1 Introduction

Nilaparvata lugens (Sta1) and Orseolia oryzae Wood-Mason are two major pests in rice. Over the years, many units have carried out the screening and identification of rice germplasm resources resistant to Rice Brown Planthopper and rice gall midge (Mo et al., 1981; Tan et al., 1982; Dong et al., 1989; Li et al., 1992; Wei et al., 1994; Wei et al., 2003), discovered a large number of biotypes of Germplasm Resources resistance to Rice Brown Planthopper and rice gall midge (Li et al., 1997; Wei et al., 2003), and selected and bred a better variety of resistance (Wu et al., 1986; Wei et al., 1988; Tan et al., 1995). However, insect resistant varieties have a large collection and scale, and become a barrier to the utilization of germplasm. In order to solve this problem, Huang et al., (2004) established the core collection of rice germplasm resources resistant to rice brown planthopper biotypes and rice gall midge, which was made up of 53 copies of the material. The ultimate goal of the core collection is to make use of it effectively, therefore, apply the grey incidence analysis method (Deng et al., 1983) to the comprehensive assessment of core collection, which can understand the distance between core collecton and breeding objectives. Thus provide the basis for the resistance of different rice brown planthopper biotypes and breeding parent selection scheme.

2 Materials and Methods

2.1 Experimental material

53 experimental materials make up core collection of rice germplasms which resistant to different rice brown planthopper biotypes and rice gall midge. Resistant to BPH biotype II: 23; moderately resistant to BPH biotype II: 8; resistant to biotype Bangladesh: 16; resistant to rice gall midge China type IV: 6.

2.2 Experimental method

2.2.1 Experimental observation

Plant above varieties was in experimental field, Institute of Plant Protection, Guangxi Academy of Agricultural Science in the 2011. Sowing was in July 14^th, transplanting in August 5^th. Individual insert, Plant spacing 13.3 cm×20.0 cm, planting 40 plants per plot, and repeat 3 times. In the field survey, 2 samples were sampled at 5 points. Observe and record the plant tillering (x₁), initial heading stage (x₂), heading stage (x₃), and full heading stage (x₄), growth stage (x₅), plant height (x₆) and effective plant (x₇). To the harvest time, take 5 clusters per plot for indoor testing. Observe and record the number of grain (x₈), ripening rate (x₉), and weight of thousand grains (x₁₀).

2.2.2 Grey relational analysis

Yuexiangzhan is a control group for experimental varieties in Guangxi district. The variety was used as the standard variety, and the series made up by agronomic characters (x₁=20.0, x₂=90, x₃=93, x₄=97, x₅=122, x₆=96.0, x₇=11.0, x₈=132.0, x₉=93.0, x₁₀=20.0) were used for reference sequence, and analyze the core collection according to the above-mentioned group. Core collection and the agronomic traits of the sequence regard as a sequence of comparison. Calculate the correlation degree between the core collection and the standard varieties and sort them, then determine the core samples are recommended for the pros and cons of the hybrid parent order.

The standardization of data processing and correlation between core collection and standard varieties were processed according to the formula (1) (2) (3).

                                                                                                                                               (1)

Note: X^’_I (k): initial data, X_i: average number of the same factor, S_i: standard deviation of the same factor, X_i (k): the results after the standardization of the original data.

                                                                                                                                                (2)

Note: L_m (k): correlation coefficient, △_m (k): the absolute difference between reference factors x₀ and comparative factors x_i, △_m (k) = |x₀ (k) - x_i (k)| (i=1, 2 … the total number of goods; k=1, 2 …agronomic characters), △_max and △_min: the maximum and minimum values of absolute difference in each time absolute difference of each time series are expressed respectively. ρ: resolution ratio, ρ=0.5.

                                                                                                                                                (3) 

Note: r_m: Correlation degree, N: length of Comparison sequence (number of Agronomic Traits in this article).

