A preliminary study on the effects of a transgenic corn event on the non-target pest Dalbulus maidis (Hemiptera: Cicadellidae)

The inclusion of the cry gene in corn may produce direct effects on non-target pests. Our research was focused on the relationship between Bt corn germplasm, expressing the cry1F protein to control the fall armyworm [Spodoptera frugiperda (Noctuidae)], and a non-target pest, the corn leafhopper [Dalbulus maidis (Cicadellidae)]. The aim of this contribution was to elucidate if Bt corn plants have influence on the oviposition preference of the leafhopper and to evaluate the effect of the transgenic plant on the hatching rate of egg. Female corn leafhoppers were released in cages each containing two potted plants in the V2 stage: a Bt germplasm and the corresponding isogenic hybrid. Laid eggs were counted and the number of hatched nymphs recorded. D. maidis females oviposited and laid more eggs in Bt plants. The egg hatching rate was negatively affected by the Bt germplasm. In addition, a field study was conducted in order to determine the abundance of D. maidis adults in Bt corn and the corresponding non-Bt isoline. Two corn plots sown with the same germplasms as used in the laboratory bioassays were sampled weekly. In the field, the population of the corn leafhopper was higher in the Bt corn plot than in the non-Bt isoline. Possible hypotheses for the differences in abundance of the vector in the field are: a) that pleiotropic effects of Bt corn could attract adults; b) the existence of a possible direct competition between the corn leafhopper and the target pest in order to utilize the whorls of corn plants as refuge and feeding sites, so the high populations of the vector could be due to the large supply of healthy whorls in the transgenic plot; and/or c) a differential attack of natural enemies occurring in non-Bt plots.     

苯并噻二唑诱发水稻对稻瘟病抗性中防卫相关酶活性的变化

分析了苯并噻二唑（BTH）诱导水稻对稻瘟病抗性中苯丙氨酸解氨酶（PAL）、肉桂醇脱氢酶（CAD）、过氧化物酶（POD）、脂氧合酶（LOX）、β-1,3-葡聚糖酶和几丁酶等活性的变化。结果表明BTH诱导处理亲和性水稻品种第3叶后提高了处理叶及其上位第4叶中CAD、LOX和β-1,3-葡聚糖酶等的活性;经BTH处理的幼苗接种稻瘟菌后,处理叶和其上位叶中CAD、POD、LOX和β-1,3-葡聚糖酶等活性快速增加,且增长幅度均显著大于对照。几丁酶活性在受稻瘟菌侵染后升高,但BTH诱导处理并不能促进其增加;PAL活性在BTH处理及稻瘟菌接种后均无明显变化。这些结果说明,BTH处理能诱导CAD、POD、LOX和β-1,3-葡聚糖酶等活性的增加,而且这些酶活性的升高可能与BTH诱发系统获得抗性的表现有关。     

Foliar Application of Benzothiadiazole and Salicylic Acid to Combat Sheath Blight Disease of Rice

A field study was undertaken to ascertain the effects of elicitors viz. benzothiadiazole (BTH) and salicylic acid (SA) on defense related enzymes viz. peroxidase, phenylalanine ammonia lyase, superoxide dismutase, chitinase and β-1,3-glucanase, and phenols in rice (Pusa Basmati I) plants. First foliar spray of BTH (50 mg/kg) and SA (50 mg/kg) was done at the maximum tillering stage and inoculation with Rhizoctonia solani was carried 24 h after elicitor treatment. Elicitors were further sprayed at every growth stage. Time course analysis showed peak accumulation of defense related enzymes and phenols in the rice leaves treated with BTH and SA, and accumulation was the highest at the flowering stage. Higher enzymatic activity was observed in elicitor treated plants inoculated with R. solani. Compared to the untreated control plants, application of elicitors before R. solani inoculation significantly elicited the defense related enzymes and phenols. Moreover, application of elicitors had a positive effect on yield and disease reduction. It is suggested that pretreatment of rice leaves with BTH and SA could be used to enhance the level of protection against sheath blight and to improve rice yield in the fields.     

