C. M. Smith

Microsatellite markers linked to six Russian wheat aphid resistance genes in wheat

Abstract The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious economic pest of wheat and barley in North America, South America, and South Africa. Using aphid-resistant cultivars has proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in wheat, Triticum aestivum, including Dn1 in PI 137739, Dn2 in PI 262660, and at least three resistance genes (Dn5+) in PI 294994. The identification of RWA-resistant genes and the development of resistant cultivars may be accelerated through the use of molecular markers. DNA of wheat from near-isogenic lines and segregating F2 populations was amplified with microsatellite primers via PCR. Results revealed that the locus for wheat microsatellite GWM111 (Xgwm111), located on wheat chromosome 7DS (short arm), is tightly linked to Dn1, Dn2 and Dn5, as well as Dnx in PI 220127. Segregation data indicate RWA resistance in wheat PI 220127 is also conferred by a single dominant resistance gene (Dnx). These results confirm that Dn1, Dn2 and Dn5 are tightly linked to each other, and provide new information about their location, being 7DS, near the centromere, instead of as previously reported on 7DL. Xgwm635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene in PI 294994, here designated as Dn8. Xgwm642 (located on 1DL) marked and identified another new gene Dn9, which is located in a defense gene-rich region of wheat chromosome 1DL. The locations of markers and the linked genes were confirmed by di-telosomic and nulli-tetrasomic analyses. Genetic linkage maps of the above RWA resistance genes and markers have been constructed for wheat chromosomes 1D and 7D. These markers will be useful in marker-assisted breeding for RWA-resistant wheat.

Monosomic analysis of Russian wheat aphid (Diuraphis noxia) resistance in Triticum aestivum line PI137739.

SummaryThe Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has become an important pest of wheat (Triticum aestivum L.) in the United States. The aphid causes a phytotoxemic reaction in wheat evidenced by local and systemic chlorosis and rolling of infested leaves. Developing resistance in wheat cultivars to D. noxia is an essential factor in controlling the damage caused by this pest. Several sources of genetic resistance to D. noxia have been identified in wheat germplasm. Monosomic analysis of the monogenic resistant T. aestivum accession PI137739 has shown that the gene (Dn1) for resistance is carried on chromosome 7D. It appears that chromosome 7B may carry a second resistance gene for D. noxia that might be a source of minor or complementary gene action for resistance.

Wheat Curl Mite Resistance: Interactions of Mite Feeding with Wheat Streak Mosaic Virus Infection

ABSTRACT The majority of plant viruses are dependent on arthropod vectors for spread between plants. Wheat streak mosaic virus (family Potyviridae, genus Tritimovirus, WSMV) is transmitted by the wheat curl mite, Aceria tosichella Keifer, and this virus and vector cause extensive yield losses in most major wheat (Triticum aestivum L.)-growing regions of the world. Many cultivars in use are susceptible to this vector-virus complex, and yield losses of 10–99% have been documented, wheat curl mite resistance genes have been identified in goat grass, Aegilops tauschii (Coss) Schmal., and transferred to hexaploid wheat, but very few varieties contain effectively wheat curl mite resistance, due to virulent wheat curl mite populations. However, wheat curl mite resistance remains an effective strategy to reduce losses due to WSMV. The goal of our project was to identify the most effective, reproducible, and rapid method for assessing wheat curl mite resistance. We also wanted to determine whether mite resistance is affected by WSMV infection, because the pathogen and pest commonly occur together. Single and group wheat curl mite infestations produced similar amounts of leaf rolling and folding on wheat curl mite-susceptible wheat varieties that were independent of initial wheat curl mite infestation. This finding will allow accurate, efficient, large-scale screening of wheat germplasm for wheat curl mite resistance by infesting plants with sections of wheat leaf tissue containing mixed stages of wheat curl mite. The wheat curl mite-resistant breeding line ‘OK05312’ displayed antibiosis (reduced wheat curl mite population development). The effect of WSMV infection on wheat curl mite reproduction was genotype-dependent. Mite populations increased on infected wheat curl mite- and WSMV-susceptible plants compared with uninfected plants, but WSMV infection had no significant effect on wheat curl mite populations on resistant plants. OK05312 is a strong source of wheat curl mite resistance for wheat breeding programs.

