Brian G. Rector

Bio: Brian G. Rector is an academic researcher from Agricultural Research Service. The author has contributed to research in topics: Eriophyidae & Population. The author has an hindex of 17, co-authored 58 publications receiving 2047 citations. Previous affiliations of Brian G. Rector include United States Department of Agriculture & University of Georgia.

A retrospective DNA marker assessment of the development of insect resistant soybean

Abstract: There has been limited success over the past 30 yr in the development of superior soybean cultivars [Glycine max (L.) Merr] with insect resistance. Success may be hampered by the quantitative nature of resistance and by linkage drag from resistant plant introduction (Pl) donor parents. Soybean insect resistance quantitative trait loci (SIR QTLs) have been identified from PI 229358 and PI 171451 by restriction fragment length polymorphism (RFLP) analysis. The objective of this study was to tag the SIR QTLs from PI 229358 with simple sequence repeat (SSR) markers and to determine the extent to which the SIR QTLs have been introgressed in registered cultivars, germplasm releases, or breeding lines that have resistance derived from this PI or from PI 171451. Marker analysis defined intervals by 5 centimorgans (cM) or less for a SIR QTL on linkage group D1b (SIR-D1b), and for SIR-G, SIR-H, and SIR-M. SIR QTLs were tracked through pedigrees by evaluating the inheritance of PI alleles at marker loci tightly linked to the QTLs during the phenotypic selection for insect resistance. It was inferred that at least 13 of the 15 SIR genotypes studied had introgressed SIR-M. PI genome introgression around SIR-M was measured to assess linkage drag. Some genotypes exhibited a dramatic reduction in the amount of linked PI genome, which likely occurred in response to phenotypic selection for agronomic performance as a means of reducing linkage drag. Only a few genotypes were inferred to possess SIR-G or SIR-H, and no genotypes possessed SIR-D1b. The results of this study indicate that marker-assisted selection for SIR QTLs is needed to introgress these loci into elite genetic backgrounds.

Quantitative Trait Loci for Antibiosis Resistance to Corn Earworm in Soybean

Abstract: In more than 25 yr since the discovery of soybean [Glycine max (L.) Merr.] resistance to defoliating insects, attempts to introgress this trait into elite germplasm have been relatively unsuccessful. Resistance to defoliating insects in soybean is expressed as a combination of antibiosis (toxicity) and antixenosis (nonpreference). Both of these resistance modes are inherited quantitatively in soybean. The objectives of this study were (i) to use restriction fragment length polymorphism (RFLP) maps to identify quantitative trait loci (QTLs) in soybean for antibiosis against corn earworm (CEW) (Helicoverpa zea Boddie), (ii) to determine the relative magnitude, gene action, and genomic locations of these QTLs, and (iii) to compare them to previously detected soybean antixenosis QTLs. Restriction fragment length polymorphism maps were constructed in three soybean F 2 populations segregating for antibiosis against CEW: Cobb' × P1171451, Cobb × PI227687, and Cobb × PI229358. Antibiosis was measured as larval weight gain in a detached leaf assay. The RFLP data were associated with insect bioassay data to detect QTLs for antibiosis in each cross. Variance component heritability estimates for antibiosis in the three crosses were 54, 42, and 62% in Cobb × P1171451, Cobb × PI227687, and Cobb × PI229358, respectively. An antibiosis QTL on Linkage Group (LG) M was detected in both Cobb X PI171451 and Cobb × PI229358 (R 2 values of 28 and 22%, respectively). An antixenosis QTL was also significant at this location in the same two crosses. This was the only insect-resistance QTL that was detected for both antibiosis and antixenosis. Antibiosis QTLs were also detected on LGs F and B2 in Cobb × PI227687 (R 2 = 33 and 12%, respectively), and LGs G and J in Cobb × PI229358 (R 2 = 19% for each). Antibiosis was conditioned by the PI (resistant parent) allele at the QTLs on LGs G, M, and B2, whereas the susceptible parent, Cobb, provided antibiosis alleles at the QTLs on LGs F and J.

