How to Identify and Control Viral Disease in A-choy (Taiwan lettuce)
A-choy, also known as youmai cai, and called bitter vegetable in some places, belongs to the Asteraceae family. It is a pointed-leaf type leaf lettuce harvested for its tender shoots and tender leaves. The leaves are long and lanceolate, pale green in color, crisp and tender in texture, with an extremely fresh, delicate taste and a distinctive flavor. It contains a large amount of vitamins and abundant calcium, iron, protein, fat, vitamin A, vitamin B1, vitamin B2 and other nutrients, making it a top-grade vegetable for eating raw, and it is known as the “phoenix tail”.
Morphological characteristics of A-choy
A-choy belongs to the Asteraceae family. It is a pointed-leaf type leaf lettuce harvested for its tender shoots and tender leaves. The leaves are long and lanceolate, and its appearance is somewhat like the “head” of celtuce, with slender, flat-spreading leaves and a thin, short stem. In terms of genetic relationship, A-choy is a variety of leaf lettuce——romaine lettuce, and is similar to the familiar lettuce, so it is also called niuli lettuce. It is pale green in color and vigorous in growth. It has strong disease resistance and adaptability, a crisp and tender texture, and an extremely fresh, delicate taste with a distinctive flavor, and it is known as the “phoenix tail”.
Identification and control of viral disease in A-choy
Symptoms of viral disease in A-choy:
The disease can occur throughout the entire growth period, and early infection at the early stage has a great impact on yield. Infection at the seedling stage: symptoms appear after several true leaves have grown, with light green and dark green mosaic mottling appearing on the leaves. Sometimes vein clearing appears, and the leaves become wrinkled and distorted. When infected at the adult plant stage, the diseased plants are obviously dwarfed and the leaves are irregularly distorted.
Pathogens of viral disease in A-choy:
Lettuce mosaic virus (LMV), called lettuce mosaic virus; Cucumber mosaic virus (CMV), called cucumber mosaic virus. Lettuce mosaic virus belongs to the family Potyviridae and the genus Potyvirus. The particles are filamentous, 750 nm long, with a dilution end point of 10 to 100 times, a longevity in vitro of 2 to 3 days, and a thermal inactivation point of 55 to 60 degrees C. It can be transmitted through sap contact or by aphids.
Transmission routes and disease conditions of viral disease in A-choy:
The source of the virus comes from virus-carrying lettuce, celtuce, spinach and others in nearby vegetable fields. Seeds can also carry the virus, and symptoms appear as soon as seedlings emerge. In the field, it is mainly spread by aphids, and the sap of diseased plants also transmits the virus when diseased and healthy plants contact and rub against each other. The green peach aphid has the highest transmission rate, and the turnip aphid, melon aphid and greater black-legged aphid can also transmit the virus. The occurrence and spread of this disease are related to weather; under high temperature and drought, with many aphids, the damage is severe. Generally, when the average temperature is higher than 18 degrees C and the field lacks water, the disease spreads very quickly.
Control methods for viral disease in A-choy:
(1) Select disease-resistant varieties.
(2) When planting in summer and autumn, using insect-proof netting or shade netting or plastic film for appropriate shading can reduce the incidence of the disease.
(3) After emergence, water frequently with a small amount of water, appropriately restrain seedling growth, and control aphids promptly when found.
(4) At the early stage of the disease, spray 2% ningnanmycin aqueous solution at 500 times dilution or 24% mixed fatty acid and copper alkali aqueous emulsion at 800 times dilution.