Introduction

Nilaparvata lugens (Sta1) and Orseolia oryzae Wood-Mason are two major pests in rice. High yield and resistance cultivation of rice is the fundamental measures against these two kinds of pests. The insect-resistant variety resources are important basic materials for high yield and resistance cultivation of rice. 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, Frankel (1984) proposed the concept of core collection. The core collection,which use the fewest germplasm materials to represent the crop species and the maximum genetic diversity of their affinis wild species. At present, the whole world has been done in more than 30 kinds of crops on the core collection research (Li et al., 2000). Research of rice core collection has been reported (Wei et al., 1999; Wei et al., 1999; Ruan et al., 1999; Li et al., 2000; Wang et al., 2000; Wei et al., 2000; Zeng et al., 2000). However, no research involve about the rice-resistant to Nilaparvata lugens (Sta1) and Orseolia oryzae Wood-Mason core collection. In order to effectively utilize the insect resistant rice variety resources, avoid the blindness when selecting resistant parent, and make the insect-resistant breeding more targeted and more productive. A total of 454 rice accessions was resistant to different rice brown planthopper biotypes and rice gall midge China type IV were used in the article. Set up rice accessions which resistant to different rice brown planthopper biotypes and Orseolia oryzae Wood-Mason core collection.

1 Material and Methods

1.1 Material

A total of 454 test material of rice accessions which resistant to different rice brown planthopper biotypes and rice gall midge China type IV were saved in Guangxi Academy of Agricultural Sciences genetic pool. 292 resistant to rice brown planthopper biotype II, 125 resistant to biology II and Bangladesh, 21 resistant to rice gall midge China type IV, 6 resistant to rice gall midge China type IV and biology II, 10 resistant to rice gall midge China type IV and biology II and Bangladesh.

1.2 Methods

1.2.1 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, initial heading stage, heading stage, full heading stage, growth stage, plant height and effective plant. To the harvest time, take 5 clusters per plot for indoor testing. Observe and record the number of grain, ripening rate, weight of thousand grains.

1.2.2 Divide into groups

In accordance with the classification standard Seed box identification method of Rice Brown Planthopper, highly resistance: average resistance level 1.0~1.9, resistance: 2.0~3.9, middle resistance: 4.0~5.9 (Li et al., 1992; Li et al., 2003).Huang Fengkuan et al., (another article) make appropriate amendments to the grading standard: highly resistance: average resistance level 1.0~2.9, resistance: 3.0~3.9, middle resistance: 4.0~5.9. In this article, we used these grading standards to divide into groups for above insect resistant germplasm resources. A total of 9 group: high resistance to biological type II, resistance to biological type II, middle resistance to biological type II, resistance to biological type II and Bangladesh, resistance to biological type II and middle resistance to Bangladesh, middle resistance to biological type II and Bangladesh, resistant to rice gall midge China type IV, resistant to rice gall midge China type IV and biological type II, resistant to rice gall midge China type IV, biological type II and Bangladesh.

1.2.3 Cluster analysis

According to the group of 1.2.2, we do the cluster analysis for 10 agronomic traits, which got from observation of 1.2.1. In each set of cluster tree, random choose one material as core collection from Euclidean distance 7.5 units, this distance just forms sample size about 10 %.

The original data of cluster analysis uses the standard transformation, distance coefficients using Euclidean distance, clustering method using sum of sguares of deviation from mean (Zhang et al., 1998; Wang et al., 2000).

1.2.4 Evaluation method

Using characteristic value comparison (Zhang et al., 1998), mean and standard deviation accordance rate (Zhang et al., 1998; Wang et al., 2000), diversity index (Li et al., 1999) evaluate representativeness of core collection.

Mean accordance rate (%) = {1- (|mean core collection- mean total sample|/mean total sample} ×100%

Standard deviation accordance rate (%) = {1- (|standard deviation core collection- standard deviation total sample|/ standard deviation total sample} ×100%

Ni: The value of a character in the i phenotype (variety), N: The sum of the values of a certain personality in all phenotypes (breeds), S: The total number of goods.

Test results using DPS software (Tang and Feng, 2002) for processing.

2 Results and Analysis

2.1 Core collection of rice germplasms which resistant to different rice brown planthopper biotypes and rice gall midge china type IV

53 varieties make up core collection of rice germplasms which resistant to different rice brown planthopper biotypes and rice gall midge china type IV (Table 1), accounted for the total sample (454) of 11.67%. Highly resistant to biotype II: 9, Resistant to biotype II: 14, Moderately resistant to biotype II: 8, Resistant to biotype II and biotype Bangladesh: 7, Resistant to biotype II and moderately resistant to biotype Bangladesh: 6, Moderately resistant to biotype II and biotype Bangladesh: 3, Resistant to rice gall midge china type IV and resistant to biotype II: 1, Resistant to rice gall midge china type IV and resistant to biotype II and biotype Bangladesh: 2 (Table 2).

2.2 Representative of core collection

2.2.1 Comparison of 6 values and index of diversity of core collection with those of 10 collections

53 core collection of the 10 characteristics of the maximum, minimum, range, mean, standard deviation, coefficient of variation of 6 and the diversity index and the corresponding value of the total sample is very similar (Table 3). It indicates that the core sample is representative of the genetic variation range of the 10 character of the total sample.

2.2.2 Index of diversity core, mean, standard deviation accordance rate of collection and whole collection

Compare with 53 core collection and 454 whole collections, the average mean of each trait was 97.75%, the average standard deviation rate was 87.44%, indicating that the core collection is representative of the total sample (Table 4).

3 Conclusion and Discussion

(1) The resistance of rice varieties to Rice Brown Planthopper and rice gall midge biotypes of China N were grouped according to the different resistance and level, using the method of cluster analysis for each group by clustering from Europe's distance of 7.5 units into a class of varieties in the random selection of 1 varieties of core products. Core samples of the total sample of 11.67%. This result is very close to the result of Wei et al. (1999).

(2) It is convenient and low cost to study the 10 main agronomic characters as the core collections, but these agronomic characters can not completely reflect the genetic essence of the germplasm materials (Wei et al., 1999). Take advantage of the genetic information from the level of morphology, biochemistry, and molecular level can truly and maximize to represent the genetic diversity of the species (Li et al., 1999). For the further application of biochemical and molecular marker technology, we research on core collections of rice germplasm resources which are resistant to Rice Brown Planthopper and rice gall midge biotypes China type N, need to future work.

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