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Inheritance of Ear Tip-Barrenness Trait in Maize
Available online at w.sciencedirect.com -'-He
Agricultural Sciences in China
2007, 6(5): 628-633
"?' ScienceDirect
May 2007
Inheritance of Ear Tip-Barrenness Trait in Maize MENG Zhao-dongl.2,ZHANG Fa-jun2, DING Zhao-hua2, SUN Qiz, WANG Liming2,GUO Qing-fa2,WANG Hong-gang1
2
Agronomy College, Shandong Agricultural University/National Wheat Improvement Sub-center, Tuian 271018, P.R.China Maize Institute, Shandong Academy of Agricultural Sciences/National Maize Improvement Sub-center, Jinan 250100, P.R.Chinu
Abstract The aim of this paper is to study the inheritance pattern of ear tip-barrenness trait in maize (Zea mays L.). Ear tipbarrenness trait in maize can be classified into two types, tip-barren and tip-barrenless. Two inbred lines, 1x01-3 (tipbarrenless type), wxO4-1 (tip-barren type), and their F,, 'F2,BC,, BC, generations were analyzed on their ear tip-barrenness types. Results showed that F, was tip-barren type; the ratio of tip-barren type versus tip-barrenless type followed a 12.78: 1 ratio in F, segregation population and a 2.75:l ratio in BC,. 2 2 test indicated that the trait of ear tip-barrenness type followed an inheritance pattern of 2 duplicate dominant genes. SPSS analysis indicated that the trait of ear tip-barrenness length is of abnormal distribution. Above results mean that: (1) The trait of maize ear tip-barrenness type is controlled by 2 duplicate dominant genes; tip-barren type is dominant over tip-barrenless type; (2) the trait of tip-barrenness length is a quantitative character controlled by polygene with major genes expected. Key words: maize, ear tip-barrenness type, fructification habit, dominant inheritance, duplicate genes
INTRODUCTION The kernel number per ear is an important factor for maize yield. Ear tip-barrenness phenomenon is composed by abortive kernels and unfertilized florets, and often causes a loss in yield at different ratios. (Lu et al. 1999). In maize breeding programs, tip-barrenness is also regarded as an undesirable trait by breeders. Hence, it is necessary to study this phenomenon, to provide references for maize breeding and improve maize production. Previous studies on the phenomenon formation mostly focused on two aspects, the environmental and physiological-biochemical factors. In a common viewpoint, the numbers of degenerated florets and florets without fecundation were mainly affected by envi-
ronmental factors (Tang et al. 1999a, b; Xiao and Ai 1998). A close relation was found between the trait of ear tip-barrenness length and planting density under a planting density of 15000 to 105000 plants per hectare (Yang et al. 2000). No evidences indicated that anatomical structure of cob vascular caused kernel abortion (Wang et al. 1996; Zhang et al. 1999a). The dynamic changes of hormone components including MA, ZR, GA,, and ABA at the top part of the ear maybe resulted in a different ratio of kernel abortion (Wang et al. 1996). Zhang et al. (1998) pointed out that the ethylene was the signal of inducement or evocation in early period of kernel abortion and thought it might be the original reason causing kernel abortion that the difference of ethylene content in different genotypes under diverse environment (Zhang et al. 1998, 1999b), while the differences of mineral elements in quality and
This paper is translated from its Chinese version in Scientia Agriculrura Sinica MENG Zhao-dong, Tel: +86-531-83179175, Mobile: 13969192366, E-mail: [email protected]
0 2007,C M S . All rights reserved.Published by Elsevier Ltd.
629
Inheritance of Ear Tip-Barrenness Trait in Maize
concentration were not the direct reasons in his opinion (Zhang et al. 2001). Little was known about the inheritance pattern of the ear tip-barrenness trait in maize. Someone regarded it as a nature of a variety and a subsequent research showed that the trait was deeply affected by gene additive effect (Ao 1999). Remarkable correlation was found between the mean of the parents’ inbred lines and their F, in the trait of tipbarren length, and the same result found in the female parent inbred line and its F, (Wang 2001). Xiang et al. (2001) found that the trait of tip-barren length was controlled by 2 pairs of positive major genes with heritability values of 72% and the genes increased the tip-barren length, respectively, without interactions. In a word, former studies mainly worked on the environmental, physiological, and biochemical factors affecting tip-barrenness trait, but the mechanism was still vague. Very few researches were found referring its genetic reasons. Hence, tip-barren and tip-barrenless types inbred lines were adopted to study the inheritance pattern of the tip-barrenness trait and provide an instruction for maize breeding programs.
