Inbred testing of tomato (Lycopersicon esculentum L.) F1 varieties by ultrathin-layer isoelectric focusing of seed protein.

To test seed lots of tomato F1 hybrid varieties for the presence of undesirable inbred seeds by electrophoresis, a method has been developed on the basis of ultrathin-layer isoelectric focusing. The method is based on the genetic variation of the seed protein PRS-1 which could be visualized by isoelectric focusing of a 5 mM NaCl-soluble seed protein extract in a pH 6-9 gel followed by protein staining. Two genetic variants of the PRS-1 protein, PRS-1+ and PRS-1(1), were found among open-pollinated varieties, as well as among F1 hybrid varieties. The isoelectric points (pI) of the PRS-1 proteins are 7.1 and 6.1 for PRS-1+ and PRS-1(1), respectively. The PRS-1 protein is unique to seed tissue and is located primarily in the embryo. A genetic 1:2:1 segregation of the gene Prs-1 among several F2 populations shows monogenic inheritance. Analysis of commercial F1 hybrid varieties from several seed companies indicated that the Prs-1(1) allele, in contrast to the Prs-1+ allele, is primarily present in gene pools of "Money-maker type" tomatoes. The described method is generally applicable to all tomato F1 varieties that are heterozygous for the gene Prs-1. With the described method one person can routinely analyze more than 768 seeds per day.