Correlation Between ASI and Yield and Drought Resistance of Maize Inbred

Yixuan WANG Ruilian WANG Cheng LI Chun ZHANG Zhaojuan WANG Hongbiao KANG Yicheng YANG

Abstract Maize is the main grain crop and important forage crop in China. The correlation between ASI and yield of maize inbred lines and whether ASI and the ASI extension time （Dct） of maize inbred lines could be used as a direct indicator of drought resistance of maize inbred lines were explored. The results showed that the goodness of fit of ASI and Dct with DI were 0.478 and 0.829， respectively， and the ASI had an extremely significant negative correlation with yield per plant. ASI and Dct could be used as a parameter to evaluate drought resistance of maize inbred lines， but Dct was more effective than ASI in determining drought resistance index （DI） of maize inbred lines.

Key words Maize; ASI; Dct; Yield; Drought resistance

Maize is one of the three major food crops， and it is extremely sensitive to drought during the reproductive growth period. Drought during the flowering period will greatly reduce maize yield[1]. At present， people have gradually realized the impact of drought on the growth and development of maize. Many studies have found that one of the most important factors that reduce maize yield is the anthesis-silking interval （ASI） in maize. Under drought stress， the ASI can be extended by up to 15 d， which will reduce the number of grains per ear of corn and lead to reduced yield[2-4]. Therefore， we studied the correlation between ASI and yield of maize inbred lines， and whether the ASI and ASI extension time of inbred lines in irrigated and stressed areas can be used as a direct indicator to determine the drought resistance of maize inbred lines.

Experimental Methods

This experiment was conducted at the Yuanziqu Experimental Station of the Bayannur Academy of Agricultural and Animal Sciences in 2019. 123 maize inbred line materials were tested， all of which were commonly used maize inbred lines introduced in recent years. The experiment adopted split block design， in which the main plot was the irrigation treatment， and the subplots were inbred materials. Two treatments of normal irrigation （control） and drought stress were set up， using drip irrigation and open field cultivation， in 3 replicates. A one-row plot was set for each test material. The row length was 3 m; the row spacing was 55 cm; and the plant spacing was 30 cm. The drought stress treatment was irrigated only once 10 d after emergence， and no water was provided during the rest of the period. During the experiment， the rainfall during the whole growth period was 89.6 mm， and the rainfall was concentrated in late June. The specific temperature and rainfall are shown in Fig. 1.

Field investigations were carried out in accordance with Appendix B "National Silage Maize Variety Regional Test Investigation Items and Standards" of NY/T1209-2006 "Regulations for the Variety Tests of Field Crop Maize （Zea mays L.）". The silking period is the date when more than 50% of the plant filaments in the plot protrude about 2 cm from the bracts. The tasseling period is the date when the tips of tassels of more than 50% of the plants in the plot are about 3 to 5 cm above the top leaves. The total number of plants and total ears in each plot were investigated. After weighing all the harvested ears， they were dried and threshed， and the dry weight was measured. The moisture content of the grains was measured with a moisture analyzer. The moisture content was converted into standard moisture content at 14%， and finally converted into yield per plant.

In the formulas， Ystress represents the yield per plant of a certain inbred line under drought stress; Yirrigation represents the yield per plant of a certain inbred line under full irrigation water condition; Ym-stress represents the average yield of all inbred lines under drought stress.

Experimental Results

Analysis of correlation between the tasseling and silking time of inbred lines

It can be seen from Table 1 that the tasseling time and the silking time under the two treatments of inbred lines was in extremely significant positive correlation， indicating that the silking time of the inbred lines in the irrigation or the stress plots could be inferred from the tasseling time of corresponding water treatment. The tasseling and silking time in the stress plot were in extremely significant positive correlation with the tasseling and silking time in the irrigation plot， indicating that the tasseling time and silking time in the drought stress plot could be inferred from the tasseling time and silking time in the irrigation plot.