MATERIALS AND METHODS Materials and field management Two inbred lines of different ear tip-barrenness trait, LxO1-3 (P,, tip-barrenless type ) and WxO4-1 (P2,tipbarren type) were selected as parents. The cross of LxO1-3 x WxO4-1 was made in Jinan in the spring season of 2003, and its F,, BC, [(P, xP,) xP,],and BC, [(PI x P,)x P,]populationswere developedin Hainan Province, China, in the winter season in the same year. Above crosses were planted in a density of 30000 plants per ha in the Experiment Station of Shandong Academy of Agricultural Sciences of China in the spring season of 2004. The plots were planted in plots of 3 rows for the parent lines and their F, population, and 30 rows for other populations in a scale of 5.0-m long, 0.67-m wide row.
Sampling The middle row of the plots of parent lines and F, population and all rows of other populations were collected
as samples. The ears of dead plants or with few kernels were eliminated. Ears were air-dried covered with bracts avoiding the tip of the ear being damaged during sampling process.
Measuring criterion and methods The length of ear tip-barrenness was referred to the distance from the bottom of the first round shrunken kernels to the ear top. The type of ear tip-barrenness was classified by the length of tip-barrenness, which is more than 0-cm for the tip-barren and 0-cm tip-barrenless types. The weight of air-dried plant without ears was defined as plant dry matter.
RESULTS Basic status of inbred lines The parent inbred lines grew vigorously under the planting density of 30 000 plant per ha and expressed their genetic traits well on female spikelets polarization and development in an abundant sunlight and rainfall maize growth season of 2004. No differences were found between the two lines in plant height and dry matter traits except the grain yield per plant, however, with 31.6 g of PI higher than that of P, (Table 1).
inheritance analysis of ear tip-barrennesstrait Inheritance pattern of ear tip-barrenness type The ears of P, plants belonged to tip-barrenless type, while the ears of F, and P, plants belonged to tip-barren type (Table 2). The ratio of tip-barren type versus tipbarrenless type ears of 248 F, plants was 12.7:1, which followed a ratio of 15:1 segregation by x2 test. This demonstrated that the tip-barren type was dominant over tip-barrenless type and the trait of tip-barrenness type maybe controlled by 2 pairs of duplicate dominant genes. Further analysis on 221 ears of BC, plants showed the ratio of tip-barren type versus tip-barrenless type was 2.75: 1, which was in agreement with a ratio of 3: 1 segregation by test. 225 ears of 226 BC, plants be-
xz
Q2007,CAAS.All rights reserved.Publishedby ElsevierLtd.
MENG Zhao-done el al.
630
Table 1 Data of the main agronomy traits of the parent inbred lines, LxOl-3(P,) and Wx04-l(P,) (Jinan, China, 2004) Tip-barren -ness type
Parent
PI P,
Plant height
Ear length
Ear diameter
(m)
(m)
Tip-barrenless
201.4
18.6
(m) 4.0
Tip-barren
201.0
13.3
4.7
Rows /ear
Kernels /row
12.4 18.9
Tip-barrenness length
36.7 25.8
1000kernel wt.
Dry matter wt. /plant
Grain yield /plant
Shelling percentage
(9) 128.0 96.4
86.9 81.2
(4
(g)
(g)
0.0 1.8
280.3 197.4
141.1 142.4
6)
Table 2 The distribution status of maize ear tip-barrenness tvDes in different generations Generation
Plant samples
No. of tip-barren type
No. of tip-barrenless type
10 10 10
0 10 10
10 0 0
248 221 226
230 162 225
18 59
p, PI F,
F, BCI BC2
x
~I = 3.84. ~ ~
~
Ratios of tip-barren type versus tip-barrenless type
12.78:l 2.75:l 225: 1
1
x2
value
0.275 0.255
,
longed to tip-barren type except one. All of these validated the above results further. According to these results, we found that maize varieties can be classified into two types, tip-barren and tip-barrenless, which was also consistent with breeding practice. The inheritance behavior of maize ear tipbarrenness type belonged to the quality trait. Inheritance analysis of ear tip-barrenness length The ear tip-barrenness length was studied using 229 ears, which belonged to tip-barren type among 248 F, plants except 1 special ear with a 11.5-cm long tipbarrenness length. The results showed the length of the tip-barren ranged from 0.3 to 6.5 cm and mainly focused on 1 to 2 cm. Statistical analysis using SPSS
program (ver. 11.0) indicated the length was distributed abnormally (significant at 0.05 probability level, Fig.). From the results above we could infer that the length of tip-barrenness was a quantitative trait controlled by polygene with major genes expected. Correlation analysis between the trait of tip-barrenness length and other traits Based on the correlation analysis between the trait of tip-barrenness length and the other agronomy traits of the 229 plants, it was presumed that there was a significant negative effect between the tip-barrenness length and the traits of kernels per row and shelling percentage, but no significant correlation was found between the trait of tip-barrenness length and other traits (Table 3). Be-
60
__
-. i2
-z
50 40
$
;
L
30
n
52
.
