non-agricultural areas, were tested in two glyphosate dose-response pot experiments. In two subsequent pot experiments, a sub-set of these populations was tested with a field rate of glyphosate when weeds of two ages were grown at different soil moistures. In the first and second experiments, most populations collected from chemical fallowed or cropped fields in north-east Australia had GR₅₀ (estimated dose for 50% biomass reduction) values three to six times greater than the susceptible populations, indicating low levels of glyphosate resistance. Several populations from roadsides adjacent to chemical fallowed or cropped fields also had higher GR₅₀ values, indicating movement of seeds from resistant plants. In the third experiment, weed biomass of all populations from chemical fallowed or cropped fields was 70-98% of unsprayed compared to 2-3% for the susceptible populations, irrespective of weed age or soil moisture. In the fourth experiment which treated older weeds, the response of several resistant populations to glyphosate was unaffected by differences in weed age and soil moisture, whereas the biomass of the other resistant populations was greater following spraying of older and/or moisture stressed plants compared with smaller non-stressed plants. Thus, exclusive reliance on glyphosate for fallow weed control in this region has resulted in the evolution of resistance in flaxleaf fleabane populations in a cropping system with annual non-transgenic crops. Prolific production of windborne seeds, combined with poor control associated with spraying large moisture-stressed weeds, is likely to have contributed also to flaxleaf fleabane becoming such a problem weed.     

Response of Eleusine indica and Paspalum distichum to glyphosate following repeated use in citrus groves

Eleusine indica L. Gaertn. and Paspalum distichum L. are annual and perennial grasses, respectively that are widely distributed in turf and perennial cropping systems throughout Spain. Often, glyphosate is used between rows of perennial crops for control of these grasses, but variable responses have been observed. Sensitivity to glyphosate in each species was examined under greenhouse, laboratory and field conditions. In vitro tests on whole plants of both P. distichum and E. indica revealed no differences in sensitivity to glyphosate for areas with long-term use (treated; T) and no history of use (not treated; NT). The NT population of P. distichum (ED₅₀ 73.1 g ae ha⁻¹) was 11.6% more sensitive to glyphosate than NT E. indica (ED₅₀ 81.6 g ae ha⁻¹). No differences between T and NT populations of both species were observed for foliar retention of glyphosate as well as accumulation of shikimate. However, glyphosate retention and shikimate accumulation were up to 64 and 24.4% greater, respectively in P. distichum compared to E. indica. Within 96 h after treatment (HAT), foliar absorption of ¹⁴C-glyphosate was similar among T and NT populations, but 8.8% higher for P. distichum compared to E. indica. Retention of ¹⁴C-glyphosate in treated leaves of P. distichum was approximately 55% lower compared to E. indica. Translocation from the treated leaf into other shoot tissue (2.8-fold) and roots (8.5-fold) was higher for P. distichum versus E. indica. This would suggest that differences in E. indica versus P. distichum response to glyphosate are based upon differential retention in treated leaves and reduced movement out of treated tissue in other shoot and root tissue. In separate field experiments in citrus orchards, glyphosate and other herbicides were applied to assess control of E. indica and P. distichum over two years. Flazasulfuron and cycloxidim resulted in 90% or greater control of both species by 60 days after treatment (DAT). Only glufosinate, oxyfluorfen, paraquat and iodosulfuron resulted in >85% control of E. indica. These corresponding treatments ranged in effectiveness from 73 to 92% on P. distichum. Integration of effective herbicides with modes of action different than glyphosate should be used for management of E. indica and P. distichum and may delay the selection for resistance to glyphosate.     

Virulence response to the Mi.1 gene of Meloidogyne populations from tomato in greenhouses

In a comparison of reproductive traits of 29 field populations of Meloidogyne spp. on resistant and susceptible tomatoes, 48% of the populations were virulent against the Mi.1 gene. Virulent populations produced more (P < 0.05) egg masses/plant, eggs/plant, eggs/g root, and showed higher infection frequencies and multiplication rates than the avirulent populations. The fecundity of females did not differ between the resistant and susceptible genotype, and did not change with the virulence status of the populations. On the resistant genotype, the populations collected from the susceptible tomato showed lower (P < 0.05) reproductive traits than those collected from rootstocks followed by those from resistant tomato. Meloidogyne javanica produced more (P < 0.05) egg masses/plant and eggs/g root than Meloidogyne incognita on the resistant genotype. A time course experiment was conducted to determine if root penetration by M. javanica populations with different Mi.1 virulence status is conditioned by the expression of resistance on tomato. Significant differences between populations were observed as early as of 2 days post-inoculation on the susceptible genotype. On the resistant genotype, low juvenile numbers from populations with acquired virulence penetrated the roots up to 4 dpi, but their numbers significantly increased 7 dpi. Juveniles of the natural virulent population followed similar penetration pattern on the resistant and susceptible genotypes. Peroxidases are involved in the oxidative burst typically associated with the hypersensitive response in incompatible host–pathogen interactions. Isoelectrofocusing isozyme analysis revealed an increase in the peroxidase activity on the resistant genotype after inoculation with the avirulent population and to a lesser degree with the populations with acquired virulence in comparison with the natural virulent population.     

