Investigation into the Cause of Leaf Tumours of Tea Seedlings.

Abstract

Tumours occurred on the early true leaves of tea seedlings derived from seed from two localities in New Guinea, and from Ceylon, India, Malawi and Australia, grown in a glasshouse and a laboratory at Port Moresby and in the field in New Guinea, New Britain and Australia. Leaves produced later on these plants were unaffected. Recently, a report of leaf tumours of tea seedlings in nurseries in Malawi bas also been received. Experiments reported herein seem to eliminate the following as possible causes of the condition: micro-organisms, mites, insecticide, copper fungicide, hormone herbicide, charcoal packing, sawdust used in pregermination beds, timber used in pregermination boxes, the water supply and the local soil. Slightly fewer seedlings with tumours occurred with whole or partial removal of the seed coat before germination than when seed remained intact, and slightly fewer with soil than with inert crushed imported quartz. No malformed leaves occurred on 66 seedlings' developed from embryos excised from their cotyledons and grown to the two to six leaf stage on nutrient agar. Ten times more seedlings developed tumours at high temperatures in the glasshouse than in a coolroom. There were ten times more tumours on seedlings grown from immature 'ripe' seed from capsules picked green from the seed bearers than from mature seed which had dehisced naturally from the capsule. It is suggested that the cause of the tumours may be a growth substance found in immature ripe' seed, with little or no residual substance present in mature seed. The concentration or activity of the substance appears to be affected by the removal of the seed coat and by temperature.