Embryological studies on ‘URS Campestre’, a new seedless orange cultivar

In citrus, seedlessness is a sought-after trait. Absence of seeds is advantageous for the juice industry as wellas is meeting consumer demands. Close to the city of S?o Sebasti?o do Caí, 70 km north of Porto Alegre,the capital city of the southernmost state in Brazil, a new orange cultivar was identified and selected as aseedless cultivar. However, the cause for the nonexistence of seeds has yet to be determined. The objectiveof the present work was to analyze reproductive flower structures such as anthers and seminal rudiments todetermine the grounds for the absence of seeds. ?URS Campestre? flowers of different developmental stageswere collected, fixed and examined. The flowers have anthers and ovaries of typical dimensions. Pollen grainscharacteristics analysis point to a standard developmental pattern, normal meiosis and high viability (84%) andelevated in vitro pollen tube germination rates (63%). However, so far, characteristics of generative cell andsperm cells have not been evaluated. Preliminary studies of seminal rudiments allowed detect abnormalitiesat the nucellus and embryo sac development, which seems to be one of the limiting causes of the fecundationprocess hindering seed production.