1 Sour Skin Detection in Vidalia Onions Using Hyperspectral Imaging

Sour skin is a common bacterial disease that can affect most onion varieties all over the world (Burkholder 1950; Sotokawa and Takikawa 2004). Because sour skin bacteria have an uncanny ability to survive in moist environments, it is one of the major threats to the sweet onion industry with up to 50% losses in some fields or storage rooms (Howard F. Schwartz 2008). Sour skin bacteria can enter the onion plant when onion tops are cut at harvest, or through other wounds caused by mechanical injuries in the neck area. Infection can also occur via rain splashing of infested soil or by contaminated irrigation water (Gitaitis 1994). Sour skin is often limited in a few inner bulb scales at the early stage, and infection can remain latent until the onion becomes mature (Howard F. Schwartz 2008). Therefore, it is difficult to identify sour skin symptoms from onion surface visually when the disease is in an early or latent stage. Currently, human visual inspection (HVI) is used by most onion-packing houses. Obviously, HVI cannot prevent onions with only internal infections from entering into controlled atmosphere (CA) storage rooms or fresh vegetable markets. In this research, a near-infrared hyperspectral imaging system was developed using a liquid crystal tunable filter (LCTF) and it was applied for sour skin detection in Vidalia onions. A number of preliminary experiments were conducted to test the efficacy of the hyperspectral imaging technology for sour skin detection.