Evaluation of corn germplasm lines for multiple ear-colonizing insect and disease resistance

Ear-colonizing insects and diseases that reduce yield and impose health threats by mycotoxin contaminations in the grain, are critical impediments for corn (Zea mays L.) production in the southern United States. Ten germplasm lines from the Germplasm Enhancement of Maize (GEM) Program in Ames, IA, and Raleigh, NC, and 10 lines (derived from GEM germplasm) from the Texas Agricultural Experiment Station in Lubbock, TX, were examined in 2007 and 2008 with local resistant and susceptible controls. Four types of insect damage and smut disease (Ustilago maydis) infection, as well as gene X environment (G X E) interaction, was assessed on corn ears under field conditions. Insect damage on corn ears was further separated as cob and kernel damage. Cob penetration rating was used to assess corn earworm [Helicoverpa zea (Boddie)] and fall armyworm [Spodoptera frugiperda (J.E. Smith)] feeding on corn cobs, whereas kernel damage was assessed using three parameters: 1) percentage of kernels discolored by stink bugs (i.e., brown stink bug [Euschistus serous (Say)], southern green stink bug [Nezara viridula (L.)], and green stink bug [Chinavia (Acrosternum) hilare (Say)]; 2) percentage of maize weevil (Sitophilus zeamais Motschulsky)-damaged kernels; and 3) percentage of kernels damaged by sap beetle (Carpophilus spp.), "chocolate milkworm" (Moodna spp.), and pink scavenger caterpillar [Pyroderces (Anatrachyntis) rileyi (Walsingham)]. The smut infection rates on ears, tassels, and nodes also were assessed. Ear protection traits (i.e., husk tightness and extension) in relation to insect damage and smut infection also were examined. Significant differences in insect damage, smut infection, and husk protection traits were detected among the germplasm lines. Three of the 20 germplasm lines were identified as being multiple insect and smut resistant. Of the three lines, entries 5 and 7 were derived from DKXL370, which was developed using corn germplasm from Brazil, whereas entry 14 was derived from CUBA117.     

荔枝蝽取食行为的研究

在越冬前和产卵期,荔枝蝽Tessaratoma papillosa Drury在寄主植物-荔枝树的花枝、嫩枝和老枝上都有取食行为。但在这两个不同时期, 其取食行为有显著差异。在越冬前,只有50%～70%的成虫在各类枝条上取食;而处于产卵期的荔枝蝽成虫,在各类枝条上,100%积极取食,且其取食前时间显著短于越冬前在同类枝条上的取食前时间。同一时期在不同枝叶上,荔枝蝽的取食行为也有显著差异。被置于嫩枝叶和花枝上的成虫取食前时间明显短于被置于老枝叶上者;在有选择的情况下,两个时期的成虫都明显地选择在花枝和嫩枝上取食。经分析测定：在不同生长时期,荔枝树的花枝和嫩枝的含水量与含氮量均较老枝叶中的高,可溶性糖含量的变化较大;组织结构也存在明显差异。     

Identification of multiple ear-colonizing insect and disease resistance in CIMMYT maize inbred lines with varying levels of silk maysin

Ninety four corn inbred lines selected from International Center for the Improvement of Maize and Wheat (CIMMYT) in Mexico were evaluated for levels of silk maysin in 2001 and 2002. Damage by major ear-feeding insects [i.e., corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae); maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae); brown stink bug, Euschistus servus (Say); southern green stink bugs, Nezara viridula (L.) (Heteroptera: Pentatomidae)], and common smut [Ustilago maydis DC (Corda)] infection on these inbred lines were evaluated in 2005 and 2006 under subtropical conditions at Tifton, GA. Ten inbred lines possessing good agronomic traits were also resistant to the corn earworm. The correlation between ear-feeding insect damage or smut infection and three phenotypic traits (silk maysin level, husk extension, and husk tightness of corn ears) was also examined. Corn earworm and stink bug damage was negatively correlated to husk extension, but not to either silk maysin levels or husk tightness. In combination with the best agronomic trait ratings that show the least corn earworm and stink bug damage, lowest smut infection rate, and good insect-resistant phenotypic traits (i.e., high maysin and good husk coverage and husk tightness), 10 best inbred lines (CML90, CML92, CML94, CML99, CML104, CML108, CML114, CML128, CML137, and CML373) were identified from the 94 lines examined. These selected inbred lines will be used for further examination of their resistance mechanisms and development of new corn germplasm that confers multiple ear-colonizing pest resistance.     

