• unlimited access with print and download
    $ 37 00
  • read full document, no print or download, expires after 72 hours
    $ 4 99
More info
Unlimited access including download and printing, plus availability for reading and annotating in your in your Udini library.
  • Access to this article in your Udini library for 72 hours from purchase.
  • The article will not be available for download or print.
  • Upgrade to the full version of this document at a reduced price.
  • Your trial access payment is credited when purchasing the full version.
Buy
Continue searching

Molecular approaches to facilitate marker-assisted selection for soybean aphid resistance in soybean

ProQuest Dissertations and Theses, 2009
Dissertation
Author: Ki Seung Kim
Abstract:
This study was conducted to enhance marker-assisted selection (MAS) for soybean aphid (Aphis glycines Matsumura) resistance in breeding programs and to test the associated effect of the aphid resistance gene Rag1 on several important agronomic traits in soybean [Glycine max (L.) Merr.]. The objective of the first study was to test for biotype variation of A. glycines in North America. Six soybean genotypes previously shown to be resistant to the Illinois soybean aphid isolate and two susceptible genotypes were tested with the Ohio and Illinois isolates in nonchoice tests. The same genotypes were also tested with the Ohio isolate using a choice test. In both the nonchoice and choice tests, there was a significant effect of isolate, genotype, and an interaction of the isolate and genotype. These tests demonstrated that at least two A. glycines biotypes exist in North America and that three soybean genotypes were resistant to both A. glycines biotypes. The objective of the second study was to identify single nucleotide polymorphisms (SNPs) near the A. glycines resistance gene Rag1 from Dowling and fine map the gene on soybean chromosome 7 [linkage group (LG) M]. SNPs closely linked to Rag1 were identified by hybridizing Affymetrix soybean GeneChip microarrays and re-sequencing sequence tagged sites (STSs) and selected regions near the gene. For fine mapping of the gene, 824 BC4 F2 and 1,000 BC4 F3 plants developed using Dowling as a donor parent and Dwight as a recurrent parent were screened with markers and 12 lines developed from recombinant plants were selected and tested for resistance to the Illinois A. glycines biotype and with SNP markers. These tests mapped Rag1 to a 115 kb interval on soybean chromosome 7. This interval contains several candidate genes including two nucleotide binding leucine-rich repeat (NBS-LRR) genes. The objective of the third study was to identify SNPs near the A. glycines resistance gene Rag2 from PI 200538 and fine map the gene on soybean chromosome 13 [(LG) F]. PI 200538 is a source of resistance to both the Illinois and Ohio A. glycines biotypes. Ninety-five F2:3 lines derived from the crosses LD02-4485 x (Ina x PI 200538) and 185 recombinant lines having various pedigrees and backgrounds were tested with the Ohio A. glycines biotype and markers. Eight SNP markers were developed from resequencing of STSs near the gene and the gene was mapped to a 1.6 cM interval between two SNP markers. Five recombinant lines with key recombinations within the Rag2 interval were tested for resistance to the Ohio A. glycines biotype and with SNP markers. These tests mapped Rag2 to 213 kb interval defined by two SNP markers on soybean chromosome 13. The objective of the fourth study was to test the associated effects of Rag1 on several important agronomic traits including yield in two elite Midwest adapted soybean backgrounds. This study was done because sometimes the introgression of resistance genes from nonadapted sources can carry undesirable genes through genetic linkages. To test for associated effects, field evaluations of two backcross populations segregating for Rag1 were conducted in multiple environments with no detectable soybean aphid infestations. This study revealed that Rag1 had no significant (P=0.05) associated effect on yield, plant height, and lodging score in either population. Rag1 was significantly (P=0.034) associated with a two-day delay in maturity in one population, and this maturity delay is likely caused by linkage between Rag1 and gene(s) that delayed maturity. This study indicates that Rag1 can be used for developing A. glycines resistant cultivars without an associated yield reduction in the Midwestern region of the USA.

