Characteristics of panicle stem growth and flowering period of the parents of hybrid rice in machine-transplanted seed production

Abstract

: To study the characteristics of panicle and stem growth and flowering period of restorer line and sterile line under mechanized transplanting mode, and to analyze the reasons for the difficulty of parental flowering period meeting under mechanized transplanting mode Chenghui 727×Shu 21A and Yahui 2115×Yixiang 1A were selected as the materials, and the field ex-periment was carried out from 2019 to 2020 in this study. Two transplanting methods and seedling ages were determined. Leaf age dynamics, panicle stem growth dynamics, and heading dynamics of restorer line and sterile line were investigated, and the effects of different treatments on the growth and development of panicle, line were statistically analyzed. The results were as follows: (1) The total number of leaves in mechanical transplanting parents decreased by 0.3–0.8 leaves in restorer lines while the sterile line added 0.1–0.4 leaves. Meanwhile, the total number of leaves in restorer lines decreased with the decrease of seedling age, while there was no significant change in the total number of leaves of male sterile lines. (2) The growth process of panicles, stems and leaves of restorer lines in mechanical transplanting was delayed by 2–5 days, while that of sterile lines was delayed by 5–10 days. The panicle differentiation of restorer lines began after jointing, while the panicle differentiation of sterile lines began 5–10 days after jointing. The panicle differentiation duration of restorer lines and sterile lines did not change significantly. The young ear growth curves of all treated parents were well fitted with Logistic curves ( R 2 >0.99). (3) The duration from seeding to heading of machine transplanting parents was longer than that of artificial transplanting parents. The effect of lengthening seedling age was the same as the change of transplanting method and the response of sterile lines to transplanting method and seedling age was more significant than that of restorer lines. (4) The flower encounter index of long seedling age under artificial transplanting in each combination was 100%, and the flower encounter was the best. Flowering encountering index was between 40%–60% of long seedling age under mechanical transplanting and short seedling age under artificial transplanting, followed by flowering status. However, the flowering index of the short seedling age combination of Chenghui 727 × Shu 21A and Yahui 2115 × Yixiang 1A was 0 and 18.18% under mechanical transplanting, respectively, indicat-ing that the absent of flowering date seriously. In conclusion, the growth and development of ear, stem, and leaf of parents were delayed under mechanized transplanting mode, and the prolonged seedling age aggravated the growth and development lag phe-nomenon of parents. There were some differences in the growth, development, and flowering characteristics between restorer lines and sterile lines under different transplanting methods and seedling ages. The difference in the response of restorer lines and sterile lines to cultivation measures was the main reason for the absence of flowering dates of parents.