Effects Of Waterlogging On Growth And Grain Yield Of Different Wheat Varieties

Soil waterlogging stress is a world-wide abiotic stress,which has restricted wheat production for long time in high-precipitation areas.In recent years,the frequent occurrence of abnormal global climates has led to severe inequality of temporal and spatial precipitation and aggravated the occurrence of waterlogging stress in high-precipitation areas.As one of the main wheat producing areas in China,the middle and lower reaches of the Yangtze River have abundant rainfall during the growth period,but which often exceed the normal water requirement for wheat growth,resulting in waterlogging stress occurring at all growth stages.The selection and application of wheat varieties with high waterlogging tolerance is a major measure to deal with waterlogging stress.This experiment was carried out in the experimental farm of the Jiangsu Key Laboratory of Crop Genetics and Physiology of Yangzhou University and the Yizheng Modern Agriculture Demonstration Base in 2018-2019 and 2019-2020.Different wheat varieties which are currently mainly promoted in the middle and lower reaches of the Yangtze River were planted as materials,and soil waterlogging treatments were set up separately at the three-leaf stage,jointing stage,and flowering stage.We studied the effects of waterlogging treatments on the growth,physiology,and grain yield of different wheat varieties and analyzed the differences in agronomic and physiological characteristics at the key growth periods between different varieties subjecting to different stages conducting waterlogging.This study was be expected to clarify the mechanism of high-yield and waterlogging tolerance of the varieties and explore the possibility using image data to evaluate the waterlogging tolerance of varieties.The results could provide theoretical and technical references for selecting waterlogging-tolerance varieties and conducting high-yield cultivation in the middle and lower reaches of the Yangtze River.The main results are as follows:1.The 15-day waterlogging treatment during the three-leaf stage significantly reduced shoot dry weight,seedling height,leaf number of main stem,stem and tiller number,leaf area,and green leaf SPAD value of wheat at the three-leaf stage,with an average reduction percentage of 28 varieties 14%(0%-28%),11%(1%-18%),6%(0%-12%),13%(0%-38%),14%(2%-28%),and 15%(5%-24%).Correlation analysis showed there was a different degree of correlation between the declines of individual agronomic indexes subjecting to waterlogging stress,indicating that a single indicator cannot be used to comprehensively and accurately evaluate the waterlogging tolerance of varieties.Therefore,a multivariate analysis method was used to construct a comprehensive evaluation index value(D value)for waterlogging tolerance.The results verified that the estimation accuracy of the D value of each variety was greater than 0.999,which could better comprehensively reflect the differences in waterlogging tolerance among wheat cultivars.Correlation analysis between agronomic indicators and D value also suggested that the higher plant dry weight,stem and tiller number,and leaf area after waterlogging stress could be the agronomic indicators for selecting the varieties with high tolerance of waterlogging.The relationships between RGB image parameters and plant agronomic traits were further analyzed.The results showed that the color parameters H,b,and 2G-RB of the RGB image obtained from the top view could reflect the leaf color,and the texture parameters,including dissimilarity,homogeneity,and ASM obtaining form the side view and top view images,could reflect the morphological characteristics of wheat plant.In conclusion,the color parameter H of the top-view image and the texture parameter dissimilarity,homogeneity,and ASM of the side-view image after waterlogging stress could be used as the intelligent evaluation indexes selecting the wheat varieties with high waterlogging tolerance during the seedling period.2.The 10-day waterlogging treatment at the jointing stage significantly reduced the grain yield of wheat with an average 30-59%decline of 22 varieties.Waterlogging treatment reduced the number of spikes,grains per spike,and 1000-grain weight in different degrees and significantly reduced the accumulation of dry matter,LAI,and SPAD values of the top three leaves at the booting,flowering,and maturity stages,resulting in the decline of photosynthetic productivity.According to the grain yield and the reduction rate due to waterlogging,the varieties were divided into four groups:low-yield and waterlogging-tolerance,high-yield and waterlogging-tolerance,low-yield and waterlogging-sensitive,and high-yield and waterlogging-sensitive.Under the natural growth conditions,compared to the lower-yielding type,the high-yielding type had greater biomass and LAI at booting and flowering stages and top third leaf SPAD value at booting stage,robust single stem at flowering stage,and significantly higher biomass and nitrogen accumulation weight and single ear weight at mature stage.The results also showed that high-yielding varieties have strong individual photosynthetic production capacity during the medium and late stages of growth,and increasing the accumulation of photosynthetic substances.Under the waterlogging condition,more waterlogging-tolerance groups exhibited significantly higher SPAD values of the top 2ed leaf and top 3th leaf at the flowering stage,and higher biomass,nitrogen accumulation,number of fertile spikelets,the number of spikelets,the number of grains per spike,the thousand-grain weight,and the weight per spike.It implies that the waterlogging-tolerant varieties have strong post-flowering photosynthetic production and accumulation ability when they were suffered by waterlogging stress.Under different water treatments,the high-yield waterlogging tolerance type had higher LAI types at the booting stage and the flowering stage compared with other,and its single-stem green leaf at the flowering stage was heavier.The