A comparative study of two-line early season hybrid rice with lepidopteran resistance

- The two-line early season hybrid rice with lepidopteran resistance was firstly reported.
- The Cry2Aa protein content of B2A68 was significantly higher than those of its hybrids.
- The Bt hybrids exhibited higher resistance to rice leaf roller than non-Bt hybrids.
- Three Bt hybrids were selected out by yield, grain quality and lepidopteran resistance.

In our previous study, an early season rice restorer line B2A68 expressing Cry2Aa# gene was obtained. In order to evaluate the performance of B2A68's hybrids, a total of six hybrids from crossing B2A68 with six thermo-sensitive genic male sterile (TGMS) lines of early season rice were compared for expression level of Cry2Aa protein, as well as in insect resistance, agronomic traits and grain quality with their non-Bt null controls. Our results showed that the highest Cry2Aa protein content among B2A68's hybrids was detected in leaf, where the Cry2Aa content was nearly three times of that in stem. The Cry2Aa content of B2A68 was significantly higher than those of its derived hybrids, indicating the Cry2Aa# gene was incompletely dominant in hybrids. The hybrids with Cry2Aa# gene exhibited higher plant protection against rice leaf roller than the hybrids without Cry2Aa# gene in field. Significant differences were observed in plant height, panicle length, number of grains per panicle, seed set, 1000-grain weight and yield per plant between hybrids with Cry2Aa# gene and hybrids without Cry2Aa# gene in 2013 or 2014. There were significant differences in chalky grain rate and chalkiness degree between paternal lines B2A68 and D68, and between hybrids with Cry2Aa# gene and hybrids without Cry2Aa# gene. All of the differences in agronomic traits and grain quality varied among parental lines and hybrids. In this paper, three hybrids with high lepidopteran resistance, high yield, elite agronomic traits and acceptable grain quality was selected out, that could serve as elite resistant hybrids to control lepidopteran pests in early season rice production.