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Cold Inury to Grapevine TrunksRole of Bud Survival in Recover from Injury |
In studies that Charlotte Pratt and I made, we noticed that shoot development and trunk cambial activity are interrelated. When few buds survive the winter trunk, growth suffers. When we excised all buds above, there was no phloem reactivation or vascular cambial activity. If we let buds develop and then later excised the shoots, cambial activity which had started would cease.
We simulated winter injury to trunks by applying a stream of liquid nitrogen to freeze portions of canes. When we excised the buds above the frozen tissue, there was no new cambial activity. When shoots were allowed to develop, only non-frozen vascular cambium resumed growth in the spring. However, pprovided shoot growth continued, eventually undifferentiated cells in the rays cells of the frozen canes would begin to divide and a new vascular cambium would form at these sites. A portion of non-differentiated parenchyma would remain buried in new xylem.
Developing shoots produced a substance which stimulated unorganized callus growth similar to that produced by crown gall. A continued flow of these substances allowed the creation of a new vascular cambium. We found that we could replace the growing shoot with a paste of the plant hormone, auxin. We believe that vascular cambium is reactivated in response to a flow of auxin produced by the developing shoots. In uninjured trunks the "old cambium" is regenerated in response to auxin flowing down the reactivated phloem in the last formed phloem bundle. The last soft phloem is always produced adjacent to the cambium of the previous year.
This interrelationship between bud survival, shoot growth and cambial reactivation helps to understand the nature of trunk cold injury and the appropriate response to it.
Chardonnay vines were planted in Geneva in 1974. Following the growing season of 1976, canes were selected to become trunks. In January, 1977 many of these canes became injured just above the snow line. Most injury was restricted to a few inches. Ms. Pratt and I were able to follow the development of these injured canes in their second year of life. The figures below show what we found.
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Normal undamaged cane after two months of growth in year 2Note complete resumption of cambial activity in yr. 2 around the circumfrence os the cane. Tissues in order (starting at center)
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Partially winter injured cane following 2 months of year 2 growthYear 1 pith, xylem and vascular cambium are distinct. Most year 1 phloem was not dislodged by new cambial activity. In lower left there has been callus growth originating in the phloem ray cells. A new vascualr cambium has formed there and is producing xylem and phloem |
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Cane in year 2 following complete cambial death in winter following year 1All that is visible is pith and year 1 xylem |
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Detail of extensively cold damaged but recovering caneIn the lower section pinkish, undifferentiated callus has proliferated. Such growth generally begins in the phloem region, if phloem survives, or in xylem ray tissue if the phloem sector is dead. Near the lower center at the margin of last year's vascular cambium, new xylem and phloem cells have been produced by a new vascular cambium. This tissue formed inside the callus growth in response to a supply of plant hormones produced by growing shoots above the cold damaged area and translocated down to the wound. |