Written By Joe Connell, UCCE Farm Advisor, Butte County
Krymsk 86 is a peach-plum hybrid rootstock (Prunus persica x P. cerasifera) that originated in the Krasnodar region of Russia. As such, this hybrid rootstock is different than any other rootstock in use in the California almond industry. Now that it is planted in commercial orchards under many different conditions we are learning more about how it behaves when grafted to almond.
When grafted to peach, plum, or apricot it is thought to be tolerant of cold temperatures, drought, water logging, resistant to phytophthora, and somewhat resistant to lesion nematodes. It was observed to be precocious, productive, and appeared to increase fruit size. Now that it is grafted to almond in California we are discovering that trees behave differently than almond grafted on peach rootstocks and differently than almond grafted on Marianna 2624 plum. In fact, it behaves uniquely like almond grafted on Krymsk 86.
The first trial in Butte County including this rootstock was planted in 2003. Just completing their ninth growing season, the Nonpareil trees on Krymsk 86 are larger than adjacent trees on Lovell peach. What we know so far is that Krymsk 86 appears to be compatible with almond and it has a vigorous root system with good anchorage as a young tree. Krymsk 86 roots are susceptible to root knot nematodes and this will limit its usefulness in the San Joaquin Valley and on light textured soils where root knot can be a problem. In sandy soils in Stanislaus County, trees on Krymsk 86 are less vigorous than trees on peach roots.
In spring 2011, soils were wet and cold for an extended period causing trees to get a slow start. Several young orchards had yellow trees showing up on Krymsk 86. Trees were yellow for several reasons, none of which appeared fatal. In one young orchard planted on heavy clay adobe soil, trees yellowed at the wettest end of the field showing normal sized leaves that were just pale. They had not received nitrogen fertilizer and I believe the wet saturated conditions denitrified available nitrogen present resulting in a transient nitrogen deficiency. As soil dried out and warmed up they improved.
In another orchard, the yellowing was displayed as interveinal chlorosis symptomatic of manganese deficiency. Yet another young orchard displayed both zinc and manganese symptoms in the leaves where the trees on Krymsk 86 were yellowing. An older orchard on peach rootstock was also displaying manganese deficiency in an adjacent area. These micronutrient deficiencies usually occur in soil related areas in orchards and are more prevalent when soils are wet, cold, and saturated reducing root activity and nutrient uptake. Krymsk 86 appeared to be sensitive to these conditions. In the past I have observed trees on Marianna 2624 plum rootstock displaying fewer manganese deficiency symptoms than adjacent trees on peach roots.
Finally, some young yellow trees on Krymsk 86 displayed symptoms similar to the union mild etch (UME) problem that occurs on Marianna 2624 plum rootstock when soils are too wet during the growing season. On Marianna 2624 this problem is more prevalent on varieties in an orchard that are the least compatible with the rootstock such as Butte and Monterey. On Marianna 2624, once growth is affected by UME, leaves turn pale yellow and growth may stop. When severely affected, leaves roll and scorch on the margins, and trees may defoliate. Some trees die or remain weak enough to be removed although most affected trees recover the following year. Some possibly less compatible varieties on Krymsk 86 displayed similar symptoms with pale yellow trees or trees with rolled leaves where growth stopped in the late spring as they coped with saturated soils. Once soils warmed and the irrigation season progressed some trees began to improve and put out a new flush of growth.
In conclusion, Krymsk 86 behaves somewhat like its plum half while other times it behaves like its peach parent. With field trials of this rootstock planted throughout California, and more commercial plantings within the Sacramento Valley, only time will tell if these trees can tolerate extensive winter waterlogging like Marianna 2624, resist wood rots and blow-overs, or tolerate oak root fungus better than peach rootstocks.
Editors Note: For more information on Krymsk-86, please view Progressive Genetics Group’s (P2G) one page information sheet. Since this is a relatively new rootstock, this handout may posses a more positive forward outlook, but the highlighted points are correct based upon our current knowledge. Keep in mind that we have no experience with this rootstock beyond the 9th leaf. This makes it hard to make a recommendation for an orchard planting that is expected to last 20+ years.