Simple sequence repeat markers linked to the soybean Rps genes for phytophthora resistance

Abstract: Simple sequence repeat (SSR) markers with linkages to the Rps1, Rps2, Rps3, Rps4, RpsS, and Rps6 loci that govern soybean [Glycine max (L.) Merr.] resistance to Phytophthora root rot (caused by Phytophthora megasperma Drechs. f. sp. glycinea Kuan and Ervin) are desired. Near-isogenic lines (NILs) of Clark or Williams, homozygous resistant (RpsRps) at just one of those Rps loci, were mated to a NIL of Harosoy homozygous susceptible (rpsrps) at all six loci. From the 100 to 120 F 2:3 progenies per mating, 20 F 3 seedlings were evaluated for resistance (R) or susceptibility (S) following inoculation with the race of P. megasperma affected by the segregating Rps allele. About 15 RpsRps and 15 rpsrps F 2 individuals were used to construct contrasting DNA bulks. Presumptive linkage (i.e., SSR marker polymorphism between two bulks) was confirmed or refuted by SSR assay of 15 to 40 F 2 individuals within each homozygous class. Recombination values were maximum likelihood estimates from the SSR allelic segregation data of both classes, although the rpsrps class was less prone to phenotypic classification error. SSRs on linkage groups (LGs) N, J, F, and G were identified with linkages to Rps1, Rps2, Rps3, and Rps4, respectively. A skewed R:S segregation in the Rps5 population precluded detection of linked SSRs. The Rps6 locus, whose map position was heretofore unknown, was linked with three SSRs in a region of LG-G that contains Rps4 and Rps5. SSR-Rps linkages of P < 0.05 could only be identified for the Rps1 alleles because of a paucity of SSR markers and/or parental monomorphism in the genomic regions surrounding other Rps loci.

Identification of molecular markers linked to quantitative trait loci for soybean resistance to corn earworm

Abstract: One hundred and thirty nine restriction fragment length polymorphisms (RFLPs) were used to construct a soybean (Glycine max L. Merr.) genetic linkage map and to identify quantitative trait loci (QTLs) associated with resistance to corn earworm (Helicoverpa zea Boddie) in a population of 103 F2-derived lines from a cross of ‘Cobb’ (susceptible) and PI229358 (resistant). The genetic linkage map consisted of 128 markers which converged onto 30 linkage groups covering approximately 1325 cM. There were 11 unlinked markers. The F2-derived lines and the two parents were grown in the field under a plastic mesh cage near Athens, Ga., in 1995. The plants were artificially infested with corn earworm and evaluated for the amount of defoliation. Using interval-mapping analysis for linked markers and single-factor analysis of variance (ANOVA), markers were tested for an association with resistance. One major and two minor QTLs for resistance were identified in this population. The PI229358 allele contributed insect resistance at all three QTLs. The major QTL is linked to the RFLP marker A584 on linkage group (LG) ‘M’ of the USDA/Iowa State University public soybean genetic map. It accounts for 37% of the total variation for resistance in this cross. The minor QTLs are linked to the RFLP markers R249 (LG ‘H’) and Bng047 (LG ‘D1’). These markers explain 16% and 10% of variation, respectively. The heritability (h2) for resistance was estimated as 64% in this population.

Cryptic speciation in the Acari: a function of species lifestyles or our ability to separate species?

Abstract: There are approximately 55,000 described Acari species, accounting for almost half of all known Arachnida species, but total estimated Acari diversity is reckoned to be far greater. One important source of currently hidden Acari diversity is cryptic speciation, which poses challenges to taxonomists documenting biodiversity assessment as well as to researchers in medicine and agriculture. In this review, we revisit the subject of biodiversity in the Acari and investigate what is currently known about cryptic species within this group. Based on a thorough literature search, we show that the probability of occurrence of cryptic species is mainly related to the number of attempts made to detect them. The use of, both, DNA tools and bioassays significantly increased the probability of cryptic species detection. We did not confirm the generally-accepted idea that species lifestyle (i.e. free-living vs. symbiotic) affects the number of cryptic species. To increase detection of cryptic lineages and to understand the processes leading to cryptic speciation in Acari, integrative approaches including multivariate morphometrics, molecular tools, crossing, ecological assays, intensive sampling, and experimental evolution are recommended. We conclude that there is a demonstrable need for future investigations focusing on potentially hidden mite and tick species and addressing evolutionary mechanisms behind cryptic speciation within Acari.

