Abstract

Total 24 hybrid combinations were formulated by NC II design using hybrids (J. sigillata x J. regia) Yunxin 7926 (P₁₁), 8064 (P₁₂), 8034 (P₁₃), 7914 (P₁₄) as female parent and 6 superior trees of J. sigillata from Sichuan as male parent. The combining ability and heritability of walnut characters were studied, including diameter, weight, thickness and rate of kernel. The result shown that: both additive variation and non-additive variation were significant in these 4 characters, but the additive variation was principle. Different parent had different excellent genes. P₂₄, P₂₃, P₂₂ and P₁₄ were the best parent to improve walnut diameter and weight, followed by P₂₁, P₁₃ and P₁₁. In contrast, P₂₅ and P₂₆ shown poor effect on diameter and weight. Cross P₁₁xP₂₃, P₁₁xP₂₄ and P₁₂xP₂₄ were good for increasing diameter, while cross P₁₁xP₂₆ was the best in increasing rate of kernel. The broad-sense heritability was ordered from high to low as diameter (0.990)>thickness(0.968)>rate of kernel (0.970)>weight (0.968) and the narrow-sense heritability was ordered as diameter (0.844)>thickness (0.821)>weight (0.735)>rate of kernel (0.693).

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INTRODUCTION

Cross breeding of Juglans between interspecies began in the 60s of the 20th century in China. According to incompletely statistics, about 35 hybrid varieties were cultivated up to 2002 (Hua-Bai and Fang, 2004). There were few reports about genetic development of walnut at home and abroad. Only Hansche et al. (1972), analyzed heritability of 18 characters of J. regia L. by standard deviation method and no any report about combining ability. This study analyzed and estimated the combinding ability and heritability of progenies of 24 hybrid combinations by their 4 main characters can reflect walnut’s quality, which provides references for selective mating of hybrid parent, the selection of hybrid progeny and the collocation of clones and families in breeding garden.

MATERIALS AND METHODS

Female parents (P₁) are 7926 (J. sigillata x J. regia), 8064 (J. sigillata x J. regia), 8034 (J. regia x J. sigillata) and 7914 (J. sigillata x J. regia) cultivated by cross breeding of (J. sigillata) and (J. regia Dode). P₁₁~P₁₄ represent 4 female parents respectively, which were introduced from Yunnan Province in China in 2001 are characterized by early bearing and thin shell. Six male parents (P₂) are J. sigillata with characteristics of thin shell and high yields, which were selected from Sichuan province in China represented by P₂₁~P₂₆, respectively. There are 1080 hybrid nuts picked from above 24 hybrid combinations in 2006 in the present study.

Experiment site located in Cheng Du city in Sichuan province of China, where the altitude is 480 m, mean annual temperature is 16.5°C, annual amount of precipitation is 900 mm and annual sunshine hours are 1298.2 h has a subtropical climate, the wet summer, moderate and moist climate and the space of seed tree is 5x5 m.

NCII was used in experiment, data was processed by Excel 2003, genetic parameter was estimated by the method of Zhi-Ren (1986). Combining ability was estimated by fixed model and variance component and the genetic parameters were estimated by random model. The nuts were picked after they are fully matured, then natural withered. Measure their thickness of abdomen, diameter of abdomen, diameter of seam and height by vernier caliper, calculate the average of above 3 values as nut diameter, weigh their weight and kernel weight by electronic balance and calculate the rate of kernel. Each combination repeated 3 times, each repetition selected 5 nuts randomly from 3 seed trees. Analyzed their average means, the percentage should be transferred into arcsine by their square root.

RESULTS AND DISCUSSION

Measured characters: In this study, the characters have obvious differentiation between single nuts. Diameter: 29.5-46.1 mm, weight: 9.05-18.91 g, thickness: 0.56-1.06 mm, kernel rate: 50.02-68.33%. But, there is no obvious difference between repetitions in a combination. Four characters of each combination are shown in Table 1.

Four characters of hybrid nuts and parents in original place shown in Table 2.

From Table 2, hybrid nuts showed a significant heterosis on the whole, which is consistent with Zhi-Yuang and Xue-Liang (2002). The values of 4 characters of hybrid nuts are not only higher than their parents average, but also surpass the dominant parent reflecting heterobeltiosis to some extent, which is in line with Yin and Mei-Yong (2005).

