May the crossing between diploid and tetraploid Italian ryegrass transfer glyphosate resistance to the next generation?

Italian ryegrass (Lolium multiflorum Lam.) is a grass weed found in winter cereals, with several glyphosate-resistant diploid populations. Furthermore, the use of Italian ryegrass tetraploid genotypes creates an opportunity to increase the forage demand in replacement of diploid populations. The aim of this research was to evaluate the crossing capacity between glyphosate-resistant diploid and tetraploid Italian ryegrass to transfer glyphosate resistance to the next generation. Reciprocal crosses were performed using the susceptible tetraploid cultivar INIA Titan and resistant diploid (SVA04 biotype) plants to obtain the F1 progeny. Germination testing, survival percentage, inheritance of glyphosate-resistance, and ploidy level were evaluated in F1 progeny. Crossing of susceptible tetraploid plants ♂ and glyphosate-resistant diploid ♀ affected the germination and exhibited 4.5% of triploid plants. F1 progeny from the glyphosate-resistant diploid ♂ and susceptible tetraploid ♀ did not show germination problems, but 46% of the plants died during the initial seedling stage. For this progeny, 10 and 25% of the seedlings were composed of triploid and pentaploid individuals, respectively. Crosses between susceptible tetraploid ♀ and resistant diploid ♂ did not transfer the glyphosate-resistant for the plants. Susceptible tetraploid ♂ crossing with diploid resistant ♀ had a reduction of 47% the glyphosate-resistant plants compared to the homozygous glyphosate-resistant progeny. Overall, tetraploid Italian ryegrass can be a safe tool to reduce and manage the increase of glyphosate-resistant diploid ryegrass in field conditions.