Dataset on the agronomic characteristics and combining ability of new parental lines in the two-line hybrid rice systems in Vietnam

This article provides a dataset on the analysis of morphological characteristics and combining ability of some parental lines in the two line hybrid rice system in Vietnam. Four thermo-sensitive male sterile lines and seven pollen restorer lines were used in a Line x Tester mating system to produce twenty-eight hybrids. The parental lines were characterized on 14 agronomic traits in a completely random design experiment. The 28 hybrids were evaluated on 10 traits related to grain yield and morphology in a randomized complete block design experiment with three replications. A line x tester analysis was conducted to estimate the combining ability, genetic variance, and the contribution of parental lines to genetic variation in hybrids. This dataset is valuable for rice breeders in subtropical countries to orient the strategy for breeding of hybrid rice varieties with high efficiency.


Specification
Agriculture Specific subject area Hybrid breeding, Self-pollinated crops Type of data Table, Figure  How data were acquired  Line x Tester analysis  Data format  Raw  Parameters for data collection Research materials included eleven parental lines (4 TGMS lines and 7 pollen restorer lines) and their 28 hybrids. The parental lines were grown in winter-spring 2017-2018, the hybrids were grown in summer-autumn 2018. Description of data collection Total of 14 agronomic characteristics were evaluated on parental lines; the hybrids were monitored on 10 traits related to grain yield and morphology to conduct a Line x Tester analysis. The data collection method was in accordance with standards suggested by International Rice Research Institute. Data source location Institution: Vietnam National University of Agriculture City/Town/Region: Gia Lam, Ha Noi Country: Vietnam Data accessibility With the article

Value of Data
• Evaluation of combining ability is mostly used for selection of potential parental lines for breeding new hybrid rice varieties. • The dataset shows the combining ability of new parental rice lines on important characteristics related to grain yield and morphology. Moreover, the data on parental lines will be a valuable reference to establish a model of TGMS line for the two-line hybrid rice system in Vietnam. • The Line x Tester analysis described in details could be applicable for hybrid breeding in other self-pollinated crops in Vietnam. Fig. 1 presents the micro-climate data for temperature and humidity during the period from January 2018 to December 2018. Fig. 2 shows the typical phenotypes of parental lines.

Data Description
Eleven parental lines were characterized on 14 agronomic characteristics, including plant growth and morphological characters ( Table 1 ), grain yield-related traits ( Table 2 ) and some special characteristics of female parent lines (TGMS) ( Table 3 ).
Twenty-eight hybrids were evaluated on 10 characteristics, including number of panicle per plant, number of filled grain per panicle, proportion of filled grain, 10 0 0-grain weight, grain yield, proportion of husked grain, proportion of milled grain, proportion of whole grain, white grain length and white grain width. The data were collected to analyze the variance of combining ability ( Table 4 ), general combining ability of parental lines ( Table 5 ), specific combining ability between male (line) and female (tester) parental lines ( Tables 6 and 7 ) and the contribution of parents towards genetic variance among hybrids ( Table 8 ).

Plant materials and cultivation
The experimental materials in this study comprised of seven male (Pollen Restorer) rice lines, four female (Thermo-Sensitive Genic Sterile-TGMS) rice lines, and their 28 hybrids derived from a Line x Tester (7 × 4) mating system. The name and origins of parental lines were described in Table 9 . The parental lines were grown in summer-autumn 2017 to generate with agronomic traits that were characterized in winter-spring 2017-2018. The hybrids were grown in summerautumn 2018 to evaluate the combining ability of parental lines. All experiments were conducted at Crops Research and Development Institute (CRDI) of the Vietnam National University of Agriculture, Hanoi, Vietnam. In winter-spring 2017-2018, seeds of eleven parental lines were sown on 25 December 2017. After 25 days, the seedlings (with 5.5 leaves) were transplanted in a completely randomized design (CRD) without replication as described previously [2] . In summer-autumn 2018, seeds of 28 hybrids were sown on 20 June 2018. The 18-day old seedlings were transplanted in a randomized complete block design (RCBD) with three replications. Each experimental plot area was 15 m 2 ; the growing density was 40 plants

Data collection
Fourteen traits were collected from parental lines while 28 hybrids were assessed on 10 characteristics for evaluating combing ability. The data collection was in accordance with practices of International Rice Research Institute [1] , the detailed description of data collection was displayed in Table 10 .

Data analysis
The data analysis was conducted on the "Variance analysis LINE x TESTER Ver. 2.0 software following the Line x Tester analysis method proposed by Kemphthorne [ 4 , 5 ].

Variance analysis
The variation of GCA and SCA were calculated basing on the variation of GCA of line and tester In which, Msl: mean square of GCA line; Mst: mean square of GCA tester; Mse: mean square of error; Mst * l: mean square of SCA line x tester; l, t, and r: number of line, tester, and replication, respectively; σ 2 GCA: variance of GCA; σ 2 SCA: variance of SCA.

Heritability analysis
The narrow sense heritability formula was estimated basing on the assumption that the total variation among hybrids equals to twice the GCA variance plus SCA variance while the genetic variance is equivalent to the variance of additive effects [6 , 7] .

Combining ability analysis
The contribution of combining ability effect on the morphological value was based on the models of Singh (1977) [8] : In which, Y ijk : value of hybrid between i th line and j th tester in k th replication; μ: the average value of all hybrids in all replication (the general mean value); g i : general combining ability (GCA) of i th line; g j : general combining ability (GCA) of i th tester; S ij : specific combining ability (SCA) between i th line and j th tester; e ijk : error (environmental and replication effects to the (ijk) th individual).
The combining ability data was estimated by the following formulas [ 8 ]:

Estimating the contribution of parental lines to genetic variance of hybrid's traits
The contribution of line, tester, and line x tester towards the genetic variance of each character in F 1 was calculated from the value of mean square of GCA line, GCA tester, and SCA line * tester as follows [4] :