EVALUATION OF TRANSGENIC TOMATO FRUIT WITH REDUCED POLYGALACTURONASE ACTIVITY IN COMBINATION WITH THE RIN MUTATION

Tomatoes (Lycopersicon esculentum Mill. cv. Ailsa Craig) homozygous fo r polygalacturonase antisense (PGAPGA) and heterozygous for the 'ripen ing inhibitor' (rin) allele (RinrinPGAPGA) were compared with heterozy gous rin (Rinrin), homozygous PG antisense (PGAPGA) and wild-type Ails a Craig (RinRin) control fruits. Thus the presence or absence of PGA w ere combined with rin or Rin in a two-by-two factorial design. Polygal acturonase (PG) activity was reduced to 26% of the wild-type by hetero zygous rin, and to less than 1% by the PGA genes. There was no additiv e effect on PG activity of the rin allele in the PGAPGA background. Bo th PGA and the rin allele had beneficial effects on processing attribu tes. 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 th ereafter. Fruit with the rin allele were firmer than the controls. The PGA genes had a small beneficial effect on firmness, which was only m anifested in the wild-type but not in the rin background. The PGA gene s and the rin allele improved survivability, but the rin allele was mo re effective. Analysis of colour showed that both the rin allele and t he PGA genes resulted in a small reduction in the tomato colour index (TCI), although not additively. The Rinrin fruit composition was impro ved in relation to the wild-type, although the beneficial effect of th e rin allele was not generally apparent in the PGAPGA background. It i s concluded that the enhanced firmness and survival of the Rinrin frui t is not primarily due to reduced PG activity. PGAPGA and Rinrin give increased survivability by two different mechanisms. The data show tha t firmness and survivability are not inextricably linked.