Preliminary Breeding of Superior Maize Combinations in Zhaotong, Yunnan

Shimin WANG Jianjun LIU Dongyang KAN Xuangui CHEN Shijun ZHANG Xianzhu HE Jinpeng CHENG

Abstract ［Objectives］ This study was conducted to select superior maize combinations.

［Methods］With the control maize variety Haihe 2 in the middle altitude area of Yunnan Province as the control, adopting a single-factor randomized block three-replicate experiment design, a one-year field cultivation experiment was carried out in Luyin Village, Yongfeng Town, Zhaoyang District, Zhaotong City.

［Results］ A total of 11 new superior maize combinations including ZT-1 and ZT-2 were obtained. Through comprehensive comparison analysis with Haihe 2 (CK), we selected six superior combinations of ZT-1, ZT-3, ZT-4, ZT-6, ZT-7 and ZT-9, which showed overall performance better than the control Haihe 2 (CK) in terms of resistance, yield, and ear traits.

［Conclusions］The selected 6 superior combinations have promotion value, and are recommended for higher-level trials and demonstrations.

Key words Zhaotong, Yunnan; Plateau agriculture; Maize breeding; Dominant traits

Received: January 21, 2021  Accepted: April 4, 2021

Shimin WANG (1982-), female, P. R. China, associate professor, master, devoted to research about plant genetic breeding.

*Corresponding author. E-mail: 35830097@qq.com.

Zhaotong is located in the northeastern part of Yunnan Province, in the hinterland of the Wumeng Mountains at the junction of Yunnan, Guizhou, and Sichuan. It is at the junction of the Yunnan-Guizhou Plateau, and most of its agricultural resources are plateau agriculture, with maize and potato as the main crops. In recent years, due to the single germplasm of maize planted in Zhaotong, the genetic basis is weak, and the resistance of crops to diseases, pests and adversity has decreased. It is urgent to discover new and high-quality germplasm resources.

In order to promote the development of local plateau characteristic agriculture, study the comprehensive advantages of new maize combinations［1-3］, and speed up the process of variety selection, College of Agronomy and Life Sciences, Zhaotong University and Zhaotong Academy of Agricultural Sciences have strengthened cooperation in variety selection and breeding, and actively carried out the scientific research work in the improvement and innovation of maize germplasm resources and the selection and breeding of new varieties［4-5］. Through the development of different levels of test experiments, they speeded up the testing and screening of superior maize combinations, and achieved the goal of quicker breeding of more varieties through the scientific testing system. To identify specific and excellent new varieties suitable for local promotion in Zhaotong by improving the breeding efficiency and improving the variety structure is of great significance to the local variety layout in accordance with local conditions.

Excellent hybrid maize seeds should have good high yielding ability and wide adaptability.  Making full use of the existing hybrid maize seed resources, conducting scientific evaluation and analyzing their high yield and stable yield can provide a reliable basis for seed department management and agricultural production. New hybrid maize varieties and dominant test-cross combinations can be cultivated and managed in the same field［6-8］, and they can be analyzed and compared with the control varieties set in the same field in tests according to the performance of test subjects in terms of resistance and yield［9］. Analyzing the actual field performance of the new hybrid maize combinations in terms of variety growth period, disease resistance, ear traits and yield traits and identifying the adaptability of new hybrid maize combinations to identify their adaptability, high yielding ability and stress resistance are conducive to accurately grasping the characteristics and yield indexes of varieties［10］. The new maize varieties currently promoted in the field are screened and identified through this approach.

The project research carried out in Luyin Village, Yongfeng Town, Zhaoyang District, Zhaotong City, can represent the vast mid-elevation area of Zhaotong, and even the same type of ecological regions in northeastern Yunnan. In this study, an experiment was designed by the  randomized block three-replicate method, and the data of all combinations were analyzed and compared after the planting cycle was over to obtain the comprehensive performance of the new combinations［11］, so as to screen out new maize varieties suitable for large-scale promotion.

Materials and Methods

Experiental materials

The 11 new maize combinations tested were: ZT-1, ZT-2, ZT-3, ZT-4, ZT-5, ZT-6, ZT-7, ZT-8, ZT-9, ZT-10, and ZT-11, which were all provided by Institute of Food Crops, Zhaotong Academy of Agricultural Sciences. The experimental control species Haihe 2 (CK) was provided by Yunnan State-owned Capital Operation Jinding Hepu Agricultural Technology Co., Ltd.