Simultaneous selection for stem borer resistance and forage related traits in maize (Zea mays ssp. mays L.) × teosinte (Zea mays ssp. mexicana L.) derived populations

Maize spotted stalk borer (Chilo partellus Swinhoe Pyralidae) (MSSB) is a serious pest of the maize (Zea mays ssp. mays L.) crop in Pakistan. This study was conducted to introgress resistance in maize against MSSB by exploring wild sources of resistance for the development of a resistant maize variety. To achieve this, teosinte (‘PI566674’) × maize (‘Sargodha-2002’) crosses were conducted and three populations (F₁, F₂ and F₃) were established. These populations were screened at various locations and in a contrasting artificial insect infestation experiment. Teosinte species ‘PI566674’, following screening, was shown to be highly resistant to MSSB and had the ability to produce a high biomass (5 times higher than susceptible genotypes) under high temperatures (36–40 °C). The biomass of the F₁ hybrid, which was highly susceptible to MSSB, was significantly reduced (P ≤ 0.05) following infestation by MSSB in all experiments. The introgression from teosinte for genes conferring resistance to MSSB was screened in segregating F₂ and F₃ generations. Despite a susceptible F₁ population, F₂ was resistant to MSSB. Twenty new recombinant plants with resistance to MSSB and a high leaf soluble solid (16 °Brix) content were identified. They were selected to grow the F₃ population. Mean values of F₃ progenies showed similar resistance to the F₂ population but a high percentage (60%) of resistant plants was recovered.     

Cyperus difformis evolves resistance to propanil

Cyperus difformis L. is one of the worst weeds of rice world-wide and has evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in rice fields of California. Propanil use was intensified to control the widespread resistant biotypes. Rice growers have recently experienced poor control, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to detect the presence of propanil resistance, to establish resistance levels, and to investigate involvement of enhanced herbicide detoxification as mechanism of resistance through the use of metabolic inhibitors. Four C. difformis populations collected in rice fields from the Sacramento Valley of California were confirmed resistant to propanil. This is the first case of such resistance outside the Poaceae and the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl and malathion applied individually in mixture with propanil had minor effects on herbicide toxicity suggesting metabolic detoxification was not a resistance mechanism. A resistant biotype produced more than 80% biomass after a propanil (6.7 kg a.i. ha⁻¹) and carbaryl (1.9 kg a.i. ha⁻¹) or propanil and malathion (1.0 kg a.i. ha⁻¹) treatment compared to <20% by a susceptible biotype, suggesting substantial resistance still persisted in spite of insecticide addition. Propanil-resistant plants were cross-resistant to bensulfuron-methyl, imazosulfuron, halosulfuron-methyl and penoxsulam, but susceptible to carfentrazone. The loss of propanil to control this important weed of rice underscores the fragility of herbicide-based weed control in monoculture rice. Integrated weed management approaches to decrease herbicide selection pressure are needed to mitigate the evolution of multiple-herbicide resistance in C. difformis of California rice.     

