Expression of the apomictic potential and selection for apomixis in sorghum line AS-1a

Abstract

Expression of elements of apomixis was studied for ten seasons in sorghum line AS 1a and its backcross hybrids in the 9E and A3 sterile cytoplasms. Cytoembryological analysis revealed aposporous embryo sacks (apo ESs), their initial cells, and, rare, parthenogeneic proembryos in ovules of line AS 1a and its BC 2 and BC 3 hybrids on the 9E cytoplasm. The A3 sterile cytoplasm suppressed the development of par thenogenetic proembryos, but did not affect the apo ES formation. The frequency of apomictic elements increased in seasons with high daily temperatures and total precipitation deficiency in the period of ovule and megagametophyte development (r = -0.805, p < .01). Selection was used to isolate the families where the fre quency of ovules with apo ESs was 28% and the frequency of parthenogenetic proembryos was 14%. Emas culated panicles of line AS 1a were pollinated with pollen of line Volzhskoe 4v, which carried the Rs marker dominant gene, responsible for the anthocyan color of coleoptyles and leaves in seedlings. Plants of the maternal type were found in the progenies of these crosses at a frequency of 1.4-28.1%. The genetic structure of the endosperm in grains with maternal type seedlings was inferred from the electrophoretic patterns of storage proteins (kafirins). The kafirin spectra of grains producing maternal type seedlings was similar to the spectrum of line AS 1a and differed from the spectra of grains producing hybrid seedlings, indicating that the endosperm developed autonomously when apomictic grains formed in line AS 1a. The results showed that lines with facultative apomixis can be constructed in functionally diploid plants.

Pseudogamous Apomixis in Maize and Sorghum in Diploid-Tetraploid Crosses

“…In sorghum, the presence of aposporous and, rarely, diplosporous ESs have been described [26][27][28][29]. In the progeny of lines selected for a high frequency of aposporous ESs, parthenogenetic embryos and maternal-type plants were found [30][31][32].…”