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

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Abstract
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‐11, 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‐11, 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‐11 allele, in contrast to the Prs‐1+ allele, is primarily present in gene pools of „Moneymaker 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.