/
Std. Dev = 0 Y8
G
Mean = 1.76
20
N = 229.00
10 0
A
1.00 0.50 1 .00
2.00 2.50 3.00 3.50
4.00 4.50 5.00 5.50 6.00 6.50
Length of tip-barrenness (cm)
Fig. Frequency distribution of tip-barrenness length of tip-barren type ears in F, population.
02007. CAAS. All rightsreselved. Published by Elsevier Ltd.
Inheritance of Ear Tip-Barrenness Trait in Maize
63 1
sides that, the tip-barrenness length had no significant correlation with dry matter, and so, we could conclude that the tip-barrenness trait may be a genetic
trait and its formation is not due to the dry matter deficiency.
Table 3 Correlation between the trait of tip-barrenness length and the other traits of the 229 plants Characters
Ear length
Ear diameter
Rowdear
Kerneldrow
Cob diameter
Dry matter wt. /plant
1000-kernel wt.
Shelling percentage
Coefficient
0.013
0.040
0.027
-0.308"
0.047
-0.067
0.049
-0.259"
rues (200) = 0.138, ru
D,
(200) = 0.18 1.
DISCUSSION Understandingof the ear tip-barrenness trait in maize The ear tip-barrenness trait has been regarded as a quantitative trait that is easily influenced by the environmental factors for a long time. But, the fact is that maize germplasm can be classified into two types, tip-barren and tip-barrenless types. Most of the ear tip-barrenness phenomena were resulted from adverse environment factors, and this often concealed the differences between types of ear tip-barrenness. The ear tip-barrenness phenomenon has two aspects in our opinions, the first one is the tip-barrenness type which means whether the ear tip part barren or not. It belongs to a qualitative trait behavior according to our study result. The other one, discussed mostly by former researchers, is the ear tip-barrenness length, which is a quantitative trait controlled by major genes. It has been proved that some crops such as cotton and tomato can be classified into two types, determinate and indeterminate growth types; and soybean has two flowering styles including determinate and indeterminate flowering styles. Sesame, an indeterminate flowering style crop, was induced successfully to create a mutant of determinate flowering trait controlled by a pair of recessive genes (Zheng et al. 1998). Besides that, Liu (1990) also discovered the determinate flowering sesame by natural mutation. We found, in our breeding practice, that the female spikelets polarization are of two types, determinate and indeterminate polarization, and guessed maize ear fructification habit might have certain relationship with the female spikelets polarization (for further research).
Accordingly, two concepts of determinate fructification and indeterminate fructification, were applied to distinguish the trait of maize ear fructificationhabit based on the classification of above crops and the status of kernels development at the top part of an ear (Meng et al. 2001). For determinate fructification varieties without tip-barren, there was no obvious difference in kernel size and weight between the top and the other part of an ear, and no shrunken kernels under natural growth environment. But for indeterminate fructification varieties with tip-barren, there were certain shrunken kernels and florets without fecundation at the top of an ear. In this experiment, plants are classified into two types, tip-barren and tip-barrenless, simply based on the length of their ear tip-barrenness being 0 cm or not. There were 2 of the 248 ears in F, population, which belonged to tip-barren type, having no shrunken kernels at the top of the ears, but a certain length tipbarrenness. These 2 ears should be also classified to determinate fructification type considering their female spikelets' determinate polarization.
Inheritanceanalysis of the ear tip-barrennesstrait Results from this experiment showed that the ear tipbarrenness type was a qualitative trait controlled by 2 pairs of duplicate dominant genes. As the length of tipbarrenness was mostly selected as research object in former studies on the tip-barrenness phenomenon, the ear tip-barrenness trait was often regarded as a quantitative trait that was easily influenced by environmental factors. By that way, the trait of tip-barrenness type was mostly ignored. Based on the analysis of tip-barrenness length of F, plants, we found that the trait of tip-barrenness length
Q2007,C M S . All rights reserved. Published by Elsevier Ltd.
