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Trend of Low Nitrogen Tolerance in Maize Cultivars and Their Parental Lines Released at Different Years in China

Author: ZhangHaiYan
Tutor: DongShuTing
School: Shandong Agricultural University
Course: Crop Cultivation and Farming System
Keywords: maize yield low nitrogen agronomic traits
CLC: S513
Type: Master's thesis
Year: 2013
Downloads: 11
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Abstract

Maize (Zea mays L.) has been the first food crop in China and the world, and it is veryimportant in national economy. But corn production has being threatened severely byadversity such as low nitrogen, drought, pests and diseases. Therefore, new breeding objectiveand scheme are needed to established, for improving the ability adapting to severeenvironment. Experience of nations with developed seed industries such as America,indicated that retrospective study could be useful instruction for improving yield ability.Definition experiments on low nitrogen tolerance were carried out for Chinese maize cultivarsreleased at different years. Field trials was performed in Sanya Hainan province in winter of2011, Langfang Hebei province in summer of2012, thirty-five maize varieties from1950to2000and their parental lines were tested. The material of the research was mainly spanningcultivars in maize central production region from1950to2000, including4OPVs in1950s,4double-cross hybrid in1960s and27single-cross hybrids after1970s. The objectives of thestudy are to reveal:(1) trend of yield, plant traits and heterosis of Chinese cultivars in normalnitrogen and low nitrogen environments.(2) trend of low nitrogen tolerance of Chinesecultivars and their parental lines. The results will help to explore further improve yieldpotential breeding strategies, and provide a theoretical basis for the high-yield breedingpractice. Main results and conclusions were as following:(1)The change between grain yield of maize cultivars and decades was linear increase innormal nitrogen environment. Under low nitrogen treatment, yields of maize varieties in eachdecade were lower than yields under normal nitrogen treatment.The coefficient of low nitrogen tolerance of maize hybrids increased slightly withdecades, the general trend remains unchanged. That is to say, the low nitrogen tolerance ofmaize cultivars in China has little change. But we need more data from other experiments toconfirm our conclusion.In normal N environment, plant height, ear height, LAI and green leaves numberincreased from1950s to2000s. Tassel length and tassel branch number decreased, chlorophyllcontent was relative stable, and ASI shortened clearly. Low nitrogen stress reduced plant andear height, LAI, chlorophyll content, the number of green leaves, tassel length and tasselbranch number, increased ASI value. All the traits, except tassel length and tassel branchnumber, were extremely significantly correlative with grain yield. The trend of ear length, ear diameter, barren tip length, kernel number per ear and weightper hundred kernels was increased with decade both in normal and low N conditions. Low Nstress decreased ear diameter, ear length, kernel number per ear and weight per hundredkernels. Shelling percentage was more stable. Most plant traits of maize varieties in China arebetter improved, but the maize cultivars stress tolerance changed not much; the next tusk weshould focus on increasing the selection pressure and improving kernel number per ear andweight per hundred kernels in low N tolerance breeding in maize.(2)The absolute heterosis of grain yield in low N stress was less than that of normal Ncondition. It indicated that the yield reduction velocity of hybrids was higher than theirparental lines. Absolute heterosis increased with decades from1970s to2000s in both twotreatments. No obvious different exists between relative heterosis in normal N and low Nstress. Relative heterosis increased slightly from1970s to2000s, but kept stable generally.Thus we can conclude the increased of hybrids grain yield is not due to the improvement ofheterosis but the stress resistance.(3)The parental lines grain yield increased linearly with decades in both Hainan andLangfang cites. The grain yield of inbred lines in low N treatment declined comparative withnormal N treatment. From the coefficient of low nitrogen tolerance of inbred lines, we canconclude low N stress affected hybrids greater than parental lines.The coefficient of low nitrogen tolerance of inbred lines was not changed obviously withdecade. That is to say, the low nitrogen tolerance of maize parental lines has little change. Weshould introduce new germplasm and strengthen nitrogen pressure in breeding process in thefuture.ASI, plant and ear height, tassel length and tassel branch number declined with decades,LAI increased, chlorophyll content changed not obvious in normal N treatment. Under low Nstress, ASI increased, tassel branch number changed little, all the other traits decreasedobviously. Weight per hundred kernels of newer inbred lines was more than old lines. Kernelnumber per ear and weight per hundred kernels were larger in normal N treatment than in lowN treatment. Barren tip length increased result of low N. Chlorophyll content, ASI, ear length,Kernel number per ear and weight per hundred kernels was extremely significantly correlativewith grain yield.

Trend of Low Nitrogen Tolerance in Maize Cultivars and Their Parental Lines Released at Different Years in China

Abstract

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