TABLE OF CONTENTS CHAPTER 1: REVIEW OF LITERATURE: SOYBEAN APHID AND SOYBEAN APHID RESISTANT CULTIVAR BREEDING IN SOYBEAN 1 SOYBEAN PRODUCTION IN THE UNITED STATES OF AMERICA 1 SOYBEAN APHID IN NORTH AMERICA 3 BIOLOGY AND SEASONAL CYCLE OF SOYBEAN APHID 6 DAMAGE TO SOYBEAN BY SOYBEAN APHID 8 NATURAL ENEMIES OF SOYBEAN APHID 10 CHEMICAL CONTROL OF SOYBEAN APHID 12 RESISTANCE OF PLANTS TO INSECT PESTS 13 RESISTANCE OF SOYBEAN PLANTS TO SOYBEAN APHID 16 THE USE OF MOLECULAR MARKERS IN SOYBEAN BREEDING PROGRAMS 19 REFERENCES 22 CHAPTER 2: DISCOVERY OF SOYBEAN APHID BIOTYPES 37 ABSTRACT 37 INTRODUCTION 38 MATERIALS AND METHODS 41 RESULTS 44 DISCUSSION 46 vii

ACKNOWLEDGEMENTS 49 TABLES 50 REFERENCES 53 CHAPTER 3: FINE MAPPING THE SOYBEAN APHID RESISTANCE GENE RAG1 IN SOYBEAN 57 ABSTRACT 57 INTRODUCTION 58 MATERIALS AND METHODS 60 RESULTS 67 DISCUSSION 71 ACKNOWLEDGEMENTS 75 TABLES AND FIGURE 76 REFERENCES 81 CHAPTER 4: FINE MAPPING OF THE SOYBEAN APHID RESISTANCE GENE RAG2 IN PI 200538 86 ABSTRACT 86 INTRODUCTION 87 MATERIALS AND METHODS 89 RESULTS 95 DISCUSSION 97 viii

TABLES AND FIGURE 100 REFERENCES 106 CHAPTER 5: THE ASSOCIATED EFFECTS OF THE SOYBEAN APHID LOCUS RAGl ON SOYBEAN YIELD AND OTHER AGRONOMIC TRAITS 110 ABSTRACT 110 INTRODUCTION I l l MATERIALS AND METHODS 114 RESULTS 117 DISCUSSION 120 ACKNOWLEDGEMENTS 124 TABLES 125 REFERENCES 127 AUTHOR'S BIOGRAPHY 132 IX

CHAPTER 1 REVIEW OF LITERATURE: SOYBEAN APHID AND SOYBEAN APHID RESISTANT CULTIVAR BREEDING IN SOYBEAN SOYBEAN PRODUCTION IN THE UNITED STATES OF AMERICA Soybean [Glycine max (L.) Merr.] is the world's primary source of vegetable protein and oil with numerous uses in human food, livestock feed supplements, and industrial applications. World production of soybeans has tripled in the last 20 years, rising from about 70 million metric tons to over 220 million metric tons (www. Soystats.com). The United States of America is the leading soybean producer and soybean production in the USA produced for 33% of the total world production in 2008. In the USA, soybean production has increased from 44.5 million metric tons in 1983 to 80.5 million metric tons in 2008 and soybean yield has also increased from 1.76 metric tons/hectare in 1983 to 2.66 metric tons/hectare in 2008. In 2008, the USA exported 31.6 million metric tons of soybean grain, oil, and meal totaling about 20 billion dollars (www.Soystats.com). Although molecular breeding techniques have played a more important role in recent soybean improvements, most yield improvements have resulted from conventional breeding efforts (Lee et al., 2007). Yield is the most important trait in soybean breeding because it has the greatest impact on growers' profits (Orf et al., 2004). Specht et al. 1

