Incidence of Citrus Tristeza Virus and its Vector Toxoptera citricida in Different Parts of Assam and Nagaland, India

A field survey was conducted in 2018 to study the incidence of citrus tristeza virus (CTV) and its aphid vectors, in different citrus growing regions of the states of Assam and Nagaland, India. Leaf samples of Assam lemon (Citrus limon) and Khasi mandarin (Citrus reticulata) were collected from four districts of Assam (Jorhat, Tinsukia, Sivasagar and Golaghat) and two districts of Nagaland (Mokokchung and Wokha). Citrus leaf samples were collected from a total of 190 citrus plants and were used for detection of CTV infection through Double Antibody Sandwich-Enzyme linked Immuno-Sorbent Assay (DAS-ELISA). According to the results, 75 per cent CTV disease incidence was detected in surveyed areas of Assam and 24.55 per cent CTV disease incidence was detected in surveyed areas of Nagaland. District wise, the highest CTV disease incidence (96.67 %) was detected in Tinsukia district of Assam and the lowest (21.43 %) was detected in Mokokchung district of Nagaland. Aphid samples were also collected during the survey and the presence of the vector Toxoptera citricida, in all the locations was determined.

Numerical and Species Composition of Insects Transmitting Viral Infection in North Ossetia

One of the major tasks in the production of original and elite potato seeds is to prevent the rapid re-infection of the healthy material with viruses in the open field. The high rate of infection with each subsequent reproduction reduces seed productivity and worsens the tuber varietal quality. Currently, about two dozen viruses that infect potatoes have been identified. In the field, most of the harmful viruses of potatoes are transmitted by insects such as aphids, cicadas and bedbugs. The purpose of our research was to study the species composition of transmitters and the intensity of their flight in North Ossetia. Studying the activity of the winged aphid vector is a prerequisite for the implementation of protective measures against re-infection of the sanitized material with viruses. The most important criteria characterizing aphids in transferring potato viruses during the growing season were as follows: the species composition, the dynamics of the potato planting periods, the timing of the critical threshold with regards to the number of aphids, and the total vector intensity during the growing season. There are very few aphid vectors in the mountain zone of the Republic of North Ossetia, which is at and above an altitude of 1,650 meters above sea level. Therefore, mountain regions of this height are a natural insulator against viral infection. In the foothill zone, the most numerous aphid vectors are bean, buckthorn, and alder buckthorn-willowherb aphids, whose number varies from 35 to 280 individuals per year on a Merike trap. Keywords: potatoes, insect vectors, a Merike trap, mountain zone, spatial isolation

Plum pox virus (Sharka).

Plum pox virus disease (Sharka) is one of the most destructive diseases of stone fruits. The causal agent, Plum pox virus (PPV) is easily transmitted by many aphid species in a non-persistent manner, by manmade grafting (nursery trade), and has a very wide host range among Prunus species. Infected plants may not show symptoms for several months and symptoms are often transient in appearance. The disease symptoms are often mistaken for other maladies and the virus can become established before the first recognition of the disease. Although spread is difficult to control within a local area because of aphid vectors, the long distance spread can be controlled by strict quarantine regulations and use of virus-free certified nursery stock.

Temporal and spatial progress of Cowpea aphid-borne mosaic virus (CABMV) in passion fruit (Passiflora edulis Sims)

Among the diseases that affect passion fruit, those causing fruit woodiness is considered the most important. Cowpea aphid-borne mosaic virus (CABMV) is an important vírus that is transmitted by several aphid species during the bite, making the use of insecticides infeasible to control these vectors. In order to understand the epidemiological behavior of the disease, this study aimed to study the temporal progress and spatial pattern of CABMV in the field. Healthy seedlings of passion fruit with 2.0 meters height were implanted in the field condition at the experimental station of the IDR-Paraná, Brazil. The evaluations were performed weekly observing the symptoms of blister, mosaic, chlorosis and crinkled leaves. For the analyses, the logistic, gompertz and monomolecular models were adjusted to CABMV incidence data in passion fruit. The spatial pattern of the disease was characterized by the dispersion index and Taylor's Power Law. The logistic model was the one that best described the progress in the incidence of the disease. The incidence progress rate of CABMV was 0.037, 0.077 and 0.060 % day-1. At the beginning of the epidemic, the pattern was random. The initial dispersion mechanism was occured through aphid vectors, como Aphis gossypii Glover, Aphis fabae Scopoli, Aphis solanella Theobald, Toxoptera citricida Kilkaldy, Uroleucon ambrosiae Thomas and Uroleucon sonchi L. infected with CABMV that starts its test bite randomly. The pattern of disease dispersion began to be added when the incidence of plants reached 10 and 7%, in the 2015/16 and 2017/18 harvests, respectively. The random spatial pattern suggested that infected aphids enter several points of the orchard and infected plants become a source for secondary infections, characterizing aggregate pattern. Thus, the eradication of alternative hosts abroad can be adopted as management strategies of CABMV

Interspecific interactions within a vector-borne complex are influenced by a co-occurring pathosystem

Potato virus Y (PVY) and zebra chip (ZC) disease are major threats to solanaceous crop production in North America. PVY can be spread by aphid vectors and through vegetative propagation in potatoes. ZC is associated with “Candidatus Liberibacter solanacearum” (Lso), which is transmitted by the tomato/potato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae). As these two pathosystems may co-occur, we studied whether the presence of one virus strain, PVY°, affected the host preference, oviposition, and egg hatch rate of Lso-free or Lso-carrying psyllids in tomato plants. We also examined whether PVY infection influenced Lso transmission success by psyllids, Lso titer and plant chemistry (amino acids, sugars, and phytohormones). Lso-carrying psyllids showed a preference toward healthy hosts, whereas the Lso-free psyllids preferentially settled on the PVY-infected tomatoes. Oviposition of the Lso-carrying psyllids was lower on PVY-infected than healthy tomatoes, but Lso transmission, titer, and psyllid egg hatch were not significantly affected by PVY. The induction of salicylic acid and its related responses, and not nutritional losses, may explain the reduced attractiveness of the PVY-infected host to the Lso-carrying psyllids. Although our study demonstrated that pre-existing PVY infection can reduce oviposition by the Lso-carrying vector, the preference of the Lso-carrying psyllids to settle on healthy hosts could contribute to Lso spread to healthy plants in the presence of PVY infection in a field.