Glyphosate management strategies,weed diversity and soybean yield in Argentina

From their introduction in 1996, glyphosate resistant (GR) soybean cultivars have been rapidly adopted by farmers in Argentina and in other countries in the world. The high rate of adoption of this technology seems to be based on the simplicity of use provided by a single herbicide (glyphosate), its high efficacy to control many weeds and, the low costs of the technology relative to that used in conventional crops. During 2001–2002, 2002–2003 and 2003–2004 soybean growing seasons, field surveys and field experiments were performed with the aim of studying the effect of different glyphosate management strategies on the diversity of soybean weed communities, weed control, individual survival, fecundity and crop yield. In addition, the emergence pattern of three important weeds, Digitaria sanguinalis, Cyperus rotundus and Anoda cristata, was also studied. Both field surveys and field experiments were carried out on no-till soybean crops sown immediately after wheat or barley harvest (double cropped system). Experiments were set up in commercial soybean crops and consisted of different times of a single glyphosate application, two glyphosate applications and also the application of glyphosate plus a residual herbicide imazethapyr. A. cristata, D. sanguinalis, Stellaria media, Chenopodium album and Cyperus sp. were the most prevalent weeds recorded at pre-harvest of the soybean crops, showing regional constancy higher than 80% in both years. In three out of four field experiments, crop yield was not increased when glyphosate was applied twice compared with a single application of the herbicide. In addition there was a lower negative effect on weed species richness when glyphosate was applied once during the crop cycle than with two applications of glyphosate or glyphosate plus imazethapyr. D. sanguinalis escaped the glyphosate early treatment because of the long weed emergence period, while A. cristata and C. rotundus survived treatments due to their high individual tolerance. The results suggest that it is possible to manage glyphosate application to get high crop yield with a low impact on weed diversity, depending on the weed species and their abundance.     

Tolerance of Amaranthus palmeri populations from California to postemergence herbicides at various growth stages

In recent years, poor control of Amarathus palmeri S. Wats. plants with glyphosate in many agricultural and non-crop has been observed in the San Joaquin Valley (SJV), California, USA. Studies were conducted to assess if these were glyphosate-resistant (GR) populations. Populations from 23 different locations of the SJV were exposed to glyphosate application of 840 g ae ha⁻¹ at the 5 to 8 leaf stage of the plant and compared against a known GR and glyphosate-susceptible (GS) population from New Mexico, USA. None of the plants from the SJV survived the glyphosate application suggesting that they were GS. Plant mortality following application of glyphosate (840 g ae ha⁻¹), glufosinate (490 g ai ha⁻¹), paraquat dichloride (660 g ai ha⁻¹), saflufenacil (50 g ai ha⁻¹), rimsulfuron (70 g ai ha⁻¹⁾, and a tank-mix of glyphosate (840 g ae ha⁻¹) + saflufenacil (50 g ai ha⁻¹) applied at the 4 to 6, 8 to 10, and 12 to 16 leaf stages of A. palmeri was determined on potted plants grown outdoors. Complete control was obtained with all the treatments applied at the 4 to 6 leaf stage but control was reduced to less than 70% and 20% with glyphosate and glufosinate, respectively at the later stages. The other treatments provided 100% control at all growth stages. Combinations of saflufenacil + glyphosate, saflufenacil + glufosinate, saflufenacil + dicamba, rimsulfuron + glyphosate, tembotrione + glyphosate, flumioxazin + pyroxasulfone + glyphosate, flumioxazin + pyroxasulfone + glyphosate, dicamba + paraquat dichloride, and glyphosate + glufosinate were also tested on 8 to 10 leaf stage A. palmeri plants and all the combinations provided 100% control.     

Integrated management of postharvest banana anthracnose (Colletotrichum musae) through plant extracts and hot water treatment

The aim of the present study was to determine the integrated effect of plant extracts and hot water treatment on postharvest anthracnose and banana fruit quality. Artificially inoculated banana fruit were dipped in 10% and 20% (w/v) extracts of four plant species, viz. Acacia albida, Argemone mexicana, Dovalis abyssinica and Prosopis juliflora at room temperature (20 °C), 45 °C and 50 °C. Fruit treated separately with 20% extracts of A. albida and P. juliflora at 50 °C had reduced anthracnose incidence and severity. These treatment combinations also had the highest percentage of marketable ripe banana fruits. In conclusion, applying aqueous plant extracts at 50 °C enhanced the antifungal activity of extracts without affecting the physico-chemical properties of banana.     

Effects and side effects of penicillin injection in huanglongbing affected grapefruit trees

Trunk injection with penicillin has been tested to control citrus huanglongbing (HLB), but side effects and environmental safety must be assured before approval of penicillin injection can be considered. We investigated effects of penicillin injection on densities of Candidatus Liberibacter asiaticus (Las) in leaves, as well as culturable bacterial populations in rhizospheres and petioles of grapefruit trees in field and greenhouse experiments. Trees were injected with penicillin G, and leaf and root concentrations were assessed in bioassays with Bacillus subtilis. Las densities were determined by qPCR, and bacteria were isolated on a low carbon medium from roots plus rhizosphere and surface-sterilized petioles at various times after penicillin injection. Selected bacterial isolates were tested for penicillin resistance (20 μg/mL) and glyphosate resistance (7000 μg/mL), because glyphosate is widely used and cross-resistance against antibiotics had been documented. One month after penicillin injection half of the greenhouse trees were inoculated with Phytophthora nicotianae. Cycle threshold (Ct) values of Las in old and young leaves significantly increased 90 days after trunk injection with penicillin. Bacterial populations in petioles and root-rhizospheres initially increased after penicillin injections, probably due to nutrient release, then returned to control levels after one week. Penicillin resistance was common in isolates from penicillin-injected and control trees (30–94%). Significantly more glyphosate resistant than sensitive isolates were penicillin resistant (81% versus 52%). Phytophthora root rot was not increased after penicillin injection. Thus, side effects of penicillin injection tested here were minimal, while Las titers were reduced after three months.     