(1999) estimated that soybean yields are improving at a rate of 23 kg/ha/year due to improved varieties, productions practices, and greater atmospheric CO2. Soybean yield improvement is limited by a variety of diseases and insect pests that can have devastating effects on yield and seed quality. Viruses, bacteria, fungi, and nematodes are primary causes of soybean diseases. Insects can also cause serious damage on soybean plants any time from plant emergence until harvest. In the Midwest, where most of the USA soybeans are produced, only sporadic outbreaks of insect pests have occurred until recently. However, because of the vast number of hectares in the region, outbreaks of pests considered minor in other regions can have a serious economic impact. (Boethel, 2004). In contrast to the Midwestern USA, the subtropical climatic conditions with mild winters and long growing season of the southern USA make soybean grown there vulnerable to economic losses resulting from insect infestations (Boethel, 1999). Soybean insect pests can be categorized into three groups based on the plant parts they attack and damaged. These groups are 1) pod, stem, and seed feeders, 2) foliage feeders, and 3) root and nodule feeders (Boethel, 2004). Among pod, stem, and seed feeders, stink bugs such as the southern green stink bug [Nezara viridula (L.)], green stink bug [Acrosternum hilare (Say)], and brown stink bug [Euschistus servus (Say) or Euschistus spp.] species are annual pests in the Southern USA and cause serious damage to soybean in the region (McPherson and McPherson, 2000). Bean leaf beetle [Ceratoma trifurcate (Forster)] and corn earworm [Helicoverpa zea (Boddie)] also are important pod, stem, and seed feeders (Hunt et al, 1995; Tery et al., 1987). Of the foliage feeders, mexican bean beetle {Epilachna varivestris Mulsant), potato leafhopper [Empoasca fabae (Harris)], grasshopper (Melanoplus spp.), Japanese beetle (Popillia japonica Newman), and soybean aphid (SA: Aphis glycines Matsumura) are important defoliators and can 2

cause serious damage to soybean in Illinois (http://ipm.illinois.edu). The economic impact of the soil-inhabiting insect complex on soybean is poorly understood (Turnipseed and Kogan, 1976). Among root and nodule feeders, larvae of the soybean nodule fly [Rivella quadrifasciata (Macquart)] feed on soybean nodules (Eastman and Wuensche, 1977) and larvae of the grape colspis [Colospis brunnea (F.) and C. louisianae Blake] feed on roots causing plant stunting (Lambert, 1994). SOYBEAN APHID IN NORTH AMERICA The S A is a new invasive insect pest of soybean in North America and was first identified in Wisconsin in July 2000 (Hartman et al., 2001). The SA is the only aphid in North America that can reproduce on soybeans. Therefore, any large cluster of aphids found on soybean in North America must be SA (Rice et al., 2007). It has rapidly spread throughout the Midwestern USA and southern Canadian provinces since its first report (Venette and Ragsdale, 2004). By 2008, SA had dispersed to all soybean growing states in the USA except the Carolinas, Florida and Texas (Voegtlin, 2008). The SA is a small (<1/16 inch long when mature), greenish-yellow insect with distinct dark-tipped cornicles near the end of its abdomen. Without careful inspection, they can be confused with other small arthropods living on soybean, including spider mites, thrips, and leafhoppers. SA can be found on stem apices and young leaves of growing soybean plants, and on the undersides of leaves of mature plants (Hill et al., 2004a). The SA is native to eastern Asia, and the range of the SA stretches from southern Siberia and the Korean peninsula south through China and Japan to the Indochina 3

peninsula, the Philippines and Indonesia (APPPC, 1987; CAB International, 2001). Another recent range expansion of S A includes its discovery in New South Wales and Queensland in Australia during early 2000 (Baute, 2004; Fletcher and Desborough, 2004; Venette and Ragsdale, 2004). The origin of the SA that invaded the USA has not been conclusively determined. Three possibilities to explain the entry of the SA into North America include: (1) Winged females on edamame imported from Asia. Edamame is a soybean dish made from boiling non-ripened soybean in the pod. It is commonly found in China and Japan and consumption in the USA is growing due to an increasing Asian American population as well as a rise in popularity of Asian cuisine. (2) Eggs on a common buckthorn {Rhamnus cathartica L.) or other Rhamnus imported into the USA and (3) Winged females from airplane cabins with horticultural cargos arriving from Asia. Although the exact route into the USA has not been determined, its distribution and spread in the USA implicates an introduction near Chicago. Chicago is at the epicenter of the initial distribution of the SA in the U.S (www.soybeans.umn.edu). Considering its initial distribution and the rate of spread, the SA may have been in the USA since at least the mid-1990s. This is supported by an unconfirmed observation of aphids on soybean in July of 1995 by Paul Hogg, a crop consultant near Ft. Atkinson in southeast Wisconsin (www.soybeans.umn.edu). Early reports of SA in 2000 were from the same area of Wisconsin, as well as northern Illinois and Michigan. Many factors affect SA populations including the environment (e.g., temperature, precipitation, humidity), number of over-wintering aphid eggs, synchronization of soybean and SA development, natural enemies, pathogenic fungi, insecticide usage, and host plant resistance (Wu et al., 2004). Among these factors, temperature and 4