Experimental methods

The experiment adopted random block arrangement (Table 1), in three replicates. Each plot had an area of 4 m×5 m, or 20 m2. Each plot had 5 rows in wide and narrow row spacing. Specifically, the wide rows and narrow rows were 1.2 and 0.4 m, respectively, and the width was 1.6 m; and the row length was 5 m. Each row was planted with 24 plants in 12 holes, 2 plants per hole. Each plot had 120 plants, and the design density was 60 000 plants/hm2. The three rows in the middle of each plot were harvested to weigh the fresh weight of ears, which was converted to the average ear weight per plant. According to the average ear weight per plant, ear samples of 10 plants were randomly taken and tested for the ear traits, and the drying rate was calculated by drying and threshing, as well as the yield per unit area of each combination. All data collection and calculation methods were carried out in accordance with the standards of the General Maize Variety Test Investigation Items and Standards in Yunnan Province. In order to ensure data accuracy and reduce test errors, each field management and data collection work was completed on the same day. The field randomized block design scheme of the experiment is shown in Table 1.

Field management and operation

The first crop of the test site was maize. The sowing method was direct seeding, and sowing was carried out on March 31, with 4-8 seeds per hole. After the seedlings emerged, and after the three leaves and one heart were reached, final singling was performed in the whole area, and two seedlings were left in each hole. The date of final singling was April 23.

In the experiment, a special long-acting slow-release fertilizer for maize (N∶P∶K=30∶10∶10) was used as the base fertilizer. The base fertilizer was applied at 750 kg/hm2, and no topdressing was applied in the middle of the cultivation process. In order to ensure the normal emergence of seedlings in the experiment, irrigation was performed once at the time of sowing, and because the rain was relatively normal in the later period and the soil moisture was relatively good, subsequent irrigation was not carried out. The experimental harvest period was September 28.

Results and Analysis

Disease level and resistance analysis of varieties

With reference to the General Maize Variety Test Investigation Items and Standards in Yunnan Province, statistics and analysis were conducted on the field resistance of different combinations, and the results are shown in Table 2. It can be seen from Table 2 that each combination showed good resistance to northern leaf blight, southern leaf blight, stalk rot, head smut, stem borer, etc. Gray leaf spot, ear rot, and rust are main field diseases in Zhaotong. In terms of gray leaf spot, ZT-1 and ZT-2 showed the highest disease level, reaching level 5, that is to say, they were moderately resistant, while the disease in ZT-3, ZT-5, ZT- 7 and ZT-9 was lightest, at level 1, which meant that they were highly resistant. From the prespective of ear rot, except for ZT-8, other combinations all suffered from lighter disease of level 1, belonging to the highly resistant type, while ZT-8 exhibited the highest rate of diseased plants, up to 8.2%, so it was susceptible. As to the resistance to rust disease, the disease in ZT-3, ZT-4, ZT-5, ZT-10 and ZT-11 reached level 3, which was the highest, while the disease in ZT-1, ZT-2, ZT-6, ZT-8, ZT-9 and Haihe 2 was the lightest, of level 1. Because northern leaf blight, southern leaf blight and ear rot are the main monitoring diseases in Yunnan Province, they are diseases of one-vote veto, that is, after field and indoor inoculation, the combinations with a disease level up to 9 are the targets of direct elimination. Therefore, it can be seen that the comprehensive disease performance of these combinations basically meets expectations and can meet the needs of promotion in Zhaotong City.

Analysis of variety ear traits

According to the statistical standards for data recording, we conducted data collection and analysis on the ear traits of each dominant combination (see Table 3 for details). Ear traits such as ear length, ear thickness, bald tip, and cob color are important for variety specificity, and are also important indexes for determining whether a variety meets the needs of the market and has promotion value. It can be seen from Table 3 that the ear length ranged from 16.9 to 21.2 cm, with the largest value in ZT-3 of 21.2 cm, the smallest value in ZT-10 of 16.9 cm, and an amplitude of variation of 5.3 and a coefficient of variation of 9. The ear diameter varied from 4.2 to 5.5 cm, with the largest value in ZT-2 up to 5.5 cm, the smallest value in ZT-11 of 4.2 cm, and an amplitude of variation of 1.3 and a coefficient of variation of 8. The bald tip was 0.2-2.8 cm, the longest in Haihe 2 (CK) of 2.8 cm, the shortest in ZT-4 of 0.2 cm, and the amplitude of variation was 2.6. The experimental results of Yang et al.［12］ showed that proper bald tip did not affect maize yield, but according to the breeding and marketing experience of maize breeders for many years, whether the tip is bald or not is mainly determined by the genetic internal factors of maize varieties. Varieties with good tip character have better planting stability, and varieties with the character of bald tip have better yielding ability and are greatly affected by environmental factors［12］. The number of ear rows was in the range of 12-18 rows, with an amplitude of variation of 6 and a coefficient of variation of 10. The number of grains per row varied from 33 to 42.6 grains, with an amplitude of variation of 9.6 and a coefficient of variation of 8. The 100-grain weight determines the volume weight of a variety, that is, the amount of nutrients per unit volume.  The larger the 100-grain weight, the smaller the volume weight, and the smaller the 100-grain weight, the greater the volume weight［13］. The 100-kernel weight ranged from 29.4 to 51.1 g, with an amplitude of variation of 21.7 and a coefficient of variation of 15. It fluctuated the most in ear traits, indicating that the grain quality of different varieties had a large difference, and the 100-kernel weight had a greater impact on maize yield. Seed rate reflects the commodity of a variety. The seed rate ranged from 82.2 to 86.6%, with an amplitude of variation of 4.4 and a coefficient of variation of 2. Its fluctuations were the smallest among ear traits, and the differences were not significant. It can be seen that improving the level of seed rate is a difficult link in breeding. The effective ears per plant ranged from 1.00 to 1.46, with an amplitude of variation 0.46. The grain weight per ear varied from 133.3 to 233.3, with an amplitude of variation of 100.  Based on the above analysis, the variation fluctuations of ear traits in descending order were: 100-kernel weight, number of ear rows, ear length, ear diameter, number of grains per row, and seed rate. Therefore, in actual breeding practice, more attention should be paid to the breeding of maize hybrid combinations with larger 100-kernel weight, thicker ears and more grain rows to achieve better experimental screening results, so as to achieve the goal of high-yielding efficient breeding.