Induction of resistance to root-knot nematodes by SAR elicitors in tomato

Different concentrations of the systemic acquired resistance (SAR) elicitors, salicylic acid (SA), methyl-salicylic acid (MetSA), acibenzolar-S-methyl (ASM) and 2,6-dicholoroisonicotinic acid (INA), were provided to tomato seedlings as root-dip or soil-drench one day before inoculation with the root-knot nematode, Meloidogyne incognita. Nematode infestation was evaluated by counting egg masses/plant (EM), eggs/plant (Pf), and sedentary forms/plant (SF) in treated and untreated plants seven weeks after inoculation. An index of plant fitness (PF) was also calculated to assess the costs of chemically-induced resistance and the possible phytotoxicity of the treatments. SA and ASM were found to be effective elicitors of resistance when applied at suitable concentrations and method of application. Soil-drench with SA and root-dip in ASM were the most effective treatments as they markedly reduced both nematode reproduction (less than 50% that of untreated plants) and infestation (50–70% EM reduction). MetSA was less effective than SA in eliciting resistance because of its negative effects on plant fitness when it was provided as soil-drench. INA did not reduce nematode infestation at any of the non-phytotoxic rates. The reduction of nematode infestation and reproduction by SA applied as soil-drench was potentiated when the soil was enriched with humic acids. Soil-drenching with SA and MetSA were the only treatments that caused a long-lasting induction of plant defences as they inhibited the infestation by the second generation of the nematode.     

Control of chickpea blight disease caused by Didymella rabiei by mixing resistance inducer and contact fungicide

Elicitors of systemic acquired resistance are well known to reduce severity of several plant pathogenic diseases caused by fungi, bacteria and viruses. Their field applications for management of plant diseases are, however, limited because of yield penalties. Our studies on affect of Benzo (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), an elicitor of systemic acquired resistance, on chickpea blight caused by a fungal pathogen Didymella rabiei showed that multiple foliar applications of the chemical were effective in management of the disease under economic threshold levels. Multiple applications, however, affected chickpea grain yield adversely. The BTH induced yield penalties could be prevented by foliar spray schedule comprised of BTH and a contact fungicide mancozeb. One spray of BTH (50 ppm) followed by another of mancozeb (0.2%) was less effective (8.3% severity) than three sprays of BTH (4.2% severity) in blight control, however, this treatment enhanced grain yield significantly (1.241 t ha⁻¹) over three sprays of BTH (0.922 t ha⁻¹).     

水稻矮缩病毒对介体昆虫黑尾叶蝉生物学参数及种群增长的影响

【目的】 水稻矮缩病毒(RDV)是水稻普通矮缩病的病原。该病害主要依赖于黑尾叶蝉经卵以持久增殖方式传播,危害水稻。本研究旨在明确RDV对黑尾叶蝉存活、发育、繁殖和种群增长的影响,分析病毒对介体昆虫的间接影响。【方法】 采用室内实验比较了黑尾叶蝉在健康水稻及感病水稻上的发育繁殖情况,组建了实验种群生命表,并调查了RDV对种群增长的影响。【结果】 与健康水稻相比,感病水稻上叶蝉若虫期存活率更高,雌若虫发育历期显著缩短,雄成虫寿命显著延长,产卵量显著增加,其他生物学参数无显著差异。五个生命表参数仅净生殖率(R₀)存在显著差异,感病水稻上叶蝉R₀显著高于健康水稻。饲喂感病水稻的养虫笼内叶蝉种群增长更快,总成虫数量更多,在接虫后的第4、5和6月显著高于健康水稻上的数量。【结论】 水稻矮缩病毒可以提高黑尾叶蝉的存活率和产卵量,并促进种群的增长。     

Control of maize pests with imidacloprid seed dressing treatment in Catalonia (NE Iberian Peninsula) under traditional crop conditions

The effects of treating maize seed with imidacloprid to prevent damage by soil pests, aphids, leafhoppers and the first generation of corn borers was evaluated in the field by comparing treated with untreated commercial plots in a 5-year study in Catalonia (NE Iberian Peninsula). The treatment reduced the incidence of cutworms (Agrotis segetum), wireworms (Agriotes lineatus), the first generation of the corn borer Sesamia nonagrioides and leafhoppers (Zyginidia scutellaris). However, treated plots were attacked significantly more by Ostrinia nubilalis. The treatment was effective in reducing aphid densities from maize emergence to mid June. What happened later depended on the relative abundance of aphid species. Rhopalosiphum padi seems to be more sensitive than Metopolophium dirhodum whose population can be enhanced after flowering in plots treated with imidacloprid. The treatment did not avoid aphid alate colonisation and MDMV infection was not prevented. The greater damage on untreated plants caused by wireworms, cutworms and the first generation of S. nonagrioides, and the densities achieved by aphids, was insufficient to produce yield differences between treatments, and only leafhopper damage led to economic damage. Imidacloprid favours the attack of the European corn borer, thus masking the potential increase in yield.     

