Distribution and Genetic Variability of Bemisia tabaci Cryptic Species (Hemiptera: Aleyrodidae) in Italy

Coat protein is responsible for tomato leaf curl New Delhi virus pathogenicity in tomato

Tomato leaf curl New Delhi virus (ToLCNDV), a bipartite Begomovirus belonging to the family Geminiviridae, causes severe damage to many economically important crops worldwide. In the present study, pathogenicity of Asian (ToLCNDV-In from Pakistan) and Mediterranean isolates (ToLCNDV-ES from Italy) were examined using infectious clones in tomato plants. Only ToLCNDV-In could infect the three tomato cultivars, whereas ToLCNDV-ES could not. Genome-exchange of the two ToLCNDVs revealed the ToLCNDV DNA-A segment as the main factor for ToLCNDV infectivity in tomato. In addition, serial clones with chimeric ToLCNDV-In A and ToLCNDV-ES A genome segments were generated to identify the region determining viral infectivity in tomatoes. A chimeric clone carrying the ToLCNDV-In coat protein (CP) exhibited pathogenic adaptation in tomatoes, indicating that the CP of ToLCNDV is essential for its infectivity. Analyses of infectious clones carrying a single amino acid substitution revealed that amino acid at position 143 of the CP is critical for ToLCNDV infectivity in tomatoes. To better understand the molecular basis whereby CP function in pathogenicity, a yeast two-hybrid screen of a tomato cDNA library was performed using CPs as bait. The hybrid results showed different interactions between the two CPs and Ring finger protein 44-like in the tomato genome. The relative expression levels of upstream and downstream genes and Ring finger 44-like genes were measured using quantitative reverse transcription PCR (RT-qPCR) and compared to those of control plants. This is the first study to compare the biological features of the two ToLCNDV strains related to viral pathogenicity in the same host plant. Our results provide a foundation for elucidating the molecular mechanisms underlying ToLCNDV infection in tomatoes.

Evidence of the association between the Q2 mitochondrial group of Bemisia tabaci MED species (Hemiptera: Aleyrodidae) and low competitive displacement capability

The whitefly, Bemisia tabaci (Gennadius), is one of the most serious agricultural pests worldwide. Bemisia tabaci is a cryptic species complex of more than 40 species among which the invasive MEAM1 and MED species are the most widespread and economically important. Both MEAM1 and MED present intraspecific genetic variability and some haplotypes are reported to be more invasive than others. MED can be further deconstructed into different genetic groups, including MED-Q1 and MED-Q2. However, distinct biological phenotypes discerning the different MED mitochondrial haplotypes are yet to be characterized. Competitive displacement and life-history trials were carried out between MED-Q2 and MEAM1 populations collected in Florida, USA. In addition, a phylogenetic analysis was carried out including populations from previous whitefly competitive displacement studies for identification and comparison of the MED mitochondrial groups. In contrast to other studies with MED-Q1, the MED-Q2 population from Florida is less likely to displace MEAM1 on pepper. In addition, both pepper and watermelon were a more favorable host to MEAM1 compared to MED-Q2 according to the life history trials.

Dominance of Asia II 1 species of Bemisia tabaci in Pakistan and beyond

Globally, Whitefly (Bemisia tabaci) is one of the most important insect pests of crops that causes huge economical losses. The current study was designed to exclusively screen the B. tabaci species in the cotton field of Pakistan during 2017-2020 and have to conduct comparative analysis of B. tabaci species in Asia where Asia II 1 has been reported. A total of 5142 B. tabaci sequences of mitochondrial cytochrome oxidase 1 (mtCO1) from Asian countries were analyzed to determine the species and their distribution in the region. Our analysis over time and space showed that Asia II 1 has gradually dominated over Asia 1 in Punjab Province and over both Asia 1 and MEAM1 in Sindh Province. Asia has been divided into three regions i.e., South Asia (2524 sequences), Southeast Asia (757 sequences) and East Asia (1569 sequences) and dominance of different species of B. tabaci has been determined by calculating the relative percentage of each species. Interestingly, Asia II 1 has been found dominant in the neighboring region (northern zone) of India and also being dominant in its central zone. The dominance of Asia II 1 in Pakistan and northern India explains whitefly epidemic being reported in recent years.