PERENNATION IN CUSCUTA REFLEXA ROXB.

Transcription

1 [474] PERENNATION IN CUSCUTA REFLEXA ROXB. BY L. NARAYANA RAO Central College, University of Mysore, Bangalore (With I figure in the text) INTRODUCTION uscuta is a common parasite in several parts of India. Of the Indian species, C. rcflexa Roxb. has a wide range of distribution extending sometimes up to 6000 ft. or even more above sea-level in the hills of South India (Gamble, 1921) as well as North India (Singh, 1933). All the Indian species of Cuscuta are described as annuals (Cooke, 1908) like most of the European species. Even though they are attached to perennial woody hosts, they die after flowering. Kerner & Oliver (1902) state that perennial species are found in the tropics, and mention as an example C. Verrucosa, the suckers of which "continue to exercise their function throughout the year, wherever they have once attacked the host". According to the Index Kewensis (1, 674) C. Verrucosa Sweet is a synonym of C. reflexa Roxb. C. reflexa growing on Salvia in a greenhouse at the Cambridge University Botanic Gardens has been mentioned by Thoday (1911) as a perennial species. In the United States of America Cuscuta eplthymum on alfalfa has been described as a perennial which produces seeds only rarely, and the continuation of infestations is more often due to resumption of growth by overwintered stems than to the germination of new seed (Steward & French, 1909). It seems clear that in all these cases the parasite as a whole persists. No species of Cuscuta has so far been recorded as perennial in habit in India, and the mode of perennation to be described seems not to have been observed before. MATERIAL AND FIELD OBSERVATION Material of Cuscuta reflexa Roxb., growing parasitically on species of Strobilanthes {S. Gossypinus and 5. Canaricus) (Hooker, 1885), was collected in several infected areas of the Mysore Forests some 5000 ft. above sea-level. Observations recorded show that Cuscuta flourishes, attacking practically every host plant in the area by the end of the

2 Perennation in Cuscuta reflexa Roxb. 475 south-west monsoon, i.e. October and November. The growth gradually deelines during the next three months, when the parasite produces flowers and fruits in abundance. By the time the summer sets in, nothing remains of the parasite except occasional dried black pieces of its stem coiled round the host (Fig. i). This feature was observed year by year for a long time. Mean while, a search was made in the early part of the rainy season for germinating seeds and seedlings of Cuscuta in the areas where it had been found growing extensively in the previous season, but without success. Fig. I. A portion of the old stem of Strobilanthes with a black dead piece of Cuseula stem (c), on either side of which young buds (b) have emerged to develop into new shoots. Higher up the stem are other Cuscuta buds arising from buried haustoria. x 2. However, on one host plant a peculiar growth was noticed from which numbers of Cuscuta branches were spreading in all directions. Further observation revealed, in a number of instances, groups of young shoots of Cuscuta of varying lengths (1-20 mm.) emerging from the host stem, each one of them starting the attack independently. Subsequently, similar growths were found in all the areas on several hosts. Sometimes pieces of black dead stem of the previous growing season were found still adhering to the host stem with new young shoots of the parasite emerging on either side of them (Fig. i). ANATOMY OF THE PARASITE DURING PERENNATION The mode of attack and the formation of the sucker in this species are similar to those described by Peirce (1893). After flowering, the parasite dies and the host repairs the wounds inflicted by the parasite. However, the haustorial tissues of the parasite often

3 476 L. NARAYANA RAO persist in the body of the host during the dry months of the year. While the healing of the wound is going on, the subsequent secondarygrowth of the host not only encloses the absorbing tissue completely, but also breaks it up into a number of isolated groups or islands by penetrating into it. The islands are well protected and nourished by the host. They begin their activity only in the next rainy season, when they grow out of the host tissue, each forming a new shoot. From one sucker wound as many as 8-10 shoots may arise to renew the attack. DISCUSSION This type of perennation is different from the perennial habit in a uniform tropical climate or in a greenhouse, where the conditions favour indefinite continuance of growth. The perennation of Cuscuta reflexa Roxb. in the manner described appears to be an adaptation to the ecological conditions under which the parasite is obliged to grow. It could not continue its vegetative growth throughout the year by reason of the marked variations in climatic conditions, especially rainfall. Propagation by seed is rarely possible in view of the absence of suitable hosts at proper stages of growth in the neighbourhood of the seedling. It is necessary to remember in this connexion that so dense is the thicket of Strohilanthes in the undergrowth of forest that under ordinary natural circumstances, it is only at the time of the periodical flowering that the tree seedlings can establish themselves (Gamble, 1888). What is true of tree seedlings appears to be true for Cuscuta seedlings. SUMMARY A new method of perennation of Citseitta has been observed where perennation takes place by the survival of only the haustorial tissue within the host during the dry months, the parasite body completely disappearing. The haustorial tissue gives rise to a number of young shoots early in the next growing season. I wish to thank Prof. Dr R. Ruggles Gates, not only for his advice and assistance but also for encouragement in the publication of this paper, and Prof. D. Thoday who kindly read and criticized the manuscript before publication. I wish to express my thanks to Dr M. A. Sampathkumaran for his continued interest during this work. REFERENCES CooKE, T. (1908). Flora of the Presidency of Bombay, 2, 224. GAMBLE, J. S. (r888). The Nilgiri StroUlanthes. Indian For. 14, (iy2i). Flora of the Madras Presidency, pp

4 Perennation in Cuscuta reflexa Roxb. 477 HOOKER, Sir J. D. (1885). Flora of British India, 4, KERNER & OLIVER (1902). Natural History of Plants, 1, Eng. ed. PEIRCE, G. J. (1893). On the structure of the Haustoria of some phanerogamic parasites. Ann. Bot., Lond., 7, SINGH, T. C. N. (1933). Cuscuta as a parasite on a fern. Ann. Bot., Lond., VI, 243. STEWARD, F. C. & FRENCH, G. T. (igog). The perennation in clover dodder, Cuscuta epithymum. Torreya, 9 (quoted by F. D. Heald in Manual of Plant Disease, 1933). y, M. G. (igii). On the histological relations between Cuscuta and its host. Ann. Bot., Lond., 25,

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