Injury to preflowering and flowering cotton by brown stink bug and southern green stink bug

The impact of brown stink bug, Euschistus servus (Say), and southern green stink bug, Nezara viridula (L.), injury was evaluated on preflowering and flowering cotton, Gossypium hirsutum L., plants in no-choice tests. Vegetative stage cotton seedlings and reproductive structures, including flower buds (square) and bolls, were infested with adults and/or nymphs of both species. There were no significant differences in height, height to node ratio, square retention, and flower initiation for cotton seedlings or plants with a match-head square between southern green stink bug adult- or brown stink bug adult-infested and noninfested treatments. Abscission for individual large squares (precandle) and multiple squares (medium and small square on the same sympodial branch) was not significantly different among infested and noninfested treatments for the following species and developmental stages: brown stink bug adults, southern green stink bug adults, and third and fourth to fifth instar southern green stink bug nymphs. In boll infestation studies, the relationship between boll maturity, expressed as heat units beyond anthesis, and boll growth, abscission, hard locked carpels, seedcotton yield, and seed germination was measured. Brown stink bug induced abscission in bolls that had accumulated > 0-350 heat units beyond anthesis. Boll growth and seedcotton yield was significantly lower for bolls infested with brown stink bug through 266.5 and 550 heat units beyond anthesis, respectively. The proportion of hard locked carpels per boll was significantly greater for the infested treatment in a cohort of bolls that accumulated from 51 to 400 heat units beyond anthesis. Seed germination in bolls infested with brown stink bug was significantly lower in bolls aged 101-600 heat units beyond anthesis.     

Ustilago maydis Produces Cytokinins and Abscisic Acid for Potential Regulation of Tumor Formation in Maize

The infection of maize (Zea mays) by the basidiomycete fungus Ustilago maydis leads to common smut of corn characterized by the production of tumors in susceptible aboveground plant tissues. LC-(ES)MS/MS profiles of abscisic acid (ABA) and 12 different cytokinins (CKs) were determined for infected and uninfected maize tissues over a time course following fungal exposure. Samples were taken at points corresponding to the appearance of disease symptoms. Axenic cultures of haploid and dikaryon forms of U. maydis were also profiled. This study confirmed the capability of Ustilago maydis to synthesize CKs, ABA, and auxin (IAA). It also provided evidence for the involvement of CK and ABA in the U. maydis-maize infection process. Significant quantities of CKs and ABA were detected from axenic cultures of U. maydis as was IAA. CKs and ABA levels were elevated in leaves and stems of maize after infection; notable was the high level of cis-zeatin 9-riboside. Variation among hormone profiles of maize tissues was observed at different time points during infection and between infections with nonpathogenic haploid and pathogenic dikaryon strains. This suggested that CKs and ABA accumulate and are likely metabolized in maize tissue infected with U. maydis. Because U. maydis produced these phytohormones at significant levels, it is possible that the fungal pathogen is a source of these compounds in infected tissue. This is the first study to confirm the production of CKs and document the production of ABA by U. maydis. This study also established an involvement of these phytohormones and a possible functional role for ABA in U. maydis infection of maize.     

Evaluating potential trap crops for managing leaffooted (Hemiptera: Coreidae) and phytophagous stink bug (Hemiptera: Pentatomidae) species in peaches

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Cotton boll age influences feeding preference by brown stink bug (Heteroptera: Pentatomidae)

Cotton plants were infested with brown stink bug, Euschistus servus (Say), to define cotton boll age classes (based on heat unit accumulation beyond anthesis) that are most frequently injured during each of the initial 5 wk of flowering. Bolls from each week were grouped into discrete age classes and evaluated for the presence of stink bug injury. Brown stink bug injured significantly more bolls of age class B (approximately 165-336 heat units), age class C (approximately 330-504 heat units), and age class D (approximately 495-672 heat units) during the initial 3 wk in both years and in week 5 in 2002 compared with other boll ages. Generally, the frequency of injured bolls was lowest in age class A (< or = 168 heat units) during these periods. The preference by brown stink bug for boll age classes B, C, and D within a week was similar when ages were combined across all 5 wk. Based on these data, bolls that have accumulated 165.2 through 672 heat units beyond anthesis (approximately 7-27-d-old) are more frequently injured by brown stink bug when a range of boll ages are available. The boll ages in our studies corresponded to a boll diameter of 1.161-3.586 cm with a mid-range of 2.375 cm. A general protocol for initiating treatments against stink bugs is to sample bolls for evidence of injury as an indicator of presence of infestations in cotton. Sampling bolls within a defined range, which is most likely to be injured, should improve the precision of this method in detecting economic stink bug infestations in cotton.     

Transgenic maize plants expressing the Totivirus antifungal protein, KP4, are highly resistant to corn smut

The corn smut fungus, Ustilago maydis, is a global pathogen responsible for extensive agricultural losses. Control of corn smut using traditional breeding has met with limited success because natural resistance to U. maydis is organ specific and involves numerous maize genes. Here, we present a transgenic approach by constitutively expressing the Totivirus antifungal protein KP4, in maize. Transgenic maize plants expressed high levels of KP4 with no apparent negative impact on plant development and displayed robust resistance to U. maydis challenges to both the stem and ear tissues in the greenhouse. More broadly, these results demonstrate that a high level of organ independent fungal resistance can be afforded by transgenic expression of this family of antifungal proteins.     

