Phoma macdonaldi Boerema, teleomorph Leptosphaeria lindquistii Frezzi, is a widespread pathogen of sunflower. The aim of this research was to identify the presence of fungus P. macdonaldi in seed of different sunflower hybrids, as well as the correlation between seed and field infection. Phoma black stem assessment was performed on three hybrids grown in six localities in Serbia. Untreated and processed seeds of these hybrids were used in the seed health test. Severity of the disease did not differ between localities. Average disease index for hybrids H7, H9 and H19 was 14.01%, 13.25% and 11.83% respectively, and it shows that there are no significant differences in hybrid susceptibility. The index of disease indicates tolerance of these hybrids to Phoma black stem. Seed analysis showed the presence of fungi from the following genera: Phoma, Alternaria, Botrytis, Sclerotinia, Penicillium and Aspergillus. Seed infection with Phoma (of the untreated seeds) per hybrid ranged from 1.2-3.5%. There is no significant correlation between stem and seed infection.

In tests of sunflower hybrids' susceptibility to broomrape under artificial inoculation conditions, a high germination rate of broomrape seed used for infestation is prerequisite. On the other hand, one of the ways to reduce the great potential of broomrape seeds is biological control.Seed germination was evaluated on three different media. The first medium was water agar with giberellic acid (GA3) and presence of roots of the susceptible sunflower hybrid NS-H-111. The medium for the evaluation of influence of the biological agent on seed germination was the same with bioagent Trifender added in concentration of 1%. The check was a medium with GA3 only. Seeds of Orobanche cumana were collected in sunflower fields in Vojvodina at five different localities. The seeds were placed in Petri dishes with nutritive media and incubated at 25°C in the dark. Germination rate, germ length and distance of germinated broomrape seed from sunflower root were determined at 7 day intervals under the dissecting microscope.After 28 days on the GA3 medium with sunflower roots broomrape seeds germinated at the rate of 44-68%, while on media with Trifender they had significantly lower germination (4-41%). There was no broomrape seed germination on water agar with GA3 only in any sample. Germ lengths of seeds on the GA3+sunflower roots media were significantly longer than those on the medium with Trifender. Orobanche seed which were closer to the sunflower root had better germination on both media.