The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a major pest of soybean, Glycine max (L.). Merr., that significantly reduces yield in northern production areas of North ...America. Insecticides are widely used to control soybean aphid outbreaks, but efforts are underway to develop host plant resistance as an effective alternative management strategy. Here, previously identified resistant lines were evaluated in laboratory tests against field-collected populations of soybean aphid and in field-plot tests over 2 yr in South Dakota. Six lines previously identified with resistance to soybean aphid—Jackson, Dowling, K1639, Cobb, Palmetto and Sennari—were resistant in this study, but relatively high aphid counts on Tie-feng 8 in field plots contrasted with its previously reported resistance. Bhart-PI 165989 showed resistance in one of two laboratory tests, but it had relatively large aphid infestations in both years of field tests. Intermediate levels of soybean aphid occurred in field plots on lines previously shown to have strong (Sugao Zairai, PI 230977, and D75-10169) or moderate resistance to soybean aphid (G93-9223, Bragg, Braxton, and Tracy-M). Sugao Zairai also failed to have a significant proportion of resistant plants in two laboratory tests against aphids field-collected in 2008, but it was resistant in laboratory tests with aphids collected in 2002, 2005, and 2006. Overall, results showed that lines with Rag (i.e., Jackson) or Rag1 gene (i.e., Dowling) had low aphid numbers, whereas lines with Rag2 (i.e., Sugao Zairai, Sennari) had mixed results. Collectively, responses of soybean aphid populations in laboratory and field tests in 2008 resembled a virulence pattern reported previously for biotype 3 soybean aphids, but virulence in soybean aphid populations was variable and dynamic over years of the study. These results, coupled with previous reports of biotypes virulent to Rag1, suggest that deployment of lines with a single aphid-resistance gene is limited for soybean aphid management, and that deployment strategies relying on multiple resistance genes may be needed to effectively use plant resistance against soybean aphid.
The soybean aphid, Aphis glycines Matsumura, is a pest of soybean Glycine max L. (Merrill) in Asia, and its recent establishment in North America has led to large, recurring outbreaks that have ...challenged pest management practitioners there to seek environmentally responsible means for its control. Growth-chamber experiments were conducted to determine and characterize host-plant resistance among several soybean accessions. Soybean plants were first screened for resistance by rating the population growth of A. glycines in two tests. All plants of PI 230977 and 25% of PI 71506 plants were resistant (≤100 aphids per plant) in the first screening test. All 'Dowling', PI 71506 and PI 230977 were resistant (≤150 aphids per plant), and 50% of plants of line 'G93-9223' were resistant in the second test. Follow-up experiments showed that antixenosis was a modality of resistance based on reduced nymphiposition by A. glycines on Dowling, PI 230977 and PI 71506 in no-choice tests and on fewer numbers of A. glycines on Dowling, PI 230977, PI 71506 and G93-5223 in distribution tests. Antixenosis in Dowling and PI 230977 was stronger in the unifoliolate leaves than in other shoot structures, whereas distribution of A. glycines within plants of PI 71506 and G93-5223 suggested comparable suitability between unifoliolate leaves and other shoot structures of these accessions. Antibiosis to A. glycines was evident as a lower proportion of aphids that reproduced on PI 230977 and from fewer progeny on PI 230977 and Dowling than on 91B91. The number of days from birth to reproduction by A. glycines did not differ among accessions. Results confirmed Dowling and PI 71506 as strong sources of resistance to A. glycines. The levels of antixenosis and antibiosis to A. glycines in PI 230977 and antixenosis to A. glycines in G93-9223 suggest that these accessions may also be valuable to soybean breeding programs as sources of resistance.PUBLICATION ABSTRACT
The rate of breeding progress of 10 medium and 11 late maturing promiscuous soybean varieties developed by IITA for the savanna zones of Nigeria from 1980 to 1996 was assessed at two locations in ...2001 and 2002. The two maturity groups were evaluated in separate experiments using randomized complete block design with four replications. There were highly significant effects of variety on grain yield, fodder yield, and another set of eight traits both in the medium and late maturity groups. In the medium varieties, grain yield increased linearly from 1184 kg ha⁻¹ for an old variety TGx 1019-2EN to 1764 kg ha⁻¹ for TGx 1910-7F released in 1996. The annual rate of progress against year of release was 23.61 kg ha⁻¹ (1.99%). Modern varieties of the medium maturity group had high number of pods per plant, high harvest index, and reduced pod shattering. For late varieties, grain yield ranged from 1569 kg ha⁻¹ for an old variety Samsoy-2 to 2303 kg ha⁻¹ for a recently developed variety TGx 1910-14F. The annual rate of breeding progress during the improvement period of 16 years for late varieties was 22.23 kg ha⁻¹ or 1.42%. The overall yield of the late maturing varieties was 19% higher than the medium maturing varieties.
