EMBRYOLOGICAL STUDIES IN '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 well as is meeting consumer demands. Close to the city of São Sebastião 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 a seedless cultivar. However, the cause for seedlessness has yet to be determined. The objective of the present work was to analyze reproductive flower structures, such as anthers and seminal rudiments to determine the origin of seedlessness. ‘URS Campestre’ flowers of different developmental stages were collected, fixed and examined. The flowers have anthers and ovaries of typical dimensions. Pollen grains characteristics analysis point to a standard developmental pattern, normal meiosis and high viability (84%) and elevated in vitro pollen tube germination rates (63%). However, so far, characteristics of generative cell and sperm cells have not been evaluated. Preliminary studies of seminal rudiments allowed detect abnormalities at the nucellus and embryo sac development, which seems to be one of the limiting causes of the fecundation process hindering seed production.