precipitation are key abiotic factors that can regulate the longevity, reproduction, and seasonal occurrence of SA (McCornack et al., 2004; Yue and Hao, 1990). Yue and Hao (1990) showed that higher average temperature (22 to 23°C) and less rainfall (<20 mm) from 21 June to 10 July greatly favored SA development, whereas light infestations occurred during the years when the average temperature was 20 to 21°C and precipitation >55 mm. Studies of longevity and reproductive rates of SA at different temperatures suggest that optimal population growth occurs with temperatures ranging from 22 °C to 27 °C (Hirano et al., 1996) and population growth rates were greatest at 25°C, at which populations can double in 1.5 d (McCornack et al., 2004). McCornack et al. (2004) reported that net fecundity, gross fecundity, generation time, and life expectancy decreased as temperature increased from 25°C, the optimal developmental temperature. They estimated that lower, upper and optimal developmental thresholds of SA to be 8.6°C, -34.9°C and 27.8°C, respectively. Extremely low air temperatures of-34 °C during the winter negatively affect the overwintering of SA eggs (McCornack et al., 2005). Temperature of-15°C or below will kill non-winged SA (oviparae) and winged fall migrant SA (gynoparae). Generally, SA with a small volume body size survives low temperatures better than large aphids. The small aphids are thought to contain fewer impurities such as gut content and bacteria, which reduce the number of sites for ice nucleation and lower supercooling points (Wilson et al., 2003). SAs that fed on buckthorn are also tolerant to low temperatures (McCornack et al., 2005). The lack of tolerance of SA to very low temperatures suggests that it is likely that SA populations present in the far northern USA (northern Minnesota, northern Wisconsin, and the upper peninsula of Michigan) and southern Canada are more 5

likely to result from SA migration than that of localized overwintering aphids (McCornack et al, 2005). S A and other phloem-feeding herbivores are known to be sensitive to variation in leaf Nitrogen (N) whereby higher N results in increased insect developmental rates and higher fecundity (Awmack and Leather, 2002). A positive correlation between N content of the apex leaves and the occurrence of the SA was reported (Hu et al., 1992), whereas lignin content negatively affected aphid infestations (Hu et al., 1993). Myers et al. (2005) suggested that SA might perform better on Potassium (K)-deficient plants but it remains unclear whether K-deficient soybean plants promote SA outbreaks in the field. BIOLOGY AND SEASONAL CYCLE OF SOYBEAN APHID The SA has a heteroecious holocyclic lifecycle pattern (host-alternating with sexual reproduction during part of its life cycle) and usually has as many as 15 to 18 generations annually (Hartman et al., 2001; Ragsdale et al., 2004). SA populations have the potential to increase 10-fold every week (http://www.nsrl.uiuc.edu). To complete its life cycle, SA requires two hosts. The woody shrub or understory tree called buckthorn serves as the primary host in the spring, fall, and winter. In North America, two confirmed buckthorn species, common buckthorn (Rhamnus cathartica L.) and native alderleaf buckthorn {Rhamnus alnifolia L'Her), are used as primary hosts (Voegtlin et al., 2004). SA prefers seedling or sapling trees on which to lay their eggs in the fall. Soybean is a secondary host of S A during the summer and the aphids do not reproduce sexually on 6

