Grondonderzoek op phytophthora sabdariffae

Summary For the successful cultivation ofHibiscus sabdariffa for fiberproduction in Java a preceding determination is necessary whether either soil or organic manure are contaminated byPhytophthora sabdariffa or not. To this end a method has been elaborated analogous to the method to determined soil contamination byPhytophthora nicotianae.According toGarrett's scheme ofWaksman's classification of soil fungi into soil inhabitants and soil invaders,Phytophthora sabdariffa has to be classified as soil invader.To test the presence of this fungus in soil or in organic manure leaves ofRicinus communis prove to be useful as a detector, since leaves ofHibiscus sabdariffa are too small and too quickly given tot decay. A method is to spread a paste of the soil or of the organic manure on the leaves and to keep these leaves contaminated during 24 hours (spreading method). Afterwards the paste is washed away and the leaves are kept in humid conditions during another 24 hours or 2×24 hours.The number of spots caused by Phytophthora is a measure of soil- or manureinfection (Table I). A more sensitive method is obtained by making a suspension of the soil or of the manure and by streaming this suspension (submersion method) during two hours over Ricinus leaves (Thung, 3). Afterwards the leaves are kept in humid air to give the fungus occasion to form spots (Table 2). Since Ricinus leaves are also susceptible to tobacco- and Ricinus-Phytophthora, these fungi will also be detected by these leaves. Owing to the fact that these fungi are also a parasite ofHibiscus sabdariffa, these method prove to be useful to detect suspected soil or manure regarding the cultivation of this fiberplant.