The interaction of Phoma terrestris, Pythium irregulare and Fusarium acuminatum in causation of red root rot of corn (Zea mays L.)

Laboratory and greenhouse tests were conducted in 1992 and 1993 to determine: (1) whether red root rot of corn (RRR) was caused by P. terrestris alone or by a combination with Pythium irregulare and Fusarium acuminatum; (2) the effects of the pathogen(s) on root rot and wilt development; (3) the resistance or susceptibility of corn hybrids to RRR, and whether soybean and sorghum were good alternatives for crop rotation with corn.;Field fumigation tests (non-irrigated, 1992 & 1993) and a natural field survey (irrigated, 1992) were conducted in Newark and Seaford, Delaware. Inocula of the same fungi as used in the above tests and corn hybrids DK 572 (susceptible) and DK 582 (resistant) were used in the tests. The major objectives of the tests were to determine: (1) the etiology of RRR of corn; (2) the changes in pathogen population levels over the growing season; and (3) the effects of the disease and pathogen population levels on development and severity of root rot, basal stalk rot, wilting, and the weight of roots and grain.;Results of the complex studies showed that P. terrestris was the major causal pathogen of RRR of corn. The combination of P. terrestris and P. irregulare resulted in an interaction on the susceptible hybrid, DK 572, with rapid development of symptoms and significantly higher ratings of root rot, basal stalk rot and wilting. There was also greater decline of grain yield and faster increase in the rhizosphere population of the two fungi. F. acuminatum played a minor role in inducing the disease, with little interaction on symptom development when combined with P. terrestris and P. irregulare.;DK 582 was more resistant to RRR than DK 572, resulting in reduced symptom development and population densities of the fungi and higher yield. Sorghum might be a good alternative for crop rotation with corn because it was not susceptible to any of the tested pathogens in the greenhouse trails. Soybean might also be an alternative, but it was very susceptible to P. irregulare.