Browsing by Subject "resistance"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Behavioral defenses of honey bees against Varroa jacobsoni Oud.
    (1999) Boecking, Otto; Spivak, Marla
    Two behaviors of honey bees, hygienic behavior and grooming, are mechanisms of defense against brood diseases and parasitic mites. Studies have shown that Apis mellifera colonies remove worker brood infested with Varroa jacobsoni mites from the nest (hygienic behavior), and groom the mites off other adult bees, but to a limited extent compared to the original host of V. jacobsoni, A. cerana. Research is reviewed on hygienic and grooming behaviors with respect to their potential as mechanisms of resistance to V. jacobsoni. Studies related to hygienic behavior include the removal of experimentally infested and naturally infested brood, measurements of heritability, the uncapping and recapping of cells containing infested pupae, and the detection of infested brood. Studies on grooming include the process by which a groomer detects and damages a mite found on itself or on another adult bee, how the behavior is quantified, and problems with these methods of quantification. Finally, unresolved questions concerning grooming and the effects of hygienic and non-hygienic behaviors on limiting the population growth of V. jacobsoni are discussed.
  • Thumbnail Image
    Item
    Detecting Corn Rootworm (Diabrotica spp.) Resistance to Transgenic Bt-RW Traits: Emergence, Root Injury, and Species Interactions
    (2020-09) Benkert III, Edwin
    Western (Diabrotica virgifera virgifera LeConte) and northern (D. barberi Smith and Lawrence) corn rootworms remain economically important pests of field corn (maize; Zea mays L.) in the U.S. Corn Belt. With western corn rootworm resistance documented against all commercially available transgenic corn rootworm-active Bacillus thuringiensis Berliner (Bt-RW) traits, and northern corn rootworm resistance documented against two Bt-RW traits, corn rootworm continues to be a challenge for corn growers to manage. Methods to detect early resistance development to Bt-RW traits would enable growers to change management tactics earlier and allow for appropriate resistance mitigation to be practiced. This research proposes two methods to aid in the field detection of corn rootworm Bt-RW resistance development, an emergence model for the pyramid of Cry3Bb1 + Cry34/35Ab1 and a more sensitive pruning criteria for rating nodal injury. A greater understanding of interspecific competition under field conditions between western and northern corn rootworm, and implications for management is also discussed. Historically, scouting adult beetles has been an effective method to estimate the oviposition potential of a field population and its ability to injure corn roots the following growing season. Timing of adult scouting is critical to successfully estimating the egg-laying potential of a population, but because of protracted emergence of corn rootworm beetles, successful timing can be difficult. Corn rootworm adult emergence models have been developed and successfully used to determine the appropriate time for scouting adult beetles, but current models do not account for delays in emergence that occur when a population is exposed to a corn rootworm-active transgenic proteins derived from Bacillus thuringiensis Berliner (Bt-RW). This paper presents an emergence model developed to predict corn rootworm emergence after exposure to a hybrid expressing a pyramid of two Bt-RW proteins: Cry3Bb1 + Cry34/35Ab1. A logistic regression model of the form y = 0.94 / 1 + e (595.29 – x) / 43.22 was chosen to model adult emergence. Cumulative degree days were calculated using 11 and 18C as lower and upper temperature thresholds, and accumulations starting January 1 of each year. The predicted model estimated a scouting window of 35.5 days for Cry3Bb1 + Cry34/35Ab1, and the window began 13.1 days after the non-Bt-RW hybrid. Predicted emergence was significantly different from actual emergence for decreased efficacy sites and sites with suspected resistance to Cry3Bb1 + Cry34/35Ab1. The lack of statistical differences between actual emergence delays from decreased efficacy sites and suspected resistant sites suggests that emergence delays decrease drastically once a population falls below 94.5% efficacy. This model has important implications for corn rootworm scouting and resistance management. If actual emergence occurs earlier than predicted, the population may be undergoing resistance development to the Bt-RW protein, necessitating a change in management. Rating the injury corn rootworm causes on corn roots has long been used to evaluate not only the efficacy of different management tactics, but also the feeding intensity of the larval population. The current 0-3 nodal injury rating (NIR) utilizes 3.8 cm pruning criteria to evaluate root injury. Although sufficient for evaluating the efficacy of soil insecticides, the current pruning criteria is unable to detect lower levels of root feeding that could reveal developing Bt-RW resistance. We propose using pruning criteria of 7.6 cm to evaluate corn rootworm injury in populations that may be undergoing early resistance development to transgenic Bt-RW traits. We compared the relationship between root injury using both the 3.8 cm criteria and the 7.6 cm criteria from a non-Bt-RW hybrid and a Cry3Bb1 expressing hybrid with lodging, proportional yield, and beetles emerged per hectare. The 7.6 cm criteria provided three advantages: 1) the 7.6 cm criteria detected increased root feeding at lower injury levels; 2) these levels were associated with greater sensitivity to lodging susceptibility and yield reductions; and 3) were indicative of increased beetle emergence and reduced trait efficacy. For these reasons, the 7.6 cm criteria should be used when investigating developing resistance to transgenic Bt-RW traits. Despite differences in evolutionary history, host preferences, environmental tolerances, and resistance to management tactics, corn growers embrace the same management approach for both species. Previous studies have suggested western corn rootworm may out-compete northern corn rootworm under lab and greenhouse conditions. But do these results hold true under field conditions? These studies, conducted from 2017-2019 near Rosemount, MN, explored the competitive impacts of western and northern corn rootworm in mixed populations under field conditions. Differing ratios of western to northern corn rootworm eggs were used to infest seedling corn in these species’ competition field studies. Resulting impacts on species survival and corn root injury provide insights into interspecific competition. Emerged beetles were heavily skewed toward western corn rootworm; e.g., western corn rootworm comprised over 50% of emerging beetles when constituting only 25% of infested eggs. Root injury increased with higher western corn rootworm egg ratios. Patterns in root pruning lengths between treatments suggested western corn rootworm prefer to feed closer to the plant base while distal pruning increased with higher northern corn rootworm egg ratios, but statistical evidence for these differences was not found in this study. These results have important implications for the management of both species and provide a better understanding of how changing production situations (climate, weather, crop and rootworm management, insect resistance) could affect the competitive outcome between these species particularly in regard to Bt-RW resistance monitoring.
