Andhra University, Department of Botany Visakhapatnam 530 003, INDIA
From a study of pachytene chromosome complements of one wild variety (L. esculentum f. cerasiforme) and four cultiavars (Big Boy, Break O'Day, Punjab Chhoara and Ponderosa) of L. esculentum differences in chromosomes were observed with reference to the position of centromere, length of eu- and heterochromatic segments and number, position and size of chromomeres especially in chromosomes 2, 3, 4, 5, 7 and 8. The differences between the wild form (L. esculentum f. cerasiforme) and cultivated varieties are striking in that the former has interspersed euchromatic segments in the heterochromatic regions and smaller chromomeres. However, post pachytene stages of meiosis in F1 intervarietal hybrids showed normal bivalent formation and regular meiosis. Therefore, the structural differences observed were believed to be cryptic.
Such cryptic structural differences were clearly reflected as defects in pachytene pairing like unpaired segments, buckle or hump formation, loose pairing, heterozygosity for chromomeres etc. in the 4 intervarietal hybrids studied (chromosomes 2,3,4 and 5 in Big Boy x cerasiforme; chromosomes 1, 2, 4 and 9 in Punjab Chhoara x Break O'Day; chromosome 5 in Break O'Day x Big Boy and Chromosome 2 in Punjab Chhoara x Big Boy). Therefore these differences between the varieties concerned were presumed to be genetic.