Embryo sac composition and fertility assessment in Paspalum ovale Nees 8x: insights into reproductive mechanisms

ESCOBAR, LUCAS MATEO; SCHNEIDER, JUAN SEBASTIAN; DAVIÑA, JULIO; MARTÍNEZ, ERIC JAVIER; HONFI, ANA ISABEL

Rosario

Congreso; IV international congress on Apomixis; 2023

Paspalum ovale Nees ex Steud., a native grass to southern Brazil, Paraguay and northeastern Argentina, exhibits two distinct cytotypes: heptaploids (2n= 7x= 70) and octoploids (2n= 8x= 80). Utilizing Flow Cytometry of Single Seeds studies, 8x was categorized as apomictic. However, comprehensive information regarding the composition of the embryo sac and the potential for apomixis or sexuality during the ovule's development, as well as seed fertility, remains missing. The embryo sac constitution in at least 30 mature ovules and seed fertility in eighteen individuals from three populations from Argentina were analyzed. Seed set was determined in three inflorescences under open-pollination conditions, with the Fertility Index (FI) calculated as number of seeds per inflorescence divided by number of spikelets per inflorescence. At anthesis, ovules had one meiotic embryo sac (MES) at 44.21%, or one MES alongside 1-4 apomictic embryo sac (AES) in 52.62%, while 3.16% remained undeveloped. The MES of the Polygonum type consisted of an egg apparatus with one oosphere, 1-2 synergids, a central cell containing 2-3 polar nuclei, and 2-12 antipodals cells. Conversely, the AES displayed characteristics typical of aposporous Paspalum types, consisting of one egg-cell, 2-4 polar nuclei in the central cell, and an absence of antipodals. The FI was low, ranging from 2% to 22%. The data strongly suggests that P. ovale 8x is facultative apomictic aposporous type. The observed low fertility appears to be associated with pollen limitation, rather than the absence of embryo sacs available for fertilization.