Hevea Bark Anatomic Characteristics Of Difference Latex Flow Phenomenon During Tapping Panel Dryness Occurrence

Tapping Panel Dryness (TPD) in Hevea brasiliensis is one of the most pivotal diseases at the present time, and the pathogenesis of TPD has not been clarified yet till now although a large amount of research has been carried out during the last about 100 years. This study was carried out by microscopic observation and statistical comparison on the anatomical structure of the bark under tapping cut of the rubber clones, Reyan7-33-97 and PR107, base on the result that there were 8 types of latex flow phenomenon during TPD occurrence, and there were internal relation among them interiorly, assumed by our research group's previous on observations on TPD in Hevea brasiliensis. The main results shown as follows,1. There were obviously differences in the microscopic structure characters among the 8 types of TPD symptomsCompared with the healthy plants'bark, in the inter-flowing symptom, the laticifer diameters of conducting phloem and yellow phloem in the plants were smaller; although newly developed laticifer's columns number was normal in conducting phloem, its arrange was loose, sometimes the laticifer columns were not successive, even vanished; the yellow phloem's available laticifer number obviously decreased, and these laticifer became tuberous, the total amount of stone cells'percentage out of the available laticifer's total areas in yellow phloem increased. In the middle-flowing symptom:the laticifer diameters of conducting phloem and yellow phloem were smaller than those of healthy plants, ever 1/3 out of healthy plants'laticifer diameter; The number of conducting phloem's laticider decreased, the columns of newly developed laticifer in conducting phloem were less, and arranged untightly, sometimes these laticifer arrange was not successive, even vanished; the available laticifer columns in yellow phloem were not obvious, but the total amount of stone cells and tuberous laticifer'percentage out of the available laticifer's total areas in yellow phloem obviously increased; the most remarkable character was that several successive stone cells appeared in yellow phloem, then 3 to 7 columns of laticifer which could normally yield latex appeared; and stone cells appeared in the inside of yellow phloem. In the outer-flowing symptom, the laticifer diameter in conducting phloem and available laticifer diameter in yellow phloem presented were similar with those of healthy plants; the laticifer columns in conducting phloem obviously decreased, and were too loose to form columns; the available laticifer amount in yellow phloem obviously decreased, and the laticifer inside the yellow phloem became tuberous laticifer, and arranged loosely, with very small relative density; the total amount of stone cells and tuberous laticifer's percentage out of the available laticifer's total areas in yellow phloem remarkably increased; stone cells appeared inside the yellow phloem, and a certain amount of stone cells appeared outside and in the middle of yellow phloem. As per the slowness-flowing symptom, the diameters of laticifer in the conducting phloem and the available laticifer in yellow phloem were similar without much discrepancy; the laticifer's columns in conducting phloem decreased obviously, and too loose to form a column, basically out of observation; the available laticifer columns in the yellow phloem appreciably decreased, basically couldn't form column, and some tuberous laticifer intermingled among the laticifer, the amount of tuberous laticifer out of the available laticifer's total areas in yellow phloem remarkably increased. Stone cells appeared inside the yellow phloem; racial and laticifer distributed disorganizedly. As per the punctate-flowing symptom, the diameter of conducting phloem's laticifer and available laticifer presented were larger than those of healthy plants; the laticifer columns in conducting phloem decreased, arranged loosely, and had small relative density; without much change, nearly each available laticifer in the yellow phloem presented tuberous laticifer; the amount of stone cells and tuberous laticifer's percentage out of the available laticifer's total areas in yellow phloem remarkably increased; stone cells widely arranged, even appeared in the conducting phloem. As per partly-flowing symptom of partial tapping line, both of the diameters of the laticifer in conducting phloem and the available laticifer in yellow phloem were remarkably decreased; the laticifer columns in conducting phloem remarkably decreased, basically out of awareness; the available columns in conducting phloem were basically similar, but the laticifer was not successive, with a large amount of stone cells and tuberous laticifer intermingling; the amount of stone cells and tuberous laticifer's percentage out of the available laticifer's total areas in yellow phloem remarkably increased; inside the yellow phloem was basically stone cells, the first laticifer column of yellow phloem was stone cell column. As per non-flowing symptom of whole tapping line, the diameters of the laticifer in conducting phloem and the available laticifer in yellow phloem were slightly smaller; the laticifer columns in conducting phloem remarkably decreased, and were not successive; yellow phloem possessed few available laticifer, from inside to outside of which distributed stone cells, intermingling some tuberous cell, and distributing almost stone cells and tuberous laticifer; the amount of stone cells and tuberous laticifer's percentage out of the available laticifer's total areas in yellow phloem was larger than 85%. As per the entire dryness symptom, the diameters in the conducting phloem and yellow phloem were similar, the amount of laticifer columns in conducting phloem was rather small, the conducting phloem was relatively thick, and the relative density of laticifer was small; there was almost no available laticifer columns in the yellow phloem, but nearly stone cells and tuberous laticifer distributed among the columns; the amount of stone cells and tuberous laticifer's percentage out of the available laticifer's total areas in yellow phloem was larger than 90%; and large stone cells presented in the conducting phloem.2. There was internal relation among the 8 types of latex flow phenomenon interiorlyThe observation result indicated, the microstructure variation of the bark with difference latex flow phenomenon during TPD development process would be classified into two types. The first, the stone cell and tuberous laticifer appeared in group at somewhere of yellow phloem of the tapping cut. So our speculated that there were some stress from some outer-factors induced the stone cell and tuberous laticifer appeared in the outer, middle and inter yellow phloem individually that would conduce laticifer recess symptom, middle symptom, inner symptom. The other type was that, the stone cell and tuberous laticifer dispersedly distributed on the yellow phloem in the tapping cut. We can speculated that there were some stress from outer-factor induced the stone cell and tuberous laticifer appeared in the yellow phloem individually and increased gradually. That would conduced latex flow slowness symptom, punctate latex flow symptom, non-latex flow symptom and entirely non-latex flow symptom. These two types of all could develop into irreversible and completely TPD.