This stunting may not be apparent for many months after initial infection. Taproot is normal size, but slicing it diagonally or horizontally down the root reveals wood with an abnormally yellowish color, with fine dark steaks of dead tissue scattered throughout the wood. In recently infected plants the yellowing is mostly in a ring beginning under the bark, with a normal white-colored cylinder of tissue inside the yellowed outer layer of wood. Dwarf disease progressively worsens over 1-2 years after first symptoms and eventually kills plant. Noticeable dwarfing requires 6-9 months after inoculation in the greenhouse, probably longer in the field.
Several methods are now available in research labs.
AgDia sells a detection kit. Cultures take about a week to confirm. Contamination of cultures may obscure results. Low sensitivity but usually adequate for alfalfa except for some infected plants that do not show symptoms. PCR a molecular technique that amplifies genes unique to Xylella .