By: Hector Garcia O., Co-Founder and General Manager of Laboratorios Diagnofruit Ltda, SOCHIFIT and AMICH Member. [email protected]
Viruses have certainly changed the way we view them since last season. SARS-CoV-2, the virus that caused the COVID-19 pandemic and nearly 37,000 confirmed deaths in our country to date (25 Sep 2021, MINSAL/DEIS) We are still waiting for a new wave. This has not only affected the population in the unfortunate events reported, it has also had a great impact on the economy and we will continue to experience its consequences in the coming months.
In our industry, this virus, from the beginning, put the export process in check due to possible contamination of products, packaging, etc., which could be "vectors" of the disease; despite the advances in epidemiological knowledge, there are still situations based on this risk; recently a detection of New Zealand kiwi tests positive for virus, generating questions and eventually difficulties in the marketing process. Beyond COVID-19 and its global consequences that we cannot ignore, we have a situation at the local level, which is added, and which will keep us busy this season and the coming ones, due to the quarantine implications of this with China. Its name: Prunus Necrotic RingSpot Virus (PNRSV), which we will discuss and give some keys to successfully overcome the season, in a short question and answer exercise.
What is PNRSV?
PNRSV is a pathogen of ancient description, the first antecedents date back to the 1930s, therefore it is an old acquaintance. It is an RNA phytovirus, with quasi-isometric particles, which belongs to the gender Ilarvirus of the family Bromoviridae.
What species does it attack?
It is considered that the first description of this virus in fruit trees was made in peach tree, but its infection range is very wide, crossing the species of Prunus and other species of the Rosaceae family, including fruit trees and ornamentals.
What is the dispersal mode of PNRSV?
This pathogen is classically classified as a pollen-borne virus. Seeds are also used for dispersal and the use of contaminated material (e.g. grafting).
What is its distribution in the world?
Due to the mode of dispersal, we can speculate about a cosmopolitan distribution and indeed this is the case. Reports are common in Europe, Asia (including China), North America (including USA) and South America (including Chile and Argentina), Africa (including South Africa and Egypt) and Oceania (including Australia and New Zealand).
What are the most common symptoms?
The name in Spanish would be: Necrotic Ringspot Virus Prunus, which tells us a lot about its main symptoms. The initial symptom (shock) consists of chlorotic spots and rings that evolve into necrotic ones, especially on young leaves. The necrotic tissues end up falling off, leaving holes in the leaves, similar to symptoms caused by Pseudomonas or fungi such as disease “Ammunition shot”. Many times, after the aforementioned Shock symptom, the plants return to their normal state, without the presence of symptoms towards the end of the season.
In cherry trees, the most common symptoms have been described in fruit, deformations, ring spots and delayed ripening. However, it should be mentioned that, often, in order for us to observe these types of symptoms, the plants must have two characteristics: they must carry more than one virus or they must have been subjected to stress.
Something that should not be left unmentioned and is very relevant, because it has to do with the diagnostic decision, a plant can be a carrier of PNRSV and be absolutely asymptomatic, so the use of analysis techniques such as molecular ones such as RT-PCR or serological ones such as ELISA, are essential to make an accurate diagnosis of the presence and prevalence of the virus in our orchards.
Is there a better time to test for the presence of this virus?Using nearby information, a study in Argentina, was able to infer through ELISA-type analysis, using absorbance levels, the presence of PNRSV in peach plants during the season. They were able to quantify, starting from dormant buds, without major problems, with a peak in November, when leaf development is close to its maximum, and then declines in summer below the detection level. This indicates that the best period for sampling is spring, which in the case of cherries and adjusted to the Chilean reality, would extend from October to mid-December.
