PHENOTYPIC VARIATIONS IN CROTON CODIAEUM VARIEGATUM (L.) BLUME CHARACTERIZED BY DIGITAL IMAGE-BASED PROCEDURE
Croton Codiaeum variegatum (L.) Blume is a tropical-origin ornamental tree or shrub. Over 300 cultivars are found within this species. The croton cultivars exhibit remarkable leaf phenotypic variety that is apparently ascribed to a high frequency of somatic mutation on the leaves. Until recently, the variation-producing mechanism has yet not been clarified and we do not have a systematic procedure to distinguish the croton cultivars. Even newly developed cultivar has given an attractive trade name. The cultivar names of croton are subjective and may depend on individual preference. Therefore, a new procedure is required to characterize and classify croton cultivars. We investigated 29 croton cultivars found in Okinawa islands, Japan. The cultivars were characterized by 6 quantitative and 7 qualitative leaf parameters. Quantitative leaf parameters were quantified through ImageJ software (NIH), while qualitative characters were assessed through visual comparison. Considerable phenotypic variations were found among the croton cultivars. Scatter plot analysis revealed that leaf length was weakly correlated with leaf width (r = 0.41). Leaf length varied 2.5-fold (12.7 to 26.42 cm), leaf width - 5-fold (2.4 to 12.2 cm), leaf index - 3.7-fold (2.1 to 7.8), petiole length - 8.7-fold (1.1 to 9.8 cm), leaf area - 6.8-fold (30.8 to 209.8 cm2), leaf perimeter - 2.4-fold (34.2 to 81.7 cm). Analysis of variance (ANOVA) suggested that significant variations were observed among the cultivars for all quantitative leaf parameters. These results indicated that croton cultivars can be distinguished by the leaf dimensions. In leaf attachment and arrangement, no difference was observed among the cultivars. However, variations were observed among the cultivars in leaf base, margin, apices, shape and coloration and color patterns. Based on the results we propose a new classification procedure using the five parameters: leaf base (B1-B2), margin (M1-M3), apices (A1-A3), shape (S1-S7) and coloration and color pattern (C1-C5).
Mollick , A.S. and Yamasaki, H. (2012). PHENOTYPIC VARIATIONS IN CROTON CODIAEUM VARIEGATUM (L.) BLUME CHARACTERIZED BY DIGITAL IMAGE-BASED PROCEDURE. Acta Hortic. 937, 393-400
cultivars, leaf phenotypic variation, leaf parameters, digital image-based procedure, cultivar classification