Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 4.30

SEARCHING FOR MOLECULAR MARKERS LINKED TO THE TOMATO PARTHENOCARPIC FRUIT (PAT) GENE

BERALDI D., OLIMPIERI I., CACCIA R., PICARELLA M., MAZZUCATO A.

Dipartimento di Agrobiologia e Agrochimica, Sezione di Genetica, Università degli Studi della Tuscia, Via S.C. de Lellis snc, 01100 Viterbo, Italy

mazz@unitus.it

AFLP, gene mapping, Lycopersicon esculentum, parthenocarpy, tomato

Parthenocarpy, the formation of seedless fruits in the absence of functional pollination or other stimulation, occurs in tomato and in several important horticultural crops. Seedlessness is a desirable commodity for consumers as well as a useful trait for genetic improvement since it would allow good yields even in environments unfavorable for pollination and fertilization. Moreover, the knowledge of the genetic and physiological mechanisms behind parthenocarpy represents an interesting challenge for scientific research.

In tomato different genes able to confer parthenocarpy have been described, even though none of them has been mapped yet. Aim of the present work has been the searching for molecular markers linked to the tomato parthenocarpic fruit (pat) gene, whose recessive allele induces parthenocarpy, in order to locate the locus in the tomato genetic map, as a prerequisite for a positional cloning approach.

We searched for AFLP molecular markers using a BC₁F₁ population derived from the interspecific cross Lycopersicon esculentum X L. pennellii LA0716. We classified the BC₁F₁ progeny for the pat phenotype taking in account the characteristic aberrations of anthers and ovules. The screening of 3843 AFLP loci yielded five linked markers, whose relative positions and approximate genetic distances were assigned, in a first instance, by exploiting a sub-population of 48 plants. Surprisingly all of the 5 markers mapped on the same side with respect to the Pat locus, with genetic distances ranging from 4,2 to 12,8 cM. Later, two of the five linked markers, including the closest one, were sequenced and transformed in site-specific markers (SCAR).

By means of the two SCAR markers we screened a larger population in order to establish more accurately their genetic distances from Pat, which turned out to be 1,1 and 4,2 cM. Interestingly the former marker showed a codominant behaviour due to a 39 bp insertion/deletion distinguishing the two alleles. The reliability of this marker was checked by screening a F₂ population where, actually, all the three possible amplification patterns were found with the expected segregation ratio 1:2:1

.

This codominant SCAR marker seems to be a good starting point for positional cloning, although the genetic/physical distance ratio has not yet been established for this genomic region; furthermore it may represent a useful tool for Marker Assisted Selection programs involving parthenocarpy.