What causes citrus yellow vein disease?
1 Symptom characteristics
Citrus yellow vein disease can infect most citrus species and hybrids, of which lemons, limes and other most seriously affected. After lemon and lime infection with citrus yellow vein disease, severe leaf shrinkage and rewinding occur, lateral vein yellowing, vein bright, leaf back water immersion. The symptoms of yellowing of the old mature leaves subside and partially turn green, but the symptoms of leaf shrinkage cannot be recovered, and the yellow veins are still obvious to the light. Causes leaf shedding, resulting in fewer fruits, lower yields, and even no harvest. The disease is currently the most serious viral disease for lemon production. In addition, citrus yellow vein disease will also cause different degrees of pulse symptoms on the young leaves of sugar orange, Zhenxi grapefruit, some Wenzhou mandarin varieties and some orange varieties, but as the leaves mature, the symptoms will gradually reduce or even disappear.
2 Routes of transmission
Studies in recent years have shown that in addition to transmission through diseased seedlings and scion, citrus xanthosis can also be transmitted through vector insects such as the citrus whitefly Dialleurodes citri. In addition, the use of tools contaminated with citrus xanthophora virus is also an important route of transmission . In recent years, the area under citrus cultivation has been expanding, and by 2018, the area under citrus cultivation in China has exceeded 266. 7 million hm2. The scale of citrus cultivation has caused a large gap in the supply of high-quality citrus virus-free seedlings, driven by economic interests, seedling producers have relaxed disease risk management in order to accelerate the emergence of seedlings, and some seedling enterprises (individuals) have even directly cultivated ordinary open-field seedlings pretending to be virus-free container seedlings, and citrus yellow vein disease is not a quarantine disease, there is no quarantine control link, which eventually leads to the rapid spread of citrus yellow vein disease with seedlings. It can be said that the transportation and cultivation of diseased seedlings is the most important first transmission route of citrus yellow vein disease in Wanzhou and even the whole country in recent years.
3 Prevention and control measures and effects
At present, there is a lack of effective agents for the prevention and treatment of citrus yellow vein disease, and no lemon varieties that are resistant to citrus yellow vein disease have been found, so prevention and control is difficult. Through cooperation with the Citrus Research Institute of the Chinese Academy of Agricultural Sciences, the following prevention and control measures have been formulated by drawing on the experience of citrus huanglongbing disease prevention and control.
The first is to strengthen publicity. Attach great importance to the harm of citrus yellow vein disease to the lemon industry, strengthen the risk prevention and control publicity of citrus yellow vein disease hazards, improve the awareness of growers of the disease, and take the initiative to prevent disease.
The second is to use virus-free seedlings for breeding. Seedling enterprises should strictly control the quality of seedlings, strengthen the sampling of mother trees, especially Yulik lemon mother trees, and reduce the risk of seedling disease. At the same time, in order to prevent the seedlings from being re-infected, the seedlings should be reared in the insect-proof net room. In addition, considering the greater risk of introduction from other places, yulik lemons that perform healthy in the field and are tested to be non-toxic can be selected locally as temporary ear mother trees, and qualified enterprises (institutions) can be entrusted to breed seedlings.
The third is to eradicate diseased trees. Under the organizational leadership of the district government, the town and township cadres are responsible for publicity, and the village community cadres are responsible for the work of the growers, and the sporadic Yulik lemon disease plants are eradicated in accordance with the principle of "discovering one plant and digging out one plant". In addition, the unsymptomatic Beijing lemons around the Yulik lemon orchard (most of which carry the yellow vein virus but do not show symptoms) also need to be eradicated. After the diseased tree and vector insects have been completely removed, the virus-free Euric lemon can be replanted.
The fourth is to truncate the transmission route. For orchards that do not have citrus xanthosis or sporadic occurrences, it is necessary to timely and systematically control major vectors such as citrus whitefly, especially to seize the pest control of important periods such as spring and summer shoots. At the same time, before using farm tools that can cause wounds, such as prunes and picking tools, disinfect them with freshly supplied 1% sodium hypochlorite or a saturated soapy water solution.
Since May 2017, the Wanzhou District Plant Protection Station has carried out a field prevention and control demonstration of citrus yellow vein disease in Dawu Village, Baiyang Town, Wanzhou District. As of May 2019, the total area of prevention and control demonstration is 159.5%. 8hm2, a total of 61 981 plants were cut down. At present, the spread rate of citrus xanthosis in this area has weakened significantly, and no new areas of occurrence have been found for the time being.