this plant. Additional secondary hosts include crimson clover and red clover (Alleman et al, 2002). The SA and a close relative cotton or melon aphid {Aphis gossypii Glover) are the only species that colonize soybean in the USA. Several other aphid species feed on soybean, but they are migratory and do not colonize soybean. In other parts of the world, Aphis craccivora Koch (Homoptera: Aphididae), Aulacorthum solani (Kaltenbach), and other species have been found colonizing soybean (Hill et al., 2004b). The SA life cycle begins each spring when nymphs hatch and develop into wingless adults. The third and subsequent generations on buckthorn consist primary of winged morphs that emigrate in search of soybean, their summer host (Ragsdale et al., 2004). From early June, SA is found on soybean plants. At this period, the odor of the soybean plants might play an important role in attracting S A. Antenna of S A contains olfactory receptors that recognize volatile chemicals emitted from the soybean plants (Du et al., 1994; 1995). Du et al. (1994) also found that odors of other plants interfered with the attraction to soybean, suggesting that odors from non-host plants might hinder aphids in their search for a host. This fact may explain the decrease of SA density when maize and soybean are grown together (Wang and Ba, 1998; Wang et al, 2000). Adults and nymphs of SA accumulate on the tenderest leaves of plants and on stems. When soybean flowering peaks, SA frequently infest the upper leaves, apex buds on branches, flowers, and pods (Wu et al., 2004). The summer SA population can be non-winged or winged (dispersal phase), but all are female. No males are present or needed for reproduction during this time period because females reproduce parthenogenetically (egg development without fertilization), so aphid numbers can increase dramatically on soybean in a short period of time. If crowding on stressed plants occurs, winged females develop and fly 7

away from the field in search of other soybean fields to colonize (http://ipm.illinois.edu). In the fall, as temperatures drop and the day length shortens, a generation of winged females and males are produced. Both migrate from soybean to their overwintering host plant (buckthorn) where mating and oviposition occurs. During the following spring, the eggs hatch and a few generations are produced before alate (winged females) fly to soybean. DAMAGE TO SOYBEAN BY SOYBEAN APHID S As penetrate plant tissues by probing intercellularly through epidermal and mesophyll cell layers with their stylet-like mouthparts to feed on photoassimilates that are being translocated in the phloem sieve elements (Pollard, 1972). Plant damage occurs as a consequence of a large number of SA removing significant amounts of water and nutrients from leaves and stems causing leaves to wilt, curl, yellow, and even drop (Mensah et al., 2005). High SA densities reduce crop production directly when their severe feeding causes stunting, leaf distortion, reduced pod set, poor pod fill, and nutrient deficiencies (Hill et al., 2004a; DiFonzo and Hines, 2002). In addition to yield losses, reductions in seed quality such as discoloration and deformation are an important concern for soybean growers who produce food-grade soybean and consumers who want to purchase these soybeans (Mian et al., 2008a). The most important effect of SA damage on soybean is a reduction of the number of soybean pods per plant. Thus, significant yield loss (8 to 25%) occurs when SAs attack plants during the early reproductive stages such as flowering (R1-R2) and pod set (R3-R4) (DiFonzo and Hines, 2002). Therefore, 8

