Proc. Indian Aead. Sei. (PI. Sci.), Vol. 89, Number 1, January 1980, pp. 5%60. 9 Printed in India. Translocation of Southern sunnhemp mosaic virus in Crotalaria juncea L. J J SOLOMON and C B SULOCHANA Centre for Advanced Studies in Botany, University of Madras, Madras 600 005 MS received 17 February 1979 Abstract. The translccation of Southern sunnhemp mosaic virus (SSMV) in its primary host Crotalariajuncea was studied by local lesion assay. The systemic spread of the virus was rapid and efficient; 24 hr after inoculation of the primary leaves, the virus could be recoveredfrom the developing stem and leaves as well as the hypo- cotyls showing movement and multiplication of the virus in the stem axis in both directions of the primary node. In the roots, the multiplication of Southern sunnhemp mosaic virus was delayed but the titre reached a 1 igh level by the fifth day. The pattern of movement of Southern sunnhemp mosaic virus in vivo differed from those of TMV and other plant viruses. Keywords. Translccation; Southern sunnhemp mosaic virus; Crotalaria juncea. 1. Introduction Southern sunnhemp mosaic disease of Crotalaria juncea L. (Capoor 1962) is of economic importance. This crop is raised extensively for green manuring of fields in rotation with cereals and sugarcane, and as a fibre crop in Bengal. When seed- lings of sunnhemp were manually inoculated with the Southern sunahemp mosaic virus (SSMV), there was invariably cent percent infection; the virus titre in vivo reached the maximum level 10 days after inoculation and remained high till the emergence of the inflorescence pdmordia (Solomon 1972). These observations prompted us to study the pattern of translocation and the systemic spread of SSMV in sunnhemp plants and the results are presented in this paper. 2. Materials and methods Sunnhemp seedlings (vat K 12 yellow) were raised in washed river sand in earthen- ware pots. The primary leaves of 6-7 day-old plants were inoculated ~ith SSMV inoculum. The seed'ings were subjected to 24 hr dark treatment prior to inocu- lation. 2.1. Inoculum One gram of SSMV infected tissue ground in 1 ml of distilled water plus 7 mg of celite 503 per ml was used as standard inoculum, 57 58 J J Solomon and C B Sulochana Following inoculation, plants were carefully uprooted from the pots at 24 hr intervals and washed thoroughly; sap inocula were prepared from roots, hypo- cotyls, inoculated leaves, emerging stem and leaves and assayed on the primary leaves of Cyamopsis tetragonoloba Taub. (cluster beans). The results are presented in figure 1. 3. Results One day after the inoculation, the presence of SSMV outside the inoculated leaves was recorded in the hypocotyls as well as in the emerging stem and leaves, indi- cating movement of the virus particles from the site of inoculation on the lamina of the primary leaves through the petioles to the stem, the spread of the virus in the stem in both upward and downward directions and viral multiplication in these tissues in 24 hr. Up to the third day, viral multiplication ~as greater in hypo- cotyl region than in the stem and emerging leaves in which the rate of increase enhanced from the fourth day. Despite the quick movement of the virus into the hypocotyl, SSMV could not be detected in the roots until the tt, ird day, but there- after the rate of increase of the virus particles was the 1-,ighest in the roots. Five days after the inoculation, the virus concentration in the various plant parts assayed reached comparable levels establishing an equilibrium of the virus titre in vivo. 4. Discussion The most striking feature about ~MV infection of its primary host, C. juncea, is the rapidity with which it becomes systemic (figure 1). There is a quick move- ment of ~,VIV from the mechanically inoculated leaf through its petiole to the stem in the downward direction to the hypocotyl and upwards to the stem and emerging, le~. It is noteworthy that the movement of SSMV in the sunnhemp seedlings is found to be faster than what has been recorded in literature for TMV, PVX, tomato aucuba rriosaic strain of TMV by Samuel (1934), and Capoor 0949) in experiments done with mature plants. It was thought that with the mechanically inoculated viruses there was considerable delay before the v~rus particles left the inoculated leaves and this is attributed to slow cell-to-cell movement through the parenchyma. While it took no longer than 24 hr for some particles of TMV (Bennett 1956), and Southern bean mosaic virus (Worley and Schneider 1963) to spread from the inoculated epidermis to the other epidermal layer, yet it required more than 24 hr for the virus particles to egress from the inoculated leaves (Beemster 1958). In the case of tobacco ratt.le virus, it was shown by Zoeten (1966) that it could be detected in the axillary buds two days after inoculation. The delayed entry of ~kSM'V into the root system, more possibly the delay in the initiation of viral multiplication in sunnhemp roots is contrary to the general observation that systemic viruses first move to the root system. For instance, TMV remained in the root system or moved into the tips only after an interval (Bennett 1940; Fulton 1941). It was explained by Bax~den (1964) that viruse~ de not usually reach high concentration in the roots and the movement out of the roots is slow. In contrast to these earlier observations and explanations, it was Translocation of sunnhemp mosaic virus in C. juncea 59 160 / 120 "5 o 80 -6 ,,J 40 / / l I ~ I ___/i 1 2 3 4 5 Days after inoculation Figure 1. Systemic infection of C. juncea by SSMV as measured by relative infecti- vity of roots (O), hypocot~ls (,t,), stem and leaves (O) following inoculation of the primary leaves (A). found in the present study that there was an initial lag phase in the occurrence of infectious virus particles in the roots but the virus concentration did reach high levels quickly. Thus the pattern of translocation of SSMV in its systemic host differed markedly from those recorded for TMV and other plant viruses. Acknowledgement The authors thank the University of Madsas for permission to publish this work. References Bawden F C 1964 Plant viruses and virus diseases 4th ed. (New York : Ronald Press) p 361 Beemster A B R 1958 Translocation of virus X in the potato (Solanum tuberosum L.) in primarily infected plants (Wageningen : Veeman and Zinen) 1-98 Bennett C W 1940 Acquisition and transmission of viruses by dGdder (Cuscuta subinclusa); Phyto- pathology 30 2 Bennett CW 1956 Biological reactions of plant viruses; Annu. Rev. PI. Physiol. 7 143-170 Capoor S P 1949 The movement of tobacco mosaic viiaases and potato virus X through tomato plants; Ann. Appl. Biol. 36 307-31~ 60 J J Solomon and C B Sulochana Capoor S P 1962 Southern surmhemp mosaic virus: A strain of tobacco mosaic virus; Phyto- pathology 52 393-397 Fulton R W 1941 The behaviour of certain viruses in plant roots; Phytopathology31 575-594 Samuel G 1934 The movement of tobacco mosaic virus within the plant; Ann. Appl. 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