Cotton leaf trichomes and populations of Empoasca lybica and Bemisia tabaci

Breeding cotton, Gossypium spp., for resistance to leafhoppers of the genus Empoasca and to sweetpotato whitefly, Bemisia tabaci (Gennadius), poses a dilemma. Glabrous (smooth-leaved) cotton plants have higher leafhopper populations but fewer whiteflies and less leaf and bract trash in mechanically harvested seedcotton than plants with pubescent leaves. In this study, both leafhopper and whitefly populations were observed in 31 cotton entries planted at Bet She'an, Israel, in 1987. Leafhopper populations decreased but the whitefly populations increased as the number of trichomes increased. At the end of June, plants with 40 trichomes per 13.7 mm² supported relatively low populations of both leafhoppers and whiteflies. However, the whitefly populations increased later in the season to 43 times the earlier population levels. Whitefly populations increased as the number of trichomes increased up to 70 trichomes per 13.7 mm² and then decreased as the trichomes became more dense. Various control measures and breeding schemes that might interact to provide an answer to the control of these pests are discussed.     

Evidence for the role of an invasive weed in widespread occurrence of phytoplasma diseases in diverse vegetable crops: Implications from lineage-specific molecular markers

During the period from 2011 to 2013, several plant diseases repeatedly occurred in vegetable crops grown in Yuanmou County, Yunnan Province, China. Affected plants included cowpea, sword bean, string bean, tomato, lettuce, and water spinach. The diseased plants exhibited symptoms of witches'-broom growth and floral deformations, linking each disease to phytoplasmal infection. Phylogenetic and virtual RFLP analyses of the phytoplasmal 16S rRNA gene sequences amplified from DNA of diseased plants revealed that all of the individual strains present in the diverse vegetable plants were affiliated with a single ‘Candidatus Phytoplasma’ species (‘Ca. Phytoplasma aurantifolia’) and a single ribosomal subgroup (16SrII-A). While presence of subgroup 16SrII-A phytoplasma in this geographic region was reported previously, such widespread infections in diverse plant hosts are unveiled for the first time in this study. In pursuing the source of the infections, we found that areas surrounding the affected vegetable fields were extensively invaded by parthenium weeds (Parthenium hysterophorus); and many of the weed plants exhibited abnormal morphologies that were suspicious of, and later diagnosed with, phytoplasmal infections. Results from genotyping of 16S rRNA and lineage-specific immunodominant membrane protein genes revealed that the vegetable-infecting phytoplasmas and the parthenium weed phytoplasma belong to the same genetic lineage. The findings indicate that parthenium weed poses a substantial risk as a reservoir of phytoplasmal infection of nearby agricultural crops in the geographic region since the ecosystems of Yuanmou are insect-rich, and parthenium weed is known to attract diverse leafhoppers. Further studies are warranted to assess the impact of farmland invasions by the noxious weed and to devise practical measures for improved weed control.     

Comparison of chemical treatments for reducing epiphytic Pseudomonas savastanoi pv. savastanoi populations and for improving subsequent control of olive knot disease

The economic impact of the olive knot disease caused by Pseudomonas savastanoi pv. savastanoi (Psv) has dramatically increased in recent years, especially in high-density plantations. Here we report chemical control trials, performed in an olive grove planted with two susceptible cultivars, Arbequina and Picudo, over a four-year period. The effect of treatments made with copper oxychloride, cuprocalcic sulfate plus mancozeb or acibenzolar-S-methyl on the Psv populations and subsequent appearance of the disease were evaluated. Both copper treatments reduced the proportion of samples where Psv was isolated, and greatly reduced Psv populations in trees of cv. Picudo. The effect of copper on Psv populations was observed after the first application, but the greatest differences between copper-treated and untreated plants were observed in the third year, after five copper applications. No resistance to copper was detected in the remaining epiphytic Psv populations in treated plants. The average number of knots per plant was significantly lower in copper-treated plants than in untreated plants. By contrast, acibenzolar-S-methyl did not reduce either Psv populations or the disease during the study. These results support the usefulness of copper treatments for olive knot management. Results indicate that two copper treatments should be performed regularly under an integrated control program, especially in high-density groves, since their efficiency was demonstrated not only in decreasing olive knot incidence, but also in reducing Psv populations.     

