DEVELOPMENTAL ABNORMALITIES IN THE OVULE AND EMBRYO SAC OF ULLUCO (ULLUCUS-TUBEROSUS) AND THEIR EFFECT ON SEED SET

Ulluco (Ullucus tuberosus) is a vegetatively propagated crop plant tha t flowers abundantly but sets only few seeds. We examined if the low s eed/ovule ratio can be explained by morphological abnormalities in ovu les, embryo sacs or embryos. In 35 clones growing in the actual area o f cultivation in Ecuador and in 5 clones grown in Finland flowers were analysed by clearing technique. About half of all analysed clones con tained ovules and embryo sacs whose development was arrested, in two c lones there were embryo sacs whose cell patterns were abnormal and in four clones there were double embryo sacs. There were both normal and abnormal ovules and embryo sacs in the same plant. Genetic load is sug gested to be one of the causes for the low sexual fertility found in u lluco. It may be incapable of maintaining homeostasis of development o f the ovule and embryo sac in a varying environment. The occurrence of developmental abnormalities should be studied in each clone intended for inclusion in traditional breeding programmes.