Short-distance cross-pollination of maize in a small-field landscape as monitored by grain color markers

Results of studies on cross-pollination in small field environments with regard to donor/receptor surface ratios and flower synchrony are scarce. In 2003 and 2004, six field experiments on cross-pollination were carried out in the cantons of Zug and Zurich, two hilly regions of Switzerland. Three (Monopol, Romario and PR39G12) color-dominant yellow-grain maize varieties (Zea mays L.) were planted in close proximity (0.8 m) to color-recessive white-grain maize (DSP17007). The factors of influence were size of the donor and receptor parts of the field and flower synchrony, tested in a tight grid pattern (2.4 m × 10 m; 6000 ears ha⁻¹). Widely varying field size ratios of donors to receptors (about 4:1–1:8) did not influence the cross-pollination rate at distances of 0–20 m from the pollen donor. The synchrony between pollen shedding of the donor and silking of the receptor had a large impact on cross-pollination. In relation to the mid-phase of silk emergence in the receptor field, a temporal isolation of five and seven days resulted in a significant decrease in cross-pollination by more than 80% in comparison to full synchrony. However, in a receptor field with irregular emergence of a number of weak, late-flowering plants led to a remarkable increase in cross-pollination, despite an average temporal separation of 7 days. Marked cross-pollination was restricted to distances up to 15 m; thus, average rates of cross-pollination above 0.9% were easily managed in small fields.