Microbiome diversity and composition in Bemisia tabaci SSA1-SG1 whitefly are influenced by their host’s life stage

Within the Bemisia tabaci group of cryptic whitefly species, many are damaging agricultural pests and plant-virus vectors, conferring upon this group the status of one of the world’s top 100 most invasive and damaging ‘species’ that affect farmers’ income and livelihoods. Studies on the microbiome of whitefly life stages are scarce, although their composition and diversity greatly influence whitefly fitness and development. We used high-throughput sequencing to understand microbiome diversity in different developmental stages of the B. tabaci sub-Saharan Africa 1 (SSA1-SG1) species of the whitefly from Uganda. Endosymbionts (Portiera, Arsenophonus, Wolbachia and Hemipteriphilus were detected but excluded from the further statistical analysis as they were not influenced by life stage using( Permutational Multivariate Analysis of Variance Using Distance Matrices, (ADONIS, p= 0.925 and Bray, p = 0.903). Our results showed significant differences in the microbiome composition in different life stages of SSA1-SG1. The diversity was significantly higher in eggs (Shannon, p = 0.024; Simpson, p = 0.047) than that in nymphs and pupae, while the number of microbial species observed by the amplicon sequence variant (ASV) was not significant (n(ASV), p = 0.094). At the phylum and genus levels, the dominant constituents in the microbiome changed significantly at different developmental stages, with Halomonas being an egg-associated genus while Bacillus and Caldalkalibacillus were common in all life stages. These findings provide the first description of differing microbiome diversity in the life stage of whiteflies, suggesting their putative role in whitefly development

What has changed in the outbreaking populations of the severe crop pest whitefly species in cassava in two decades?

High populations of African cassava whitefly (Bemisia tabaci) have been associated with epidemics of two viral diseases in Eastern Africa. We investigated population dynamics and genetic patterns by comparing whiteflies collected on cassava in 1997, during the first whitefly upsurges in Uganda, with collections made in 2017 from the same locations. Nuclear markers and mtCOI barcoding sequences were used on 662 samples. The composition of the SSA1 population changed significantly over the 20-year period with the SSA1-SG2 percentage increasing from 0.9 to 48.6%. SSA1-SG1 and SSA1-SG2 clearly interbreed, confirming that they are a single biological species called SSA1. The whitefly species composition changed: in 1997, SSA1, SSA2 and B. afer were present; in 2017, no SSA2 was found. These data and those of other publications do not support the ‘invader’ hypothesis. Our evidence shows that no new species or new population were found in 20 years, instead, the distribution of already present genetic clusters composing SSA1 species have changed over time and that this may be in response to several factors including the introduction of new cassava varieties or climate changes. The practical implications are that cassava genotypes possessing both whitefly and disease resistances are needed urgently

Increasing the throughput of HARQ via multi-packet transmission

International audienc

Influence of Culture Media and Environmental Factors (Water Potential and Temperature) on Mycelial Growth of Phytopythium vexans (de Bary), the Causal Agent of Dieback Disease in Apple Trees

This study aimed at evaluating the effects of culture media and environmental factors (temperature and water potential (Ψw)) on the growth of the pathogenic fungus Phytopythium vexans (de Bary) associated with root rot and dieback disease in apple trees. Tomato agar, potato dextrose agar (PDA), and soybean agar were the most favourable for rapid mycelial growth, with optimum growth recorded for PDA medium. To determine the environmental conditions that promoted the development of this phytopathogen, the effects of temperature (5–30 °C), water potential (Ψw) (−15.54; −0.67 MPa) (0.89–0.995 aw), and their interaction were evaluated on the in vitro radial growth rates of the five isolates of P. vexans and on their latency phase (time period prior to growth). The results of this study showed that temperature, water potential, and their interaction had significant effects (p < 0.001) on the radial growth rates and latency phases of all tested P. vexans isolates. All isolates were able to grow throughout the temperature range (5 to 30 °C), with the maximum radial growth rate being observed at the highest temperatures, 25–30 °C. Growth was seen to be faster at −0.67 MPa (0.995 aw) at 25 °C and 30 °C. No growth was observed at Ψw < −5.44 MPa (0.96 aw), regardless of the temperature. It was found that the length of the latency phase depended significantly on both environmental factors. The longest latency phases (5 days on average) were recorded at a temperature of 5 °C and Ψw of −0.67 MPa (0.995 aw) and −2.69 MPa (0.98 aw), while the shortest latency phases were observed at a temperature of 30 °C and a Ψw of −0.67 MPa (0.995 aw), with an average of 0.2 days. The findings from this study could help to understand the impact of these environmental factors on the occurrence of diseases caused by P. vexans and more likely to design a reliable preventive control strategy based on the avoidance of conditions that play in favour of the phytopathogen

Multi-packet Hybrid ARQ: Closing gap to the ergodic capacity

International audienceIn this work we consider incremental redundancy (IR) hybrid automatic repeat request (HARQ), where transmission rounds are carried out over independent block-fading channels. We propose the so-called multi-packet HARQ where the transmitter allows different packets to share the same channel block. In this way the resources (block) are optimally assigned throughout the transmission rounds. This stands in contrast with the conventional HARQ, where each transmission round occupies the entire block. We analyze superposition coding and time-sharing transmission strategies and we optimize the parameters to maximize the throughput. Besides the conventional one-bit feedback (ACK/NACK) we also consider the rich, multi-bit feedback. To solve the optimization problem we formulate it as a Markov decision process (MDP) problem where the decisions are taken using accumulated mutual information (AMI) obtained from the receiver via delayed feedback. When only one-bit feedback is used to inform the transmitter about the decoding success/failure (ACK/NACK), the Partial State Information Markov Decision Process (PSI-MDP) framework is used to obtain the optimal policies. Numerical examples obtained in a Rayleigh-fading channel indicate that, the proposed multi-packet HARQ outperforms the conventional one, by more than 5 dB for high spectral efficiencies