Pollen Development and Viability in Diploid and Doubled Diploid Citrus Species

Abstract

Seedlessness is one of the most important agronomic traits in mandarins on the fresh fruit market. Creation of triploid plants is an important breeding strategy for development of new commercial varieties of seedless citrus. To this end, one strategy is to perform sexual hybridizations, with tetraploid genotypes as male parents. However, while seed development has been widely studied in citrus, knowledge of key steps such as microsporogenesis and microgametogenesis, is scarce, especially in polyploids. Therefore, we performed a study on the effect of ploidy level on pollen development by including diploid and tetraploid (double diploid) genotypes with different degrees of pollen performance. A comprehensive study on the pollen ontogeny of diploid and doubled diploid “Sanguinelli” blood orange and “Clemenules” clementine was performed, with focus on pollen grain germination in vitro and in planta, morphology of mature pollen grains by scanning electron microscopy (SEM), cytochemical characterization of carbohydrates by periodic acid–Shiff staining, and specific cell wall components revealed by immunolocalization. During microsporogenesis, the main difference between diploid and doubled diploid genotypes was cell area, which was larger in doubled diploid genotypes. However, after increase in size and vacuolization of microspores, but before mitosis I, doubled diploid “Clemenules” clementine showed drastic differences in shape, cell area, and starch hydrolysis, which resulted in shrinkage of pollen grains. The loss of fertility in doubled diploid “Clemenules” clementine is mainly due to lack of carbohydrate accumulation in pollen during microgametogenesis, especially starch content, which led to pollen grain abortion. All these changes make the pollen of this genotype unviable and very difficult to use as a male parent in sexual hybridization with the objective of recovering large progenies of triploid hybrids.

Morphological characteristics and molecular markers of distyly in Primula obconica

“…Pollen and stigma are the male gamete and female gamete of plants, stigmas provide the material basis for pollen adhesion and pollen tube growth, and pollen pollination of a large number of active pollen to the stigma with good receptivity is necessary to ensure the completion of the fertilization process (Cheung et al 2022, Lobaton et al 2021. Plant pollen viability and stigma receptivity determine the success of the fertilization process, so pollen and stigma activity are also important contents of our research (Lora, Garcia-Lor and Aleza 2022). The in vitro culture of pollen simulated the growth of pollen inside the stigma.…”

Morphological and anatomical characterization of yellow diploid potato flower for effective breeding program

“…Pollen is the male gametophyte that carries plant genetic information and its study is relevant since the adequate male germline development is a prerequisite for proper crops performance 38 , 39 . Pollen development is a critical step in plant development that is needed for successful breeding and seed formation 29 .…”

Inheritance pattern of tetraploids pummelo, mandarin, and their interspecific hybrid sour orange is highly influenced by their phylogenomic structure

“…The tetraploid 'Chandler' pummelo was obtained by shoot-tip grafting in vitro combined with colchicine treatment (Aleza et al, 2009), whereas 'Sevillano' sour orange and 'Cleopatra' mandarin were recovered from the spontaneous chromosome doubling of nucellar cells (Aleza et al, 2011). Pollen fertility of parents at diploid and tetraploid ploidy levels was analyzed by in vitro germination test according to the methodology described by Lora et al (2022). The percentage of pollen grain germination was 39% and 26% for 2x and 4x 'Sevillano' sour orange, respectively; 56% and 51% for 2x and 4x 'Cleopatra' mandarin, respectively; and 92% and 74% for 2x and 4x 'Chandler' pummelo, respectively.…”