Evaluation of transgenic tomato fruit with reduced polygalacturonase activity in combination with the rin mutation

Tomatoes ( Lycopersicon esculentum Mill. cv. Ailsa Craig) homozygous for polygalacturonase antisense (PGAPGA) and heterozygous for the ‘ripening inhibitor’ ( rin) allele ( RinrinPGAPGA) were compared with heterozygous rin ( Rinrin), homozygous PG antisense (PGAPGA) and wild-type Ailsa Craig ( RinRin) control fruits. Thus the presence or absence of PGA were combined with rin or Rin in a two-by-two factorial design. Polygalacturonase (PG) activity was reduced to 26% of the wild-type by heterozygous rin, and to less than 1% by the PGA genes. There was no additive effect on PG activity of the rin allele in the PGAPGA background. Both PGA and the rin allele had beneficial effects on processing attributes. However, these improvements were much greater for juice prepared from fruit containing the PGA genes. Juice from the RinrinPGAPGA fruit showed additive improvements in serum viscosity. Fresh fruit quality characteristics were compared at ‘breaker’ and at defined intervals thereafter. Fruit with the rin allele were firmer than the controls. The PGA genes had a small beneficial effect on firmness, which was only manifested in the wild-type but not in the rin background. The PGA genes and the rin allele improved survivability, but the rin allele was more effective. Analysis of colour showed that both the rin allele and the PGA genes resulted in a small reduction in the tomato colour index (TCI), although not additively. The Rinrin fruit composition was improved in relation to the wild-type, although the beneficial effect of the rin allele was not generally apparent in the PGAPGA background. It is concluded that the enhanced firmness and survival of the Rinrin fruit is not primarily due to reduced PG activity. PGAPGA and Rinrin give increased survivability by two different mechanisms. The data show that firmness and survivability are not inextricably linked.