Cost of resistance: relationship between reduced fertility and increased resistance in a snail—schistosome host—parasite system

Natural host populations often exhibit genetic variability in resistance to parasitism. One possible mechanism for maintaining such diversity is a trade-off between fitness costs associated with resistance and fitness costs associated with parasitism. However, little is known about the nature or magnitude of these costs in animal populations. Using artificial selection experiments in a Biomphalaria glabrata–Schistosoma mansoni host–parasite system, we demonstrated that resistance and susceptibility to infection are heritable. We then investigated whether resistance had any associated costs in terms of snail reproductive success. Susceptible-selected snail lines showed significantly higher fertility (number of offspring produced) than resistant-selected or unselected control snail lines, irrespective of current infection status. There were no consistent differences between snail lines in fecundity, proportion of abnormal egg masses produced, or mean number of eggs per egg mass. Mortality rate was higher among infected than uninfected snails. These results are consistent with snails incurring costs of resistance to schistosome infection in the absence of the parasite.     

Eyespot resistance gene Pch-1 from Aegilops ventricosa is associated with a different chromosome in wheat line H-93-70 than the resistance factor in “Roazon” wheat

Summary The hexaploid wheat line H-93-70 carries a gene (Pch-1) that has been transferred from the wild grass Aegilops ventricosa and confers a high degree of resistance to eyespot diesease, caused by the fungus Pseudocercosporella herpotrichoides. Crosses of the resistant line H-93-70 with the susceptible wheat Pané 247 and with a 7D/7Ag wheat/Agropyron substitution line were carried out and F2 kernels were obtained. The kernels were cut transversally and the halves carrying the embryos were used for the resistance test, while the distal halves were used for genetic typing. Biochemical markers were used to discriminate whether the transferred Pch-1 gene was located in chromosome 7D, as is the case for a resistance factor present in Roazon wheat. In the crosses involving Pané 247, resistance was not associated with the 7D locus Pln, which determines sterol ester pattern (dominant allele in H-93-70). In the crosses with the 7D/7Ag substitution line, resistance was neither associated with protein NGE-11 (7D marker), nor alternatively inherited with respect to protein C-7 (7Ag marker). It is concluded that gene Pch-1 represents a different locus and is not an allele of the resistance factor in Roazon wheat.     

Identification of a new QTL for <Emphasis Type="Italic">Fusarium</Emphasis> head blight resistance in the wheat genotype “Wang shui-bai”

Fusarium head blight (FHB) is one of the most devastating wheat diseases, causing both yield loss and quality reduction. To detect quantitative trait loci (QTL) responsible for FHB resistance, plants of the F _2:3 population derived from a ‘Wangshui-bai’ × ‘Sy95-7’ cross were artificially inoculated. Of 396 simple sequence repeats (SSRs), 125 amplified fragment length polymorphisms were used for FHB resistance QTL analysis. Five QTLs for FHB resistance were detected on chromosomes 3B, 6B, 7A, 1B and 2D. The effect of the QTL located on chromosome 3B on phenotypic variation was 31.69%, while that of the QTL found on 2D was the smallest and only accounted for 4.98% of the variation. The resistance alleles originated from ‘Wangshibai’ and association of the QTLs using these SSR markers may facilitate marker-assisted selection to improve FHB resistance in the wheat breeding programs of southwest China.     

Quantitative and qualitative evaluation of selected wheat varieties released since 1903 to increasing atmospheric carbon dioxide: can yield sensitivity to carbon dioxide be a factor in wheat performance?

