Observation On Anatomical Mechanisms Of Citrus Corky Vein And Malformed Fruit With Boron Deficiency

In the southern part of China, the boron levels in the soil is vrey low. And the phenomenon of B-deficiency is serious in Jiangxi province where the main cultivation are Newhall Navel Orange and HB Pummelo. The boron deficiency always cause leaf senscence, reduces tree vigor rapidly and affects fruit yield and quality in the coming year. This is an important problem that urgent to be solved. The reasons of the symptom were confirmed after our study that the vascular tissue was damaged. The materials researched in this paper are the leaves of Newhall ’Navel’ orange and HB Pummelo, and the fruit of HB Pummelo. With boron deficiency supplied in greenhouse, citrus showed the similar symptoms as that in the field. The sympotom of the corky veins, anatomical mechanisms of corky split vein and fruit abnormalities were observed on. These results indicated that:1. The structure change of the vascular tissue under B-deficiency:1) Compared to the control, the vascular tissue of the Newhall Navel Orange under B-deficiency occurred meristematic hyperplasia. The vascular cambium became reactivity during the phase of moderate B-deficiency, While B-deficiency was very serious, the vascular cambium extruded epidermis and the vein was split. Moreover, along with the increasing of B-deficiency, the starch grains and saccharides to increased in the veins, but they were almost disappeared under the most seriously of B-deficiency situation.2) The hyperplasia mechanisms of HB Pummelo under B-deficiency were as same as that of the Newhall Navel Orange.3) Compared to the control, the number of the vascular bundles increased in the mesocarp of HB Pummelo, and the vessel elements increased but arranged confusion. 2. Index changes of the vascular tissue under B-deficiency:1) With the increasing of B-deficiency, the ratios of xylem/vascular area and phloem/vascular area were increasing; the number of vessels and total trachea areas increased firstly and then decreased, the total trend of vessel density was to decrease.2) Compare to the control, the ratio of xylem/vascular area and phloem/vascular area of HB Pummelo with B-deficiency as same as the Newhall Navel Orange.3) Compared to the control, the numbers of vessel elements and vessel density appeared negative correlations in HB Pummelo under B-deficiency, and the trachea areas showed no obvious varies.3. The changes of the vessel elements under B-deficiency:1) The number of the pitted vessel increased which of Newhall ’Navel’ orange with boron deficiency;2) A lager number of the pitted vessels was hyperplasia which of the nervure and mesocarp of HB Pummelo with boron deficiency;3) it showed that normal vessels were round and full, while vessels were transubstantiated shriveled under boron deficiency condition;4) Compared with the control vessels became short and narrow, cell walls turned thin, and the percentage of no-tail under boron deficiency condition, which finally led to the vascular tissue lose its function;5) The headstream of the corkification and "contract fruit" is that the vascular tissue with boron deficiency was damaged and transportation efficiency was decreased.