Tea Yellowa and its Graft Transmission

Abstract

1. Tea yellows was first reported by RYU (1952) to be a nutrient deficiency due to root injury caused by ants' attack. But it was much doubtful whether the ants' attack can be the cause of so severe chlorosis as seen in tea yellows. This study was undertaken to determine the real causal agent of tea yellows with special reference to the possibility of its graft transmission. Observations and experiments were conducted buring 1957 and 1958.
2. Characteristic symptom of tea yellows is yellow to yellowish white irregular splotching of various sizes on leaves (Fig. 1, 2). It is not accompanied by any remarkabled warf, rosette, or malformation. It can easily be distinguished from the variegation due to bud mutation (Fig. 3), mosaic symptom due to nickel excess (Fig. 4) or other unknown origin (Fig. 5), and leaf yellowing due to manganese excess.
3. Cuttings taken from tea plants affected by yellows were planted on nursery bed prepared from virgin soil. The symptom of yellows sppeared on all the shoots grown from the rooted cuttings.
No sign of their recovery was observed even after two years' growth. Cuttings taken from healthy plants did not show any symptom on the same nursery bed.
4. Graft transmission tests were made between affected scions and healthy stocks as well as between healthy scions and affected stocks. In both combinations, typical symptom of tea yellows appeared on newly grown shoots on the healthy side two to four months after the grafting (Table 1). It was noticed that the transmission was obtained even when the grafting was unsuccessful, though it does not necessarily mean the success of juice transmission because of the possibility of partial and temporary union of both tissues before the death of the scions.
5. The results obtained in this study suggest that tea yellows is due neither to any kind of nutrient deficiency nor to genetic origin, but tit is caused by an infectious agent. Since no microorganism can be detected in affected tissues with optical microscope, the causal agent is presumed to be a virus or a micoplasma-like microorganism. The symptom of tea yellows suggest the probability of being a virus disease.
6. The occurrence of tea yellows is restricted to a narro warea in Saga Prefecture, Japan. But its symptom is very much similar to that of a virus-induced varegation in Camellia japonica and C. sasanqua reported by PLAKIDAS (1954) and some other investigators. Although the identity between them has not yet been established, it is noticeable that tea yellows is often accompanied by variegated plants of spontaneous C. sasanqua (Fig. 6) in the field. Further studies are needed to identify the causal agent of tea yellows and to demonstrate its trans-mission route under the natural conditions.