Comparison of Characteristics for Breeding Utilization of Isonuclear Alloplasmic Liuqianxin A with Four Cytoplasm Sources

Abstract

The BT type of cytoplasmic male sterile (CMS) line plays a predominant role in japonica hybrid rice ( Oryza sativa L.). Incomplete sterility of the CMS line is one of the major restraints in heterosis utilization of japonica hybrid rice. This study aimed at comparing a set of isonuclear alloplasmic sterile lines that might be used in japonica hybrid rice breeding. Four Liuqianxin-based isonuclear CMS lines in WA, HL, BT, and CL cytoplasmic backgrounds were crossed with Liuqianxin B line for evaluating the male sterile stability, flowering habits, outcrossing rate, and restorable ability. The sterility was characterized as stained abortion in most pollen granules of the BT-, HL-, and CL-type Liuqianxin A and typical abortion in most pollen granules of WA-type Liuqianxin A. The selfing rate of the BT-type Liuqianxin A was 0.60%, which might cause a risk in producing seed of hybrid rice. However, no selfing spikelets were obtained in the HL- and CL-type Liuqianxin A. Length of the first internode to the top and plant height were associated with the abortion degree of pollens, and the severer abortion led to shorter panicle neck protruding from the flag leaf sheath. As a result, panicles were enclosed by flag leaf sheath in WA-type Liuqianxin A; but such a characteristic was not found in other types of Liuqianxin A. In the 4 types of Liuqianxin A, the WA type had the lowest outcrossing rate due to sporadic flowering, distinctly laggard flowering time, and stretched flowering duration. The flowering habits and outcrossing rate were similar in the HL- and CL-type Liuqianxin A, which had no significant differences to the BT type. The restorable characteristic was the best in BT-type Liuqianxin A, followed by the HL and CL types, and the worst in the WA type. The HL- and CL-type CMS lines are proposed to replace the BT-type CMS line in japonica hybrid rice breeding because they have advantages on balancing the sterility, flowering habits, and restorable characteristic. Furthermore, the HL- and CL-type japonica restorers can be selected from the BT-type restorers.