A Brassica plant, or a cell, part, seed or progeny thereof, characterized in that it comprises at least three mutant FATB alleles in its genome, which produce seed oil, in which the seed oil has less than 7% in weight of saturated fatty acids, based on the total amount of fatty acids in the seed oil, in which said mutant FATB alleles are mutant alleles of a gene encoding a functional FATB protein, in which the functional FATB gene comprises a molecule of nucleic acid selected from the group consisting of: - a nucleic acid molecule comprising at least 90% sequence identity with SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9 or SEQ ID NO: 11； and - a nucleic acid molecule encoding an amino acid sequence comprising at least 90% sequence identity with SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10 or SEQ ID NO: 12 wherein said mutant FATB alleles comprise a region of mutated DNA consisting of one or more nucleotides inserted, deleted or substituted as compared to a corresponding non-mutant DNA region in the functional FATB gene and wherein said mutant FATB alleles encode a non-functional protein that has no acyl ACP-thioesterase activity in vivo, or does not encode protein.Una planta de Brassica, o una célula, parte, semilla o progenie de la misma, caracterizada porque comprende al menos tres alelos FATB mutantes en su genoma, que producen aceite de semillas, en la que el aceite de semillas tiene menos del 7 % en peso de ácidos grasos saturados, basado en la cantidad total de ácidos grasos en el aceite de semillas, en la que dichos alelos FATB mutantes son alelos mutantes de un gen que codifica una proteína FATB funcional, en la que el gen FATB funcional comprende una molécula de ácido nucleico seleccionada del grupo que consiste en: - una molécula de ácido nucleico que comprende al menos el 90 % de identidad de secuencias con SEC ID Nº: 1, SEC ID Nº: 3, SEC ID Nº: 5, SEC ID Nº: 7, SEC ID Nº: 9 o SEC ID Nº: 11； y - una molécu
