Effects of male sterile cytoplasm on yield and agronomic characters in Japonica hybrid rice, Oryza sativa L

Effects of the male sterile cytoplasm on twelve yield and agronomic characters of F1 Japonica hybrid rice (Oryza sativa L.) were investigated. Two sets of isonucleo alloplasmic male sterile lines (A lines) of "Nankeng 11 A" and "Nankeng 34 A" with four different cytoplasms from India cultivar Chinsurah Boro II (BT), Yunnan cultivar Eshandabaigu (D), wild abortion (WA) from a pollen sterile wild plant (O. sativa f. spontanea) found in Hainan Island and wild cultivation (WC) from a red awned wild plant (O. sativa f. spontanea) and their maintainers (B lines), four restorers (r lines) of "77302-1", "Ninghui 3-2", "C57" and "C Bao" were used to make hybrids of A x R (aF1) and B x R (bF1) lines. Cytoplasmic effects were determined by the difference of aF1-bF1. Significant negative effects on plant height (PH), panicle neck length (PNL), number of seeds per panicle (NSP), seed setting percentage (SSP), harvest index (HI) and grain yield per plant (GY) and significant positive effects on number of panicles per plant (NP), spikelet number per panicle (SNP), 1000-grain weight (GW) and dry weight per plant (DW) were observed. Cytoplasmic effects significantly varied with different male sterile cytoplasms, which may be explained by the different restoring ability of R lines for the four male sterile cytoplasms. BT and D type cytoplasms which had proper R lines showed positive effect on grain yield, and their hybrids showed midparent heterosis and heterobeltiosis with an average value higher than 20%. Also, cytoplasmic effects significantly varied with different nuclear genetic background of B and R lines and their interaction. These results suggested that it would be possible to minimize the negative cytoplasmic effect so as to obtain a hybrid with marked heterosis on grain yield by the proper selection of the male sterile cytoplasm, B and R lines