HETEROZYGOUS DIPLOID PLANTS REGENERATED FROM ANTHER CULTURE OF F1 RICE PLANTS

Plants derived from anther culture are theoretically haploid, but dipl oid plants are also known to arise. Anther culture-derived diploid pla nts are usually homozygous and are believed to be due to spontaneous d oubling of chromosomes in either microsporocytes or callus cells durin g the culture process. However, heterozygous diploid regenerants may a lso arise from a) regeneration from cultured somatic cells, b) mutatio n occurring during or after a spontaneous doubling event, c) fusion of unlike haploid cells in chimeric callus, and d) regeneration from dip loid microsporocytes resulting from aberrant meioses. This study was d esigned to elucidate the frequency and origin of diploid regenerants f rom rice anther culture. Regenerants were obtained from 11 F-1 genotyp es. Progeny testing detected heterozygosity in 7 out of 211 regenerant s. Each of the heterozygous regenerants were from 'Calrose 76'/waxy 'M -101'. Half of the diploid regenerants from this cross were heterozygo us. No heterozygous regenerants arose from the other 10 F-1 genotypes. Progeny testing indicated that two of the heterozygous regenerants we re as heterozygous as the F-1 plants for three parental characters. Th e other five regenerants exhibited decreased levels of heterozygosity. One of the heterozygous regenerants exhibited evidence of mutation fo r a non-parental character. However, mutation is an unlikely cause of the observed high levels of parental-type heterozygosity. No evidence for the occurrence of chimeric callus was detected, making this an unl ikely cause as well. The most likely origin of the observed partial he terozygosity is regeneration from diploid microspores, which could als o produce plants exhibiting complete parental-type heterozygosity.