results showed that the high-yield and waterlogging-tolerance wheat varieties have the characteristics of large leaf areas and large storage of leaf photosynthetic materials.The relationships between the high-altitude near-infrared image parameters and plant agronomic traits was further analyzed.The results showed that the DN values of the near-infrared,blue,and green light bands obtained during the flowering period under the control and waterlogging conditions were not correlated with the agronomic indicators measured during the same period and grain yield,indicating that the obtained image parameters had a poor reflect on the growth of wheat.3.The 7-day waterlogging treatment after flowering significantly reduced the grain yield with an average 8-49%decline of 22 varieties.Waterlogging treatment significantly reduced the number of grains per ear and 1000-grain weight.The stress also significantly reduced the green leaf area,SPAD value,and green leaf area of the upper three leaves at the milk-maturity stage.The results also showed waterlogging significantly lowered the RUBP,POD and CAT enzyme activities of the flag leaf at the milk-maturity period,GOGAT,GS enzyme and NR enzyme activities,but significantly increased the MDA content.These resulted to a significant reduction in the dry matter and nitrogen accumulation at the mature stage.The results showed that waterlogging after flowering caused premature leaf senescence,decreased photosynthetic capacity and nitrogen metabolism,and restricted the supply of grain filling material,reducing grain yield per spike.Under the natural growth conditions,there was a significant linear positive correlation between the grain yield of different varieties and the yield decline after flooding,indicating that the higher the yield of the variety caused the more yield losses after flooding.Under the conditions of natural growth and waterlogging,high-yielding varieties have higher ear number,grain number per ear,and yield per ear.Varieties that cause a large decrease in grain number per ear and 1000-grain weight due to waterlogging have a greater reduction in grain yield.The results suggest that increasing the number of effective ears of varieties and reducing the dependence of grain yield on single ear yield can be used as ways to cope with waterlogging after anthesis and reduce yield loss.High-yield varieties have higher mature biomass and nitrogen accumulation under different water treatments.Varieties that have a large decrease in mature biomass and nitrogen accumulation caused by waterlogging have a greater reduction in yield.High-yield varieties showed higher flag leaf and first green leaf area and RUBP enzyme activity at the milk-maturity stage.Waterlogging caused a large decrease in the total green leaf area and RUBP enzyme activity of the upper three leaves,the single ear yield,and grain yield.There was no significant correlation between the decrease in the area of flag leaf and the green leaf of the first two leaves at the milk maturity stage after waterlogging and the decrease in grain yield.The results showed that the varieties with higher flag leaf and second leaf area and slower photosynthetic area attenuation after anthesis could achieve high yield and tolerant to waterlogging.In addition,high-yield varieties have higher antioxidant enzymes and key enzyme activities of nitrogen metabolism during the milk maturity period,but they also have a greater decline after waterlogging.4.The relationships between RGB image parameters and plant agronomic traits was further analyzed.The results showed that the texture parameters contrast,homogeneity,energy,correlation,ASM,and entropy were significantly correlated with the green leaf area of three leaves per unit area under natural growth conditions,but under waterlogging treatment texture parameters reflect poorly on the green leaf area of three leaves per unit area.There was a significant positive correlation between the morphological parameter area and the area of three green leaves per unit area under natural growth and waterlogging conditions.The morphological parameter area changes after anthesis waterlogging treatment were significantly correlated with the decrease in grain yield,yield per ear,biomass at maturity and nitrogen accumulation.It shows that the morphological parameter area can better reflect the area of green leaves at the milk-maturity stage,and its variation range can be used for the evaluation of the waterlogging tolerance among verities.5.Through analyzing the waterlogging-tolerant varieties under the three-leaf stage waterlogging conditions,the results showed that Yangmai 25 not only had a higher yield and a smaller decline after waterlogging at the jointing stage,but also showed a higher level of waterlogging under different water treatments after flowering.Grain yield,but its growth decline after waterlogging at seedling stage was large compared with other measured verities,indicating its resistance to waterlogging was not high.In summary,waterlogging at the seedling,jointing,and post-flowering stages all had significant negative impacts on the growth of wheat.Waterlogging at the jointing stage and post-flowering caused a significant reduction in yield.Whether the growth of wheat can be restored after waterlogging at the seedling stage and the degree of influence on the grain yield of the control remain to be studied.The waterlogging tolerance of different varieties of wheat under the waterlogging treatment in the three periods is not consistent.Some cultivars are sensitive to waterlogging at the seedling stage,but tolerant to waterlogging at the jointing stage and after anthesis.The reasons for this difference need to be further studied.The image parameters had a good response to wheat growth and grain yield in the waterlogging test at the three-leaf stage and after anthesis,but they are poorly reflected in the waterlogging test at the jointing stage.This difference may be related to the image acquisition distance,sharpness,and population size,which also needs to be tested and verified.