The soybean aphid, Aphis glycines Matsumura, is a pest of soybean Glycine max L. (Merrill) in Asia, and its recent establishment in North America has led to large, recurring outbreaks that have ...challenged pest management practitioners to seek environmentally responsible means for its control. Growth-chamber experiments identified resistance to A. glycines in soybean lines ‘Perrin’; ‘Tracy-M,’ its glabrous near-isoline ‘D88-5328,’ and its densely pubescent near-isoline ‘D88-5272’; ‘D75-10169,’ its glabrous near-isoline ‘D90-9216,’ and a densely pubescent near-isoline ‘D90-9220.’ Tracy-M and D75-10169 were antixenotic to A. glycines in host-selection tests. In no-choice nymphiposition tests, the number of nymphs deposited by A. glycines on D75-10169, Perrin, and Tracy-M did not differ from that on other lines after 24- and 48-h test periods. Under conditions in which A. glycines were free to distribute on plants over a 48-h period, aphids were found primarily on stems and trifoliolate leaves of Perrin, Tracy-M, D75-10169 and a resistant control, ‘Dowling,’ whereas the majority of aphids infesting susceptible lines ‘91B91’ and ‘Davis’ were distributed on unifoliolate leaves. Irrespective of shoot structure, low numbers of A. glycines were found on Dowling compared to other lines. The mean number of days to reproductive maturity for A. glycines did not differ among lines. Aphis glycines produced fewer nymphs during the first 7 d of reproduction on Perrin, Tracy-M, D75-10169 and Dowling compared to Davis, and fewer A. glycines progeny were produced on D75-10169 and Dowling than on 91B91. Results show that Dowling continues to be a strong source of resistance to A. glycines. Perrin, Tracy-M, and D75-10169 have been used as sources of resistance to other insects, and discovery of resistance to A. glycines in these three lines may increase their utility in soybean breeding programs.
Predatory mites are important components of subterranean food webs and may help regulate densities of agricultural pests, including western corn rootworms (Chrysomelidae: Diabrotica virgifera ...virgifera). Implementing conservation and/or classical biocontrol tactics could enhance densities of specialist or generalist predatory mites and lead to pest suppression, but first relevant mite species must be identified and their predatory capabilities evaluated. We conducted lab assays to quantify consumption of immature rootworms and oviposition rates of various mite species. Our study indicates that rootworms are a sub-optimal food source for the mite taxa tested. However, all mite species fed upon rootworms to some degree, although consumption by nematophagous Eviphis ostrinus was extremely low. Predators consumed more rootworm larvae than eggs, and mite size was correlated with prey consumption, with larger predators eating more prey. Four mite taxa (Gaeolaelaps sp., S. miles, Gl. americana, and G. aculeifer) had detrimental effects on survival of rootworm larvae, and the latter two species also had negative impacts on densities of pest eggs. Although it is unlikely that any of these mite species by itself has a major impact on rootworm control, the community of generalist soil-dwelling mites may play an important role in regulating immature rootworm populations in the field.
Larval corn rootworms (Coleoptera: Chrysomelidae) are soil-dwelling insect pests that damage maize (
Zea mays L.) by consuming root tissues, thus lowering grain yield. Little is known about ...interactions between rootworms and soil bacteria, including potential impacts of maize rhizobacteria, such as entomopathogenic
Serratia spp., on subterranean rootworm pests. We used selective growth medium (caprylate-thallous agar, CT) to quantify and isolate
Serratia spp. from: (1) bulk soil, (2) roots of four field-grown maize genotypes, half of which were infested with rootworm eggs from a reared colony, and (3) non-diseased, larval rootworms from the same colony. Phenotypic testing and 16S rRNA gene sequencing were used to identify bacteria, including non-
Serratia spp., that were successfully isolated on the CT solid medium. We also isolated and identified
Serratia spp. associated with non-diseased and diseased
Diabrotica adults.
Serratia spp. associated with maize roots were more abundant than those associated with bulk soil, where they were undetectable with our methods except for
Serratia grimesii. There was no impact of plant genotype on densities of bacteria isolated from maize roots.
S. grimesii was frequently associated with maize roots, regardless of infestation with rootworm eggs.
Serratia marcescens biotype A4,
Serratia plymuthica and several other Enterobacteriaceae genera were also associated with maize roots. Infesting the soil with rootworm eggs enhance the occurrence of two strains of the
S. marcescens biotype A1b, with comparable densities of these orange and pink strains within infested roots. However, both strains were associated with larval rootworms from the reared colony, which may indicate that rootworms were introducing these bacteria into infested maize roots. In addition, within larvae the orange strain was significantly more abundant than the pink strain, and was also associated with diseased rootworm adults. Our studies identified specific
Serratia strains associated with diseased rootworms that may have potential as biological control agents, and additional
Serratia biotypes associated with the maize rhizosphere that, based on the literature, may function as plant growth promoting agents via antagonistic action against plant-pathogenic fungi.