632
was distributed abnormally. So, it should be a quantitative trait controlled by polygene with major genes action. This was consistent with Xiang et al. (2001) result, if the tip-barrenless ears were excluded in this experiment. Further studies are required to make clear whether more genes control the trait of maize ear tip-barrenness type. After all, the conclusion deduced from this experiment was only based on one set of materials. No reports on molecular mapping of genes controlling maize tip-barrenness type were found up to now (Lu and Bernardo 2001; Xu et al. 1999; Wang and Li 2000; Sharopova et al. 2002; Scanlon and Myers 1998; Gao and Glover 1994). The marking results on the trait of tip-barrenness type and the QTL mapping on the trait of tip-barrenness length will be published in our following studies.
CONCLUSION The fundamental reason of the formation of maize tipbarrenness phenomenon was not the dry matter deficiency but a genetic element. The tip-barrenness trait was represented not only on difference of tip-barrenness length but also on tip-barrenness type. Maize ear tip-barrenness type was a qualitative trait controlled by 2 pairs of duplicate dominant genes; the ear tip-bmenness length was a quantitative trait controlled by polygene with major genes action, which was easily influenced by environmental factors.
Acknowledgements This study was supported by the National 863 Program of China (2002AA207008), and the Project of Agricultural Structure Adjustment in China (04-03-03B).
References Ao J. 1999. Analysis on combining ability for major quantitative character in maize inbred lines. Journal of Maize Sciences, 7, 41-42. (in Chinese) Gao Q Y, Glover D V. 1994. The relationship of dNA content in corn endosperm nuclei to kernel traits during kernel development.Acta Agronornica Sinca, 20,46-51. (in Chinese) Liu Y. 1990. Discovery of determinate sesame and studies on its hybrid progeny. Chinese Oil Crops, 4, 88. (in Chinese) Lu G Y, Hao R L, Han Y, Zhang J M, Zhao F L, Xie X H, Sun S
MENG Zhao-dong et al.
Z. 1999. Correlation and path analysis on ear characteristics of maize. Foreign Agronomy-Rain Fed Crops, 19,52-53. (in Chinese) Lu H, Bernardo R. 2001. Molecular marker diversity among current and historical maize inbreds. Theoretical and Applied Genetics, 103,613-617. Maize Institute of Shandong Academy of Agricultural Sciences. 1987.Maize Physiology. Agricultural Press, Beijing. pp. 288289. (in Chinese) Meng Z D, Han J, Zhang F J, Guo Q F, Wang L M, Liu Z X, Zhang Q W. 2001. Discussion on waxy corn breeding strategies. Journal ofMaize Sciences, 4, 14-17. (in Chinese) Michael J S, Alan M M. 1998.Phenotypic analysis and molecular cloning of discolored-1(dscl), a maize gene required for early kernel development. Plant Molecular Biology, 37,483-493. Scanlon M J, Myers A M. 1998. Phenotypic analysis and molecular cloning of discolored-1 (dscl), a maize gene required for early kernel development. Plant Molecular Biology, 37,483-493. SharopovaN, McMullen M D, Schultz L, Schroeder S, SanchezVilleda H, Gardiner J, Bergstrom D, Houchins K, MeliaHancock S, Musket T, Duru N, Polacco M, Edwards K, Ruff T, Register J C, Brouwer C, Thompson R, Velasco R, Chin E, Lee M, Woodman-Clikeman W, Long M J, Liscum E, Cone K, Davis G, Coe E H Jr. 2002. Development and mapping of SSR markers for maize. Plant Molecular Biology, 48, 463-481. Tang Q L, Rong T Z, Huang Y B. 1999a.The study of barren ear tip in maize. I . Inheritance of the flower number per ear. Journal of Sichuan Agricultural University, 17, 34-38. (in Chinese) Tang Q L, Rong T Z, Huang Y B. 1999b. The study of barren ear tip in maize. 11. The growth rhythm of flower and kernelin differentregion of maize ear. Journal of Sichuan Agricultural University, 17, 163-166. (in Chinese) Wang J H, Wang S A, Zhao D M, Liang Z X. 1996. A study on regulation of developmentof maize kernels. I .Characteristics of development of maize kernels from different genotypes and the physiological and biochemical basis. Scientia Agricultura Sinica, 29,33-40. (in Chinese) Wang J H, Wang S A, Zhao D M, Xia H J. 1998. Effect of bundle anatomy and moisture content of maize cobon grain development. Journal of Maize Sciences, 6 , 49-51. (in Chinese) Wang M Q. 2001. Study on relativity between maize bald of filial generation and maize parent bald. Journal of Maize Sciences, 9,43-44. (in Chinese) Wang T Y, Li Y. 2000. Appilications of molecular markers in gene tagging and assisted selection in maize. Journal of Maize Sciences, 8, 3-8. (in Chinese)
