ISOLATION, CHARACTERIZATION, AND DISTRIBUTION OF A BIOCONTROL FUNGUS FROM CYSTS OF HETERODERA-GLYCINES

Seventy-six populations of Heterodera glycines were collected from 33 counties in 10 states of the United States along the Mississippi and M issouri Rivers in 1992 and 1993. A sterile hyphomycete fungus of an un named taxon, designated ARF18 and shown to be a parasite of eggs of H. glycines, was isolated from eggs and cysts of 10 of the populations f rom Kentucky, Louisiana, Mississippi, and Tennessee. Ten isolates of A RF18 obtained in this study and seven isolates obtained in earlier stu dies were characterized for cultural morphology on several growth medi a, the ability to produce sclerotium-like structures (SLS) on cornmeal agar, growth rates, pathogenicity to eggs of H. glycines in vitro, an d mitochondrial (mt) DNA restriction fragment length polymorphisms (RF LPs). All 17 isolates of ARF18 readily grew on potato dextrose agar, c ornmeal agar, and nutrient agar. Based on colony morphology and SLS ap pearance on corn-meal agar, the isolates could be grouped into two mor phological phenotypes. Isolates that produced SLS that were composed o f a compact mass of hyphae were designated ARF18-C, whereas isolates t hat produced SLS composed of a mass of loosely clumped hyphae were des ignated ARF18-L. Only minor differences in growth rates were detected among the ARF18-C and ARF18-L isolates. Ail 10 ARF18-C isolates, which were from Arkansas, Louisiana, Mississippi, and Tennessee, belonged t o a single mtDNA RFLP haplotype. The seven ARF18-L isolates shared man y comigrating mtDNA restriction fragments with one another, but belong ed to three distinct mtDNA RFLP haplotypes. Ability to infect eggs of H. glycines in vitro varied considerably among the various isolates of ARF18. In particular, several of the ARF18-C isolates were consistent ly able to infect over 50% (mean = 70.0%, standard deviation = 16%) of the eggs of H. glycines, whereas ARF18-L infected eggs to a lesser de gree (mean = 25%, standard deviation = 27%). ARF18-C was isolated only from H. glycines populations from below 37 degrees N latitude. The pr esence of ARF18 was associated with soils with Mg levels <314 kg/ha, c yst numbers >4.5 per 100 cm(3), and iron levels >203.5 kg/ha; or with Mg levels >314 kg/ha and Na levels <121 kg/ha. The widespread distribu tion of ARF18 and the ability of some isolates to aggressively coloniz e eggs of H. glycines are indications that it has potential as a biolo gical control agent for H. glycines.