Seven maize, Zea mays L., genotypes selected for native resistance to western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), larval feeding damage (SUM2068, ...SUM2162, CRW3 (S1) C6, NSS1×CRW3 (S1) C6, PI583927, CRW2 (C5), and AR17056–16) were evaluated along with three control maize genotypes in the field for plant damage, larval recovery, adult emergence, root size, and root regrowth. Larvae recovered were further analyzed for head capsule width and dry weight and adults for dry weight. All factors evaluated with the exception of adult dry weight varied significantly among maize genotypes. Control genotypes included a highly susceptible hybrid, B37×H84, a transgenic rootworm-resistant hybrid expressing the modified Cry3A protein (MIR604), and the untransformed modern hybrid with the same genetic background as the MIR604 we used (isoline) as a second susceptible control. In general, the genotypes previously selected for resistance to western corn rootworm larval feeding had less damage, fewer larvae recovered, smaller larvae recovered, and fewer adults recovered than the susceptible controls. SUM2162 was significantly less damaged than all other native sources of resistance. Western corn rootworm larvae recovered from SUM2162 and SUM2068 were significantly smaller in terms of head capsule width and average weight than larvae recovered from all other maize genotypes, indicating that antibiosis is a mechanism of resistance for these two hybrids.
The direct effects of three soybean parentages, each represented by an Aphis glycines-resistant and susceptible isoline, on the fitness and performance of two key predators (Orius insidiosus and ...Harmonia axyridis) were evaluated in the laboratory. Predators were reared from hatch through adulthood in Petri dishes with cut trifoliolate leaves of the designated soybean variety, using eggs of Ephestia kuehniella as surrogate prey to eliminate prey-mediated effects of the host plant. Preimaginal survival and development, sex ratio, adult longevity, fecundity, and size were compared among treatments and a no-plant control. An additional experiment compared life-history parameters of predators caged with soybean versus Ipomoea hederacea (ivyleaf morning glory). Aphid resistance reduced the adult longevity of H. axyridis, but O. insidiosus was unaffected by resistance traits. However, adult O. insidiosus lived longer on soybeans with Group C base genetics than the other soybean varieties. Other parameters were not affected by soybean base genetics or resistance, but both predators generally performed worse on soybean than on I. hederacea or no-plant controls. The results suggest that soybean varietal selection, particularly with respect to A. glycines-resistance, may directly affect biological control agents. Also, implications of the generally poor suitability of soybean for natural enemies are discussed within the context of current crop production practices.
The western corn rootworm, Diabrotica virgifera virgifera (LeConte), is a major pest of maize, Zea mays L., in the United States and Europe, and it is likely to increase in importance as a trend ...toward increased nonrotated maize favors larger rootworm populations. Options for rootworm management in nonrotated maize in Europe and in nontransgenic “refuge” areas in countries that permit transgenic maize are limited to insecticides. Development of additional options for growers would be helpful. Screening maize germplasm (e.g., landraces, populations, inbreds) for native resistance to western corn rootworm is labor-intensive and is usually conducted on unfinished germplasm and not on hybrid materials. However, we have recently observed that topcrossed (hybrid) materials tend to have reduced western corn rootworm damage. To formally test whether rootworm damage to inbreds and associated hybrids were correlated, we evaluated 25 diverse inbred lines and their B73 hybrids for western corn rootworm damage in seven environments. Overall, hybrids had significantly less damage than inbreds, but unfortunately, the correlation between inbreds and hybrids was not significant. These findings have important implications regarding screening germplasm for western corn rootworm resistance, namely, that inbred materials and perhaps populations should be topcrossed to form hybrid materials before screening for western corn rootworm damage to ensure that valuable sources of resistance to western corn rootworm are not missed during the screening process.
Conventional breeding is widely used for modification of various crop and oilseed traits such as fatty acid composition and disease resistance. The effect of these modifications on the nutritionally ...beneficial bioactive plant components is usually overlooked unless these components are the specific targets for the modifications. The objective of this study was to examine the effect of breeding on nutritionally beneficial bioactive peanut components. The modified peanut lines Tamrun OL 01, Tamrun OL 02, TX977164 and TX977239 were analyzed for their tocopherol, phytosterol, and phospholipid compositions. Sunoleic and Tamrun 96 were the parent lines of these breeding lines. Parent lines were used as controls to examine the compositional changes resulting from breeding. The experimental results indicated that these peanut breeding lines were rich in
α-tocopherol. Tamrun OL 01 had the highest total phytosterol content among the peanut breeding lines examined in this study. All the breeding lines were rich in phosphatidylcholine. Although there were some statistical differences in chemical composition among the peanut breeding lines, these variations were within the range reported for traditional peanut varieties.
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