High sorgoleone autotoxicity in sorghum (Sorghum bicolor(L.) Moench) varieties that produce high sorgoleone content

Sorghum autotoxicity can inhibit germination and growth, resulting in low plant densities and reduced crop productivity. Three sorghum varieties (Dhlakama, Shirikure and Macia) were evaluated for autotoxicity in 2018 at the University of Zimbabwe. Experiments were set up for 3 x 4 factorial testing of the effect of sorgoleone from the three varieties on sorghum seeds and seedlings at four serial dilutions. Crude sorgoleone was extracted using methanol, from seedlings of each variety at six days after emergence. To test autotoxicity, serial dilutions of sorgoleone were prepared by mixing the crude methanol extract with distilled water in the ratio 0:0; 1:10; 1:5 and 1:3 (v/v). Sorgoleone from Dhlakama significantly (p< 0.001) reduced germination of that variety by 76.1%. Germination in Shirikure and Macia was inhibited by 69.4% and 58.9%, respectively. Increasing the strength of the serial dilution of crude sorgoleone from all varieties significantly (p< 0.001) reduced plumule length of the three sorghum varieties. Sorgoleone from Shirikure and Dhlakama significantly (p< 0.001) reduced the dry weight of these two varieties by 76.9% and 69.4% respectively compared to crude sorgoleone from Macia. Sorghum varieties producing high concentrations of sorgoleone are highly autotoxic, and autotoxicity in the sorghum is variety dependent.