Stoneless plums-from Luther Burbank to the present

Authors: Callahan, Ann; Dardick, Christopher - Chris; Scorza, Ralph

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2012
Publication Date: 4/1/2013
Citation: Callahan, A.M., Dardick, C.D., Scorza, R. 2013. Stoneless plums-from Luther Burbank to the present. Acta Horticulturae. 985:71-75.

Interpretive Summary: One goal of our program is to introduce traits into fruit that makes the fruit more desirable to consumers. One such trait is the lack of a stone and seed in stone fruits such as plums, cherries, and peaches. The idea is to extend the popularity of fruit like seedless grapes, bananas, citrus, and watermelon to stone fruit. This is not a new idea as Luther Burbank released two nearly stoneless plum cultivars 100 years ago. These were not completely stoneless. We have begun a program of traditional breeding as well as a molecular breeding program to improve upon Burbank’s plums with the ultimate goal of a completely stoneless and seedless plum. Our initial progress has resulted in a better understanding of why Burbank’s stoneless plums were stoneless and a better understanding of how the cells forming the stone are regulated.

Technical Abstract: At the beginning of the 20th century, legendary breeder, Luther Burbank, released the first of his stoneless plums, 'Miracle'. It and a subsequent release, 'Conquest', were not commercially successful and can no longer be found. In a quest to understand stone formation, germplasm was obtained from California and Oregon that is likely related to Burbank’s stoneless germplasm. Our initial experiments suggested that this material is stoneless because fewer cells are present that would form the endocarp which is the tissue that hardens into the stone. In a selection called ‘Stoneless’, an empty space around the seed is evident where the stone would normally be found. We confirmed Burbank’s observation that in ‘Stoneless’, the stone is not completely absent but contains at minimum a sliver of stone along the suture region that is part of the finiculus. The amount of stone tissue appears to be related to climate and may vary between years from nearly stoneless to containing a complete, intact stone. We have begun to analyze the differences in stone development just prior to pollination until about 10 days after pollination when we can observe differentiation of the endocarp. Using techniques such as real-time PCR and RNA sequencing to measure gene expression, we have identified a number of candidate genes that may be involved with stone development.