Effects Of Different Wx Gene Null On Yield Traits And Starch Quality In Wheat

To investigate the effects of wx genes null on traits related with yield and starchquality in wheat, which could be meaningful for waxy wheat breeding and starchquality improvement, diploid breeding method was adopted to develop 8 genotypeswith different wx genes combinations. 59 DH lines were obtained from (Yangmai10/Waxy C) F₁, and their wx genes were identified by STS markers related to wx genesloci. With these DH lines and other waxy wheat varieties derived from the crosses of(Yangmai 9×different waxy wheat varieties) as test materials, the effects of wx genesnull on plant height, spikes per plant, kernels per spike, 1000-kernel weight, volumeweight and percentage of vitreous kernel were studied. And together with additional 17waxy wheat varieties from different crosses as the test materials, the effects of wxgenes null on grain soluble sugar content and starch content were determined;Simultaneously 3 waxy varieties and 2 check varieties were selected to study the characteristics of sugar degradation and starch accumulation in waxy wheat bydetecting the dynamics of sugar degradation and starch accumulation in waxy wheatgrains after anthesis. In 11 waxy wheat varieties from different crosses, 11 varietieswith one or two wx genes null, 2 normal wheat varieties and 1 white grain normalcultivar as a PHS check, pre-harvest sprouting (PHS) percentage,α-amylase activity,soluble sugar content in grains and grain external appearance characters were analyzedto determine the cause leading to high PHS percentage in waxy wheat. And the indicesfor breeding varieties with high starch quality were also to study with 94 wheatvarieties as the test material. The main results were as follows.1 Wx genes null could not significantly effect plant height, spikes per plant, andkernels per spike, and 3 wx genes null did not increase the plant height of waxy wheat.But wx genes null decreased 1000-kernel weight in a varying degree, with normalwheat (Wx-A1aWx-B1aWx-D1a) greatest and waxy wheat lowest. The volume weightof all genotypes with wx gene null was less than that of normal wheat, but 1 or 2 wxgenes null could not decrease volume weight significantly, and only 3 wx gene nullcould bring a significant decrease. The percentage of vitreous kernel of normal varietiesand those with 1 or 2 Wx genes null was determined by the genotypes of their parents,not by wx genes, but the endosperm of waxy wheat were floury or nearly floury nomatter what kind of endosperm their parents had. Probably it was more small starchgranules in endosperm rather than low protein content in grains that led to a floury ornearly floury endosperm.2 Wx gene null could decrease amylose content. The order of the effects of wxgene null in decreasing amylose content was 3 wx genes null＞2 wx genes null＞1 wx gene null. The amylopectin accumulation in waxy wheat grains was higher than normalwheat and those with 1 or 2 wx genes null, but the amylopectin accumulation of othergenotypes was less than that in normal wheat. Starch content in normal wheat washigher than other 7 genotypes, which had no significant difference in starch contentamong them. Wx gene null might decrease starch content by 7.36%-12.95%, with 3 wxgenes null＞2 wx genes null＞1 wx gene null. However the amylose, amylopectin andstarch contents of wheat with Wx-B1 protein deficiency were significantly lower thanthose of normal wheat. Wx gene null influenced not only the synthesis of amylose, butalso amylopectin synthesis, leading to a decline in starch content.3 In terms of grain soluble sugar content, waxy wheat was higher than normalvarieties and those with 1 or 2 genes null, and 1 or 2 genes null did not lead to theincrease of soluble sugar content. As for grain starch content, waxy wheat was lowerthan normal varieties. The decreasing rate of soluble sugar content in waxy wheatgrains was less than normal wheat before 17th day after anthesis, while afterwards therewas no apparent difference. A "pause stage" of starch content increase occurred inwaxy wheat varieties after the 17th day post-anthesis, during which starch contentstopped increasing and prior to which there were no apparent difference in starchcontent. The reason might be that waxy wheat could not use sugar to synthesizeamylose for GBSS deficiency, but all enzymes related to starch biosynthesis werebecoming inactive at the end of filling, and GBSS deficiency would not make anydifference on sugar transformation between waxy wheat and normal wheat. As forstarch accumulation, there were no difference at the beginning of filling between waxywheat and normal wheat, but at "pause stage", no amylose was synthesized for GBSSdeficiency when amylose should be synthesized in a large amount, however for the enzymes involved in amylopectin biosynthesis had reached their peak before theamount of arnylopectin synthesis decreased greatly at the same time.4 The starch quality of waxy wheat was completely different from othergenotypes. No amylose could be identified in waxy wheat grains in this research. Waxywheat has highest amylopectin content, but its starch content was not high. It indicatedthat the amylopectin synthesis could only compensate a fraction of amylose deficiency.The peak viscosity, trough viscosity, breakdown, final viscosity and setback of starch inwaxy wheat were 1055.5cP, 641.5cP,414cP, 1059cP and 417.5cP respectively, whereasthe value of normal wheat were 2373.5cP, 1384.2cP, 989.3cP, 2977.2cP and 1593cP.The reason why 1000-kernel weight and volume weight of waxy wheat were less thannormal weight might be the bad plumpness, which may be caused by the inadequateamylopectin synthesis in waxy wheat that could not completely compensate theamylose deficiency.5 Except waxy wheat, 6 genotypes with different wx gene null had aninsignificantly higher peak viscosity than normal wheat, with significantly higherbreakdown but lower setback than normal wheat, and the same trough viscosity, finalviscosity as normal wheat. However the peak viscosity and breakdown of wheat withWx-B1 protein deficiency were significantly higher than that of normal wheat, butother RVA parameters had no significant difference with normal wheat. This differencebetween genotypes with wx gene null and varieties with Wx-B1 protein deficiency inRVA parameters might be caused by that the varieties with Wx-B1 protein deficiencywere screened from a large population and had better grain plumpness, which relayedon amylopectin content increasing, thus make amylose/amylopectin ratio significantly lower than normal wheat; whereas the genotypes with wx gene null tested in thisresearch were produced without any selection by breeder, its amylose/ amylopectinratio had no significant difference with normal wheat for when the amylase contentdecreased, its amylopectin content decreased too.6 PHS percentage and soluble sugar content in grains of waxy wheat werehigher than normal wheat, but there was no significant difference inα-amylase activitybetween waxy wheat and non-waxy wheat. Theα-amylase activity significantlyaffected PHS percentage for non-waxy wheat varieties, and soluble sugar content ingrains was significantly related to pre-harvest sprouting percentage in waxy wheat.High soluble sugar content and external character of grains might be the inducers ofPHS in waxy wheat. 1 or 2 wx gene null did not bring heavy PHS. There might be anon-dormancy gene in Waxy C making the appearing of varieties with heavy PHS inany genotypes. The non-dormancy gene increased the complex for PHS research ofwaxy wheat.7 Peak viscosity was positively correlated with volume weight significantly, butnegatively correlated with the ratio of flag leaf area (FLA) to penultimate leaf area(PLA). Generally, high viscosity hardly occurred in those varieties with small volumeweight or large ratio of FLA to PLA. Although genotypes with 1 or 2 wx gene nullshould have a significant higher peak viscosity, no significant difference was foundbetween them and normal wheat. Some varieties with Wx-B1 protein deficiency had anormal peak viscosity for their volume weights were low. Because many varieties withWx-B1 protein deficiency and few with Wx-A1 or Wx-D1 deficiency were found inChina, Grain volume weight, FLA/PLA and Wx-B1 null (deficiency) could be used as the indices for starch quality selection.