The germplasm release of NYL 235–4, a clone with resistance to the Colorado potato beetle

Clones selected from the wild diploid species,Solanum berthaultii, have been shown to possess valuable levels of resistance to the Colorado potato beetle (Leptinotarsa decemlineata), as well as to insects such as aphids, flea beetles, leafhoppers and the potato tuber moth. Resistance is associated with the presence of glandular trichomes on the foliage ofS. berthaultii (2). Six generations after producing a hybrid between the diploid species and a tetraploid variety, a clone with good beetle and leafhopper resistance, as well as reasonable agronomic characteristics has been produced.     

Tolerance to potato leafhopper inSolanum tuberosum L. gp. Tuberosum clones

We identified clones inSolanum tuberosum L. gp. Tuberosum breeding populations that, although susceptible to infestation by potato leafhopper,Empoasca fabae (Harris), exhibited a tolerance which was manifested by the ability to produce higher than expected tuber yields when heavily infested with leafhoppers. Such tolerance was noted in a number of clones in varying degrees, but one, B6930-1, was exceptional. It sustained only a 19% loss in tuber yield compared to ‘Katahdin,’ a susceptible cultivar, that averaged 33% lower tuber yields under similar infestation levels. We studied the seasonal growth patterns of this clone and compared them to those of Katahdin, and B6705-10, a breeding clone with known resistance to leafhopper infestation. We found that much of B6930-l’s tolerance results from its early, vigorous vine growth and its early and rapid rate of tuber bulking, enabling this clone to escape some of the effects of leafhopper feeding, whereas Katahdin was usually just beginning to tuberize at the height of leafhopper infestation.     

Population Dynamics of Wolbachia in the Leafhopper Vector Yamatotettix flavovittatus (Hemiptera: Cicadellidae)

Wolbachia (Rickettsiales: Alphaproteobacteria) infections induce abnormalities in the reproductive system and affect various biological traits of the host insects. The density of Wolbachia is one of the major parameters that influence induced phenotypes and interactions with the hosts. Wolbachia occurs naturally in populations of the leafhopper Yamatotettix flavovittatus Matsumura (Hemiptera: Cicadellidae), which transmits phytoplasma that cause white leaf disease in sugarcane. However, the quantity and dynamics of Wolbachia in this leafhopper are not well understood. In the current study, we estimated the number of Wolbachia by absolute quantification of the copy number of wsp, which encodes the outer surface protein, using real-time quantitative polymerase chain reaction (PCR). This investigation was performed using natural populations and laboratory colonies from three lineages of leafhoppers (designated as UD, KK, and SK). There was no significant difference in the number of wsp copies in most of field-collected adults. During the immature developmental stages, there were differences in the dynamics of Wolbachia infection between the UD lineage and the other two lineages. However, the number of wsp copies increased in the early instar and plateaued in the later nymphal instars. Sex had no influence on the number of Wolbachia within the same lineages. The number of Wolbachia was relatively constant during the adult stage in the UD lineage but fluctuated in the other two lineages. In conclusion, the present data provide a framework for exploring the relationship between Wolbachia and the leafhopper and could facilitate future research into management strategies using Wolbachia.     

Selection for resistance to potato leafhopper in potatoes I.selection methods

A randomly mated potato (Solarium tuberosum L.) population (3 generations, without selection) derived from clones from several breeding programs, displayed considerable resistance in the field to potato leafhopper,Empoasca fabae (Harris). Leafhopper population levels on 161 clones ranged from 2 to 28 nymphs per 45-sec count (mean = 12), whereas a susceptible check averaged 20 nymphs per count. Clones selected for low leafhopper counts in 1971 were compared with the population in 1972 to evaluate the effectiveness of selecting from small plots (three-hill) with minimum replication. The selected clones averaged 30% fewer leafhoppers than the population average in 1971 and 10% fewer in 1972. The average heritability (broad sense) for one plot per clone per location, two locations, and two 45-sec nymph counts per plot equaled 36%.     

