Determination of palynological characters of commercial cultivars is significant in determining thecompatibility and intraspecific relationship, an important criterion in tuberose breeding. The presence ofself-incompatibility and seed sterility in tuberose has greatly hindered the conventional breeding methods asconfirmed through various studies. However, regulation of the incompatibility system and the principal factorbehind it has not been thoroughly investigated. The understanding of both male and female gametophytes andtheir functioning is a prerequisite which is still a less explored area in tuberose. Seventeen tuberose genotypesstudied showed the same inclination towards viability and germination determining a positive correlation.Analysis of pollen morphology and ultra-structure using a scanning electron microscope (SEM) revealed markedvariations among the genotypes. The distinct pollen ultra-structures revealed would serve as important featuresfor classification and character identification in taxonomy. It also ascertains the pollen function as evidenced bythe shrunken pollen of genotypes previously reported as sterile. These findings are vital to fully comprehendingthe breeding systems and reproduction biology of tuberose cultivars.
Background: Incompatibility occurs frequently in the plant system upon intra- or interspecific crosses resulting in several pollination barriers. The modest understanding on the breeding behaviour and mechanisms governing tuberose (Polianthes tuberosa L.) through this study will direct us to appraise the pollination and post pollination events on self- and cross- incompatibility and seed set behaviour for cross breeding programme.Results: Self-pollination of tuberose cultivars Arka Prajwal, Mexican Single and Arka Sugandhi failed to produce pods upon autogamy and geitonogamy. Pollen-pistil interaction study of incompatible cultivar Arka Prajwal substantiates that pollen tube enters the ovule within 24 hours after pollination. It discharges its contents into the embryo on the 1st day after pollination and polysaccharide granules evident upon fluorescence microscopic study. The pollen tube growth rates of self and controlled pollination were similar; however, sterility was expressed in the ovary. The female gametophytic development in self and cross incompatible cultivar Arka Prajwal showed normal development initially after pollination whereas embryosac degeneration was observed at later stage. Complete degeneration of the integument and nucellar cells was also observed. Conclusions: This study is the first to elucidate the occurrence of pseudo self-incompatibility in tuberose by identifying tuberose cultivars and breeding lines which produce pods upon geitonogamy. A positive pollen-pistil interaction with the degeneration of embryosac, integument and nucellar cell and pod shrinkage, abortion and fall confirms the prevalence of the ‘Ovarian Incompatibility’ or ‘Late-Acting Incompatibility’ in tuberose.
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