Tomato Leaf Curl Virus
Leaf curl disease of tomato, locally known to farmers as kulot or kulot ti bulong has been a major constraint to tomato production in the Philippines since the 1990s. Tomato plants affected by the disease are usually stunted and are unproductive. The symptoms on the leaves include interveinal yellowing, upward and downward curling and crinkling. Leaflets are also smaller than those of healthy plants. Symptom expression, however, may vary depending on the crop stage at the time of infection, variety, and whitefly population. The disease can be observed on tomato seedlings about two to three weeks after transplanting and depending on the pressure of the whitefly population in the field, disease incidence can increase rapidly and infection can go as high as 100%.
In the Philippines, tomato leaf curl is caused by Tomato leaf curl Philippines virus) To1CPV; formerly known as ToLCV-Ph), a whitefly-transmitted Begomovirus of the family Geminiviridae (ICTVdB Management, 2006). ToLCPV is considered as distinct virus species in the genus Begomovirus based on the relatively low nucleotide sequence identity between the genomic DNA of ToLCPV and other Gemini viruses like Tomato yellow leaf curl virus (TYLCV) (Kon et al., 2002). ToLCPV affected tomato plants, however, show similar symptoms as TYLCV-affected plants. Because of this similarity in symptomatology, most people associate leaf curl symptoms to TYLCV, which is considered as the most serious disease of tomato worldwide. TYCLV has been reported to occur in several countries in Asia but not in the Philippines (CABI 2007).
The control and management of tomato leaf curl have been proven difficult as with any other insect-transmitted virus diseases. The use of chemical insecticides for instance, can provide only partial control even with regular spraying. Moreover, continued use of insecticides is not environmentally safe and can promote development of resistant whitefly populations. The best way to reduce ToLCPV spread is by planting resistant or tolerant tomato varieties (e.g. the new tolerant tomato variety Diamante Max). In addition to using resistant or tolerant varieties, the following management strategies are recommended to effectively reduce the incidence of tomato leaf curl disease.
1. Protect seedlings and seedbeds by providing physical barriers (e.g. nets) to prevent early infection by whitefly feeding.
2. Avoid planting tomato crop during the dry months when whitefly populations are usually highest.
3. Intercrop with crops known to be good hosts for the whiteflies, but are immune to the virus (e.g. eggplant, cabbage) to attract the insect vectors.
4. Eliminate common weed hosts such as Datura stramonium (nightshade), Ipomoea triloba (morning glory/kamute-kamutehan) within or near the tomato crop.
5. Remove infected plants and volunteer tomato plants before the emergence of whitefly populations.
6. Control whitefly population by using yellow sticky traps and/or spraying with chemical insecticides (e.g. imidacloprid, thiamethoxam, acetamiprid).
By Cherry A. Relevante