Saccharin-induced systemic acquired resistance against rust (Phakopsora pachyrhizi) infection in soybean: Effects on growth and development

We examined the effect of saccharin on the systemic acquired resistance (SAR) response of soybean to the fungus Phakopsora pachyrhizi, the causal agent of soybean rust. Plants were grown hydroponically in half-strength Hoagland’s solution and were challenged with the pathogen 1, 5, 10 and 15 d after treatment with 3 mM saccharin applied either as a foliar spray or a root drench at the 2nd trifoliate (V3) and early reproductive (R1) stages. Plants were destructively harvested and assessed for visible rust symptoms 2 wk after inoculation. Mode of saccharin application was a significant factor influencing the severity of rust infection. Saccharin applied as a root drench was more effective than the foliar spray treatment at inducing SAR, with increased resistance observed 1 d after application. Systemic protection against rust infection was still apparent 15 d after application of saccharin as a root drench. In contrast, foliar treatment with saccharin did not increase systemic protection until 15 d after treatment. When systemic protection was induced by the application of saccharin in either manner, there was no significant reduction of plant growth, except when plants were inoculated 15 d after the saccharin application as a root drench at the R1 stage of development.     

Management of the root-knot nematode Meloidogyne incognita on tomato with combinations of different biocontrol organisms

The nematicidal effect of Pseudomonas fluorescens, Paecilomyces lilacinus, Pichia guilliermondii and Calothrix parietina singly or in combination was tested against root-knot nematode, Meloidogyne incognita. Treatments with P. fluorescens and P. lilacinus caused mortality of M. incognita as 45% and 30% of juveniles after 48 h of exposures, respectively compared to water control in vitro. Under greenhouse conditions, all treatments reduced the disease severity and enhanced plant growth compared to untreated control. Application of P. fluorescens, P. lilacinus and P. guilliermondii Moh 10 was more effective compared to C. parietina. There was a negative interaction between C. parietina and either P. lilacinus or P. guilliermondii. Fresh and dry weight of shoots and roots of plants were significantly reduced as a result of infection with M. incognita, however application of biocontrol agents singly or in mix recovered this reduction. Moreover, they enhanced the growth parameters compared with the control. Our results proved that application of different biocontrol agents (P. fluorescens, P. lilacinus and P. guilliermondii) not only has a lethal effect on nematode, but also enhances the plant growth, supplying many nutritional elements and induction the systemic resistance in plants. Presence of C. parietina as a soil inhabitant cyanobacterium could antagonize biocontrol agents leading to the reduction of their practical efficiency in soil.     

Direct control of virus diseases

The prospects for the direct control of virus diseases are reviewed by examining relevant areas of current scientific research: (1) research aimed at elucidating the processes involved in the development of virus diseases; (2) research designed to improve our understanding of the natural defence mechanisms in plants. The development of a virus disease can be divided into three phases: (a) infection; (b) multiplication and spread; (c) symptom expression. First, large numbers of substances have been screened for effects on the processes of infection but so far without practicable results. The greatest effort has been devoted to studies of virus inhibitors already present in plants and other organisms. These are listed and their properties discussed. The effects of virus multiplication and on the host plant following treatment of infected plants with nucleic acid base analogues are described. The uracil analogues ribavirin and dioxohexahydrotriazine (DHT) have shown promising results. In extensive field trials, treatment of virus-infected potatoes with DHT significantly increased yield compared with untreated controls. Carbendazim has been used successfully to suppress virus-induced symptoms in tobacco, lettuce and rise. Secondly, plants possess a wide range of natural defence mechanisms, the nature of which is not understood. There has been considerable research into the question of how plants can localize some virus infections to a small number of cells around the point of infection. Research on the active agents possibly responsible is described, together with studies on the various chemicals that have been shown to activate or enhance this defence mechanism.     

