The infected root‐hair count for estimating the activity of Plasmodiophora brassicae Woron. in the soil

Abstract

A method is described for estimating the relative numbers of Plasmodiophora brassicae spores germinating in different soils, by counting infected root hairs. Cabbage seedlings are grown for 1 week at 25d̀C. in glass tumblers of the infected soils; after washing out, the tap roots are stained in 1% aceto‐carmine and a count is made of the number of root hairs containing zoosporangia of P. brassicae , along 2 cm. of root. It is shown that by this method it is possible to study, for example, the action of different bases in inhibiting root‐hair infection; the main inhibiting factor was found to be soil alkalinity, however produced. Other factors were found to influence infection in lesser degree; thus the number of infected root hairs was reduced in soils receiving N /10 sodium and potassium chlorides in place of distilled water. Root‐hair infection was also inhibited by low soil‐moisture content.