Whiteflies are small Hemipterans that typically feed on the undersides of plant leaves. More than 1550 species have been described. Bemisia tabaci, commonly known as silverleaf whitefly or sweet potato whitefly, is one of the most threatening pests in tomato. Another whitefly, Trialeurodes vaporariorum, commonly known as the glasshouse whitefly or greenhouse whitefly, inhabits the world's temperate regions. It is frequently found in glasshouses, polytunnels, and other protected horticultural environments. Adults are 1–2 mm in length, with yellowish bodies and four wax-coated wings held near parallel to the leaf surface.

Whiteflies damage tomatoes directly by sucking sap from leaves and indirectly by transmitting viruses and producing a sticky secretion known as honeydew which is a substrate for fungal growth (“sooty molds”). This makes tomatoes unmarketable.

Trialeurodes vaporariorum became an economical important insect pest of greenhouse vegetable and ornamental crops in the 1970s. More recently, it has become a serious horticultural pest within areas of southern Europe, where an increase in the incidence of viruses can be attributed to it. The piercing and sucking mouthparts of T. vaporariorum provide an excellent mode for transmitting disease-causing viruses from one plant to another. As immature whitefly stages do not move to new plants, virus transmission is only a concern with adult whiteflies.

Biological control

Trialeurodes  vaporariorum is attacked by species of Encarsia, Eretmocerus and fungal pathogens. The small chalcid wasp, Encarsia formosaI, is commercially produced and used for biological control in greenhouses.

 

Breeding for resistance to whitefly in tomato: set up

Whitefly (B. tabaci) resistant tomatoes are an answer to many whitefly induced problems and an important part of an integrated approach of pest management. In this assignment we will follow the steps a tomato researcher resp. breeder has to take to introduce resistance in commercial tomato cultivars during the breeding process. This is a conventional approach and no genetic modification (GM) is used. The breeder needs to take the following necessary steps:

 

  • Develop a reliable screening method for whitefly resistance
  • Search for the best donorplant with whitefly resistance in wild tomatoes that can be crossed with tomato
  • Making crosses between resistant wild tomato plants and susceptible cultivated tomato plants
  • Develop segregating populations
  • Linkage analysis using phenotyping and genotyping data
  • Application of the linked molecular markers in a breeding program to obtain new commercial varieties

Questions background:

2.1  Can you find a picture of a tomato plant damaged by white flies?

2.2  What viruses can white flies transmit to tomato plants?

2.3   Where can you find wild tomato species?

2.4   What is the ploidy level of a tomato plant?

2.5   What is the breeding strategy of a tomato plant?