Effect of time of harvesting and disease resistance in reducing Cassava (Manihot esculenta Crantz) yield losses by two viral diseases

Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic constraints for cassava (Manihot esculenta Crantz) production in Eastern and Southern Africa. CMD causes a general decline in yield in affected plants of susceptible cassava varieties but CBSD causes rotting of edible roots. Delayed harvesting can increase rotting of roots and making them unfit for consumption or marketing, and thus affecting the livelihoods of poor farmers. This study investigated the effect of interaction between time of harvesting and levels of disease resistance to identify ideal harvesting times for reducing yield losses. The resistant cassava variety Namikonga remained in the field for the duration of the study, up to 24 months after planting without incurring significant yield losses, while the tolerant varieties Kiroba and Kizimbani could only be maintained up to 21 months. Susceptible varieties Mreteta and Albert suffered significant yield losses beyond 15 months. Among the varieties, Kizimbani had the least CBSD and CMD foliar symptoms as well as farmer desirable traits including high root weight, quantity of marketable roots and dry matter content. Harvesting of cassava can depend on the resistance or susceptibility of the varieties grown. Therefore, the above harvesting times for different varieties were recommended for minimizing yield losses due to the diseases and thus maximizing yields to the farmers

Heavily glycosylated, highly fit SIVMne variants continue to diversify and undergo selection after transmission to a new host and they elicit early antibody dependent cellular responses but delayed neutralizing antibody responses

<p>Abstract</p> <p>Background</p> <p>Lentiviruses such as human and simian immunodeficiency viruses (HIV and SIV) undergo continual evolution in the host. Previous studies showed that the late-stage variants of SIV that evolve in one host replicate to significantly higher levels when transmitted to a new host. However, it is unknown whether HIVs or SIVs that have higher replication fitness are more genetically stable upon transmission to a new host. To begin to address this, we analyzed the <it>envelope </it>sequence variation of viruses that evolved in animals infected with variants of SIVMne that had been cloned from an index animal at different stages of infection.</p> <p>Results</p> <p>We found that there was more evolution of <it>envelope </it>sequences from animals infected with the late-stage, highly replicating variants than in animals infected with the early-stage, lower replicating variant, despite the fact that the late virus had already diversified considerably from the early virus in the first host, prior to transmission. Many of the changes led to the addition or shift in potential-glycosylation sites-, and surprisingly, these changes emerged in some cases prior to the detection of neutralizing antibody responses, suggesting that other selection mechanisms may be important in driving virus evolution. Interestingly, these changes occurred after the development of antibody whose anti-viral function is dependent on Fc-Fcγ receptor interactions.</p> <p>Conclusion</p> <p>SIV variants that had achieved high replication fitness and escape from neutralizing antibodies in one host continued to evolve upon transmission to a new host. Selection for viral variants with glycosylation and other envelope changes may have been driven by both neutralizing and Fcγ receptor-mediated antibody activities.</p

Quasi-Two-Dimensional Fermi Surfaces and Coherent Interlayer Transport in KFe2_2As2_2

We report the results of the angular-dependent magnetoresistance oscillations (AMROs), which can determine the shape of bulk Fermi surfaces in quasi-two-dimensional (Q2D) systems, in a highly hole-doped Fe-based superconductor KFe$_2$As$_2$ with $T_c \approx$ 3.7 K. From the AMROs, we determined the two Q2D FSs with rounded-square cross sections, corresponding to 12% and 17% of the first Brillouin zone. The rounded-squared shape of the FS cross section is also confirmed by the analyses of the interlayer transport under in-plane fields. From the obtained FS shape, we infer the character of the 3d orbitals that contribute to the FSs.Comment: 4 pages, 4 figures, accepted in Phys. Rev. Let

High-Pressure Electrical Resistivity Measurements of EuFe2As2 Single Crystals

High-pressure electrical resistivity measurements up to 3.0GPa have been performed on EuFe2As2 single crystals with residual resistivity ratios RRR=7 and 15. At ambient pressure, a magnetic / structural transition related to FeAs-layers is observed at T0 =190K and 194K for samples with RRR=7 and 15, respectively. Application of hydrostatic pressure suppresses T0, and then induces similar superconducting behavior in the samples with different RRR values. However, the critical pressure 2.7GPa, where T0=0, for the samples with RRR=15 is slightly but distinctly larger than 2.5GPa for the samples with RRR=7.Comment: To be published in J. Phys.: Conf. Se

The Competition between Staggered Field and Antiferromagnetic Interactions in Cugeo3:Fe

The EPR spectra along different crystallographic axes for single crystals of CuGeO3 containing 1% of Fe impurity have been studied in the frequency range 60-360 GHz at temperatures 0.5-30 K. The analysis based on the Oshikawa-Affleck (OA) theory suggests that the temperature dependences of the line width and g-factor are formed as a result of the competition between interchain antiferromagnetic interactions and staggered Zeeman energy. It is found that staggered magnetic moments in CuGeO3:Fe are located predominantly along b axis.Comment: 9 pages, 4 figures; submitted to QSS04 symposiu

Quantum oscillations in a centrosymmetric skyrmion-hosting magnet GdRu2Si2

We have performed magnetic torque and resistivity measurements on a centrosymmetric skyrmion-host GdRu2Si2, in which the dominant magnetic interaction leading to skyrmion formation is under debate. We observe both the de Haas-van Alphen and Shubnikov-de Haas oscillations in the forced ferromagnetic phase. The angular dependence of the quantum oscillation frequencies can be reproduced by the ab-initio calculation. The de Haas-van Alphen oscillation is also observed in the double-Q phase with a different frequency to that in the forced ferromagnetic phase, indicating a Fermi surface reconstruction due to the coupling between localized spins and conduction electrons. Based on these experimental findings, the magnetic interactions in this system are discussed.Comment: 11 pages, 8 figure

Developing dual-resistant cassava to the two major viral diseases

Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are the two important biotic constraints affecting cassava production in sub-Saharan Africa (SSA). Deployment of cassava varieties dually resistant to both diseases is the most effective and realistic way of reducing losses to African farmers. Crosses were carried out between the Tanzanian local cassava variety Namikonga (CBSD resistant/CMD susceptible) with an introduced cassava germplasm AR37-80 (CBSD susceptible/CMD resistant) from South America to develop dually resistant F1 progenies and they were evaluated for 2 seasons at Naliendele in Southern Tanzania which is a CMD and CBSD hotspot area. CMD-resistant progenies had low foliar severities (≤ 1.8 on a five-point scale) similar to CMD resistant parent. CBSD resistant progenies had minimal foliar severity (≤2.0) and root necrosis (≤1.2) similar to the CBSD resistant parent while CBSD tolerant progenies had severe foliar severity of up to 3.3 but minimal root severity (≤ 1.2). Traits with minimal environmental influence also had high heritability (≥0.65) and high selection accuracy (≥0.70) and they included CMD foliar symptoms, CBSD foliar symptoms at 6 MAP, root necrosis, root necrosis incidence, root weight, root number per plant, and harvest index. Correlation analysis showed that the presence of diseases reduces usable roots, root weight, root number per plant, and harvest index. Dual resistance can improve yield as observed in the progenies, Namar 050 and Namar 371 which had high root weights of 27.5 t/ha and 28.2 t/ha with high genetic gains of 56.1% and 58.5%, respectively. Dual resistant progenies identified were Namar 050, Namar 100, Namar 130, Namar 200, Namar 334, Namar 371, and Namar 479 as they had minimal CMD and CBSD symptoms severity (≤ 2.0) and could be used for breeding cassava varieties with superior characteristics