The Ecology of Invasions by Animals and Plants

Abstract: Much as Rachel Carson's \"Silent Spring\" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic \"The Ecology of Invasions by Animals and Plants\" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. \"History has caught up with Charles Elton's foresight, and \"The Ecology of Invasions\" can now be seen as one of the central scientific books of our century.\"-David Quammen, from the Foreword to \"Killer Algae: The True Tale of a Biological Invasion\

A retrospective DNA marker assessment of the development of insect resistant soybean

Abstract: There has been limited success over the past 30 yr in the development of superior soybean cultivars [Glycine max (L.) Merr] with insect resistance. Success may be hampered by the quantitative nature of resistance and by linkage drag from resistant plant introduction (Pl) donor parents. Soybean insect resistance quantitative trait loci (SIR QTLs) have been identified from PI 229358 and PI 171451 by restriction fragment length polymorphism (RFLP) analysis. The objective of this study was to tag the SIR QTLs from PI 229358 with simple sequence repeat (SSR) markers and to determine the extent to which the SIR QTLs have been introgressed in registered cultivars, germplasm releases, or breeding lines that have resistance derived from this PI or from PI 171451. Marker analysis defined intervals by 5 centimorgans (cM) or less for a SIR QTL on linkage group D1b (SIR-D1b), and for SIR-G, SIR-H, and SIR-M. SIR QTLs were tracked through pedigrees by evaluating the inheritance of PI alleles at marker loci tightly linked to the QTLs during the phenotypic selection for insect resistance. It was inferred that at least 13 of the 15 SIR genotypes studied had introgressed SIR-M. PI genome introgression around SIR-M was measured to assess linkage drag. Some genotypes exhibited a dramatic reduction in the amount of linked PI genome, which likely occurred in response to phenotypic selection for agronomic performance as a means of reducing linkage drag. Only a few genotypes were inferred to possess SIR-G or SIR-H, and no genotypes possessed SIR-D1b. The results of this study indicate that marker-assisted selection for SIR QTLs is needed to introgress these loci into elite genetic backgrounds.

Fitness Costs of Insect Resistance to Bacillus thuringiensis

Abstract: Evolution of resistance by insect pests threatens the continued effectiveness of Bacillus thuringiensis (Bt) toxins in sprays and transgenic crops. Fitness costs of Bt resistance occur when, in the absence of Bt toxins, fitness is lower for resistant insects than for susceptible insects. Modeling results show that fitness costs can delay resistance by selecting against Bt-resistant genotypes in refuges where insects are not exposed to Bt toxins. In 77 studies including 18 species, fitness costs were detected in 62% of experiments testing for declines in resistance and in 34% of fitness component comparisons. Mean fitness costs were 15.5% for survival, 7.4% for development time, and 2.5% for mass. Although most fitness costs were recessive, nonrecessive costs can select more strongly against resistance. Because fitness costs vary with ecological conditions, refuges designed to increase the dominance or magnitude of fitness costs could be especially useful for delaying pest resistance.

Miscellaneous standard methods for Apis mellifera research

Abstract: SummaryA variety of methods are used in honey bee research and differ depending on the level at which the research is conducted. On an individual level, the handling of individual honey bees, including the queen, larvae and pupae are required. There are different methods for the immobilising, killing and storing as well as determining individual weight of bees. The precise timing of developmental stages is also an important aspect of sampling individuals for experiments. In order to investigate and manipulate functional processes in honey bees, e.g. memory formation and retrieval and gene expression, microinjection is often used. A method that is used by both researchers and beekeepers is the marking of queens that serves not only to help to locate her during her life, but also enables the dating of queens. Creating multiple queen colonies allows the beekeeper to maintain spare queens, increase brood production or ask questions related to reproduction. On colony level, very useful techniques are the measu...

Finding Evolutionary Processes Hidden in Cryptic Species

Abstract: Cryptic species could represent a substantial fraction of biodiversity. However, inconsistent definitions and taxonomic treatment of cryptic species prevent informed estimates of their contribution to biodiversity and impede our understanding of their evolutionary and ecological significance. We propose a conceptual framework that recognizes cryptic species based on their low levels of phenotypic (morphological) disparity relative to their degree of genetic differentiation and divergence times as compared with non-cryptic species. We discuss how application of a more rigorous definition of cryptic species in taxonomic practice will lead to more accurate estimates of their prevalence in nature, better understanding of their distribution patterns on the tree of life, and increased abilities to resolve the processes underlying their evolution.