SUMMARY -The karyotype and meiosis of wild and cultivated ulluco were analysed. All wild ulluco clones studied were triploids, 2n = 36, and all cultivated ones diploids, 2n = 24. A tetraploid cell line, 2n = 48 was found in a cultivated clone. Cultivated and wild ulluco have a similar set of chromosomes, with two pair of long, two pair of short and eight pair of intermediate chromosomes, and with two pair of satellite chromosomes. This indicates that the basic chromosome number of ulluco may be x = 6. Male and probably also female meiosis of diploid cultivated ulluco is regular and pollen stainability high. Reasons for the poor seed set of cultivated ulluco are to be looked for in other processes than meiosis. Meiosis of triploid wild ulluco is irregular, leading predominantly to aneuploid gametes. pollen stainability was low, and there was more variation in pollen size than in cultivated ulluco, most probably because of aneuploidy.
The fruit of the cultivatedulluco(Ullucus tuberosus Loz.)has beenreferred to in the literatureeither as non-existing or as a berry, seldom as a dry fruit. The fruit of this species as well as the genus is described here for the first time, and is shown to be a dry and indehiscentnutlet of an obovate shape and bilaterally symmetrical cross-section. The thin testaof the seedis immediately insidethe thickened fruit wall. The embryo is strongly curved and encircles the relatively scanty perisperm.
Ulluco (Ullucus tuberosus) is a vegetatively propagated crop plant that flowers abundantly but sets only few seeds . We examined if the low seed/ovule ratio can be explained by morphological abnormalities in ovules, embryo sacs or embryos . In 35 clones growing in the actual area of cultivation in Ecuador and in 5 clones grown in Finland flowers were analysed by clearing technique . About half of all analysed clones contained ovules and embryo sacs whose development was arrested, in two clones 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 suggested to be one of the causes for the low sexual fertility found in ulluco . It may be incapable of maintaining homeostasis of development of 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 .
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