Natural crossing in cotton (Gossypium hirsutum L.)

The extent of natural crossing in cotton (Gossypium hirsutum L.) was studied in 2 experiments conducted in Greece during 1998 and 1999, using glandless and red-leaf traits as genetic markers. The glandless line was planted in the middle, and the red-leaf both in the middle and the corners, of a commercial cotton field. In the first experiment where estimation of natural crossing was based upon gland status, the percentage ranged from 1.67% to 2.67% in adjacent rows, dropped to 1.42% in plants 2 m apart, and declined to almost zero after 10 m. In the second experiment, where the red-leaf marker gene was used, the mean of natural crossing was 3.85% in adjacent rows, fell to 2.79% in plants 2 m apart, and progressively diminished to 0.31% after 10 m. The mean natural outcrossing in different rows was almost the same in both experiments at the middle of the field and was actually double at the corners. Differences in the extent of natural crossing between the middle and the corners of the field continued to be significant up to 4 m distance. In all cases, distances greater than 10 m among cottons were sufficient to minimise out-crossing ranges.