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Inheritance of Ear Tip-Barrenness Trait in Maize
Xiang Q, Huang L J, Cao Y G, Dai J R. 2001. A preliminary study on genetic effect of maize yield component traits based on major gene and polygene mixed inheritance. Acta Agriculfurae Boreali-Sinica, 16, 1-5. (in Chinese) Xiao Y C, Ai H Y. 1998. The effect of athwart temperature on differentiation of maize ear. Chinese Agricultural Science Bulletin, 14, 38-40. (in Chinese) Xu M L, Melchinger A E, Xia X C, Luebberstdt T. 1999. Highresolution mapping of loci conferringresistance to sugarcane mosaic virus in maize using RFLP, SSR, and AFLP markers. Molecular and General Genetics, 261,514-58 1. Yang S M, Liao E H, Yuan J C, Tao Y Q, Li D X. 2000. Study on the relationship between maize planting density and yield constitute factor. Journal of Sichuan Agricultural University, 18, 322-324. (in Chinese) Zhang F L, Cui Y H, Wang Z M, Zhao M, Wang S A, Zhao J R, Guo J L. 1999a. Studies on the relation between pedicel
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vascular development and maize kernel abortion. Journal of Agricultural University of Hebei, 22, 16-19. (in Chinese) Zhang F L, Wang Z M, Zhao M, Wang S A, Zhao J R, Guo J L. 1999b. Studies on ethylene metabolismduring the early period of maize kernel development. Acta Agronornica Sinica, 25, 508-512. (in Chinese) Zhang F L, Wang Z M, Zhao M, Wang S A, Zhao J R, Guo J L. 1998. Studieson the regulatingmodel of maize kernel abortion. Journal of Maize Sciences, 6,49-5 1. (in Chipese) Zhang F L, Wang Z M, Zhao M, Wang S A. 2001. Distribution of mineral elements along the maize ear and its relationship with kernel abortion. Journal of Agricultural University of Hebei, 24, 8-10. (in Chinese) Zheng Y Z, Wang W Q, Mei H X, Liang X Y, Tu C L. 1998. Genetic improvement of determinate sesame (Sesarnurn indicum L.).Chinese Journal of Oil Crop Sciences, 3,21-30. (in Chinese) (Edited by ZHANG Yi-min)
02007,CA4.S.All rights resewed.Publishedby Elsevierltd.
Agricultural Sciences in China
2007, 6(5): 628-633
"?' ScienceDirect
May 2007
Inheritance of Ear Tip-Barrenness Trait in Maize MENG Zhao-dongl.2,ZHANG Fa-jun2, DING Zhao-hua2, SUN Qiz, WANG Liming2,GUO Qing-fa2,WANG Hong-gang1
2
Agronomy College, Shandong Agricultural University/National Wheat Improvement Sub-center, Tuian 271018, P.R.China Maize Institute, Shandong Academy of Agricultural Sciences/National Maize Improvement Sub-center, Jinan 250100, P.R.Chinu
Abstract The aim of this paper is to study the inheritance pattern of ear tip-barrenness trait in maize (Zea mays L.). Ear tipbarrenness trait in maize can be classified into two types, tip-barren and tip-barrenless. Two inbred lines, 1x01-3 (tipbarrenless type), wxO4-1 (tip-barren type), and their F,, 'F2,BC,, BC, generations were analyzed on their ear tip-barrenness types. Results showed that F, was tip-barren type; the ratio of tip-barren type versus tip-barrenless type followed a 12.78: 1 ratio in F, segregation population and a 2.75:l ratio in BC,. 2 2 test indicated that the trait of ear tip-barrenness type followed an inheritance pattern of 2 duplicate dominant genes. SPSS analysis indicated that the trait of ear tip-barrenness length is of abnormal distribution. Above results mean that: (1) The trait of maize ear tip-barrenness type is controlled by 2 duplicate dominant genes; tip-barren type is dominant over tip-barrenless type; (2) the trait of tip-barrenness length is a quantitative character controlled by polygene with major genes expected. Key words: maize, ear tip-barrenness type, fructification habit, dominant inheritance, duplicate genes
