Systemic Development of the Pathogen from Root Infection

Abstract

from diseased roots through the stem to infect seeds. Five-day-old blackgram seedlings var. pitsanuloke 2 were inoculated by transplanting them in soil incorporated with 2% inoculum of M. phaseolina (5 seedlings per opot) and wee watered frequently to keep soil moisture a t 60% water holding capacity (5 seedlings per pot) and were watered frequenty to keep soil moisture at 60% water holding capacity (WHC) for 52 days (3 days after the first pod turned black). Soil moisture was then gradually reduced to 57% WHC and finally to 56% WHC as planned. Fourteen replications were made. Six replications were for investigating the systemic development of the pathogen from diseased foots through the stem and seeds by the pathogen on a pototo dextrose agar medium at the same investigating times to ensure that it was M. phaseolina invading or infecting inside plant parts. A location, growth and the incidence of mycelia of the pathogen inside the stem were recorded. The severity of root rot was evaluated by using a 0-5 scale.
Results revealed that M. phaseolina from diseased toots invaded the stem tissues systemically and intracellularly at the rate of 4.4 centimeters a day. Its mycelia were located mostly in the xylem, phoem and pith but rarely in cortex. They could invade upward the top end of the plant and some pod stalks since soil moisture was reduced to 57% WHC. However, no sdde was found infected at any investigating times. The reducting of soil moisture to 57% WHC had an overwhelming effect to the diseased plants and made them death of the entire diseased plants within 1-2 days. The abrupt death of the entire diseased plants at the same time terminated growth and activities of the pathogen. Mycelia formed sclerotia and could not infect the pod, therefore, seeds were free from infecting. In contrast, under soil water which was flavoured to growth of the plants, at 60% WHC, the plant grew vigorously and could highly resist to the onset of the pathogen mycelia. So they could not reach the pod and seeds before they were mature and dry out.