Relationship of Parental Indica-Japonica Indexes with Yield and Grain Quality Traits of Japonica Hybrid Rice in Northern China

Taking the main parents （10 male sterile lines and 10 restorer lines） and their 100 combinations of japonica hybrid rice in northern China as materials, the relationships of parental indica-japonica indexes determined by the methods of the Cheng’s index as well as simple sequence repeat （SSR） markers with yield and grain quality traits of hybrid rice were studied. For the parents, the Cheng’s index （Chi） ranged from 13.5 to 19.3 and the indica index in SSR markers （ADi） were from 0.12 to 0.38. The classification of parents by Chi was not completely consistent with that by ADi. The Chi of male parent was more closely related to hybrid traits than that of female parent, as contrasted to ADi. At the same time, the difference between parents （PD） in Chi was more closely related to hybrid traits than that in ADi. The indica-japonica indexes of parents and their difference between parents appeared quadratic relationship to hybrid traits with the critical extremum. The directions of the correlation of indica-japonica indexes of parents and their differences with hybrid yield traits were on the opposition to those with hybrid grain quality traits. Therefore, the female parent should match the male parent moderately in indica-japonica index to obtain the optimum of hybrid traits, high yield as well as good quality.

The Relation between Genetic Difference for Parents of Hybrid Rice and Heterosis

Exploring the indica-japonica differentiation in parents of hybridization can provide theoretical bases for utilizing inter-subspecific heterosis. In this study, 5 sterile lines and 18 self-bred restorer lines were used as female parents and male parents respectively. Then 90 combinations were constructed by incomplete diallel cross followed by relationship analysis between parental Cheng’s index difference value and Euclidean distance and heterosis. The results showed a significant correlation between several phenotype values, super male parent heterosis and control heterosis and Euclidean distance or Cheng’s index difference value. However, it was no significant correlation for yield. Further analysis found a common interval, 3.41 - 3.46 for Euclidean distance and 3 - 4 for cheng’s index difference value of parents, which was significant or high significant positive correlated with phenotype value, super male parent and control heterosis of main yield traits. This illustrates that the larger the genetic difference of parents was, the stronger the heterosis combinations were, when the genetic differences of parents were in an appropriate range.

Subspecific Characteristics and Classification of Rice Varieties Developed Through Indica and Japonica Crossing

Six characteristics, i.e., hull color, chaff and leaf pubescences, length of 1st and 2nd rachis, grain length/width ratio andphenol reaction, of rice progenies from indica and japonica crossing were studied using the Chengs index classificationmethod. The results indicated that F1 generations performed more like indica, while F2 generations were approximately ina normal distribution. Both of the rice progenies were more affected by indica and female parents than by japonica andmale parents. Among the six Chengs index traits of the parents and F1 generations, and between the traits and Chengsindexes, significant correlations (both at a=0.05 and a=0.01) were found in most cases. No significant correlations werefound among the 6 Chengs index traits of F2 generations in most cases, but significant correlations (a=0.01) existedbetween these traits and Chengs indexes. The six Chengs index traits of F2 ranged successively, and many individualsshowed over-parent genetics, with the same trends in both direct cross and reciprocal cross. Among the 6 index traits,chaff and leaf pubescences almost presented in a two-peak value, while the others in a mono-peak value. The hull color,phenol reaction and length of 1st and 2nd rachis were distributed in deviation, with the first two traits presented more injaponica individuals and the last trait more in indica. The grain length/width ratios were nearly in a normal distribution.

Comparison of Morphological and Genetic Differentiations in Filial Generation of Cross Between Indica and Japonica Rice

A recombinant inbred line （RIL） population of F8 and F9 generations derived from a cross between a typical indica rice （Qishanzhan） and a typical japonica rice （Akihikari） was used to study the difference between morphological differentiation based on phenotype characters and genetic differentiation using indica and japonica specific SSR markers, and to evaluate the relationship between vascular bundle characters and morphological and genetic differentiations. The results showed that the frequency distributions of morphological and genetic differentiations were all inclined to japonica type in the filial generation. The population was more inclined to japonica type based on genetic differentiation than on morphological differentiation. The consistent degrees of classification based on the Cheng’s index, the ratio of large vascular bundle number to small vascular bundle number in panicle neck （RLSVB） and the ratio of large vascular bundle number in the second internode from the top to that in the panicle neck （RLVB） were all about 50% compared with the genetic differentiation, and the consistent degree of the total scores of the Cheng’s index combined with the vascular bundle number ratios was significantly increased to about 80% compared with the genetic differentiation. Therefore, the vascular bundle characters could be used as a helpful supplement for subspecies classification.