Infection of maize leaves with Ustilago maydis prevents establishment of C4 photosynthesis

The Basidiomycete fungus Ustilago maydis is the common agent of corn smut and is capable of inducing gall growth on infected tissue of the C₄ plant maize (Zea mays). While U. maydis is very well characterized on the genetic level, the physiological changes in the host plant in response to U. maydis infection have not been studied in detail, yet.Therefore, we examined the influence of U. maydis infection on photosynthetic performance and carbon metabolism in maize leaf galls.At all stages of development, U. maydis-induced leaf galls exhibited carbon dioxide response curves, CO₂ compensation points and enzymatic activities that are characteristic of C₃ photosynthesis, demonstrating that the establishment of C₄ metabolism is prevented in infected tissue. Hexose contents and hexose/sucrose ratio of leaf galls remained high at 6 days post infection, while a shift in free sugar metabolism was observed in the uninfected controls at that time point. Concomitantly, transitory starch production and sucrose accumulation during the light period remained low in leaf galls. Given that U. maydis is infectious on young developing tissue, the observed changes in carbohydrate metabolism suggest that the pathogen manipulates the developing leaf tissue to arrest sink-to-source transition in favor of maintaining sink metabolism in the host cells.Furthermore, evidence is presented that carbohydrate supply during the biotrophic phase of the pathogen is assured by a fungal invertase.     

Prevalence,damage, management and insecticide resistance of stink bug populations (Hemiptera: Pentatomidae) in commodity crops

1. Pest management of stink bugs (Hemiptera: Pentatomidae) in soybean [Glycine max (L.) Merr.], corn (Zea mays L.) and cotton (Gossypium spp.) agroecosystems has become a major concern in several countries of the Americas.
2. In this review, we report an overview on geographical distribution, injury, damage and methods used to control (plant resistance mechanisms, biological control) the most important stink bugs in the Americas, with an emphasis on Brazil, the implications of the trend towards decreased susceptibility of stink bug populations to insecticides and the current difficulties of the management of these insect pests.
3. Currently, the Neotropical brown stink bug Euschistus heros (Fabricius) is less susceptible to organophosphate insecticides than in the past. A slight reduction in E. heros susceptibility to pyrethroids and, to a lesser extent, to neonicotinoids has also been observed. In addition, the green‐belly stink bug [Dichelops melacanthus (Dallas)] is more tolerant to the three classes of insecticides (neonicotinoids, organophosphates and pyrethroids) than E. heros.
4. Metabolic detoxification is involved in organophosphate, neonicotinoid and pyrethroid differences in susceptibility. Restricted availability of insecticides with different modes of action could favour the selection of resistant phenotypes in stink bug populations.

     

Sporisorium reilianum possesses a pool of effector proteins that modulate virulence on maize

The biotrophic maize head smut fungus Sporisorium reilianum is a close relative of the tumour-inducing maize smut fungus Ustilago maydis with a distinct disease aetiology. Maize infection with S. reilianum occurs at the seedling stage, but spores first form in inflorescences after a long endophytic growth phase. To identify S. reilianum-specific virulence effectors, we defined two gene sets by genome comparison with U. maydis and with the barley smut fungus Ustilago hordei. We tested virulence function by individual and cluster deletion analysis of 66 genes and by using a sensitive assay for virulence evaluation that considers both disease incidence (number of plants with a particular symptom) and disease severity (number and strength of symptoms displayed on any individual plant). Multiple deletion strains of S. reilianum lacking genes of either of the two sets (sr10057, sr10059, sr10079, sr10703, sr11815, sr14797 and clusters uni5-1, uni6-1, A1A2, A1, A2) were affected in virulence on the maize cultivar ‘Gaspe Flint’, but each of the individual gene deletions had only a modest impact on virulence. This indicates that the virulence of S. reilianum is determined by a complex repertoire of different effectors which each contribute incrementally to the aggressiveness of the pathogen.     