protecting plants during the Rl- R4 reproductive stages helps protect soybean yield. These soybean stages typically occur from mid-July into early August in North America. Yield losses greater than 50% in Minnesota during 2001 (Ostile, 2002), 32% in Iowa during 2003 (Rice et al., 2007), and 58% in China (Wang et al., 1996; Wu et al., 2004) were attributed to SA in fields. In Michigan, 13,000 SAs per plant and a 40% loss in seed yield was recorded (DiFonzo and Hines, 2002). An intense SA outbreak occurred in 2003, which damaged approximately 1.6 million ha of soybean in Minnesota and 0.5 million ha in Illinois in 2003 (Associated press, 2003; Steffey, 2004). These aphid outbreaks result in reduced grower income due to yield reductions and/or increased production costs caused by the need to apply insecticides to control SA (Myers et al., 2005). When SA first colonizes soybean plants, they are most abundant on newly formed leaves. As SA reproduces, they spread throughout the canopy. It has been estimated that by the time the aphids colonize stems, their density has reached over 400 SAs per plant (Krupke et al., 2005). Leaves on the bottom half of heavily infested plants can be covered with shed SA exoskeletons resembling white powder, and SA honeydew, both of which indicate SA presence. Honeydew, a sticky and shiny liquid excreted by the SA as a by product from ingesting large amounts of plant juices, accumulates on the top surface of leaves (Rice et al., 2007). Excessive honeydew promotes the growth of a fungus called sooty mold (Cladosporium spp. or Sporobolomyces) that obtains nutrients from aphid honeydew, turning the leaves dark and interfering with plant photosynthesis (Baute, 2004). Plant stress from other factors such as drought, late planting, disease, and nutrient deficiency during aphid colonization appear to promote S A population growth and spread throughout fields (Krupke et al., 2005). 9

The introduction and spread of SA within North America could affect the transmission of viruses into and within soybean plants (Clark and Perry, 2002). SA is capable of transmitting a number of viruses present in the USA that naturally infect soybean, including Alfalfa mosaic virus (AMV), Soybean mosaic virus (SMV), Bean yellow mosaic virus (BYMV), Peanut mottle virus (PMV), Peanut stunt virus (PSV), and other viruses (Sama et al., 1974; Iwaki et al., 1980; Hartman et al., 2001). Clark and Perry (2002) tested the transmission of field isolates of SMV, AMV and Tobacco ringspot virus (TRSV) by the SA and found that of the three, SMV had the highest transmissibility by the SA. These viruses can cause various symptoms, including mosaic and mottling of leaves (mixture of chlorotic and green leaf tissue), leaf distortion, reduced pod number, deformed pods, and discolored seed. It is not possible to prevent the spread of these viruses by only controlling the SA with insecticides (USDA CSREES, 2002). NATURAL ENEMIES OF SOYBEAN APHID Natural enemies play an important role in controlling the SA, especially at the early stages of an infestation when S A populations have a low density and uneven distribution in China (Wu et al., 2004). In soybean fields, SAs are attacked by several predatory insects that can control aphid populations including the insidious flower bug [Orius insidiosus (Say)], lady beetles (Harmonia axyridis and Coccinella septmpunctata), hover flies (Syrphidae), green lacewings (Chrysoperla carnea), and ground beetles (Carabidae) (Leer, 2006). Lady beetles played a key role in suppressing the SA in 10

Indonesia (van den Berg et al., 1997). However, the existing predators and parasitoids in USA have frequently not controlled SA populations sufficiently to prevent outbreaks (Nielsen and Hajek, 2005). Several researchers have shown that the presence of refuges that can provide natural enemies with overwintering sites, alternative prey, shelter during early spring, and buffer the negative consequences of insecticide applications on crop fields, can increase densities of generalist predators (Lee et al., 2001). Another group of natural enemies, entomopathogenic fungal species, have been shown to attack SA in a number of regions of the USA including Minnesota and Georgia (Baute, 2004; Rutledge et al., 2004; McPherson et al., 2003). Although researchers have reported that these fungi can seriously impact SA populations, diversity and abundance of entomopathogenic fungi infecting S A have not been quantified in North America (Nielsen and Hajek, 2005). Nielsen and Hajek (2005) reported that seven species pathogenic fungi on SA were found in New York State, and Pandora neoaphidis (Remaud. et Henn.) was the most abundant species, causing 84% infection in an outbreak SA population in 2003, after which the SA population crashed. The general diversity of fungal species infecting SA was similar to literature records for other holocyclic aphid species (Nielsen and Hajek, 2005). It is, however, well documented that fungal pathogens have great potential for aphid control in other annual crop ecosystems such as Gossypium sp. (cotton) (Steinkraus et al. 1997), Solanum tuberosum (potatoes) (Soper, 1981), Medicago sativa (alfalfa) (Soper and Ward, 1981), Spinacia oleracea (spinach) (McLeod et al., 1998), Brassica species (Dara and Semtner, 2001), and Phaseolus vulgaris (bean) (Wilding and Perry, 1980). The fungi responsible for naturally occurring epizootics in these systems all belong to the Order Entomophthorales, a group of obligate pathogens known for their ability to increase rapidly in response to host population increases 11

