COMPARATIVE PEG, OVARY, AND OVULE ONTOGENY OF SELECTED CULTIVATED AND WILD-TYPE ARACHIS SPECIES

Genetic incompatibility or other reproductive barriers are thought to be the main impediments to introgression of germplasm from wild to cultivated species of Arachis. Comparative morphological development of the peg, ovary, and ovule was undertaken in two A. hypogaea L. cultivars, cv NC 6 and cv Argentine, and two closely related diploid Arachis species, A. duranensis and A. stenosperma, to determine if probable impediments could be detected. Analysis showed that there were significant differences among the four genotypes with respect to length of both basal and apical locules. The A. stenosperma basal locule was the longest but decreased slightly during development, while other genotypes had a positive linear slope. Apical locule growth patterns varied, with wild species showing curvilinear growth. Basal and apical ovules were nearly the same size for all genotypes except cv NC 6, which was longer and grew more rapidly. Basal and apical embryos reached the eight-cell phase in all genotypes by d 5. Embryo growth of the basal ovules was linear, while that of apical ovules was quadratic, tapering off after 72 h. Cv NC 6 was longer and grew more rapidly than the other genotypes and A. duranensis had the smallest embryos. Embryo width showed a linear decrease in all genotypes, with the rate greatest in cv NC 6. Peg growth was initiated within 24 h after fertilization in all genotypes, at which time only A. duranensis had a significantly faster growth rate. Differences in various component growth rates controlled from information supplied by male gametes and female egg and/or polar nuclei could conflict with each other and restrict or accelerate growth in such a manner as to induce abortion.