Meiotic behaviour and pollen fertility in an open-pollinated population of ‘Lee’ mandarin [ Citrusclementina×( C. paradisi× C. tangerina)

Abstract

As part of a mandarin genetic breeding programme in Southern Brazil cytogenetic studies of meiotic behaviour and estimations of pollen fertility were performed in an open-pollinated population of ‘Lee’ mandarin [ Citrus clementina×(C. paradisi× C. tangerina)]. For meiotic and pollen staining analysis flower buds and flowers in anthesis were, respectively, examined. In most plants microsporogenesis was regular, with meiotic indexes over 90.0% and pollen viability over 83.0%. We observed meiotic abnormalities including univalents and stickiness in metaphase I, laggards and bridges in anaphase and telophase I and II and microcytes at the tetrad stage. Dyads and triads were found in two plants (112 and 122) at the end of microsporogenesis, suggesting production of unreduced gametes. These plants had a low pollen viability (22.9 and 24.4%, respectively) probably due to observed meiotic irregularities. One plant (223) presented pollen grains with a different shape and bigger size, possibly unreduced. Plants 112 and 122 were monoembryonic and plant 223 polyembryonic with 3.5 embryos per seed. The potential fertilization ability of the pollen grains was estimated by in vitro germination tests. Pollen germination was generally high, up to 91.5%, but eight plants (039, 050, 072, 081, 087, 112, 122 and 126) had pollen germination of less than 59%. We conclude that most plants have the ability to produce viable gametes and could be used as pollen donors in programmed crosses. The monoembryonic unreduced-gamete producer plants 112 and 122 are potential progenitors in crosses aimed at producing triploid seedless fruits.