Changes in pollen fertility in forcing strawberry cv. Nyoho(Fragaria×ananassa Duch.)were investigated to clarify the factors affecting fruit malformation caused by poor fertilization which occurs with plant dwarfing and yeild decreace in February to March .Pollen were sampled from 15 greenhouses of strawberry growers,and relationships between pollen germination and climatic factors,mineral and carbohydrate concentration in leaves were analyzed.Pollen fertility decreased in January and February with decrease in
light intensity and outside air temprerature,and increace in
fruit load.It was suggested that the occurrence of fruit malfomation may be mainly caused by the decrease in pollen fetillity. There were highly significant relationships between the pollen fertility and light intensity in 1 to 3
days before anthesis,minimum outside air temperature on the day of anthesis,and carbohyrates,P,K and Ca concentration in the leaves.No constant relationship could be found between polln fertility and leaf N concentration.Pollen fertility at the beginning of harvest for second inflorescence(January)was
improved with CO2 enrichment.These results indicate that the poor pollen development may result from the shortage of photosynthate caused by low light and fruit load.