Response of selected cucumber cultivars to Meloidogyne incognita

Root-knot nematodes (Meloidogyne spp.) are one of the most destructive pathogens of vegetables. The cultivars resistant to root-knot nematodes have comparatively better crop yield than susceptible varieties and can be employed as a component of integrated nematode management. In the present study, 15 cultivars of cucumber (Cucumis sativus) were tested for their response to Meloidogyne incognita by inoculating with 3000 2nd stage juveniles of the nematode. All cultivars varied significantly in causing reductions in growth parameters over their controls. Likewise, all cultivars behaved differently regarding formation of galls and egg masses and reproductive factor. It was found that none of the tested cultivars was found immune or highly resistant. Long Green was the only cultivar which was found resistant against M. incognita as it showed minimum galls (8.2) and reductions in growth parameters. On the other hand, cultivars Mehran, Mirage, Thamin-II, and Royal Sluis were highly susceptible as evident by maximum galls (>100) on their roots and reductions in growth parameters. Similarly, the cultivars Green Wonder, Cucumber Citriolo and Poinsett were moderately susceptible (31–70 galls) while Babylon, Cobra and Falcon-560 (71–100 galls) were susceptible and reductions in growth parameters of these cultivars were less than those in highly susceptible cultivars. Four cultivars, Marketmore, Dynasty, Pioneer-II, and Summer Green, were rated as moderately resistant (11–30 galls) as these cultivars showed less damage by the nematode than moderately susceptible, susceptible and highly susceptible cultivars.     

Effect of glyphosate on Macrophomina phaseolina in vitro and its effect on disease severity of soybean in the field

Laboratory and field studies were conducted to assess the effects of glyphosate on Macrophomina phaseolina culture growth in vitro and the disease severity of charcoal rot in soybean fields at Stoneville, MS and Jackson, TN. Glyphosate inhibited M. phaseolina growth in a linear dose dependent manner when technical grade glyphosate acid (GlyCry) was used; however, growth was inhibited in an exponential dose dependent manner when a commercial formulation of glyphosate-potassium salt (Gly-K salt) was used. The glyphosate GR₅₀ values (glyphosate concentration required to cause a 50% reduction) in culture radial growth ranged from 0.25 to 9.94 mM among the M. Phaseolina isolates, temperatures, and formulations. The three isolates differed in response to various concentrations across the three temperature regimes. Among the three isolates, TN 410 was the most sensitive for both GlyCry (GR₅₀ = 7.74 mM) and Gly-K salt (GR₅₀ = 0.25 mM) at 30 °C. This research indicates that glyphosate has the ability to inhibit growth of M. phaseolina in culture in vitro. The preliminary field studies demonstrated that application of glyphosate to glyphosate-resistant soybeans did not enhance or reduce the severity of charcoal rot in a no-till field in TN but had some suppressing effect in a tilled environment in MS when single applications were made at growth stage V3 and V6.     

Distribution and frequency of resistance to four herbicide modes of action in Lolium rigidum Gaud. accessions randomly collected in winter cereal fields in Spain

Lolium rigidum is the most prevalent and damaging grass weed of winter cereals in Spain. L. rigidum infestations are frequently treated with herbicides and, consequently, populations have evolved resistance. The objective of this study was to determine the extent and frequency of herbicide resistance in L. rigidum populations in Spain to the selective herbicides chlortoluron, diclofop-methyl and chlorsulfuron, commonly used for its control in-crop, and to glyphosate. The response to these herbicides was evaluated on 123 accessions surveyed randomly across cereal cropping areas of the regions of Castile and León, Catalonia and Andalusia. The fresh weight and the frequency of undamaged plants were calculated for each accession and herbicide. At the regional level, higher frequencies of accessions displaying resistance occurred in Catalonia, an intensively cropped region with a greater herbicide selection pressure. Of concern is that in this region the 60% of the accessions displayed some level of resistance to the ALS-inhibiting herbicide chlorsulfuron. The 6.9% of the accessions found in Castile and León with some resistance to glyphosate could also indicate an incipient problem of resistance to this herbicide. For the other herbicides and regions the majority of the accessions remained susceptible. The possible mechanisms of herbicide resistance development in L. rigidum accessions (target-site versus non-target-site resistance) and their variation among regions was discussed. This study can be used to generate herbicide resistance-management schemes for farmers, based upon the herbicide the site and the potential for resistance development.     

