INTERNAL BARK NECROSIS IN ‘NIITAKA’ PEAR

The potential cause of internal bark necrosis (IBN) of ‘Niitaka’ pear trunks was determined.
The symptoms were similar for all pears growing in orchards of different locations.
Growth characteristics of trees as well as soil fertility were examined in a ‘Niitaka’ pear orchard where the IBN symptoms were severe.
Soil pH was not different from unaffected sites, but NO₃-N and NH₄-N contents of the soil were very high.
Shoots were numerous and long, but shoot growth lasted till late August.
Compared with other nutritive elements, nitrogen content was very high in the outer tissue of the cambium, low in pith tissues but was not different in the xylem.
Internal bark necrosis was induced in potted trees by applying NO₃-N and NH₄-N, at rates of 2 or 4 times higher than the recommended levels.
Leaf blackening was induced and defoliation occurred.
This was followed by internal bark necrosis of the trunk and finally death of the whole plant.
Cell walls were collapsed, vacuoles were filled with unknown materials, and middle lamellas were thickened.

International Symposium on Asian Pears, Commemorating the 100th Anniversary of Nijisseiki Pear

G.C. Song

Pyrus pyrifolia, NO₃-N, NH₄-N, outer tissue of the cambium, xylem, pith tissue

https://doi.org/10.17660/ActaHortic.2002.587.87