From Table 3 and 4 characters have no significant difference between repetitions, but have an extremely significant between combinations, which indicate that the true genetic difference dose existed. Then analyze the General Combining Ability (GCA) and Special Combining Ability (SCA).

Analysis of combining ability
Variance analysis of combining ability: The results of variance analysis of combining ability based on the average values of the repetition in combinations are as follow (Table 4).

It can clearly shown from Table 4 that the characters of nut diameter, weight and thickness are affected by parent’s GCA and SCA, while rate kernel is only affected by the male parent’s GCA and SCA. Male parent’s GCA has an extremely significant difference on 4 characters, while female parent’s GCA has difference only on rate kernel. In combinations, all SCA have an extremely significant difference on 4 characters, which indicated that the selection of parents mating is very important to the quality of nuts. From the results, we can show that both GCA and SCA will affect the characters of nut. From the standpoint of quantitative inheritance, the 4 characters are affected by additive effect and non-additive effect at the same time.

Although, thickness is also affected by GCA and SCA of parents, up to 0.01 levels notable difference on statistics, thickness of both parents is thin, so the hybrid nut has thin shell: 0.56-1.06 mm, which is thinner than top-grade (1.1 mm) one and superior tree (1.5 mm) stipulated by national standard (GB 7907-87). It reflects thickness has no large variability from commodity value.

GCA of parents and its expression: Different parents have a low GCA on thickness of hybrid nut, because both parents are characterized by thin shell. While, nut diameter, weight and rate of kernel display a significant difference between different parents. GCA ranges from 3.63-2.29 on nut diameter and P₂₄ has the highest GCA, P₂₃ takes second place, P₂₆ at lowest. For nut weight, GCA ranges -2.12-1.34, P₂₄ has the highest GCA, P₂₃ takes second place, P₂₅ at lowest. For kernel rate, GCA ranges from -2.64-1.59, P₂₁ has the highest GCA, P₂₆ takes second place, P₂₃ at lowest. GCA of the same parent is different even on different characters. For example, P₂₃ and P₂₄ have superiority on nut weight and diameter, but their GCA is lower on kernel rate. On the contrary, P₂₆ and P₂₅, with small diameter and light weight, their kernel rates display a high positive effect, which shows different parents have different excellent genes. The results indicate that not any parent can promote qualities of nut (Table 5).

SCA effect: From Table 6, SCA of different combinations has significant difference on the same character except thickness. Take kernel rate as an example, the variability of SCA between combinations is -1.34~1.28.

Table 1:	Characters means of crosses

 

Table 2:	Means of parents and hybrids character

 

 

Table 3:	Variance analysis

 

 

Table 4:	Variance analysis of combining ability

 

 

Table 5:	Effect size of general combining ability in parents

 

 

Table 6:	Effect size of special combining ability in crosses

 

 

Table 7:	Heritability and contribution rate of genotype variance of characters

 

SCA of P₁₁xP₂₆ is 1.35 on nut weight, while P₁₂xP₂₆ is -1.26. Even the same combination has obviously different SCA on different characters. For example, P₁₁xP₂₃ has a high positive effect on nut diameter, but displays a high negative effect on kernel rate. The variability of SCA on different characters is larger, P₁₁xP₂₆ has the highest value, which is 1.35, P₂₄xP₁₄ has the lowest value, which is -1.34.

GCA and SCA have no relationship by comparing their effect. For example, P₁₁xP₂₆ has a higher SCA on kernel rate, P₁₁ and P₂₆ have a higher GCA effect, while P₂₃ have the lowest GCA effect although, combination P₁₃xP₂₃ has a higher SCA; although, P₁₁xP₂₆ has the highest SCA on nut weight, the two parents have negative GCA values; there are not any combinations with a higher SCA among P₁₄, P₂₄ and P₂₃, which have a higher GCA on nut weight and diameter. The result shows that not any GCA effect can totally decide qualities of nut. All the expression of characters is depend on multiple factors and even the low GCA effect parents can form a high SCA effect combination.