Manihot flabellifolia Pohl,wild source of resistance to the whitefly Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae)

Aleurotrachelus socialis is one of the most important pests of cassava (Manihot esculenta Crantz) in the Neotropics. In Colombia, high whitefly populations can reduce crop yields by 79%; and although the farmers intensify the use of insecticides, this practice is highly contaminating, costly and leads to the development of resistance in the insect. An alternative for managing whitefly populations is to develop genetically resistant varieties. Wild parents of Manihot are a useful source of genes against pests for the cultivated species of cassava. Based on prior research that showed the existence of moderate-to-high levels of resistance to A. socialis in Manihot flabellifolia, a wild species of cassava, this study was proposed to characterize this new source of resistance, evaluating the biology and demographics of A. socialis on eight accessions of M. flabellifolia, a susceptible check (CMC-40) and a resistant (MEcu72) check. The averages of A. socialis longevity and fecundity on the accessions were not significantly different to MEcu72, but different from CMC-40 (P < 0.05). Development time was not significantly different, ranging from 35–40 days on accessions and MEcu72 and 33.5 days on CMC-40 (P < 0.05). In contrast, the population growth rate (r_m) was significantly lower on the M. flabellifolia accessions, with Fla 61 standing out with a growth rate 98 and 99% less than that obtained on MEcu72 and CMC-40, respectively. Once the resistant levels have been identified to A. socialis on the M. flabellifolia accessions, interspecific crosses of M. esculenta subsp. M. flabellifolia and backcross programs could be developed to incorporate the desirable characteristics from the wild relatives into elite progenitors of M. esculenta.     

Selection,mechanism, cross resistance and stability of spinosad resistance in Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

Spodoptera litura is one of the most destructive pests in Pakistan and in many other regions of the world. A field collected population of S. litura was selected with spinosad for eleven generations under controlled laboratory conditions to study the cross resistance, mechanism and stability of spinosad resistance in S. litura. The resistance to spinosad in S. litura increased 3921-fold (after eleven generations of selection with spinosad) as compared to a susceptible population of S. litura. No cross resistance between spinosad and emamectin benzoate, methoxyfenozide, fipronil, indoxacarb, profenofos, lufenuron or deltamethrin was found in the spinosad-selected population of S. litura. To find the possible mechanism of spinosad resistance in S. litura two synergists, Piperonyl butoxide (PBO), S, S, S-tributyl phosphorotrithioate (DEF) were tested on the susceptible and resistant strains and on the un-selected field population. The values of the synergism ratios of PBO and DEF were 2.33 and 1.06 for the spinosad-selected strain, 1.36 and 1.06 for the un-selected field population and 1.14 and 1.00 for the susceptible strain, respectively. As high PBO ratio indicates the role of microsomal O-demethylase in causing spinosad resistance in S. litura. The spinosad-resistant and field populations of S. litura were reared without any selection pressure from the 12th to the 16th generation (G₁₂–G₁₆). The spinosad resistance decreased from 3921 to 678-fold in the spinosad-resistant population and from 31.1 to 15.1-fold in the un-selected population of S. litura as compared to the susceptible strain. Spinosad resistance in S. litura has a high reversion rate (−0.15) which indicates that spinosad resistance in S. litura is unstable and can be easily managed by switching off the selection pressure for a few generations or alternating with insecticides having different modes of action.     