Analysis of correlation between yield per plant and ASI of inbred lines

It can be seen from Table 2 that the ASI in the stress area and the ASI in the irrigation area were in extremely significant positive correlation. When the ASI in the irrigation plot of the inbred lines increased， the ASI in the stress plot also increased， indicating that the ASI in the drought stress treatment could be inferred from the ASI in the irrigation plot of the inbred lines. The yields per plant of the inbred lines in the stress plot and the irrigation plot were extremely significantly negatively correlated with the ASI value of the corresponding water treatment， that is， with the increase of ASI， the yields per plant of the inbred lines under the two water treatments would be extremely significantly reduced. The relationship between yield and ASI can also be seen from Fig. 2. The inbred lines with a high yield per plant had a lower ASI， and only a few inbred lines had lower ASI but a lower yield per plant， indicating that there were other factors controlling the yields of inbred lines. The yields per plant （Y） of various inbred lines under each water treatment and the corresponding ASI （X） were further fitted for a linear equation， and the optimal equation was established as Y=112.703-13.124X， R2= 0.478， F=221.258， and the significant probability values of the regression coefficients were all less than 0.01， so the linear relationship of the regression equation was extremely significant. The equation showed that ASI was a direct factor affecting the yields per plant of the inbred lines， and the determination coefficient was 0.478， indicating that 47.8% of the yields per plant of the inbred lines was determined by ASI.

Changes of ASI after water stress

It can be seen from Table 3 that the inbred lines' Dct had a very significant negative correlation with the inbred lines' DI. The larger the DI， the stronger the drought resistance of the inbred line. The Dct of the inbred lines with strong drought resistance was extremely significantly reduced. The ASI in both the stress and irrigation plots showed a very significant negative correlation with DI， that is， the smaller the ASI， the stronger the drought resistance of the maize inbred line.

The relationship between Dct and DI can also be seen from Fig. 3. The Dct of the materials with a DI value greater than 1.5 was less than or equal to 1， that is， the flowering and tasseling periods of the inbred lines with strong drought resistance were not significantly affected when they were exposed to water stress. It can be seen from Fig. 4 that the ASI and DI of the inbred lines under various water treatments were in a linear relationship. With the increase of ASI， the drought resistance of the inbred lines was extremely reduced， but the ASI in the irrigation plot showed more discrete values. Although the ASI was larger， the drought resistance of the inbred lines was also stronger. Therefore， it is inferred that the drought resistance of the inbred lines cannot be judged solely by the ASI of the irrigation plot.

Through stepwise regression， it was found that the most important factor contributing to the drought resistance of maize inbred lines was Dct， which was the direct factor that could represent the drought resistance of maize inbred lines， followed by the ASI in the stress plot， and the least contributing factor was the ASI in the irrigation plot. Further by linearly fitting the DI （Y2） and Dct （X2） of the inbred lines， the optimal equation was established as Y2=1.471-0.332X2， R2=0.829， F=583.670， and the significant probability values of the regression coefficients were all less than 0.01， so the linear relationship of the regression equation was extremely significant. This equation showed that the Dct of the inbred lines was a direct factor affecting the drought resistance， and the determination coefficient was 0.829， indicating that 82.9% of the DI values of the inbred lines was determined by the Dct of the inbred lines.

Discussion and Conclusions

Effects of maize inbred lines' ASI on the yields of the inbred lines

A number of studies have shown that drought stress is one of the main factors affecting ASI of maize inbred lines， and has a greater impact on maize reproductive growth. Drought stress during the flowering and tasseling period of maize will cause changes in the physiological metabolism of maize， and the ears of maize thus cannot be pollinated normally， which affects the seed setting rate of maize and further affects the yield of maize[2，5-7]. This study also found that regardless of drought or not， the maize inbred lines' ASI had a very significant negative correlation with the yield per plant， which is consistent with the results of Martiniello[8]and Bolaos[9].

Relationship between maize inbred lines' ASI and drought resistance of maize

There are various methods for evaluating drought tolerance of maize， and DI has always been favored by many researchers. With the in-depth research on drought tolerance of crops， it has been found that DI developed from DC is a good index of drought resistance of maize inbred lines[10-12]. Therefore， in this study， DI was used as the evaluation index of drought resistance of the inbred lines. A number of studies have found that ASI can be used as a secondary index to evaluate drought resistance of maize inbred lines[13]， but ASI is only a necessary condition for screening high-resistant maize germplasms. High-resistant varieties must be varieties with low ASI， but not all varieties with a low ASI were highly resistant[6，14]， which is consistent with the results of this study. When selecting drought-resistant inbred lines， the degree of change in ASI of the inbred lines under stress should be used for the determination， rather than simply relying on the ASI value of maize under normal irrigation conditions. Through stepwise regression analysis， it was found that Dct was the first determinant of drought resistance in maize inbred lines. The research point of view on Dct is that varieties with strong drought resistance must be varieties with a low Dct value， but not as long as the Dct value is small， the drought resistance of maize inbred lines is strong[6，14]. There is no relevant report on the correlation between DI and Dct in maize inbred lines at present， and therefore， the viewpoint on whether Dct can be used as a drought resistance index in maize inbred lines needs to be further studied through many years of tests.

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