(Nielsen and Hajek, 2005). This suggests that there is the potential for using aphid pathogenic fungi for conservation biological control of the SA. CHEMICAL CONTROL OF SOYBEAN APHID Because SA resistant cultivars are still not widely available in USA, the application of registered chemical insecticides is essentially the only available means for aphid control. The SA can be controlled efficiently if insecticides are applied before flowering and podding stages. When the SA density reaches the economic threshold of 250 aphids per plant, insecticide applications are recommended to avoid severe yield loss. According to the survey of Landis et al. (2003), nearly 3 million hectares of soybean fields in the USA were sprayed with insecticides to control the SA during 2003. This includes from $9 to 12 million spent on insecticide applications to control SA in Illinois that year (Steffey, 2004). A negative side effect of this extensive use of pesticides, especially synthetic pyrethroid insecticides, is that these non-selective or broad-spectrum insecticides concurrently kill many natural enemies of S A along with the S A. This can result in a rapid resurgence of SA populations after the insecticide applications and a reduction of biodiversity in agricultural systems. Frequent applications of broad-spectrum pesticides also can lead to the buildup of S A tolerance to the chemicals, resulting in more chemicals being used with potentially severe environmental side effects (Wu et al., 2004). Wang et al. (1993) identified that phosalone effectively controlled SA without negative effects to beneficial pentatomid insects and parasitoids at the seedling stage. Dai and Zu 12

(1997) also reported that G-P compound, a mixture of a bacterial metabolite and a plant extract compound, effectively controlled S A. RESISTANCE OF PLANTS TO INSECT PESTS Host plant resistance to insects is an important component of integrated pest management (IPM) programs to control pests of most crops. Painter (1951) defined host plant resistance as the relative amount of heritable qualities possessed by the plant that influence the ultimate degree of damage done by the insect in the field. There are four important characteristics of host plant resistance. First, resistance must be heritable. Second, resistance must be measurable. Third, resistance must be relative, meaning that resistance could be measured only by comparison with a susceptible cultivar of the same plant species. Fourth, resistance may be affected by the environment such that the magnitude of resistance is affected by abiotic factors (including soil fertility and water availability) and biotic factors (such as disease infection). Structural defenses can provide resistance to a broad spectrum of insect pests. Simple and glandular hairs (trichomes) have been shown to provide resistance to sap- sucking insects like the potato leafhopper in alfalfa (Medicago sativa)/Luceme (Medicago falcata) (Shade et al., 1979). In leafhopper-resistant soybean, resistance has been related to the orientation and size of trichomes rather than their density (Turnipseed, 1977). Trichome length and density also has been implicated in resistance to bean fly (Ophiomyia phaseoli), whitefly {Bemisia argentifolii), pod borer (Maruca vitrata), and bean leaf beetle (Cerotoma trifurcata) (Edwards and Singh, 2006). In the case of SA 13

resistance, dense pubescence does not provide protection (Hill et al., 2004a) although extra-dense pubescence has been shown to significantly reduce the incidence of SMV infection at the Rl growth stage (Pfeiffer et al., 2003). There are three modalities of plant insect resistance that have been described (Painter, 1951) and two of them, antixenosis and antibiosis, have been found to occur in soybean responses to SA (Hill et al., 2004a). Antixenosis or non-preference is the ability of a variety to repel insects, causing a reduction in oviposition or feeding (Kogan and Ortman, 1978). Antibiosis is the ability of a variety to reduce the survival, growth, or reproduction of insects that feed on it and can be measured by comparing the survival, size, fecundity, or rate of development of insects that have fed on different test varieties. Antibiosis is often caused by the production of toxic chemicals or the secondary metabolites by the plant. The Third modality, tolerance is the ability of a variety to produce a larger crop of better quality than other varieties when being fed upon by a similar number of insects. Tolerance is difficult to measure in experiments because yield or plant growth must be compared while insect numbers or biomasses are kept constant on all test varieties. Unlike antixenosis and antibiosis, tolerance does not affect the behavior or health of insects feeding on the plant. Regardless of the mode of plant insect resistance, resistance to insect pests can be inherited in two ways. Vertical (major gene) resistance is a form of pest resistance that is generally controlled by a single gene, referred to as an R-gene. These R-genes can be remarkably effective in controlling diseases or pests and can confer complete resistance. However, each R-gene confers resistance to only a certain group of pathogen or pest races. Therefore, depending on the races present in the area, a variety may appear strongly resistant or completely susceptible. Horizontal resistance also is known as multi- 14

