Inheritance of apospory in tetraploid Paspalum notatum

MARTÍNEZ, ERIC J.; QUARIN, CAMILO L.

Como, Italia

Congreso; 2nd International Apomixis Conference APO2001; 2001

APONET

In the beginning of the 60's Burton and Forbes (1961) investigated the inheritance of apomixis in Paspalum notatum. Induced sexual autotetraploids were the female parents in crosses with apomictic natural tetraploids. Visual observation of the progenies allowed the identification of the reproductive mode of eaeh F1, plant. There are at least two reasons to re-investigate the inheritance of the trait in this species: a) recent studies demonstrated that colchicine treated 2x plants may originate sexual as well as facultative apomictic autotetraploids. b) visual analyses of the progeny would underestimate the proportion of apomictic individuals in the F, progeny because any facultative apomictic plant may produce a segregating population. We conducted exhaustive embryological analyses of a sexual plant of experimental origin to be sure that it was free of aposporous embryo sac (ES) formation. We used this 100% sexual plant as female parent in crosses with an apomictic natural tetraploid. The progeny was analysed embryologically (about 60 ovaries for each plant) to determine whether they produced aposporous ES or not. Plants producing aposporous ES were considered to be apomictic. We analysed the F, (213 plants), some F2 and backcrosses (BC). The results could be summarized as follow: 1) F1, progeny showed a sexual:aposporous segregation close to 3: 1. 2) Sexual F1s generated exclusive sexual progenies, and 3) F2 and BCs involving sexual-apomictic crosses produced progenies in which the sexual:apomictic proportion was approximately 3:1. In a parallel research we observed some molecular markers (RAPD and AFLP) completely linked to apo trait in the F, population. These results discard any hypothesis considering recessiveness for apo gene, dominance of the apo gene determined by allele dosage, or interaction of two or more genes on the apo trait. Our results favour the hypothesis of monogenic control with dominance of apospory in a tetrasomic inheritance model. The deviation toward a higher proportion of sexual plants than it was expected could be ascribed to some pleiotropic effect of the dominant allele for apospory with incomplete penetrance for lethality.