Nondestractive Determination of the Symptom of Verticillium Black Spot in Japanese Radish Using Visible and Near-infrared Spectoroscopy

Abstract

The symptom of Verticillium black spot in Japanese radish (Raphanus sativus L.) is black discoloration at the vascular bundle of the root: However, it is difficult to detect the symptom by visual inspection. Thus diseased roots are often mixed with normal roots after inspection in packinghouses. So we attempted to develop a nondestractive determination method using visible (VIS) and near-infrared (NIR) spectoroscopy under practical conditions. The spectra of radish roots were continuously measured by transmittance mode: the scanning range was 450-1,000 nm. Measured roots were then cut and the degree of symptom was converted to an index of 0 (no symptom) to 3 (severely affected) by visual inspection of the cut root. Partial least squares regression was carried out relative to the indices to the second derivative spectra. In a validation set, the standard error of prediction for the index was 0.299 (R = 0.958, n = 70). For each root without the symptom, the predicted indices were less than one, and for 91% of the roots with the symptom, the predicted indices were more than one. Using this method, the roots with an index of 0 could be completely separated from those with an index 2 or higher. It is suggested that VIS/NIR spectroscopy is an effective tool for accurate and rapid elimination of radish roots with the internal symptom of Verticillium black spot.Key Words：PLSR, rapid evaluation, second derivative spectra, transmittance