Tetraploidization in citrus rootstocks : effect of genetic constitution and environment in chromosome duplication

The objective of this study was to identify polyploid plants from citrus rootstocks and to evaluate the influence of the genetic constitution and of the environment on the frequency of chromosome duplication. Populations obtained from rootstock seeds of Trifoliata [Poncirus trifoliate (L.) Raf], citrumelo ‘Swingle’ [C. paradise Macf. × P. trifoliate], citrange ‘Troyer’ [C. sinensis (L.) Osb. x P. trifoliate] and citranges Fepagro ‘C13’, ‘C37’ and ‘C41’ [C. sinensis (L.) Osb. cv. Pêra x P. trifoliata] were evaluated under field and greenhouse conditions. Flow cytometry analysis of 415 field plants and 435 greenhouse plants identified seven (1.69%) and 29 (6.67%) tetraploids, respectively. Differences in the number of tetraploid plants among genotypes and locations were observed in field progenies of ‘C 37’ (2.12%) and ‘C 13’ (2.04%) and in greenhouse progenies of ‘C 13’ (15.52%) and ‘C 37’ (6%). The frequency of autotetraploidization events in citrus rootstocks is common and appears to be associated to genetic constitution and environmental conditions