AN ABSTRACT OF THE THESIS OF HAYATI_OIEZ for the _ M.S. _ in Horticulture_ (Name) (Degree) (Major) Date thesis is presented (O^^^-S^J^J*2~ Title.MEIOSIS ^ POLLINATION AND INCOMPATIBILITY IN

Abstract approved ^o^'-^.^^-^?^ — <£K-i.-/)'—'-.) (Major Profe^Or)" This study was initiated to determine the incompatibility status of Bartlett and Seckel pears in Oregon, The investigations as to the cause and site of this reaction were directed at studying meiosis in Bartlett and Seckel pears, pollination experiments in three different geographical locations to determine the possible effect of environmental conditions on fruit setting, pollen tube growth studies in reciprocal cross-pollinations, and embryo development. Meiosis in Bartlett and Seckel pears occurred normally with the exception of two per cent of pollen mother cells showing chromosome lagging and bridges at anaphase I in Seckel,, Cross-pollination of Bartlett with Seckel yielded no fruit in Corvallis, low in Medford and in Hood River. All the fruits from this cross in Medford were seedless. The reciprocal pollination yielded 1.3 per cent fruit set with an average of three seeds per fruit in Corvallis; 4665 per cent fruit set in Medford, with 5 per cent of them containing one seed; 15e2 per cent fruit set in Hood River, with 1,S per cent of these being seedless. Bartlett pollen tubes grow considerably faster in Seckel styles than Seckel pollen tubes in Bartlett. No pollen tubes were found beyond the base of the style in the cross of Bartlett x Seckel; two out of 36 ovules were fertilized in the reciprocal cross. One /f-celled embryo was observed from the cross of Seckel x Bartlett, fifteen days after pollination. It is concluded that Bartlett and Seckel pears, under the conditions of these experiments are at least partially, if not completely, inter-incompatible. Inter-incompatibility varies greatly in reciprocal crosses and in different environmental conditions. The incompatibility reaction takes place when the tubes are about half way down the style and increases in intensity through the base of the style