Assessment of the risks of cross-pollination during co-cultivation of maize lines in the south-east European Russia

The new Russian Federal law (No. 358 of 03.07.2016) prohibits the commercial use of GM plants in agriculture, but allows, since 2018, for the first time in Russia their cultivation and testing for research purposes. Consequently, there is a need to assess and develop criteria for safe co-cultivation of non-GM and GM varieties, which are currently absent in Russia. In this paper, it was established for the first time that the 10-15 m distance is sufficient to prevent cross-pollination between maize lines with an acceptable presence of 0.9 % of the donor’s genetic material, regardless of the recipient line, donor and recipient time flowering, and the wind direction in Saratov condition (South-West region of European part of Russia). The work aimed to assess the influence of the distance between pollen donor and recipient, wind direction, donor and recipient time flowering, and a buffer zone presence between them on the crossing frequency in mixed maize crops. The maize lines Korichnevyi marker (KM), GPL-1, Zarodyshevyi marker Saratovskii Purpurnyi (ZMS-P), Purpurnaya Saratovskaya (PS), as well as hybrids Purpurnyi (GP), Raduga and Tester 3 were grown (the experimental field of the Rossorgo, Saratov, South-West region of European Russia, 2018-2019). We planted the GP and ZMS-P lines as pollen donors in 2018 on a 3×80 m2 area with planting density of 7-10 plants per 1 m2. Between the pollen donor area, maize KM and GPL-1 lines were planted, and around them there were a 1290 m2 area of yellow-colored grain recipients (Raduga and Tester 3 hybrids). In September, 5-12 ears from each pollen recipient were harvested. The cross-pollination frequency was calculated as the ratio of purple grains (GP pollination result) or yellow grains with a purple spot (ZMS-P pollination result) to the total grain number in recipient lines. In 2018 it was established that the maximum percentage (from 0.1 to 13.2 %) derived from cross-pollination with two pollen donors depends on different factors. At closer distances (1-4 m), the cross-pollination increased 4-fold for the earlier flowering recipient. The percentage of crosses for recipient Raduga decreased 3 times with a 10 m increase in the distance and 11 times at a 40 m distance from the donor plants. Experiments in 2018 indicate that the 10 m distance from the pollen donor guarantees the percentage of crosses not exceeding the 0.9 % GM threshold in food products accepted in the European Union and Russia. In 2019, we used PS inbred line as a pollen donor. The PS was planted on a 3×5 m plot with Sudanese grass ( Sorghum × drummondii ) Allegory cultivar as a buffer zone 3 m wide to the East and West and 15 m long to the South-West and North-East. Yellow-grain hybrid Raduga was planted around the buffer zone. The frequency of crosses was calculated as the ratio of the number of purple grains to the total number of Raduga grains per ear. In 2018, the frequency of crosses was also estimated depending on the synchronism of flowering between pollen donors and recipients. The GPL-1 recipient with a 9-day difference from PG (pollen donor) in the beginning of flowering showed a 4 % lower pollination rate compared to a KM line with a flowering period closer to the PG pollen donor (1-day difference). Tall plants of PG donor of pollen prevented spreading pollen from a short ZMS-P donor to the Tester 3 and Raduga recipients in the direction of the wind rose. In 2019, no more than 0.9 % of purple grains were observed for the recipient Raduga when using a buffer zone of 15 m and more from the pollen donor in the wind rose direction. Based on the results of field experiments, the isolation distance from 15 m or more can be recommended to exclude cross-pollination of maize within the threshold of 0.9 % in the conditions of the South-East of the European part of Russia.