Lobo, Mario, J. J. Augustine, and L.C. Hannah     

Nor^A, a new allele at the nor locus.

            An abnormal ripening tomato from the Alcobaca region of Portugal identified as ‘Alcobaca’ was studied. In contrast to the rin and nor ripening mutants, ‘Alcobaca’ does develop red pigmentation in the ripe fruit stage. The purpose of this investigation was to elucidate the inheritance of ‘Alcobaca’ and possible allelic relationship with the ripening mutants rin and nor.

            Plants of ‘Alcobaca’ were crossed with ‘Florida 1C’, a normal ripening tomato, and the F₁, BC₁, BC₂ and F₂ generations were obtained. The ripe fruit color of each plant was classified as normal or mutant (‘Alcobaca’ type). The abnormal fruit ripening of ‘Alcobaca’ was found to be conditioned by a single recessive gene (Table 1). The respiration, ethylene evolution, color of the ripe fruit, polygalacturonase (PG) activity and fruit storage life was determined for the nonsegregating population. Although the mutant phenotypically fit a single recessive gene model and the F₁ plants had normal red fruit color, in the heterozygous condition several of the ripening processes were affected (Table 2). Compared to ‘Florida l C’, the F₁ respiratory and ethylene peaks were reduced 18 and 31%, respectively, PG activity was decreased 47%, and storage life (ASI) was increased two fold.

            Allelism test between ‘Alcobaca’ and rin indicated they were not allelic (Table 3).

            In the allelism test of nor x ‘Alcobaca’, the fruit from the F₁ plants had a mutant phenotype similar to that of ‘Alcobaca’. The F₂ segregated 3 plants of ‘Alcobaca’ type fruit: 1 plant of nor type fruit (Table 4). ‘Alcobaca’ is another allele of nor and is dominant to the recessive nor allele in phenotypic expression. Physiological evaluation of the ripening processes of nor, ‘Alcobaca’ and their hybrid also indicates an allelic relationship between nor and the allele in ‘Alcobaca’. The values for the respiratory and ethylene peaks, color (ratio a/b), firmness at different stages, PG activity, and storage life (ASI) of the nor x ‘Alcobaca’ hybrid were between the parents (Table 5). The dominant nature of the allele in ‘Alcobaca’ over nor is supported by the physiological data. The nor x ‘Alcobaca’ hybrid has a climacteric pattern for respiration and ethylene evolution and some PG activity was detected in the fruit which is similar to ‘Alcobaca’,

            Phenotypically the allele of nor in ‘Alcobaca’ is dominant to nor but the alleles are co-dominant when physiological parameters of the fruit ripening processes are examined. It is proposed that the symbol nor^A be used to refer to the mutant allele of ‘Alcobaca’.

Table 1. Inheritance of the abnormal tomato fruit ripening ‘Alcobaca’,

     Classification

                                    Number of           Number of plants                   Expected

Population                    plants               Normal             Mutant             ratio                 X²

Florida 1C (P₁) 40                    40                    0                      1:0                   —

Alcobaca (P₂)               40                    0                      40                    0:1                   —

F₁ (P₁   x P₂)                 40                    40                    0                      1:0                     —

Rec F₁  (P₂ x P₁)           40                    40                    0                      1:0                    —

BC₁                              80                    80                    0                      1:0                     —

BC₂                              82                    39                    43                    1:1                   0.7-0.5

F₂                                 211                  154                  57                    3:1                   0.7-0.5