Data processing was made by statistical analysis software (DPS) (Tang and Feng, 2002).                                                                                                                                                                                                                      

3 Results and Analysis

3.1 Grey correlation analysis of BPH biotype II core collection

BPH biotype II core samples of main agronomic traits and correlation degree and ranking (Table 1). The main agronomic characters of the core collection showed different, and the difference was very large (Table 1). If from a single point of view, such as seed setting rate, IR19735-5-2-3-2-l and Yuexiangzhan are the most close to, and can be chosen as preferred antigen. But in the selection of anti - source parents, the main agronomic characters of the core collection were comprehensively considered. Grey correlation degree can provide a very valuable index. Maximum grey correlation degree between core collections and Yuexiangzhan is IR29692-99-3-2-1, second is IR15847-135-1-1, and Min is ASD7. Therefore, in the selection of breeding parents of biotype II, IR29692-99-3-2-1 can be chosen as preferred antigen.                                                                                                                                                                                                  

3.2 Grey correlation analysis of BPH biotype II core collections

Moderately resistant to BPH biotype II core samples of main agronomic traits and correlation degree and ranking (Table 2). The main agronomic characters of the core collection showed different, and the difference was very large (Table 2). If from a single point of view, such as seed setting rate, 520471 and Yuexiangzhan are the most close to, and can be chosen as preferred antigen. But Maximum correlation degree between core collections and Yuexiangzhan is IR36, second is RD9, and Min is 520541. Therefore, in the selection of breeding parents of BPH biotype II, IR36 can be chosen as preferred antigen.

3.3 Grey correlation analysis of resistance biotype Bangladesh core collection

Resistant to biotype Bangladesh core samples of main agronomic traits and correlation degree and ranking (Table 3). The main agronomic characters of the core collection showed different, and the difference was very large (Table 3). If from a single point of view, such as Growth period, 570056, RP2397-406-50 and Yuexiangzhan are the most close to, and can be chosen as preferred antigen. But Maximum correlation degree between core collections and Yuexiangzhan is RP1579-1862-72-31-52, second is IR45131-59-2-3-2-3, and Min is IR31892-46-3-2. Therefore, in the selection of breeding parents of biotype Bangladesh, RP1579-1862-72-31-52 can be chosen as preferred antige

3.4 Grey correlation analysis of rice gall midge resistance China type IV core collection

Resistant to China type IV core samples of main agronomic traits and correlation degree and ranking (Table 4). The main agronomic characters of the core collection showed different, and the difference was very large (Table 4). If from a single point of view, such as Growth period, 60140, RP1976-18-6-4-2 and Yuexiangzhan are the most close to, and can be chosen as preferred antigen. But Maximum correlation degree between core collections and Yuexiangzhan is DUO KANG No.1, second is RP1976-18-6-4-2, and Min is 510322. Therefore, in the selection of breeding parents of China type IV, DUO KANG No.1 can be chosen as preferred antigen.

4 Conclusions and Discussions

(1) The core samples and the standard varieties (Yuexiangzhan) of different biotype of Brown Planthopper and rice gall midge China type IV grey correlation analysis results show that in the resistant to BPH biotype II, moderately resistant to BPH biotype II, resistant to biotype Bangladesh, resistant to rice gall midge China type IV, IR29692-99-3-2-1, IR36, RP1579-1862-72-31-5, and DUO KANG No.1 are closest to standard variety. In the selection of breeding parents can be chosen as preferred antigen.

(2) In the breeding of the resistant to BPH and rice gall midge, selection of resistant parents is very important. It is not comprehensive and accurate that only considers a single trait, while ignoring other traits. And the main agronomic characters of various anti-sources should be considered synthetically. Grey correlation degree can provide a very valuable index.

(3) Grey correlation analysis we used, with Yuexiangzhan as standard varieties. But in breeding practice, should be determined according to the standard variety breeding objective, comprehensive evaluation and the standard varieties of rice germplasm resources resistant to Rice Brown Planthopper and rice gall midge core collection. And determine the best source of resistance to meet the actual needs of the parents.

(4) Application of gray correlation analysis of rice germplasm resources resistant to Rice Brown Planthopper and rice gall midge biotypes of core collection for comprehensive evaluation, the conclusions are preliminary. The core collection under different environmental conditions, the agronomic traits will change. Therefore, in practical work, should also be grey analysis and field observation organically, so as to improve the actual effect of core sample application further.

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