The efficacy of four gametocides for induction of pollen sterility in Eragrostis tef (Zucc.) Trotter

Effective chemical hybridizing agents (CHAs) or male gametocides enhance cross pollination in plant breeding and genetic analysis of traits. The present study examined the efficacy and optimum concentration of four CHAs, namely: 2-chloroethyl phosphonic acid (Ethrel), ethyl 4'-fluorooxanilate (E4FO), 2, 4-dichlorphenoxy acetic acid (2, 4-D) and Promalin ® (1.8% GA 47 – gibberellins A 4 +A 7 and 1.8% 6-BA–benzyladenine) on pollen sterility and seeding of a tef line (DZ-01-3186). Seed-derived and individually grown tef plants were treated with foliar applications of the four CHAs (at four levels each) sprayed once at the early booting stage, and bagged to control cross pollination. Female fertility was assessed by recording seed set following controlled  pollinations. Although all the CHAs caused some pollen sterility, their efficacy levels varied from 9.77 to 99.50% in treated plants compared to the control (6.68 +/- 1.04%). Pollen sterility increased with increasing CHA concentration. Near-complete pollen sterility (99.50 ± 0.50%) was achieved by the application of E4FO at rates of 1500 to 3000 ppm, and Ethrel at 5000 ppm. All the CHAs significantly reduced seed yield, with E4FO, Ethrel and Promalin ® at 5000 ppm causing the highest reduction, essentially yielding no seed. In the period following the application of the CHAs, plants treated with E4FO (1000 – 1500 ppm) exhibited stigmas that remained fertile. Hence, it is recommended that E4FO (at 1000 – 1500 ppm) can be used as a chemical emasculation agent for tef, with the least phytotoxicity and the highest female fertility. Key words: Eragrostis tef, Ethrel, ethyl4-florooxanilate, female fertility, gametocides, pollen sterility.