How to prevent and control peach latent mosaic viroid? Key points for disease prevention in peach tree cultivation

Peach latent mosaic viroid is also known as peach mosaic disease, peach yellow mosaic disease, peach variegation disease, etc. It occurs in many countries such as the United States and Japan, and similar diseased plants have also been found in China. The only host of this disease is peach.

(1) Symptoms Peach latent mosaic viroid is a latent disease, and the leaves generally do not show mosaic symptoms. The main feature of this disease is slow growth, and peach flowering and ripening are delayed by 4 to 6 days. In the first year, plant vigor is slightly affected, and the fruit is somewhat flattened, not as clean and bright as normal fruit. Diseased fruit is streaked, deformed, and dull, often faded, and lacking aroma. The pit is also somewhat flattened, with cracking, and the fruit suture is suberized; cracking is an external feature of this disease.

By the fifth year of infection, diseased plants begin to age prematurely, many buds die, and the plants appear bare, with many branches but weak growth. Diseased plants produce reduced fruit yields, and quality is also inferior to normal fruit. Fertilization cannot restore diseased plants to normal, and the decline of diseased plants is irreversible. As the tree gradually weakens, diseased plants are very sensitive to parasitic fungi and adverse climatic conditions, and their resistance decreases.

A few leaves have mosaic without deformation, merely showing bright yellow diseased areas or milky white variegation, or developing chlorotic spots and diffuse mosaic. Only a few severely infected plants show yellowing of the whole tree, leaf curling, and cankers on large branches. High temperatures are suitable for the obvious appearance of such diseased plants. The white petals of Rosaceae plants develop rose-colored mottling.

Sometimes large, deep stripes appear in the xylem of new shoots, but there is no damage to the bark, and no cracking or necrosis. The earliest leaves show spots that penetrate to the underside.

(2) Disease cycle and epidemiology According to reports from the United States, 20% of peaches, cling peaches, and nectarines are infected with this disease. 60% of varieties shipped from Japan to France are diseased, often showing mosaic, with some leaves affected in spring. Within a radius of 20 m around infected plants, latent mosaic is quite common. According to experiments, peach buds can transmit this disease. A tree takes 3 to 4 years before it is largely infected.

(3) Detection This disease can be detected in the greenhouse using the peach seedling GF305 as an indicator plant. The inoculated indicator plants must be replicated 10 times. After 2 months from the first inoculation, bud grafting is then carried out with a severe strain. Due to the effect of the mild strain on the severe strain, if the plant has previously been infected by the peach latent strain, the severe strain will not show any symptoms on the indicator plant, which indicates the presence of the latent strain. This technique has been tested abroad for 15 years and has proven reliable.

The purification of the viroid has recently been successfully achieved in the laboratory.

(4) Control methods Use viroid-free propagation material, and disinfect tools during pruning to avoid transmission.