Abstract
Hybrid breakdown, a form of postzygotic reproductive barrier, has been reported to hinder gene flow in many crosses between wild and cultivated rice. Here, the phenomenon of hybrid breakdown was observed as low-tillering (i.e., low tiller number) in some progeny of an interspecific cross produced in an attempt to introduce Oryza meridionalis Ng (W1625) chromosomal segments into Oryza sativa L. ssp. japonica “Taichung 65” (T65). Low-tillering lines were obtained in BC4-derived progeny from a cross between W1625 and “Taichung 65,” but the locus for low-tillering could not be mapped in segregating populations. As a second approach to map the locus for low-tillering, we analyzed an F2 population derived from a cross between the low-tillering lines and a high-yielding indica cultivar, “Takanari.” A major QTL for low-tillering, qLTN4, was detected between PCR-based markers MS10 and RM307 on the long arm of chromosome 4, with a LOD score of 15.6. The low-tillering phenotype was associated with weak growth and pale yellow phenotype; however, low-tillering plant had less reduction of grain fertility. In an F4 population (4896 plants), 563 recombinant plants were identified and the low-tillering locus was delimited to a 4.6-Mbp region between markers W1 and C5-indel3729. This region could not be further delimited because recombination is restricted in this region of qLTN4, which is near the centromere. Understanding the genetic basis of hybrid breakdown, including the low-tillering habit, will be important for improving varieties in rice breeding.
Highlights
Panicle number in rice (Oryza sativa L.) is a yield component that is directly influenced by tillering ability during the growth period
The number of panicles per plant of W1625 was higher than that of Taichung 65” (T65) at the maturing and greatly reduced in the low-tillering line compared with both parents
These data suggested that the total number of panicles in the low-tillering line was affected by one or more introgressed segments from W1625
Summary
Panicle number in rice (Oryza sativa L.) is a yield component that is directly influenced by tillering ability during the growth period. Tiller number is an important trait for improving rice varieties in breeding programs. In the late 1980s, new plant type (NPT) breeding was launched at the International Rice Research Institute (IRRI, Los Banos, Philippines) to increase rice yield potential. Substitution Mapping of Hybrid Breakdown Locus (i.e., low number of tillers) because low-tillering varieties have fewer unproductive tillers (Janoria, 1989). Rice varieties with high tiller number are generally suitable under some conditions; excessive tillering can lead to yield reductions due to an increased number of unproductive tillers. The development of rice varieties with optimal tiller number for a specific environment could play an important role in increasing production (Kebrom et al, 2012)
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