Influence of phosphorus and potassium fertilization on damage to alfalfa,Medicago sativa L., by the alfalfa weevil,Hypera postica (Gyllenhall) and potato leafhopper,Empoasca fabae (Harris)

In a field study, the effects of phosphorus and potassium fertilization on damage caused by the potato leafhopper, Empoasca fabae (Harris), and alfalfa weevil, Hypera postica (Gyllenhall), to alfalfa, Medicago sativa L., were studied. Potato leafhopper and alfalfa weevil populations were either controlled with insecticides or allowed to develop as untreated controls. Insect management treatments were applied to alfalfa managed under high and low soil fertility regimes. Alfalfa grown under high soil fertility appeared more favourable for alfalfa weevil populations but was able to tolerate more defoliation. Populations of alfalfa weevil larvae were 34% higher on fertilized stands. On the other hand, potato leafhopper populations were as much as 43% higher on low-fertility stands. Alfalfa weevil damage caused a carry-over effect which reduced both plant height and yield of the second cutting. Fertilization negated this effect on height but not on yield. Stands damaged by potato leafhopper recovered more slowly after harvest, but fertilization reduced this effect. Yields from first-cutting alfalfa (which is not infested by the potato leafhopper) the following year were 10% greater on fertilized stands where leafhopper control had been applied the previous season. Plots infested by potato leafhopper suffered greater yield losses under low-fertility management. Leafhopper control and fertilization, alone and in combination with one another, negated these effects.     

Visual inspections of nursery stock fail to protect new plantings from Blueberry scorch virus infection

Blueberry scorch virus (BlScV) is one of the most pervasive pathogens of highbush blueberry. The virus is aphid-vectored and exhibits a latent period between infection and symptom expression in the host plant of up to 5 years. In many cases, we have observed BlScV symptom expression in new fields that appears inconsistent with aphid-vectored introduction and spread. It was, therefore, speculated that the virus may be introduced through infected nursery stock. To examine this possibility, we first surveyed selected nurseries to determine if mother plants, used for propagation by cuttings, were BlScV-infected. Two nurseries were found to harbor symptomless, infected, mother plants (cv. Duke). Cuttings from one nursery were collected from infected and non-infected plants and rooted in propagation beds. The survival and infection of cohorts from each mother plant were determined one year after planting. A significantly greater proportion of cuttings survived from non-infected mother plants (0.7) than from infected mother plants (0.5). Of the cohort from infected mother plants that survived, 40% tested positive for BlScV. We also surveyed the distribution of infected, symptomatic plants in recent ‘Duke’ plantings that originated from nurseries with BlScV-infected mother plants and compared distribution with older plantings with more advanced BlScV outbreaks. In all cases, the distribution of BlScV symptom development in young fields was random, which is consistent with introduction from planting stock. Older plantings showed a strong clustered distribution, which is consistent with aphid transmission. This study identifies infected nursery stock as an important source of BlScV dissemination and underscores the importance of having symptomless mother plants virus tested.     

Yield performance and pest resistance among peanut genotypes when grown without fungicides or insecticides

Yield trials without fungicides or insecticides were conducted four consecutive years (2007–10) at the University of Georgia, Coastal Plain Experiment Station, Tifton Campus to evaluate for peanut (Arachis hypogaea L.) pest resistance. The most endemic diseases in the southeast U.S. are tomato spotted wilt (TSW) caused by Tomato spotted wilt virus, white mold (WM) caused by Sclerotium rolfsii Sacc, and both early and late leaf spot caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk & Curt.) Deighton, respectively. The most endemic insects are tobacco thrips (Frankliniella fusca Hinds) and potato leafhopper (Empoasca fabae Harris). Results from these replicated field tests showed significant differences (P ≤ 0.05) among advanced Georgia breeding lines and cultivars. Three Georgia cultivars ‘Georgia-01R’, ‘Georgia-05E’, and ‘Georgia-10T’ consistently produced among the best yields with high levels of resistance to TSW, white mold, leafhoppers, and leaf spot each year. Georgia-01R is a multiple-pest-resistant, runner-type cultivar with late maturity; whereas, Georgia-05E is a multiple-pest-resistant, virginia-type cultivar with medium-late maturity. Georgia-10T is a new runner-type cultivar with high level of TSWV and white mold resistance and late-maturity, similar to Georgia-01R, one of its parents. However, Georgia-10T does not appear to have the high level of leaf spot and leafhopper resistance as Georgia-01R, but it still had high yields in the absence of fungicides or insecticides.