Shattering ability of red rice seeds in cultural conditions

Two experiments were carried out in 1996-1997 and 1997 with the objective of studying the shattering ability evolution of red rice seeds. In the 1996-1997 experiment, the shattering behaviour was studied by collecting 10 panicles which had previously been marked and closed in gauze bags (in 1997). The panicles were collected at 7- and 3-day intervals in 1996 and 1997, respectively. In the 1997 experiment the shattering capacity was determined by collecting red rice plant panicles, which were grown at different competitive conditions, at 3-day intervals for 2 rice varieties, Arborio and Thaibonnet, for 3 densities of 10, 20 and 30 plants m-2 with 2 N supplies of, 100 and 150 kg ha 1. The results of the 1996-1997 experiment showed that red rice seeds were already able to shatter 9 DAF (days after flowering). From that time shattering gradually increased, reaching about 65% at 30 DAF. The 1,000-seed weight evolution was consistent with the shattering behaviour, showing an increase from 10 to 27 g in the period between 12 and 24 DAF. In the 1997 experiment the shattering of red rice grown in competition with Arborio was not influenced by the N supply and reached the highest percentage (about 60%) for the 20 plants m 2 density. In Thaibonnet the greatest shattering was observed for the 10 plants m 2 density with the supply of 100 kg ha 1 of N.