In vitro screening of fungi for parasitism against sugar beet cyst nematode Heterodera schachtii

Abstract

Heterodera schachtii is one of the major limiting factors in sugar beet growing areas in Iran. Thirty fungal strains, isolated from the beet cyst nematode, were studied on water agar for their pathogenicity to the nematode. The rate of colonization of eggs by different fungi and hatch of second stage juveniles were measured after a month on water agar at 20 °C. The largest and smallest colony growth on potato dextrose agar medium, recorded after 5 days at 25 °C, were 67 and 12 mm for Chrysosporium keratinophilum and Rhizoctonia sp., respectively. Species of Fusarium grew from 26 to 68 mm, Pochonia chlamydosporia var. chlamydosporia and Phoma 17 mm, Gliocladium 27 to 37 mm, Cylindrocarpon 22 mm and Paecilomyces lilacinus 30 mm. The most virulent isolates were Gliocladium cf. roseum, F. oxysporum, Ph. pomorum, P. c. var. chlamydsoporia and F. equiseti, which colonized 72, 68, 67, 63 and 58% of the eggs respectively; 13 to 20% of juveniles hatched on these plates. Fusarium graminiarum, E. chlamydospora, F. acuminatum armeniacum, C. destructans, P. lilacinus and Rhizonctonia sp., with 51 to 41% pathogenicity, were moderately virulent. Fusarium polyphialidicum, F. acuminatum acuminatum, G. roseum, F. oxysporum, F. solani, F. equiseti, C. obtusisporum, C. keratinophilum and F. camptoceras were less virulent strains to H. schachtii and parasitized 38 to 12% of the immature eggs. Non-spore-producing strains colonized 18 to 50% of the eggs on agar.