The Influence of Organic Manuring On the Development of the Potato Root Eelworm, Heterodera Rostochiensis

Abstract

Plant parasitic nematodes such as the potato root eelworm are obligate parasites. Investigations of such parasites are promising only, if both parasite and host are studied. A method was developed to estimate the number of eelworms present in one gram of root. Our experiments were confined to pot plants. Here it is possible at any required time to harvest the complete root-system. The roots were weighed, milled for 30 seconds in a Waring Blendor and stored in F. A. fixative. The suspension of root particles and eelworms was diluted in water and the different larval stages of the eelworms were counted. In 22 days old plants significant numerical differences were found in eelworm population between the organic manure series (farmyard manure or compost) and the fertilizer series; those in the former being much lower. Moreover, the organic matter in the soil hampers the growth of the nematodes in the plants themselves. The percentage of the second and third stage larvae is lowest in the organic manured series. At the end of the growing period, however, extensive root production in the compost series caused the production of numerous cysts, but when calculated per gram of root the increase of cysts is largest in fertilized plants. The influence of organic matter on the development of nematodes has been known for several years. LINFORD presumed that the increased development of their natural enemies in soil treated with organic matter might be the cause of this phenomenon. Hence, biological control of nematodes would take place when plants were treated with organic matter. It was found in the author's experiments that eelworms, already penetrated into the roots of plants treated with organic matter, developed significantly more slowly than in those treated with fertilizer or in none-manured plants. No direct influence of soil conditions could be found to account for this. It is concluded that plants treated with organic materials such as farmyard manure or compost, develop a slight resistance to nematodes. Physiological changes in the plant itself may be the reason.