FURTHER STUDIES ON ACREMONIUM WILT OF GRAIN SORGHUM

Acremonium-wilt of grain sorghum has become an important dis­ease in Egypt and many of the sorghum-growing countries. The patho­gen, Acremonium strictum Gams is a soil-borne pathogen invading the roots prior to colonizing the vascular tissues and is probably best con­trolled by host resistance. Eight methods of inoculation were tested to identify a reliable, efficient and large-scale inoculation technique for the evaluation of gen­otypes in the field and in the greenhouse. Soil inoculation (infestation) was effective, uniform, and can be used for greenhouse evaluations, and probably for a small disease nursery. Stalk-inoculation using the tooth­pick technique was not effective in the greenhouse, but was effective, uniform and more practical for field evaluations. A soil drench with a spore suspension, 25 days after sowing, accompanied by root injury was also effective, but too laborious to be practical on a large scale. None of the other inoculation techniques tested was satisfactory. Highly significant variation in virulence of 19 monospore isolates of A.strictum, from different hosts, was detected when the pathogenici­ty of these isolates was tested on four grain sorghum cultivars in the greenhouse, using the soil-infestation technique. Mean percentage infec­tion ranged from 22.75% to 59.99%. Isolate No. 8 was the most ag­gressive, whereas isolates No. 11 was the least virulent. Dorado cultivar, on the other hand, was the most resistant (7.28% mean infection), whereas Giza-15, was the most susceptible (55.01%). The most aggres­sire isolate No. 8 (from grain sorghum), showing 90.0% infection on 8- 15, and only 5.3% infection on Dorado cultivar. Isolate No. 4 (from maize), exhibiting 55,01% infection on Giza-1 5, while it showed the highest infection on this resistant cultivar (32.46%). Isolate No. 3 (from maize) caused the highest infection (77.94%) on local-129, whereaas isolate No. 11 (from grain sorghum) showed the least infection (1 5.1 7%) on the same cultivar. The reaction of 24 selected grain sorghum genotypes to A.strictum was tested in field trial, using toothpick stalk-inoculation. Seven entries namely; Dorado, BTX 623, BTX 631, ICSB-1, ICSB-14, ICSB-18 and ICSB-37 were highly resistant, while Giza-54 and Giza-114, were highly susceptible to infechin.