Tomato yellow leaf curl virus (TYLCV) is considered one of the most devastating diseases of tomatoes worldwide, especially in Mediterranean climates similar to that of Southern California. Thus, TYLCV may be considered a serious threat to tomato production in California should it become established.
In the 1990’s TYLCV was found in the Dominican Republic, and has since become established in Florida and found in Georgia, Louisiana, and North Carolina. In 2006-2007, there was a severe outbreak of TYLCV in the northern states of Mexico (states of Sinaloa and Tamaulipas). In fall 2006, TYLCV was found in Texas and Arizona. TYLCV was first detected in greenhouse tomato transplants in March of 2007 in Brawley, Calif. The virus was found to be 99.7 percent similar (total nucleotide sequence) to the virus isolate from Northern Mexico. Additionally, the greenhouse tomatoes were seed-grown and only developed the viral symptoms later in the season, indicating that the infection was introduced from Mexico through viruliferous whiteflies, and not through transplanted tomatoes.
Since that initial positive virus detection, tomatoes have been closely monitored for TYLCV symptoms so that the virus will not become a regular disease in tomatoes grown in the Imperial Valley. However, this year two tomato plants have already tested positive for TYLCV. Nonetheless, TYLCV has not become established in the Imperial Valley. In order to slow down the establishment of the virus in tomatoes of the Imperial Valley, it is important for tomato growers, homeowners (includes store bought tomatoes), and PCA’s to know what symptoms to look for in their tomato plants.
TYLCV (genus Begomovirus, family Geminiviridae) is transmitted by the sweet potato whitefly, Bemisia tabaci biotype B (silverleaf whitefly), B. argentifolii and some other whitefly species. In order for the whiteflies to acquire TYLCV from an infected plant, the whitefly must feed for five to 10 minutes. After initial infection, it takes about 10 hours before the whitefly can then transmit the virus to a new host by again feeding for five to 10 minutes.
Whiteflies can travel up to five to seven miles, but longer distance movements may occur with the aid of wind or human transport of the whiteflies in plant material. The virus is not mechanically transmitted (by hand) and is not spread through seed. This virus has numerous plant hosts including solanaceous crops (peppers, tomatoes, and some tobacco species), common bean, and various weed species (e.g., nightshade and jimsonweed). There are other weeds that are asymptomatic hosts (they do not show symptoms). However, it is not known how well whiteflies are able to acquire TYLCV from asymptomatic weed hosts.
Most of these hosts do not have the characteristic TYLCV symptoms quite like the tomato. Symptoms of TYLCV on tomato are stunted growth, abnormally upright stem and leaf growth (instead of fanning out- the leaves grow straight up), have shortened internodes (length of stem separating nodes) making the tomato short and bushy. The leaves of the new plant growth will be smaller, crumpled and show yellowing at the margins and between veins — the veins remain a vibrant green color. Flowers of infected plants may fall off prior to fruit set, dramatically reducing the fruit production potential. If your tomato plants show symptoms of TYLCV it is best to have the plant tested for the virus.
Prevention is the cure in the Imperial Valley, strategies for disease management include select TYLCV-resistant varieties, and only use virus-free and whitefly-free tomato transplants. And most importantly, try to avoid importing tomato transplants from areas known to have TYLCV (Arizona, Florida, Georgia, Texas, North Carolina, Northern Mexico).
If the virus were to become established in the Imperial Valley, there are management strategies that have been successful in other TYLCV infected areas. These include using a TYLCV resistant tomato variety, having a ‘tomato free’ period, and restricting movement of tomato transplants from TYLCV infected areas to areas where the virus has not become established.
Additionally, research is underway to identify weed hosts of TYLCV that may play a part in creating a ‘green bridge’ allowing TYLCV to survive from one growing season to the next.