Chromosome number and nuclear DNA amount in Psidium spp. resistant and susceptible to Meloidogyne enterolobii and its relation with compatibility between rootstocks and commercial varieties of guava tree

The objective of this study was to determine the chromosome number and DNA amount of accessions of Psidium sp. (arac, a tree, used as rootstocks) and accessions of P. guajava (guava tree) resistant/susceptible to M. enterolobii, which holds some morphophysiological affinity and which could enable their use as rootstocks compatible with commercial varieties of guava. Metaphase chromosomes were obtained by the squash technique and stained with 2 % Giemsa. The determination of DNA amount was done by flow cytometry using Mary buffer. The intraspecific variation in DNA amount (2C) was of the order of 9x, with 2n = 22 observed in only one species of P. guajava. The other species presented variations in the ploidy level in relation to the basic chromosome number x = 11, including the occurrence of polyploidy, cytotypes and disploidy. In some species, the interspecific variation of 2C showed a direct relationship with the ploidy level. Our data confirm that variations in the number of chromosome and in ploidy level are important events to Psidium and can support the understanding of the incompatibility of the graft on rootstocks of guava and arac, a trees resistant to the nematode M. enterolobii.