Identification of Aegilops germplasm with multiple aphid resistance

The greenbug, Schizaphis graminum(Rondani), the Russian wheat aphid, Diuraphis noxia (Mordvilko), and the bird cherry oat aphid, Rhopalosiphum padi(L.), annually cause several million dollars worth of wheat production losses in Europe and the United States. In this study, Triticum and Aegilops accessions from the Czech Research Institute of Crop Production and the Kansas State University Wheat Genetic Resources Center were evaluated for resistance to these aphids. Accessions with aphid cross-resistance were examined for expression of the antibiosis, antixenosis, and tolerance categories of resistance. Aegilops neglecta accession 8052 exhibited antibiotic effects toward all three aphids in the form of reduced intrinsic rate of increase (rm). The rm of greenbug (biotype I) on Ae. neglecta 8052 was significantly lower than that of greenbugs on plants of the susceptible U. S. variety Thunder bird. The rm of Russian wheat aphids was significantly lower on foliage of both Ae. neglecta 8052 and T. araraticum accession 168 compared to Thunderbird. The rm values of bird cherry oat aphids fed both Ae. neglecta 8052 and T. araraticum 168 were also significantly lower than those fed the susceptible accession T. dicoccoides 62. Neither Ae. neglecta 8052 or T. araraticum 168 exhibited tolerance to either greenbug biotype I or Russian wheat aphid. Preliminary data suggest that T. araraticum 168 may also possess tolerance to bird cherry oat aphid. New genes from Ae. neglecta 8052 and T. araraticum 168 expressing aphid antibiosis can be used to develop multiple aphid resistant wheat in the U. S. and Central Europe.

Greenhouse evaluation of red winter wheats for resistance to the Russian wheat aphid (Diuraphis noxia, Mordvilko)

SummaryThe Russian wheat aphid (Diuraphis noxia, Mordvilko) (RWA) is responsible for significant economic damage to cereal crops in arid and semi-arid environments. In this research 20 red winter wheats originating from Iran were evaluated for resistance to RWA. Leaf rolling, leaf folding, and leaf chlorosis were measured using 0 to 3 scales. An overall mean damage score was calculated as the average of the three measured damage symptoms. Plants from seven central Asian accessions (PI222666, PI222668, PI225226, PI225267, PI225271, PI243630, and PI243642) had mean damage scores significantly lower (p < 0.001) than ‘Stephens’ wheat (RWA susceptible) and not significantly different from ‘Border’ oat (RWA resistant). These results are consistent with previous studies which found a high frequency of resistant wheats collected from the central Asian region.

Variation of Resistance in Barley Against Biotypes 1 and 2 of the Russian Wheat Aphid (Hemiptera: Aphididae)

ABSTRACT The Russian wheat aphid, Diruaphis noxia (Kurdjumov) (Hemiptera: Aphididae), is globally one of the most devastating pests of bread wheat, Tritium aestivum L.; durum wheat, Triticum turgidum L.; and barley, Hordeum vulgare L. Host plant resistance is the foundation for cereal insect pest management programs, and several sources of D. noxia resistance have been incorporated in cultivars to manage D. noxia damage. The emergence of D. noxia North American biotype 2 (RWA2) in Colorado has made all known Dn genes vulnerable except the Dn7 gene from rye, Secale cereale, and has warranted exploration for sources of resistance to both RWA1 and RWA2. The category of resistance in resistant donor plants may exert selection pressure over the aphid population to form a new virulent population. In the current study, we report tolerance and antibiosis resistance to RWA1 and RWA2 in the barley genotype ‘Stoneham”. The rate and degree of expression of resistance in Stoneham against RWA1 and RWA2, although not similar, are greater than the partial resistance in ‘Sidney’. Antixenosis resistance to RWA1 or RWA2 was not observed in Sidney or Stoneham. The tolerance identified in Stoneham is encouraging because it may delay D. noxia biotype selection and fits well in a dryland barley cropping system.

Inheritance and categories of resistance in wheat to Russian wheat aphid (Hemiptera: Aphididae) biotype 1 and biotype 2.

ABSTRACT The Russian wheat aphid, Diruaphis noxia (Kudjumov) (Hemiptera: Aphididae), is globally one of the most devastating pests of wheat, Tritium aestivum L., and barley, Hordeum vulgare L. Host plant resistance is the foundation of cereal insect pest management programs, and several D. noxia resistance (Dn) genes from wheat have been introduced in commercial cultivars of wheat to manage Russian wheat aphid (RWA). Emergence of D. noxia biotype 2 (RWA2) in Colorado has made all known Dn genes, except the Dn7 gene from rye, Secale cereale L., vulnerable and has warranted exploration for sources of resistance to RWA1 and RWA2. Here, we report antibiosis resistance to RWA1 and RWA2 identified in the wheat breeding line KS94H871. Additional experiments indicated that tolerance and antixenosis are not operating in KS94H871. Segregation studies involving F2-derived F3 families indicated that KS94H871 resistance to RWA1 is controlled by one dominant gene and one recessive gene, whereas resistance to RWA2 is controlled by only one dominant gene. This new genetic resource may serve as a good source of resistance in future breeding programs with proper understanding of the genetics of resistance.

