Observation of microbial colonization on the surface of rice roots along with their development and degradation

Microbial colonization on the surface of rice roots along with their develo pment and degradation was examined throughout the growth period of rice pla nts with the naked eye, by light microscopy, and scanning electron microsco py. Four stages were recognized in the development and degradation processe s of rice roots and microbial colonization pattern. At stage I, both crown and lateral roots were undergoing development, white, and covered with a mu cigel layer. Microbial colonization was rarely observed. At stage II, later al roots developed further, and they stained brownish due to the deposition of iron oxides/hydroxides on the root surface. Microbial colonies commonly developed along the grooves between epidermal cells. At stage III, lateral roots ceased to develop, and the root surfaces were widely covered with de posits of iron oxides/hydroxides, Microbial colonies were found inside epid ermal and exodermal cells as well as on epidermal cells, At stage IV, the r oots became dark brown or transparent, Most of the epidermal and exodermal cells disappeared from the root surface. Roots went through stage I to stag e IV as they aged, and respective degradation stages were observed from the nodal roots from higher nodes to the nodal roots from lower nodes. There w ere fewer microorganisms on the surface of lateral roots than on crown root s. About 50% of the roots were at stages I and II on June 20 and July 20, w hich corresponded to the early to middle growth stages, while most of the r oots were at stages III or IV from August 10.