Research note Variations in morphology and disease susceptibility of micropropagated rhubarb (Rheum rhaponticum) PC49, compared to conventional plants Yipeng Zhao 1, *, Brian W.W. Grout 2 & Peter Crisp 3 1 Horticultural Department, Henan Institute of Science & Technology, Xinxiang, Henan 453003, China; 2 Faculty of Science, Writtle College, Chelmsford CM1 3RR, United Kingdom; 3 Crisp Innovar Ltd, Glebe House, Station Road, Reepham NR10 4NB, United Kingdom (*requests for offprints; Fax: +86-373- 3040666; E-mail: yipengzhao@hist.edu.cn) Received 17 October 2004; accepted in revised form 4 February 2005 Key words: crop growth, disease susceptibility, micropropagation, rhubarb, variation Abstract Variation in morphological traits and increased disease susceptibility were observed in micropropagated plants of rhubarb (Rheum rhaponticum L.), PC49. Our investigations have demonstrated that microprop- agated plants can vary substantially in morphological traits and the variation of quantitative traits was substantially greater than conventionally propagated plants. Micropropagated plants produced signifi- cantly more leaves than conventional plants under the same growth period, with a more bushy growth habit and/or recumbence. A higher incidence of disease (petiole spotting) was also observed in micropropagated plants. It is concluded that micropropagated PC49 had substantially higher incidence of somaclonal var- iation and regenerants were not suitable to establish an economic crop comparable to the conventional plants. One important requirement for successful micro- propagation of plants is that regenerants exhibit uniformity comparable to conventional propa- gated plants. However vegetative propagation of plants using tissue culture may lead, at certain le- vel, variation in phenotype compared to the ori- ginal stock material e.g. somaclonal variation (Larkin and Scowcroft, 1981). Somaclonal varia- tion is not an ‘all-or-nothing phenomenon’ but ‘a matter of degree’ (De Klerk, 1990; Bouman and De Klerk, 2001). Micropropagation of rhubarb is important to the horticultural industry as it allows a more rapid and economic production of plant material for planting compared with conventional propagation (crown division) methods. In the past micropropagation has been successfully applied to rhubarb (Rheum rhaponticum L.) producing mor- phologically uniform planting materials (Walkey and Matthews, 1979; Roggemans and Boxus, 1988) and field trials assessing crop performance of micropropagated rhubarb plants showed no abnormal morphological features (Lassus and Viopio, 1994). A new breeding line of rhubarb, PC49, with the unique characteristic of non-autumn dormancy, has demonstrated great potential for commercial production of high quality petioles. However, using the techniques of Roggemans and Boxus (1988) to micropropagate PC49, uniform plantlets were obtained via shoot-tip cultures but the re- generants had greater than expected variation in morphology and, unexpectedly, high susceptibility to spot disease after field transplantation (Zhao et al., 2003, 2004). Furthermore, under field con- ditions, the abnormal plant types were character- ized by multiple shoots with small leaves and short petioles. Increasing branching has been observed in many different plants regenerated using in vitro culture methods and in some circumstances has been used to identify somaclonal variation. This abnormality in plant morphology is termed as bushiness (Topoonyanont and Debergh, 2001; Plant Cell, Tissue and Organ Culture (2005) 82: 357–361 Ó Springer 2005 DOI 10.1007/s11240-005-1836-z