Application of Brown Planthopper Salivary Gland Extract to Rice Plants Induces Systemic Host mRNA Patterns Associated with Nutrient Remobilization

Insect saliva plays an important role in modulation of plant-insect interactions. Although this area of research has generated much attention in recent years, mechanisms of how saliva affects plant responses remain poorly understood. To address this void, the present study investigated the impact of the brown planthopper (Nilaparvata lugens, Stål; hereafter BPH) salivary gland extract (SGE) on rice (Oryza sativa) systemic responses at the mRNA level. Differentially expressed rice mRNAs were generated through suppression subtractive hybridization (SSH) and classified into six functional groups. Those with the most representatives were from the primary metabolism (28%), signaling-defense (22%) and transcription-translation-regulation group (16%). To validate SSH library results, six genes were further analyzed by One-Step Real-Time Reverse Transcriptase-PCR. Five of these genes exhibited up-regulation levels of more than 150% of those in the control group in at least one post-application time point. Results of this study allow assignment of at least two putative roles of BPH saliva: First, application of SGE induces immediate systemic responses at the mRNA level, suggesting that altering of the rice transcriptome at sites distant to hoppers feeding locations may play an important role in BPH-rice interactions. Second, 58% of SGE-responsive up-regulated genes have a secondary function associated with senescence, a process characterized by remobilization of nutrients. This suggests that BPH salivary secretions may reprogram the rice transcriptome for nutritional enhancement. When these findings are translated onto ‘whole plant’ scale, they indicate that BPH saliva may play the ‘wise investment’ role of ‘minimum input today, maximum output tomorrow’.

Scientific Notes: Natural Control Agents Affecting Spodoptera Frugiperda (Lepidoptera: Noctuidae) Infesting Rice in Puerto Rico

The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a sporadic but important pest of rice, Oryza sativa L., in the United States (Bowling 1978). Chandler et al. (1977) listed S. frugiperda as the main insect pest affecting rice production in Puerto Rico. Ashley (1979), Gardner and Fuxa (1980), and Lewis and Nordlund (1980) listed parasites and pathogens recovered from S. frugiperda larvae infesting various host plants but over one-half of the pathogens and the parasitoids listed do not indicate the host plant from which S. frugiperda larvae were recovered. To date, no parasitoids or pathogens have been reported as being recovered from S. frugiperda larvae infesting rice fields. S. frugiperda larvae (2nd and 3rd instars) were collected from infested rice fields at Arecibo, Puerto Rico on January 4 and February 2, 1984. A total of 720 larvae were collected and placed in plastic cups containing 30 ml of pinto bean diet capped, and transported to the Louisiana State University (LSU) Entomology Department under Animal and Plant Health Inspection Service permit 20 PPQ 576 and 599. Upon return to the laboratory larvae were removed from the collection containers, placed on fresh diet, and held at a 13:11 light: dark cycle and constant temperature of 26?C. Larvae were monitored daily for mortality and/or parasitoid emergence. Parasitoid puparia were removed from the diet container and placed in individual containers for emergence of adult parasitoids. Pupae of S. frugiI)erda were also monitored for emergence of parasitoids. Adult parasitoids were identified by N. E. Woodley of the USDA Insect Identification Institute at Beltsville, Maryland (IIBIII). Voucher specimens were deposited in the museum of the LSU Entomology Department, Baton Rouge, Louisiana. Pathogens were identified by personnel in the insect pathology project at LSU. Twenty eight parasitoid adults, larvae, and puparia were recovered. Eight (29%/) were identified as Lespesia sp. (Diptera :Tachinidae), one (3.6%Y.) as Archytas mntornoratts (Townsend) (Diptera:Tachinidae) and 19 (67%) were unidentifiable (possibly Chelonus sp., (Hymenoptera: Braconidae) due to premature S. frutgiperda larval death which prevented parasitoid development into puparia). The fungus Nonturaea rileyi (Farlow) Sampson killed eight larvae (1.1%) and three (3.2%F(,) were infected

Entomological and genetic variation of cultivated barley (Hordeum vulgare) from Egypt

Abstract The Russian wheat aphid (Diuraphis noxia (Mordvilko) is one of the most notorious pests and greatly limits the productivity of wheat and barley worldwide. Assessment of the genetic diversity of new barley germplasm (landraces) at both the genotypic and phenotypic levels may increase the efficiency of plant breeding and marker-assisted selection of desirable plant traits. The objective of this work was to use amplified fragment length polymorphisms (AFLPs) to assess genetic diversity among 24 Egyptian barley landraces and to identify resistance to D. noxia in the landraces. Out of 273 polymorphic bands obtained using eight primer combinations, 35 bands were discriminative AFLP markers and could be used to distinguish the Egyptian barley landraces at the DNA level. An AFLP-based dendrogram, generated by UPGMA cluster analysis, indicated that there is a correlation between genetic similarities and location. The obtained dendrogram clustered the investigated landraces into three main groups. There was significantly less D. noxia feeding damage on plants of several landraces originating near Giza compared to those originating in Sinai or Marsa Matrouh.