INTRODUCTION The kernel number per ear is an important factor for maize yield. Ear tip-barrenness phenomenon is composed by abortive kernels and unfertilized florets, and often causes a loss in yield at different ratios. (Lu et al. 1999). In maize breeding programs, tip-barrenness is also regarded as an undesirable trait by breeders. Hence, it is necessary to study this phenomenon, to provide references for maize breeding and improve maize production. Previous studies on the phenomenon formation mostly focused on two aspects, the environmental and physiological-biochemical factors. In a common viewpoint, the numbers of degenerated florets and florets without fecundation were mainly affected by envi-
ronmental factors (Tang et al. 1999a, b; Xiao and Ai 1998). A close relation was found between the trait of ear tip-barrenness length and planting density under a planting density of 15000 to 105000 plants per hectare (Yang et al. 2000). No evidences indicated that anatomical structure of cob vascular caused kernel abortion (Wang et al. 1996; Zhang et al. 1999a). The dynamic changes of hormone components including MA, ZR, GA,, and ABA at the top part of the ear maybe resulted in a different ratio of kernel abortion (Wang et al. 1996). Zhang et al. (1998) pointed out that the ethylene was the signal of inducement or evocation in early period of kernel abortion and thought it might be the original reason causing kernel abortion that the difference of ethylene content in different genotypes under diverse environment (Zhang et al. 1998, 1999b), while the differences of mineral elements in quality and
This paper is translated from its Chinese version in Scientia Agriculrura Sinica MENG Zhao-dong, Tel: +86-531-83179175, Mobile: 13969192366, E-mail: [email protected]
0 2007,C M S . All rights reserved.Published by Elsevier Ltd.
629
Inheritance of Ear Tip-Barrenness Trait in Maize
concentration were not the direct reasons in his opinion (Zhang et al. 2001). Little was known about the inheritance pattern of the ear tip-barrenness trait in maize. Someone regarded it as a nature of a variety and a subsequent research showed that the trait was deeply affected by gene additive effect (Ao 1999). Remarkable correlation was found between the mean of the parents’ inbred lines and their F, in the trait of tipbarren length, and the same result found in the female parent inbred line and its F, (Wang 2001). Xiang et al. (2001) found that the trait of tip-barren length was controlled by 2 pairs of positive major genes with heritability values of 72% and the genes increased the tip-barren length, respectively, without interactions. In a word, former studies mainly worked on the environmental, physiological, and biochemical factors affecting tip-barrenness trait, but the mechanism was still vague. Very few researches were found referring its genetic reasons. Hence, tip-barren and tip-barrenless types inbred lines were adopted to study the inheritance pattern of the tip-barrenness trait and provide an instruction for maize breeding programs.
MATERIALS AND METHODS Materials and field management Two inbred lines of different ear tip-barrenness trait, LxO1-3 (P,, tip-barrenless type ) and WxO4-1 (P2,tipbarren type) were selected as parents. The cross of LxO1-3 x WxO4-1 was made in Jinan in the spring season of 2003, and its F,, BC, [(P, xP,) xP,],and BC, [(PI x P,)x P,]populationswere developedin Hainan Province, China, in the winter season in the same year. Above crosses were planted in a density of 30000 plants per ha in the Experiment Station of Shandong Academy of Agricultural Sciences of China in the spring season of 2004. The plots were planted in plots of 3 rows for the parent lines and their F, population, and 30 rows for other populations in a scale of 5.0-m long, 0.67-m wide row.
Sampling The middle row of the plots of parent lines and F, population and all rows of other populations were collected
as samples. The ears of dead plants or with few kernels were eliminated. Ears were air-dried covered with bracts avoiding the tip of the ear being damaged during sampling process.
Measuring criterion and methods The length of ear tip-barrenness was referred to the distance from the bottom of the first round shrunken kernels to the ear top. The type of ear tip-barrenness was classified by the length of tip-barrenness, which is more than 0-cm for the tip-barren and 0-cm tip-barrenless types. The weight of air-dried plant without ears was defined as plant dry matter.