Analysis of maize yield in regional tests

Economic yield is the core index to measure the quality of a variety, and yield and resistance together constitute the core value of a variety. Good varieties must ensure that both yield and resistance reach corresponding standards and their performance is outstanding. Other indexes only reflect the specificity and commodity attributes of varieties［11-12］, and are one of the indexes that distinguish a variety from other varieties. Through the yield measurement analysis of each combination, it can be seen from Table 4 that the relative productivity of variety ZT-7 ranked first, with a yield of 13 201.5 kg/hm2, which increased by 1 813.5 kg compared with the control, i.e., an increase of 15.9%. The relative productivity of variety ZT-3 ranked second, with a yield of 12 846 kg/hm2, which increased by 1 458 kg/hm2, i.e., an increase of 12.8%. The relative productivity of variety ZT-1 ranked third, with a yield of 12 382.5 kg/hm2, which increased by 999 kg/hm2, that was an increase of 8.7%. The relative productivity of variety ZT-9 ranked fourth, with a yield of 12 292.5 kg/hm2, which increased by 904.5 kg/hm2, that was an increase of 7.9%. The relative productivity of variety ZT-6 ranked fifth, with a yield of 12 012 kg/hm2, which increased by 624 kg/hm2, that was an increase of 5.5%. The yields of above 5 new combinations increased extremely significantly. The relative productivity of ZT-4 ranked sixth, with a yield of 11 781 kg/hm2, which increased compared with the control by 393 kg/hm2, that was an increase of 3.4%. The yields of other varieties decreased to different degrees compared with the control.

Conclusions and Discussion

Compared with the control variety Haihe 2 (CK), none of the 11 combinations had serious resistance defects, and they could resist common diseases such as northern leaf blight, gray leaf spot, ear rot, etc. In terms of yield, the six combinations of ZT-1, ZT-3, ZT-4, ZT-6, ZT-7 and ZT-9 had different degrees of increase in yield compared with the control. Among them, ZT-7 had the largest increase in yield, of 15.9%, and ZT-4 showed the least increase in yield, of 3.4%. The overall high yielding ability was good.

In summary, through the one-year field cultivation experiment, it was concluded that among the 11 new testcross combinations: such six combinations as ZT-1, ZT-3, ZT-4, ZT-6, ZT-7 and ZT-9 were better than the control Haihe 2 (CK) in terms of resistance, yield, and ear traits. They performed well and had certification and promotion value, and are recommended to higher-level experimental demonstrations. The five combination varieties of ZT-2, ZT-5, ZT-8, ZT-10 and ZT-11 showed yields decreased to varying degrees, and their overall performance was poor, so it is recommended to eliminate them.

At present, only a one-year single-site single-factor experiment has been conducted in Zhaotong, which can not represent the situation in the whole province. If these excellent combinations are selected for variety certification, multi-site experimental research will need to be carried out across the province. In addition, considering that only a one-year field cultivation experiment was carried out, to determine whether these varieties are stable in promotion, at least one cycle of field testing is required to detect the stability of these selected combinations.

In view of the fact that any field phenotype of crops is the result of the interaction between genotype and environment, whether these selected combinations have the same disease resistance in other regions still needs planting identification in other regions. Taking into account the differences in disease physiological races, if conditions permit, indoor disease inoculation tests also should be carried out to identify disease resistance.

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