Xylella fastidiosa: Growing Threat to Wine or Simply Misunderstood? Microbigals Share Their Thoughts
Updated: Nov 29, 2020
Artist Credit: @organizedmike
X. fastidiosa possesses a dual personality, cleverly equipped to live in two vastly different environments—insects and xylem, the water transport system of plants. When the insect feeds on the plant, X. fastidiosa is sucked up and transported to a new home.
Xylella’s presence leads to xylem clogging, causing water stress symptoms including leaf scorch and dehydrated fruit. Other symptoms include “matchstick petioles”, burnt leaf tips, stunted growth, and uneven maturation. Symptoms arise 12–18 weeks after the initial infection.
Researchers are able to locate this microbe within the plant in a number of molecular ways. However, Xylella can be very elusive, often leading to inaccurate results and false negatives.
X. fastidiosa uses biofilm, a sticky microbial tent, for protection. For most pathogens, biofilms enhance their arsenal for war, but when X. fastidiosa is unable to produce biofilm it becomes more virulent. Most bacterial pathogens also have a T3SS (type III secretion system), a missile-launching control center. Xylella does not possess such artillery, although it does have some clever means of exploring and adapting to new environments. Xylella must be survivors and adapt to overcome the constant kidnapping by flying giants who aggressively strip them away from their home and vomit them into a foreign and hostile new land.
Once deposited into this foreign land, Xylella doesn’t attack, but explores, using its pili to twitch its way across the xylem currents. When it meets a membrane barrier, X. fastidiosa sends out its cell wall degrading enzymes to pulverize that blockade. In response, the plant will create tyloses, balloon barriers. But the joke is on the plant—those balloons are so effective, not even water gets past them. Xylem vessel diameter and water conductivity can be drastically different from one grape variety to the next. For instance, Thompson Seedless which produces more tyloses, and has wider xylem vessel diameters, is more susceptible to the disease than Merlot. The plant response to the microbe enhances disease progression. Most people quickly categorize a microbe as the villain without ever looking to see how the host provokes and exacerbates the situation.
There is no known cure for this disease. Management strategies include altering cultural practices (irrigation, pruning, vine removal) and insect control (pesticide application). Researchers have also tried to breed resistant varieties. More and more research is showing that the innate microbial community of the plant may play a role in disease progression either by changing the behavior of the plant, insect, or pathogen or through directly attacking the pathogen. Another exciting therapeutic strategy is injecting bacteriophages, tiny viruses that hunt bacteria.
What do you think? Is Xander the Xylella a killer or just a misunderstood microbe being trapped at the wrong place at the wrong time? Cast your vote in a comment below!