Anatomy And Pathophysiology Of Poplar Ice Nucleation Bacterial Canker

Poplar ice nucleation bacterial canker is a kind of important trunk and bough disease. It brings on tnmk malformation, confuses xylem grains, decreases wood value and finally causes trees to die, so it affects forestry design and production heavily. Research results on host tissue resistance, change of infected tissue and pathophysiology show that:1.The trees resistant to the canker have smaller stem epidermatic cells, vessel cavity and thicker epiderm layer, cuticle, medullaiy iays than the susceptive ones. Meanwhile, lenticels are also smaller and more than the susceptive ones. The cell walls of outer complementary tissue under lenticels are thicker. There are one to three-layer of cork cells between complementary tissue and cortex.2.Double cork layer are formed at the initial infection period. As the disease degrades, it interferes in the normal differentiation function of host cells and misleads them to form uniform parenchyma. Medullaiy rays near the infected xylem zone tend to change into biseriate rays and multiseriate rays from tmiseriate rays. The infected vessels were blocked heavily with tyloses, furthermore, some infected vessels had been decomposed. An obvious boundary formed during the vessels being blocked period. The out-of-order xylem proliferation could be observed easily because of the abnormal cell division of cambium and medullaiy ray parenchyma.3. The percent of moisture content of infected bark is a little higher than that of the healthy bark when the trees are young and the cankers are not serious. The disease decreases the content of mobile proline; otherwise it affects the pectin content of bark to increase a bit. Though the double-glucose content of infected bark is less than that of the healthy one, the glucose content of the infected bark is more above 250C and less below 20t than that of the control material. When the infection is not serious, it makes the content of chlorophyll, potassium, calcium, phosphorus and aspiration intensity of infected bark increase, yet the serious infection makes the host have opposite appearance.4.The content of endogenous phytohormone like auxin and zeatin (a kind of cytokinesin)rises in infected bark, while the content of endogenous giberellin and abscisic acid drops at thesame time in the diseased bark.5.The electrolyte leakage of the bark cells increase on account of infection. The more serious the infection is, the more electrolyte leak. The pathogen bacteria have high ice nucleation activity from -IC to -7t.6. Electrophoretograzns of enzyme such as soluble proteins, POD, EST, PPO, SOD, show that there are not obvious change between the infected trees and the control ones.