Rapid estimation of ploidy levels in in vitro-regenerated interspecific Arachis hybrids and fertile triploids

Summary A significant correlation among chromosome number, chloroplast number and pollen grain size was observed using interspecific hybrids (2n=30,60), Arachis hypogaea (2n=40), A. stenosperma (PI 338280) (2n=20), A. batizocoi (PI 468329) (2n=20) and A. villosulicarpa Hoehne (PI 336984) (2n=20), representing four ploidy groups. Both chloroplast number in guard cells and pollen grain size were found to be positively correlated with ploidy, and provided a reliable method to distinguish diploid, triploid, tetraploid and hexaploid plants from each other regardless of their taxonomic backgrounds. These methods in combination with root-tip chromosome counts enabled us to confirm ploidy determinations on all three dissue layers, L₁, L₂ and L₃ (guard cells, microsporocytes and root meristematic cells, respectively), and to detect the chimeric nature of some colchicine-treated tissue culture-derived plants. Screening pollen grains by size and the detection of highly stainable and viable, 30-chromosome pollen grains have enhanced the use of triploid hybrids in peanut breeding programs.