  • Thumbnail Image
    Item
    Effect of incubation time and temperature on the phenotypic expression of rpg4 to Puccinia graminis f. sp. tritici in barley
    (Canadian Journal of Plant Pathology, 1997-03-01) Sun, Yonglian; Steffenson, Brian
    To study the effect of incubation time and temperature on the phenotypic expression of rpg4, five barley genotypes with this resistance gene were infected with pathotype QCCJ of Puccinia graminis f. sp. tritici at the seedling stage, then subjected to various times of incubation at either 18-19°C or 27~28°C. Genotypes with rpg4 exhibited low (0, 0;, and 1), mesothetic (e.g. 3-210;, 120;3), and high (3,3) infection types at 18-19°C after initial incubation at 27-28°C for 0-28, 40-76, and 88 or more hours, respectively. A period of 88 or more hours of initial incubation at high temperature rendered the rpg4 resistance completely ineffective against this pathotype of P. g. f. sp. tritici. In contrast, high, mesothetic, and low infection types were found for the same genotypes at 27-28°C after initial incubation at 18-19°C for 0-40, 52-100, and 112 or more hours, respectively. The resistant infection types conferred by rpg4 are apparently established within the first 112 hours after the end of the infection period since subsequent shifts to higher temperature did not result in marked changes in the resistance response. These data indicate the critical importance of maintaining precise temperature control when assessing the infection phenotypes of barley genotypes carrying the stem rust resistance gene rpg4.
  • Thumbnail Image
    Item
    A multifactorial study of the resistance of honeybees Apis mellifera to the mite Varroa destructor over one year in Mexico
    (2005) Mondragon, Luis; Spivak, Marla; Vandame, Remy
    A one year study was conducted to evaluate the population growth of three kinds of honey bee colonies and Varroa destructor mites in Mexico, and to estimate the relative contributions of three resistance mechanisms of the bees: hygienic behavior, grooming behavior, and reproductive ability of the parasite. Very significant changes over the year were observed in the number of mated female offspring produced per mother mite (Wr), mite fertility and mutilation of V. destructor. These changes were correlated to the total number of mites per colony. A factorial analysis showed that two mechanisms explained the variation in the amount of mites per colony: Wr (r2 = 0.73) and proportion of mutilated mites (r2 = 0.51). A multi-factorial model including these two mechanisms was significant (r2 = 0.97). The mite fecundity and the hygienic behavior could not explain the population changes of the mite, and the different kinds of bees showed no differences in the expression of the resistance mechanisms.
  • Thumbnail Image
    Item
    Sources of FHB Resistance, Genetics and Mapping of Stem Rust Resistance in Kenyan and Ethiopian Spring Wheat Germplasm
    (2019-11) KOSGEY, ZENNAH
    Fusarium head blight (FHB or scab) and stem rust are important diseases of wheat. Fusarium graminearum is considered the primary causal agent of FHB. This study evaluated 215 wheat genotypes from Kenya and Ethiopia for their response to F. graminearum in inoculated and mist-irrigated nurseries established in St. Paul, MN in 2016, St. Paul, MN in 2017 and Crookston, MN in 2017. Six genotypes with stable resistance across the three test locations were identified. Positive associations were identified between FHB index, VSK, and DON and negative associations were identified between FHB index, plant height, and heading dates. The response of select genotypes was confirmed under greenhouse conditions. These studies identified resistance sources that can be used to improve the resistance levels in Kenyan and Ethiopian wheat germplasm. Stem rust caused by Puccinia graminis f. sp. tritici remains a threat to wheat production in East African wheat growing regions. In this study, we characterized the genetics of stem rust resistance, identified QTLs and markers associated with the resistance in spring wheat line CI 14275. The RILs together with their parents were evaluated at the seedling stage in a biosafety level 3 greenhouse against Pgt races TTKSK and TRTTF and in the USDA-ARS Cereal Disease Lab greenhouse against Pgt races TPMKC, TTTTF, and RTQQC. Screening for resistance to Pgt races in the field was undertaken in Kenya, Ethiopia, and the US in 2016, 2017, and 2018. One and three complementary genes conferred resistance to races TTTTF and RTQQC, respectively. The QTL QSr.cdl-2BS.2, that conferred resistance in Kenya and Ethiopia was validated and the marker Excalibur_c7963_1722 was shown to have potential in marker assisted selection. This is the first study to both detect and validate an adult plant stem rust resistance QTL on chromosome arm 2BS. The QSr.cdl-3B.1 is likely Sr12, QSr.cdl-4AL.1 is postulated as Sr7a, QSr.cdl-6BL.1 is likely Sr11, and QSr.cdl-6AS.1 appears to be a new QTL. Combination of QSr.cdl-2BS.2, QSr.cdl-3B.1, and QSr.cdl-6AS.1 has the potential to reduce stem rust severity in Africa. The work presented on FHB and stem rust provides resources for wheat improvement in East Africa.