Abstract
BackgroundHarnessing heterosis is one of the major approaches to increase rice yield and has made a great contribution to food security. The identification and selection of outstanding parental genotypes especially among male sterile lines is a key step for exploiting heterosis. Two-line hybrid system is based on the discovery and application of photoperiod- and thermo-sensitive genic sensitive male sterile (PTGMS) materials. The development of wide-range of male sterile lines from a common gene pool leads to a narrower genetic diversity, which is vulnerable to biotic and abiotic stress. Hence, it is valuable to ascertain the genetic background of PTGMS lines and to understand their relationships in order to select and design a future breeding strategy.ResultsA collection of 118 male sterile rice lines and 13 conventional breeding lines from the major rice growing regions of China was evaluated and screened against the photosensitive (pms3) and temperature sensitive male sterility (tms5) genes. The total gene pool was divided into four major populations as P1 possessing the pms3, P2 possessing tms5, P3 possessing both pms3 and tms5 genes, and P4 containing conventional breeding lines without any male sterility allele. The high genetic purity was revealed by homozygous alleles in all populations. The population admixture, principle components and the phylogenetic analysis revealed the close relations of P2 and P3 with P4. The population differentiation analysis showed that P1 has the highest differentiation coefficient. The lines from P1 were observed as the ancestors of other three populations in a phylogenetic tree, while the lines in P2 and P3 showed a close genetic relation with conventional lines. A core collection of top 10% lines with maximum within and among populations genetic diversity was constructed for future research and breeding efforts.ConclusionThe low genetic diversity and close genetic relationship among PTGMS lines in P2, P3 and P4 populations suggest a selection sweep and they might result from a backcrossing with common ancestors including the pure lines of P1. The core collection from PTGMS panel updated with new diverse germplasm will serve best for further two-line hybrid breeding.
Highlights
Harnessing heterosis is one of the major approaches to increase rice yield and has made a great contribution to food security
A total of 77% (101) lines were in the population 2 (P2) possessing tms5 and denoted as the thermo sensitive genic male sterile population
In the present study, the diversity, relationships, selection sweep and breeding inferences were investigated in a collection of 131 rice genotypes including, 118 male sterile lines and 13 conventional breeding lines
Summary
Harnessing heterosis is one of the major approaches to increase rice yield and has made a great contribution to food security. Two-line hybrid system is based on the discovery and application of photoperiod- and thermo-sensitive genic sensitive male sterile (PTGMS) materials. Harnessing heterosis is one of the major approaches to increase rice yield and has made a great contribution to food security in China and many other countries [2, 4]. AnnongS-1 was the first indica temperature sensitive genic male sterile line (TGMS) developed in China, which opened a new way of heterosis utilization in rice [5]. The photo or temperature sensitive genetic male sterile (PTGMS) lines have occupied millions of hectares of rice field in China for more than a decade [4]. It is valuable to ascertain the genetic background of PTGMS lines and to understand their relationships in order to select and design a future breeding strategy
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