RESULTS Basic status of inbred lines The parent inbred lines grew vigorously under the planting density of 30 000 plant per ha and expressed their genetic traits well on female spikelets polarization and development in an abundant sunlight and rainfall maize growth season of 2004. No differences were found between the two lines in plant height and dry matter traits except the grain yield per plant, however, with 31.6 g of PI higher than that of P, (Table 1).
inheritance analysis of ear tip-barrennesstrait Inheritance pattern of ear tip-barrenness type The ears of P, plants belonged to tip-barrenless type, while the ears of F, and P, plants belonged to tip-barren type (Table 2). The ratio of tip-barren type versus tipbarrenless type ears of 248 F, plants was 12.7:1, which followed a ratio of 15:1 segregation by x2 test. This demonstrated that the tip-barren type was dominant over tip-barrenless type and the trait of tip-barrenness type maybe controlled by 2 pairs of duplicate dominant genes. Further analysis on 221 ears of BC, plants showed the ratio of tip-barren type versus tip-barrenless type was 2.75: 1, which was in agreement with a ratio of 3: 1 segregation by test. 225 ears of 226 BC, plants be-
xz
Q2007,CAAS.All rights reserved.Publishedby ElsevierLtd.
MENG Zhao-done el al.
630
Table 1 Data of the main agronomy traits of the parent inbred lines, LxOl-3(P,) and Wx04-l(P,) (Jinan, China, 2004) Tip-barren -ness type
Parent
PI P,
Plant height
Ear length
Ear diameter
(m)
(m)
Tip-barrenless
201.4
18.6
(m) 4.0
Tip-barren
201.0
13.3
4.7
Rows /ear
Kernels /row
12.4 18.9
Tip-barrenness length
36.7 25.8
1000kernel wt.
Dry matter wt. /plant
Grain yield /plant
Shelling percentage
(9) 128.0 96.4
86.9 81.2
(4
(g)
(g)
0.0 1.8
280.3 197.4
141.1 142.4
6)
Table 2 The distribution status of maize ear tip-barrenness tvDes in different generations Generation
Plant samples
No. of tip-barren type
No. of tip-barrenless type
10 10 10
0 10 10
10 0 0
248 221 226
230 162 225
18 59
p, PI F,
F, BCI BC2
x
~I = 3.84. ~ ~
~
Ratios of tip-barren type versus tip-barrenless type
12.78:l 2.75:l 225: 1
1
x2
value
0.275 0.255
,
longed to tip-barren type except one. All of these validated the above results further. According to these results, we found that maize varieties can be classified into two types, tip-barren and tip-barrenless, which was also consistent with breeding practice. The inheritance behavior of maize ear tipbarrenness type belonged to the quality trait. Inheritance analysis of ear tip-barrenness length The ear tip-barrenness length was studied using 229 ears, which belonged to tip-barren type among 248 F, plants except 1 special ear with a 11.5-cm long tipbarrenness length. The results showed the length of the tip-barren ranged from 0.3 to 6.5 cm and mainly focused on 1 to 2 cm. Statistical analysis using SPSS
program (ver. 11.0) indicated the length was distributed abnormally (significant at 0.05 probability level, Fig.). From the results above we could infer that the length of tip-barrenness was a quantitative trait controlled by polygene with major genes expected. Correlation analysis between the trait of tip-barrenness length and other traits Based on the correlation analysis between the trait of tip-barrenness length and the other agronomy traits of the 229 plants, it was presumed that there was a significant negative effect between the tip-barrenness length and the traits of kernels per row and shelling percentage, but no significant correlation was found between the trait of tip-barrenness length and other traits (Table 3). Be-
60
__
-. i2
-z
50 40
$
;
L
30
n
52
.
/
Std. Dev = 0 Y8
G
Mean = 1.76
20
N = 229.00
10 0
A
1.00 0.50 1 .00
2.00 2.50 3.00 3.50
4.00 4.50 5.00 5.50 6.00 6.50
Length of tip-barrenness (cm)
Fig. Frequency distribution of tip-barrenness length of tip-barren type ears in F, population.
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Inheritance of Ear Tip-Barrenness Trait in Maize
63 1
sides that, the tip-barrenness length had no significant correlation with dry matter, and so, we could conclude that the tip-barrenness trait may be a genetic
trait and its formation is not due to the dry matter deficiency.