Estimation of colony genetic parameters: Estimate the genotype variance of GCA (P₁, P₂) and SCA (P_1x2) and analyze their contribution rate (V_g, V_s) in total variance and the GCA contribution rate (V_g1, V_g2) of two parents, respectively to know about the effect of two parents and their co-effect on nut quality shown in Table 7.

As can be shown in Table 7, 4 characters are affected by GCA and SCA at the same time, but the contribution rate of GCA is over 80%, while contribution rate of SCA is low, which reflects additive effect of gene has a leading role to decide hybrid expression and nut quality is decided by genetic traits of the parents, matching of parents has a lower effect to hybrid. GCA contribution rate of male parent is larger than that of female parent, which indicates that the hereditable character of male parent is larger than that of female one and hereditable character of male parent has a direct effect on nut quality.

CONCLUSION

Effect of combining ability and parent selection: GCA reflects additive effect of parents. If the parents have a higher additive effect, they will combine out an excellent progeny. But, it has a low possibility to possess an ideal GCA effect on several characters at the same time. So, we will select the parents by the main target breeding in cross breeding work. In this study, we can see that P₂₄, P₂₃, P₂₂ and P₁₄ has a good effect on improving nut diameter and weight, P₂₁, P₁₃ and P₁₁take the second place, P₂₅ and P₂₆ at lowest. For kernel rate, P₂₁ is the best, followed by P₂₆ and P₂₅, P₂₃ and P₂₄ are worst. SCA displays non-additive effect. Although, effect value can not decide expression of offspring directly, it has a meaning of guidance to combinations and collocation of pollination trees. We can not select the combinations only with a higher SCA, but to select the higher SCA ones based on parents with higher GCA. So P₁₁xP₂₃, P₁₁xP₂₄ and P₁₂xP₂₄ can improve diameter of nut. Although, P₁₃xP₂₅, P₁₃xP₂₆ and P₁₄xP₂₆ have a high SCA, their parents have a lower GCA, the expression of the offspring is not so good. For nut weight, P₁₁xP₂₆ has the highest SCA, but the GCA of P₁₁ and P₂₆ are negative, so their hybrid nut has no superiority. Although, SCA on kernel rate of P₁₁xP₂₆ is not the highest, P₁₁ and P₂₆ have a higher GCA and the SCA is also higher, the kernel rate of its offspring is the highest among all the combinations.

Heritability of hybrid nut: Heritability is the percentage of genetic variance to phenotypic variance, which reflects stability of parent’s property and the ability to pass their traits to offspring. Broad sense heritability reflects co-action of additive effect and non-additive effect, while narrow sense heritability is the measure of additive effect. For the 4 characters in this study, broad sense heritability is over 0.95, which is more than the heritability (≥0.8) of thickness, diameter, weight and kernel rate estimated by Hansche et al. (1972). It shows that environment has a little effect on characters can guarantee genetic stability by asexual propagation. So, we can conserve and enlarge excellent genotype by grafting on excellent individual tree. Narrow sense heritability is between 0.693~0.844 shows 4 characters have a higher additive effect, so they have a stable heritability in sexual reproduction. It will be better to reselect after the walnut tree flowering and seedling.

Effect of genetic background of parents: Six male parents used in the research are seed trees selected from Sichuan province in China, where is the regional differentiation of two main walnut populations, with complex topography, diverse climates, rich in resources and the male parents have a larger difference of hereditary basis leading the great variability of the hybrid offspring. As can be shown in Table 7, variation of offspring mainly came from male parents. Although, GCA of different female parents is different, the difference is not large. Effect on offspring variation of Female parents is up to an extremely significant difference but much weaker than that of male parents, because of their consistent genetic background. The largest genotype contribution rate of female parents on thickness is only 14.24% shown in Table 7. It also, is the main reason female variability of GCA much smaller than that of male ones.

How to cite this article:

Zhou Lan-Ying, Xiao Qian-Wen, Zhang Li, Zhang Shang-Jie and Wang Ping-Bang. Analysis of Combining Ability and Heritability about Nut Quality of Walnut.
DOI: https://doi.org/10.36478/brj.2009.24.27
URL: https://www.makhillpublications.co/view-article/1995-4751/brj.2009.24.27