Full document contains 142 pages
Abstract: This study was conducted to enhance marker-assisted selection (MAS) for soybean aphid (Aphis glycines Matsumura) resistance in breeding programs and to test the associated effect of the aphid resistance gene Rag1 on several important agronomic traits in soybean [Glycine max (L.) Merr.]. The objective of the first study was to test for biotype variation of A. glycines in North America. Six soybean genotypes previously shown to be resistant to the Illinois soybean aphid isolate and two susceptible genotypes were tested with the Ohio and Illinois isolates in nonchoice tests. The same genotypes were also tested with the Ohio isolate using a choice test. In both the nonchoice and choice tests, there was a significant effect of isolate, genotype, and an interaction of the isolate and genotype. These tests demonstrated that at least two A. glycines biotypes exist in North America and that three soybean genotypes were resistant to both A. glycines biotypes. The objective of the second study was to identify single nucleotide polymorphisms (SNPs) near the A. glycines resistance gene Rag1 from Dowling and fine map the gene on soybean chromosome 7 [linkage group (LG) M]. SNPs closely linked to Rag1 were identified by hybridizing Affymetrix soybean GeneChip microarrays and re-sequencing sequence tagged sites (STSs) and selected regions near the gene. For fine mapping of the gene, 824 BC4 F2 and 1,000 BC4 F3 plants developed using Dowling as a donor parent and Dwight as a recurrent parent were screened with markers and 12 lines developed from recombinant plants were selected and tested for resistance to the Illinois A. glycines biotype and with SNP markers. These tests mapped Rag1 to a 115 kb interval on soybean chromosome 7. This interval contains several candidate genes including two nucleotide binding leucine-rich repeat (NBS-LRR) genes. The objective of the third study was to identify SNPs near the A. glycines resistance gene Rag2 from PI 200538 and fine map the gene on soybean chromosome 13 [(LG) F]. PI 200538 is a source of resistance to both the Illinois and Ohio A. glycines biotypes. Ninety-five F2:3 lines derived from the crosses LD02-4485 x (Ina x PI 200538) and 185 recombinant lines having various pedigrees and backgrounds were tested with the Ohio A. glycines biotype and markers. Eight SNP markers were developed from resequencing of STSs near the gene and the gene was mapped to a 1.6 cM interval between two SNP markers. Five recombinant lines with key recombinations within the Rag2 interval were tested for resistance to the Ohio A. glycines biotype and with SNP markers. These tests mapped Rag2 to 213 kb interval defined by two SNP markers on soybean chromosome 13. The objective of the fourth study was to test the associated effects of Rag1 on several important agronomic traits including yield in two elite Midwest adapted soybean backgrounds. This study was done because sometimes the introgression of resistance genes from nonadapted sources can carry undesirable genes through genetic linkages. To test for associated effects, field evaluations of two backcross populations segregating for Rag1 were conducted in multiple environments with no detectable soybean aphid infestations. This study revealed that Rag1 had no significant (P=0.05) associated effect on yield, plant height, and lodging score in either population. Rag1 was significantly (P=0.034) associated with a two-day delay in maturity in one population, and this maturity delay is likely caused by linkage between Rag1 and gene(s) that delayed maturity. This study indicates that Rag1 can be used for developing A. glycines resistant cultivars without an associated yield reduction in the Midwestern region of the USA.