SELECTION FOR SPONTANEOUS TOMATO HAPLOIDS USING A CONDITIONAL-LETHAL MARKER

We describe a method for the isolation of spontaneous haploid tomato p lants from greenhouse-grown seedlings obtained from crosses involving a transgenic parental line in which a counter-selectionable chimeric g ene has been introduced. Transgenic seeds transformed with the aux2 ge ne, a gene of Agrobacterium rhizogenes that transforms naphthalene ace tamide (NAM) into naphthalene acetic acid (NAA), did not develop roots in the presence of NAM, whereas wild-type tomato seeds developed a no rmal rooting system in its presence. Transgenic plants homozygous for aux2 (cv 'UC82b') were used to pollinate male-sterile (ms322) tomato p lants (cv 'Apedice'). Using NAM as a toxic substrate to kill heterozyg ous diploid plants carrying aux2, we selected for three maternal haplo id plants resulting from the development of the female nucleus without fertilization. Maternal haploid selection using the aux2 marker was l ess efficient than the visual screening of haploid plants displaying r ecessive morphological markers of the female parent, but provided evid ence for the feasibility of haploid selection in species for which no morphological markers are available.