Research in our laboratory, conducted by Dr. Tom Fernandez and others, indicates that Mark rootstock is extremely sensitive to drought stress. The most striking evidence of this characteristic has been expressed in orchards in the arid west. There, trees inadequately watered readily go into drought stress, especially when caring heavy crops.
We have observed this phenomenon in Michigan, where the trees are grown in light soils without irrigation. Trees on Mark are extremely precocious and productive in the early years, especially on wet or heavy soils. At our Clarksville Research station, Mark has been performing well on the Riddles Sandy Loam soil. The trees are irrigated by drip and the soil is a heavy loam. Dr. Wes Autio at the University of Mass. (Autio and Lord. 1994. Fruit Notes Vol 59(2):1-7) found that trees in his 1980 NC 140 rootstock trial were most productive on Mark than M.9 EMLA and all other stocks. The soil at their Belchertown, MA site was not water limiting.
While it was the best rootstock in the trial, problems arose in the planting, as have been observed elsewhere; Root Mass Proliferation RMP (ground line swelling) and runting-out or decline in latter years. In a recent study conducted by A. Otero in our laboratory, he found that the RMP can be found on most trees over three years of age in orchards (>75% in 1992 survey). He also found that there was an inverse relationship between size of swelling and canopy growth. When studied under the microscope, he found that the tissue in the RMP portion of the trunk was made up of disorganized xylem vessels. The work suggests that there is a relationship between this characteristic and restricted water/nutrient transport.
We are currently conducting controlled irrigation studies at the Kellogg Biological Station, where we are comparing trees on Mark to Bud.9 and M.9 EMLA. We hope to have more definitive results for growers at the conclusion of the 1994 season.
Currently, I am suggesting to growers in Michigan, that if they don't have trees on Mark on heavy wet soils, that they should be irrigating at twice the volume a frequency to that of trees on M.9 and M.7. We have found M.9 EMLA to be the most frequency to that of trees on M.9 and M.7. We have found M.9 EMLA to be the most drought tolerant (canopy) rootstock (even more than MM.111). Once again, we have found Mark to be quite productive at the CHES site where trees are on a heavy so they are irrigated at 75 % of evap. pan until mid to late July, when and depending upon natural rainfall and crop, we change to 100 % of evap. pan until mid. August.
I observed that in southern France (dry arid Mediteranean climate), a grower there good success with Mark when the trees were irrigated at 160 % of evap. pan. Where soils change drastically, as with glacial soils, growers should mulch trees in dry orchards to help avoid stress. While this rootstock has disappointed many grower because of some the recent negative findings, it still has potential as a producer for heavy soil sites.
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Tree Fruit Research & Extension Center, Washington State University,1100 N Western Ave., Wenatchee, WA, 98801 USA
Wenatchee WA, 31 October 1995