The tested results indicated that the elongating seedling was induced when the content of GA3 in rice seed per gram was equal to or more than 94. 6 ng. The content of GA3 in F1 seed per gram was 23. 8, 49. 5, 53. 5 and 63. 5 ng respectively when the dosage of gibberellin was 0, 8, 13 and 18 g per 667 m2 in the hybrid rice seed production. These contents in the hybrid rice seed were much less than 94. 6 ng which could induce the rice seed to grow up elongating seedling. However, significant correlation existed between the content of GA3 in F1 seed and dosage of gibberellin in hybrid rice seed production. The further experiments proved that all of the aforementioned dosage of gibberellin could not induce the elongating seedling in F1 and that the elongating seedling in hybrid rice was caused by Gibberella fuiikuroi which infected the seed during blooming stage.
