Discovery of a seventh <Emphasis Type="Italic">Rpp</Emphasis> soybean rust resistance locus in soybean accession PI 605823

Key message

A novel Rpp gene from PI 605823 for resistance to Phakopsora pachyrhizi was mapped on chromosome 19.

Abstract

Soybean rust, caused by the obligate biotrophic fungal pathogen Phakopsora pachyrhizi Syd. & P. Syd, is a disease threat to soybean production in regions of the world with mild winters. Host plant resistance conditioned by resistance to P. pachyrhizi (Rpp) genes has been found in numerous soybean accessions, and at least 10 Rpp genes or alleles have been mapped to six genetic loci. Identifying additional disease-resistance genes will facilitate development of soybean cultivars with durable resistance. PI 605823, a plant introduction from Vietnam, was previously identified as resistant to US populations of P. pachyrhizi in greenhouse and field trials. In this study, bulked segregant analysis using an F₂ population derived from ‘Williams 82’ × PI 605823 identified a genomic region associated with resistance to P. pachyrhizi isolate GA12, which had been collected in the US State of Georgia in 2012. To further map the resistance locus, linkage mapping was carried out using single-nucleotide polymorphism markers and phenotypic data from greenhouse assays with an F_2:3 population derived from Williams 82 × PI 605823 and an F_4:5 population derived from ‘5601T’ × PI 605823. A novel resistance gene, Rpp7, was mapped to a 154-kb interval (Gm19: 39,462,291–39,616,643 Glyma.Wm82.a2) on chromosome 19 that is different from the genomic locations of any previously reported Rpp genes. This new gene could be incorporated into elite breeding lines to help provide more durable resistance to soybean rust.

     

Construction of a BAC Library for a Defoliating Insect-Resistant Soybean and Identification of Candidate Clones Using a Novel Approach

Positional cloning of an insect-resistance quantitative trait locus (QTL) requires the construction of a large-insert genomic DNA library from insect-resistant genotypes. To facilitate cloning of a major defoliating insect-resistance QTL on linkage group M of the soybean genetic map, a bacterial artificial chromosome (BAC) library for PI 229358 was constructed and characterized. The HindIII BAC library contains 55,296 clones with an average insert size 131 kb. This library represents a 6-fold soybean haploid genome equivalents, allowing a 99.8% probability of recovering any specific sequence of interest in soybean. BAC filters were screened with a genomic DNA probe Sat_258sc2 obtained through genome walking from flanking sequences of a simple sequence repeat (SSR) marker, Sat_258, which links to the insect-resistance QTL. Thirteen BAC clones were identified positive for Sat_258sc2, and two of them were confirmed to carry Sat_258. The results suggest that this library is useful in positional cloning of the major insect-resistance QTL, and the approach presented here can be used to screen a BAC library for a SSR marker without requiring the creation of BAC pools.     

Broadcasting in the airways: the fifth anniversary of the Radiation Research Podcast (1)

The Radiation Research Podcast was funded just over five years ago by a few Radiation Research Society members. To date, the volunteers running the podcast have produced and published online, open access, over 70 audio interviews. The program includes monthly interviews with authors of articles, award winners, and other recordings at conferences, such as round table discussions. We here present an overview of the podcast, from its creation to its fifth birthday, to explain how it is working, how the featured interviews are scheduled, and what future directions are taken. So, stay tuned!     

Penetration and Development of Meloidogyne incognita on Roots of Resistant Soybean Genotypes

Meloidogyne incognita penetration and development were studied in roots of highly resistant (PI 96354, PI 417444), resistant (Forrest), and susceptible (Bossier) soybean genotypes. Although more second-stage juveniles (J2) had penetrated roots of PI 96354 and PI 417444 than roots of Forrest and Bossier by 2 days after inoculation, fewer J2 were present in roots of PI 96354 at 4 days after inoculation. Juvenile development in all genotypes was evident by 6 days after inoculation, with the highest number of swollen J2 present in roots of Bossier. At 16 days after inoculation, roots of PI 96354 had 87%, 74%, and 53% fewer J2 than were present in roots of Bossier, Forrest, and PI 417444, respectively. Differential emigration of J2, not fewer invasion sites, was responsible for the low number of nematodes in roots of the highly resistant PI 96354. Some 72% of the J2 penetrating the roots of this genotype emerged within 5 days after inoculation, whereas 4%, 54%, and 83% emerged from roots of Bossier, Forrest, and PI 417444, respectively. Penetration of roots of PI 96354 decreased the ability of J2 emerging from these roots to infect other soybean roots.     