The sensitivity of yield and quality parameters to carbon dioxide concentration [CO₂] was determined for individual lines of hard‐red spring wheat released in 1903, 1921, 1965 and 1996. All cultivars were evaluated with respect to growth and vegetative characteristics, grain yield and nutritional quality in response to [CO₂] increases that corresponded roughly to the CO₂ concentrations at the beginning of the 20th century, the current [CO₂], and the future projected [CO₂] for the end of the 21st century, respectively. Leaf area ratio (cm² g^?1) declined and net assimilation rate (g m² day^?1) increased in response to increasing [CO₂] for all cultivars during early vegetative growth. By maturity, vegetative growth of all cultivars significantly increased with the increase in [CO₂]. Seed yield increased significantly as [CO₂] increased, with yield sensitivity to rising [CO₂] inversely proportional to the year of cultivar release. Greater [CO₂] yield sensitivity in older cultivars was associated with whole‐plant characteristics such as increased tillering and panicle formation. Grain and flour protein, however, declined significantly with increasing [CO₂] and with year of release for all cultivars, although absolute values were higher for the older cultivars. Overall, these data indicate that yield response at the whole‐plant level to recent and projected increases in [CO₂] has declined with the release of newer cultivars, as has protein content of grain and flour. However, if agronomic practice can be adapted to maximize individual plant performance, [CO₂] responsive characteristics of older cultivars could, potentially, be incorporated as factors in future wheat selection.     

Babjevia gen. nov. — a new genus of the Lipomycetaceae

The species described asLipomyces anomalus Babjeva & Gorin shows significant genetic and phenotypic divergence from the type speciesLipomyces starkeyi Lodder & Kreger-van Rij in terms of rRNA base sequence substitution and ascosporal and septal ultrastructure. The species is consequently reclassified in the new, unispecific genusBabjevia, asBabjevia anomala.     

Translation attenuation regulation of chloramphenicol resistance in bacteria — a review

The chloramphenicol (Cm)-inducible cat and cmlA genes are regulated by translation attenuation, a regulatory device that modulates mRNA translation. In this form of gene regulation, translation of the Cm^R coding sequence is prevented by mRNA secondary structure that sequesters its ribosome-binding site (RBS). A translated leader of nine codons precedes the secondary structure, and induction results when a ribosome becomes stalled at a specific site in the leader. Here we demonstrate that the site of ribosome stalling in the leader is selected by a cis effect of the nascent leader peptide on its translating ribosome.     

Four Cases of Syncarpy or ‘Double-Capsules’ in a Population of Bryum atropurpureum W. & M.

Abstract

Four cases of syncarpy are described from a single population of Bryum atropurpureum W. & M. A short discussion follows concerning the way in which this type of abnormality may arise, and it is suggested that an early cleavage in the young sporophyte affords the most reasonable explanation. The cases described are briefly compared with others that have been reported in the literature. Several species, belonging to unrelated genera, are instanced in this connexion.     

Recent attestations of “new” glume wheat in Turkey: a reassessment of its role in the reconstruction of Neolithic agriculture

Vegetation History and Archaeobotany - Studies of the origins of agriculture in the Near East have revealed that the eight plant species known as “Founder Crops”, i.e. emmer, einkorn,...     

Accumulation of apoplastic iron in plant roots : a factor in the resistance of soybeans to iron-deficiency induced chlorosis?

We hypothesized that the resistance of Hawkeye (HA) soybean (Glycine max L.) to iron-deficiency induced chlorosis (IDC) is correlated to an ability to accumulate a large pool of extracellular-root iron which can be mobilized to shoots as the plants become iron deficient. Iron in the root apoplast was assayed after efflux from the roots of intact plants in nutrient solution treated with sodium dithionite added under anaerobic conditions. Young seedlings of HA soybean accumulated a significantly larger amount of extracellular iron in their roots than did either IDC-susceptible PI-54619 (PI) soybean or IDC-resistant IS-8001 (IS) sunflower (Helianthus annus L.). Concurrently, HA soybean had much higher concentrations of iron in their shoots than either PI soybean or IS sunflower. The concentration of iron in the root apoplast and in shoots of HA soybean decreased sharply within days after the first measurements of extracellular root iron were made, in both +Fe and −Fe treatments. The accumulation of short-term iron reserves in the root apoplast and translocation of iron in large quantities to the shoot may be important characteristics of IDC resistance in soybeans.