M.Leeovoi (sup)1(sup), A.Parfenyuk (sup)1(sup) R.Taranyu (sup)1(sup) (sup)1{sup) Plant Protection In etitute, Ukraine (b) Background and objectivee (/b) Tie wheat is the main cereal crop in grain agriculture of Ukraine. HO'A'ever, last years the eye apot diaeaae induced by kingi Pacudocercoeporella app. pleye a aignificant part in the, diaeaae complex of the wheat. The main of the fujngi 18 Paeudocercoeporella herpotrichoidea (Fron) Deighton. ~eee pathogene induce maes lodging of the winter ~eat decreace quantity and quality of 1t8 yelld. A ver~ proepective method of yield pi::::~tection 18 breeding and gr.:~wing of varietlea regietant to the pethogene. For breeding of euch varietiec,, it le needed to uee eourcea of the reeietance. Aii effectivity of aearch f~r auch aourcea dependa on knowledge of niechaniame of interaction between the hoet~lant and the pa~ogen. i~i8 le juet the aim of our atudlea. (b) Reaulta and conclusions (/b) Tlie studieg of the isolates of the Pesudocercoeporella app. population in Ukraine eho",~d a aignificent differencietion of 9 rate of h~ieir gro~th in vitro.In so doing, the rapidjjrowing isolatee (W-type) were more pathogenic tlian the moderategrowing (R-type) once. This is in concordance 'Aqth the data by Migeon and Capin (1). Pecudocercoeporeila herpotrichoidea var. heipotrichoidee belonge with W-type wliearsae Pseudocercoeporella herpotrichoidee var. acuf:~rmia - to R-type Becauee W and R-type prevailed aicinificantly in the atudied population, we euppoced that Pseudocercoeporalla herpotrichoidea var. herpotrichoidea and Peaudocercoeporella var. acuformie dominated in Ukraine. This fact served cc a r~round for including of them in a model fr'r etudies of mechani ama of interaction "~he hoet~lant - the pathogen" with the ueage of the realatant variety Roazon and the eueceptible variety Mironovekayc ~ In the reault of fie etudisa of hyatopathogenecia in the variety Myronovakayc 808, it wae obeerved the lorming of peeudoparenchymatoue etructuree of ""isifectiouc cuelicionete." in eight daya after the inoculation. Tliey had an appearance of the compact interlacinge of niultinuclear hyphee. Under "'tlie infeetbue cuehionets1', it wee formed the intenaively coloured hyphee that penetrated into celle of epidermie. In the epidermic ar')und the hyphac, the compact atructurea were frrmed. ~ey were a reault of degradation of ceIl& walls. According to Murray and 'Huazhy (2), they are the papillac v'A'th high content of llgnin hi a result of the atudica of hyetoininiunogeneaie in the variety Roezon, it wac obeerved that ""the infectioua cuehioneta1' were formed on the affected planta in four daye lately than in the cueceptible variety. Moreover, in the reejatant variety the papillas ~'ere fornied aignificantly earlier and they lied greater eizes than it in the euaceptible variety. ~ie papillee make dow penetration of hyphee into plant tiacuce. lii the reelatant variety, in a reaponee to the inoculation it aroac necroaca. ~iey 'Aere characterized by intenaive n-i':.'rtelity of the celle in epidernile and parenchyma. Tlie mortality ware accompanied by the forrillig of the large number of the papillea and mortality of ""the infectioua cuehionete'1. TIus proceac ic cheracteriatic for the reeponce of hyperaeneivity. (b) References (b/) 1. Migeon G., Capin P., 1988. Phytoma def. Cult. 397, 12-13. 2. ~u~ey J~) Iluazhy V.,k 1986'. Phyto~~thology 7~, 737-744