Tolerance to Heterodera glycines in Soybean

Fifty-four susceptible soybean, Glycine max, cultivars or plant introductions were evaluated for tolerance to H. glycines, the soybean cyst nematode (SCN). Seed yields of genotypes were compared in nematicide-treated (1,2-dibromo-3-chloropropane, 58 kg a.i./ha) and nontreated plots at two SCN-infested locations over 3 years. Distinct and consistent levels of tolerance to SCN were observed among soybean genotypes. PI 97100, an introduction from Korea, exhibited the highest level of tolerance with an average tolerance index ([yield in nontreated plot ÷ yield in nematicide-treated plot] × 100) of 96 over 2 years. Coker 156 and Wright had moderate levels of tolerance (range in index values 68 to 95) compared to the intolerant cuhivars Bragg and Coker 237 (range in index values 33 to 68). Most of the soybean genotypes evaluated were intolerant to SCN. The rankings of five genotypes for tolerance to SCN and Hoplolaimus columbus were similar. Tolerance for seed yield was more consistently correlated with tolerance for plant height (r = 0.55 to 0.64) than for seed weight (r = 0.23 to 0.65) among genotypes.     

The association between HIV and fertility in a cohort study in rural Tanzania

Recent studies in sub-Saharan Africa have shown that fertility is reduced among HIV-infected women compared with uninfected women. The size and pattern of this fertility reduction has important implications for antenatal clinic-based surveillance of the epidemic and also for estimates and projections of the demographic impact of the epidemic. This paper examines the association between HIV and fertility in Kisesa, a rural area in Tanzania, where HIV prevalence among adults is about 6% and gradually increasing. The analysis is based on data obtained through a demographic surveillance system in Kisesa during 1994-98 and two large sero-surveys of all residents in 1994-95 and 1996-97. The HIV-associated fertility reduction among women was investigated by estimating fertility rates by HIV status and prevalence rates by fertility status. A substantial reduction (29%) was observed in fertility among HIV-infected women compared with HIV-uninfected women. The fertility reduction was most pronounced during the terminal stages of infection, but no clear association with duration of infection was observed. Use of modern contraception was higher among HIV-infected women. However, both among contracepting and non-contracepting women, a substantial reduction in fertility was seen among HIV-infected women.     

Genetic transformation, recovery, and characterization of fertile soybean transgenic for a synthetic Bacillus thuringiensis cryIAc gene.

Somatic embryos of jack, a Glycine max (L.) Merrill cultivar, were transformed using microprojectile bombardment with a synthetic Bacillus thuringiensis insecticidal crystal protein gene (Bt cryIAc) driven by the 35S promoter and linked to the HPH gene. Approximately 10 g of tissue was bombarded, and three transgenic lines were selected on hygromycin-containing media and converted into plants. The recovered lines contained the HPH gene, but the Bt gene was lost in one line. The plasmid was rearranged in the second line, and the third line had two copies, one of which was rear-ranged. The CryIAc protein accumulated up to 46 ng mg-1 extractable protein. In detached-leaf bioassays, plants with an intact copy of the Bt gene, and to a lesser extent those with the rearranged copy, were protected from damage from corn earworm (Helicoverpa zea), soybean looper (Pseudoplusia includens), tobacco budworm (Heliothis virescens), and velvetbean caterpillar (Anticarsia gemmatalis). Corn earworm produced less than 3% defoliation on transgenic plants, compared with 20% on the lepidopteran-resistant breeding line GatIR81-296, and more than 40% on susceptible cultivars. Unlike previous reports of soybean transformation using this technique, all plants were fertile. To our knowledge, this is the first report of a soybean transgenic for a highly expressed insecticidal gene.     

Cardiovascular effects after low-dose exposure and radiotherapy: what research is needed?

The authors of this report met at the Head Quarter of the International Atomic Energy Agency (IAEA) in Vienna, Austria, on 2–4 July 2012, for intensive discussions of an abundance of original publications on new epidemiological studies on cardiovascular effects after low-dose exposure and radiotherapy and radiobiological experiments as well as several comprehensive reviews that were published since the previous meeting by experts sponsored by the IAEA in June 2006. The data necessitated a re-evaluation of the situation with special emphasis on the consequences current experimental and clinical data may have for clinical oncology/radiotherapy and radiobiological research. The authors jointly arrived at the conclusions and recommendations presented here.