Marker gene excision in transgenic Brassica napus via Agrobacterium-mediated Cre/lox transient expression system

Oilseed rape (Brassica napus L.) is one of the most important oil crops in the world. However, study on marker-free transgene of B. napus for bio-safety purpose is limited in this allotetraploid crop. In order to advance marker gene excision research, a newly designed Cre/lox system combining crossing and auto-excision strategy was introduced into B. napus. The system consists of 2 sets of independent vectors including pC35Spro::T7RP carrying T7 RNA polymerase and pCT7pro::Cre carrying T7 promoter respectively. After hybridization of 2 according types of transgenic B. napus, marker gene would be removed as T7 RNA polymerase facilitate T7 promoter to promote Cre gene expression. Totally 52 and 46 positive T₀ transgenic lines of these 2 vectors were obtained after identification by PCR and test trip. T₁ plants from 3 T₀ positive pC35Spro::T7RP lines and 2 T₀ positive pC35Spro::T7RP lines were identified as single copy according to segregation ratio and were chosen for crossing. However, expression of CP4 EPSPS (glyphosate resistance gene) and OXY (bromoxynil resistance gene) were not found in F₁ progeny, which proved that the excision was not complete. The possible reasons for our limited success were investigated and detailed analyses were performed. Although this system is not applicable for generating transgenic B. napus free from selectable marker gene, it provided valuable experience and clue for further improvement of this technique. Many other advantages and further improvement will be progressed in future work.     

Resistance monitoring and enzyme activity in three field populations of cowpea aphid (Aphis craccivora) from Egypt

The cowpea aphid (Aphis craccivora) is one of the most important sucking insect pests attacking certain legumes in Egypt particularly faba bean, cowpea and pea. In this study we monitored the resistance level of three field populations of A. craccivora to seven insecticides belonging to three different chemical classes (organophosphates, carbamates and neonicotinoids). The three populations were collected from three governorates in Egypt namely Dakahlia, Qalyobia and Beni Suef. Diagnostic concentrations (LC₉₀ values for susceptible strain) for each insecticide were established using a leaf dipping technique. Resistance monitoring showed that the field population from Dakahlia was highly resistant to all the tested insecticides. In a similar manner, the population from Qalyobia was also resistant to all insecticides except for fenitrothion to which only moderate resistance was observed. The field population from Beni Suef exhibited a lower level of resistance to all the seven tested insecticides.Biochemical assay showed that esterase activity in these three field populations was generally higher as the enzyme activity ratio ranged from 4.3 to 7.8 fold more than that for the susceptible strain. The activity of the other measured detoxifying enzymes (glutathione -S- transferase and mixed function oxidases) was moderate in the populations from Qalyobia and Dakahlia. Nevertheless, the enzyme activity in A. craccivora collected from Beni Suef was variable and differed slightly from the activity measured in the susceptible strain. Monitoring insecticide resistance among the three aphid populations was a proactive approach to detect any shift in insecticide efficiency. The possible occurrence of resistance in the cowpea aphid to the tested insecticides may be due to the higher activity of carboxylesterases. Further studies on the resistance mechanism to these insecticides are needed to provide insights in how to manage and delay the onset of the resistance and thus prolong the performance of insecticides against A. craccivora.     

Response of selected okra cultivars to Meloidogyne incognita

Root–knot nematodes (Meloidogyne spp.) are major pests of vegetables especially in the tropics and subtropics. All commercial okra varieties are susceptible to root knot nematodes and cause substantial losses. The objective of this study is to find out resistant germplasm in order to facilitate our breeders for gene manipulation. A greenhouse study was conducted to evaluate 28 okra cultivars against Meloidogyne incognita inoculated with 5000 eggs. Five cultivars (Bamya Yalova, 19,232, 19,236, 1,922,121, and Green Wonder) had significantly fewer root galls and eggs and less reduction in plant growth (shoot weight and root length), than most of the other entries. A positive relationship was demonstrated between root galls and reduction in plant growth parameters measured. These cultivars may improve okra production in fields infested with M. incognita. During our study, none of the cultivars tested were observed to be immune or resistant to nematode infection according to a scale where: good host [susceptible] when Pf/Pi (Pf = Final population of nematodes after harvest and Pi = Initial population of nematodes which was used as inoculum during experiment) > 5.0, fair, better [moderately resistant] if 5.0 ≥ Pf/Pi > 1, poor if 1 > Pf/Pi > 0, and non-host [resistant] when Pf/Pi = 0. The cultivars, including 19,224, 19,235, Pusa Sawami, Ikra-1, Ikra-2 and Sabzperi China Red, were found to be susceptible with Pf/Pi > 5.0, and they were declared as good hosts of M. incognita. While all the other cultivars were moderately resistant, with 0 ≥ Pf/Pi > 1 but still a significant penetration of nematodes was found. The regression studies showed positive and significant relationships between the number of galls and the reduction in shoot weight (r² = 0.95), number of galls and reduction in shoot length (r² = 0.81), and number of galls and decrease in root length (r² = 0.89).