Dennis Tarry of Dave Wilson Nursery observes a cherry plum cross.

Dennis Tarry of Dave Wilson Nursery observes a cherry plum cross.

While looking for a winning interspecific cherry, a California fruit breeder may have stumbled upon new plant material with value as a cherry rootstock.

Zaiger Genetics, Inc., of Modesto, California, has been developing interspecific cherries, crossing hybrids of plum and cherry, in hopes of discovering a more grower-friendly cherrylike fruit.

Some of the cherry-plum crosses may have value as cherry rootstock.

Dennis Tarry of Dave Wilson Nursery, the exclusive U.S. licensor and primary propagator of varieties developed by Zaiger, said that two of the rootstocks in trial have shown traits that they are looking for–adaptability to mechanical harvesting and high-density planting, and dwarfing, precocious characteristics.

“However, they are not as disease resistant as we’d hoped, so we aren’t pushing them as a solution yet,” Tarry said.

Preliminary data from plum/cherry rootstocks show them to be cold hardy, resistant to bacterial canker and phytophthora, precocious, and dwarfing—all qualities of interest for cherry growers, he said. But more work is needed to find the winning combination.

The biggest advantage that Tarry sees in development of new cherry/plum rootstocks is a lower cost than the popular cherry interstem, the Zee Stem. “The cherry/plum rootstocks would be more economical than the Zee Stem because you wouldn’t have to pay for the double budding that must be done for the interstem.”

He estimated that the cost of a cherry/plum rootstock would be a dollar less than the Zee Stem, in line with the cost of Mazzard rootstocks.

“Where the Zee Stem makes economical sense is in bearing fruit early,” Tarry said, noting that in some locations, earlier production can greatly increase crop returns.

The patented and trademarked Zee Stem, developed by Zaiger Genetics, is an interspecific combination of peach and almond rootstocks that has expanded the area where cherries can be planted in California. The interstem allows cherries to be grown on rootstocks normally used for other stone fruit and to be planted in alkaline, saline, and even wet soils. As grower feedback filters in from commercial planting experience, the Zee Stem is showing longevity from early plantings, Tarry said. But they have also found that the interstem trees tend to be sensitive to heat in late summer and go to “sleep” for a while.

Most Zee Stems have been put on Citation rootstock, a peach and plum interspecific cross developed by Zaiger. However, Zee Stem trees on Viking rootstock show tolerance to alkaline soils and bacterial canker. Viking is a plum and almond interspecific rootstock crossed with Nemaguard and was also patented by Zaiger.