Electrical impedance measurements on alfalfa to detect infection by root lesion nematodes.

Electrical impedance measurements were made on alfalfa plants (Medicago sativa L.) infected with root lesion nematodes, (Pratylenchus penetrans (Cobb)), and on control plants under conditions of drought and cold stress. Differences were found in the daily cycles of impedance between the two groups, with the infected group showing a greater increase in percent impedance relative to the initial value in early day, and a slower and less pronounced drop of percent impedance upon watering after drought stressing as compared to the controls. The difference in electrical impedance between the two groups of alfalfa was greater at 20 C than at 2 C. It is concluded that root lesion nematodes interfere with normal water uptake and hence water potential in alfalfa roots.