Table 3 Correlation between the trait of tip-barrenness length and the other traits of the 229 plants Characters
Ear length
Ear diameter
Rowdear
Kerneldrow
Cob diameter
Dry matter wt. /plant
1000-kernel wt.
Shelling percentage
Coefficient
0.013
0.040
0.027
-0.308"
0.047
-0.067
0.049
-0.259"
rues (200) = 0.138, ru
D,
(200) = 0.18 1.
DISCUSSION Understandingof the ear tip-barrenness trait in maize The ear tip-barrenness trait has been regarded as a quantitative trait that is easily influenced by the environmental factors for a long time. But, the fact is that maize germplasm can be classified into two types, tip-barren and tip-barrenless types. Most of the ear tip-barrenness phenomena were resulted from adverse environment factors, and this often concealed the differences between types of ear tip-barrenness. The ear tip-barrenness phenomenon has two aspects in our opinions, the first one is the tip-barrenness type which means whether the ear tip part barren or not. It belongs to a qualitative trait behavior according to our study result. The other one, discussed mostly by former researchers, is the ear tip-barrenness length, which is a quantitative trait controlled by major genes. It has been proved that some crops such as cotton and tomato can be classified into two types, determinate and indeterminate growth types; and soybean has two flowering styles including determinate and indeterminate flowering styles. Sesame, an indeterminate flowering style crop, was induced successfully to create a mutant of determinate flowering trait controlled by a pair of recessive genes (Zheng et al. 1998). Besides that, Liu (1990) also discovered the determinate flowering sesame by natural mutation. We found, in our breeding practice, that the female spikelets polarization are of two types, determinate and indeterminate polarization, and guessed maize ear fructification habit might have certain relationship with the female spikelets polarization (for further research).
Accordingly, two concepts of determinate fructification and indeterminate fructification, were applied to distinguish the trait of maize ear fructificationhabit based on the classification of above crops and the status of kernels development at the top part of an ear (Meng et al. 2001). For determinate fructification varieties without tip-barren, there was no obvious difference in kernel size and weight between the top and the other part of an ear, and no shrunken kernels under natural growth environment. But for indeterminate fructification varieties with tip-barren, there were certain shrunken kernels and florets without fecundation at the top of an ear. In this experiment, plants are classified into two types, tip-barren and tip-barrenless, simply based on the length of their ear tip-barrenness being 0 cm or not. There were 2 of the 248 ears in F, population, which belonged to tip-barren type, having no shrunken kernels at the top of the ears, but a certain length tipbarrenness. These 2 ears should be also classified to determinate fructification type considering their female spikelets' determinate polarization.
Inheritanceanalysis of the ear tip-barrennesstrait Results from this experiment showed that the ear tipbarrenness type was a qualitative trait controlled by 2 pairs of duplicate dominant genes. As the length of tipbarrenness was mostly selected as research object in former studies on the tip-barrenness phenomenon, the ear tip-barrenness trait was often regarded as a quantitative trait that was easily influenced by environmental factors. By that way, the trait of tip-barrenness type was mostly ignored. Based on the analysis of tip-barrenness length of F, plants, we found that the trait of tip-barrenness length
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632
was distributed abnormally. So, it should be a quantitative trait controlled by polygene with major genes action. This was consistent with Xiang et al. (2001) result, if the tip-barrenless ears were excluded in this experiment. Further studies are required to make clear whether more genes control the trait of maize ear tip-barrenness type. After all, the conclusion deduced from this experiment was only based on one set of materials. No reports on molecular mapping of genes controlling maize tip-barrenness type were found up to now (Lu and Bernardo 2001; Xu et al. 1999; Wang and Li 2000; Sharopova et al. 2002; Scanlon and Myers 1998; Gao and Glover 1994). The marking results on the trait of tip-barrenness type and the QTL mapping on the trait of tip-barrenness length will be published in our following studies.
CONCLUSION The fundamental reason of the formation of maize tipbarrenness phenomenon was not the dry matter deficiency but a genetic element. The tip-barrenness trait was represented not only on difference of tip-barrenness length but also on tip-barrenness type. Maize ear tip-barrenness type was a qualitative trait controlled by 2 pairs of duplicate dominant genes; the ear tip-bmenness length was a quantitative trait controlled by polygene with major genes action, which was easily influenced by environmental factors.
Acknowledgements This study was supported by the National 863 Program of China (2002AA207008), and the Project of Agricultural Structure Adjustment in China (04-03-03B).
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