Characterization of ‘Stoneless’: A Naturally Occurring, Partially Stoneless Plum Cultivar

Abstract

The plum (Prunus domestica) cultivar Stoneless was characterized to determine if the lack of stone was the result of reduced endocarp development or a decrease in lignification. Fruit were sampled at several times from 37 days before stone hardening (DBH) until the stone was too hard to cut with a knife and were compared with plum fruit that had normal stones. At all sampling times there was less endocarp tissue and reduced lignin staining in the ‘Stoneless’ plum fruit. The tissue that did stain appeared to be small endocarp remnants present in the ‘Stoneless’ plum, and was concentrated at the suture side and at the blossom end as well as the stem end. The lignin stain was detected in these regions beginning at 19 DBH, while the normal plums had a progression of staining beginning at the blossom end, suture side at 23 DBH and radiating up to the stem end and throughout the presumptive stone tissue at 8 DBH. Comparison of dry weight for dissected tissues agreed with the specific lack of endocarp tissue in the ‘Stoneless’ plum. Gene activity for the lignin pathway was analyzed using four known genes required for lignification. All four genes showed endocarp-specific expression in ‘Stoneless’ similar to that observed for the control. These results support the idea that the phenotype of ‘Stoneless’ plum fruit is due to a decrease in endocarp formation rather than a decrease in endocarp lignification.