A Rapid and Efficient Method for Assessing Pathogenicity of Ustilago maydis on Maize and Teosinte Lines

Maize is a major cereal crop worldwide. However, susceptibility to biotrophic pathogens is the primary constraint to increasing productivity. U. maydis is a biotrophic fungal pathogen and the causal agent of corn smut on maize. This disease is responsible for significant yield losses of approximately $1.0 billion annually in the U.S.¹ Several methods including crop rotation, fungicide application and seed treatments are currently used to control corn smut². However, host resistance is the only practical method for managing corn smut. Identification of crop plants including maize, wheat, and rice that are resistant to various biotrophic pathogens has significantly decreased yield losses annually^3-5. Therefore, the use of a pathogen inoculation method that efficiently and reproducibly delivers the pathogen in between the plant leaves, would facilitate the rapid identification of maize lines that are resistant to U. maydis. As, a first step toward indentifying maize lines that are resistant to U. maydis, a needle injection inoculation method and a resistance reaction screening method was utilized to inoculate maize, teosinte, and maize x teosinte introgression lines with a U. maydis strain and to select resistant plants.Maize, teosinte and maize x teosinte introgression lines, consisting of about 700 plants, were planted, inoculated with a strain of U. maydis, and screened for resistance. The inoculation and screening methods successfully identified three teosinte lines resistant to U. maydis. Here a detailed needle injection inoculation and resistance reaction screening protocol for maize, teosinte, and maize x teosinte introgression lines is presented. This study demonstrates that needle injection inoculation is an invaluable tool in agriculture that can efficiently deliver U. maydis in between the plant leaves and has provided plant lines that are resistant to U. maydis that can now be combined and tested in breeding programs for improved disease resistance.     

Effect of Ustilago maydis (DC) Corda and its Toxin on Some Maize Cultivars

The pathogenic effects of Ustilago maydis (DC) Corda to five maize cultivars and four other plants were studied. It was found that none of the maize cultivars tested was resistant to the common smut disease whereas cultivars Balady was slightly susceptible. Only Sorghum rulgare from the other tested plants showed moderate susceptibility to the disease. With respect to gall formation only cultivars Giza 2 and single cross hybrid 10 formed galls after 2 weeks. The pure toxic material (Ustizeain) from Ustilago maydis was obtained, it caused chlorosis and necrosis on detached maize leaves, but it had no effect on growth of some fungi tested. Sporidia treatment showed also chlorosis on detached maize leaves.     

The Influence of Ustilago maydis Upon Free Radicals Concentration in the Reproduction Organs of Maize

The reproduction organs of maize are those most often attacked by Ustilago maydis. In the male organs it produces a decline in free radicals concentration and, conversely, a rise of concentration in the female organs (in ears). The smut proper, grown on the flower, exhibits an essentially higher free radicals concentration than the smut grown out on the ear of that plant. A smut mixture from flower and ear has only a slightly higher free radicals concentration than the separate ear smut, but an essentially lower one than the smut of the flower.     

Seeding Dates and Cultivars Effects on Stink Bugs Population and Damage on Common Bean <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L

Fields experiments were conducted during two growing seasons (2010–2011 and 2012–2013) at three seeding dates to identify stink bug (Hemiptera: Pentatomidae) species and to determine their seasonal population density fluctuation and damage caused to three common bean (Phaseolus vulgaris L.) cultivars “Ica Pijao,” “Cubacueto 25–9,” and “Chévere.” Stink bug species observed were Nezara viridula (L.), Piezodorus guildinii (Westwood), Chinavia rolstoni (Rolston), Chinavia marginatum (Palisot de Beauvois), and Euschistus sp. The most prevalent species was N. viridula in both seasons. The largest number of stink bugs was found in beans seeded at the first (mid September) and third (beginning of January) seeding dates. Population peaked at BBCH 75 with 1.75, 0.43, and 1.25 stink bugs/10 plants in 2010–2011 and with 2.67, 0.45, and 1.3 stink bugs/10 plants in 2012–2013 in the fields seeded the first, second, and third seeding dates, respectively. The lowest numbers of stink bugs were found in beans seeded at the second (mid November) seeding date. A significant negative correlation between relative humidity and number of stink bugs was found in 2010–2011, and a similar tendency was observed in 2012–2013. The highest seed and pod damage levels occurred in cv. “Chévere” and the lowest in cv. “ICA Pijao” during both seasons. Results suggest that cv. “ICA Pijao” and the second (mid November) seeding date is the best choice to reduce stink bug damage.     

Completion of the sexual cycle and demonstration of genetic recombination in Ustilago maydis in vitro

The heterobasidiomycetes responsible for plant smuts obligatorily require their hosts for the completion of the sexual cycle. Accordingly, the sexual cycle of these fungi could so far be studied only by infecting host plants. We have now induced Ustilago maydis, the causative agent of corn smut, to traverse the whole life cycle by growing mixtures of mating-compatible strains of the fungus on a porous membrane placed on top of embryogenic cell cultures of its host Zea mays. Under these conditions, mating, karyogamy and meiosis take place, and the fungus induces differentiation of the plant cells. These results suggest that embryogenic maize cells produce diffusible compounds needed for completion of the sexual cycle of U. maydis, as the plant does for the pathogen during infection. Received: 16 February 1999 / Accepted: 30 June 1999