Lobo, Augustine and Hannah (TGC 32) have recently reported a third allele nor^A at the nor locus in the cultivar Alcobaca. Mutschler (J. Amer. Soc. Hort. Sci. 109:500-503), in contrast, has proposed that Alcobaca possesses a new ripening gene alc which is distinct from nor but linked to nor (17 map units) and to u (20 map units) on chromosome 10.
We have completed tests of allelism with Alcobaca and several additional aberrant ripening cultivars which are similar to the cultivar Italian Winter from which the nor gene was first described (TGC 23:33). Our results support the conclusions of Lobo et al. that Alcobaca possess a gene affecting fruit ripening which is allelic with nor. Results from Fl and F2 populations support this conclusion since normal ripening recombinants are not recovered in F1 or F2. These studies have led us to the conclusion that the cultivars Alcobaca, Long Keeper, Spanish Winter and Italian Winter all carry a similar allele at the nor locus which influences both fruit ripening and shelf life. A wide range of variation in the degree of inhibition of fruit ripening has been found among lines containing the nor allele. This variation may result from more than 2 alleles at the nor locus as suggested by Lobo et al., or, conversely, from the action of modifier genes which influence the expression of nor. We have found that the degree of inhibition of ripening by nor varies widely depending upon genetic background. This observation implies that modifier genes exist which alter the degree of inhibition of ripening by nor. This considerably increases the potential practical value of this material for plant improvement purposes since long shelf life and more acceptable quality can be combined in inbred or hybrid cultivars.