Beneficial bacteria in underground organs of potato (Solanum tuberosum L.)

摘要

The microenvironment of the rhizosphere contains soil that surrounds plant roots and is directly influenced by plant metabolism (14). The surface of the tuber with adhering soil was termed geocaulosphere (gea = earth, caulos = stem, sphaera = sphere). There are major anatomical differences between roots and tubers since the tuber is a modified shoot in soil. This suggests that in this microenvironment abiotic conditions varied from the rhizosphere like in the geocarposphere investigated by Kloepperand Bowen (10). The effects of bacteria living in these microenvironments on the host plant may be beneficial, neutral or deleterious (14). Beneficial bacteria can influence plant growth and health in two ways: a direct beneficial effect on plant growthwill be achieved by the bacterial production of phytohormones, e.g. auxin (indole-3-acetic acid) and enhancement of phosphate uptake. An indirect effect will be achieved by biological control of plant pathogens. Bacterial antagonism responsible for biological control, may result from the production of antibiotics, competition, parasitism and induced resistance. Verticillium dahliae Kleb. is a soilborne pathogen causing vascular wilt in potatoes. The pathogen is responsible for high yield losses in potato growing areas all over the world, e.g. up to 20 percent in the western part of the U.S.A. (13). V. dahliae is the most important pathogen of potato under stress conditions in Negev desert (16). V. dahliae invades root tips of growing plants throughoutthe growth season. Additionally, microsclerotia of V. dahliae can survive in a dormant stage for up to 30 years in agricultural fields. There exists no possibility to control the pathogen with chemicals (3). The development of alternative protection methods is needed. Biological control with beneficial bacteria able to colonize both microenvironments and protect the rhizosphere is one possibility (18). The goal in manipulating the rhizosphere is to increase the balance of beneficial over harmful effects (14). The objective of our research was to characterize and compare the potential beneficial bacterial populations in the rhizosphere and geocaulosphere of potato. This information is necessary for designing new approaches to biological control to V. dahliae.