| The Northeast China Plain is one of the three "corn belt" in the world. In China, the region has become one of the most important regions for cereal grain production because of it fertile soils and high yield in maize cultivation, which accounts for 35% of the total maize production in China, and is contributing significantly to the national food security programmer in China.At present, due to limited maize breeding technology, practices of agricultural production management and agro-meteorological disasters in China, maize lodging is common and becomes the main factor of yield improvement in the spring maize production zone of this area. Customarily, maize lodging is frequently associated with conditions that reduce the lodging resistance of plants by excessive maize planting density. In this study, we evaluate the effect of kernel growth and yield loss caused by maize lodging during grain filling stage,mechanism of lodging resistance with variety genotype, ecological and biological mechanisms in improvement of lodging resistance by plant growth regulator(PGRs). Our main conclusions can be summarized as follows:1. Lodging has been a serious problem causing grain reduction in the sector and significantly reduce the Grain Filling Rate. Lodging can affect the lower part initially and then the upper. Therefore it is necessary to make grave effort to support the plant against lodging in order to prevent losses in production output to a very low degree. Lodging can also limit the grain size of the “kernel sink”. We found out that, the dry kernel weight of the Lower parts(LL), Upper parts(UL), the disposition of lodging treatment(DL) were reduced by 20.13%, 4.36% and 7.56% concomitantly as compared to no Lodging treatment.2. Lodging during filling stage significantly reduced the later kernel dehydration rate, which resulted in higher kernel water content during harvest time. Lodging also influenced grain nutrients accumulation. We observed that kennel fat and protein content were significantly affected by lodging than starch content, but litter effect on starch content, and which lowered range of 1.07~12.83%,5.15~9.33% and 0.81~3.30%, respectively.3. The reduced grain yielded as a result of the lodging had maximum and minimum yield reduction rate of 29.68% and 7.02% respectively. The average yield reduction rate was 14.75% throughout the 17 field experiments in Nong’an and Li’shu County, and has caused an average of 34.17 kg/ha production losses with a 1% lodging rate increased under this condition. The yield losses were also affected by different parts. Yield were reduced to 10.51% and 29.88% to control(CK) for the treatment of UL and LL maize treatment respectively. Further variance analysis indicated that, the kennel’s number and kennel weight decreased were the main reasons for the yield loss caused by lodging.4. Stem lodging is the main lodging type in later grain filling stage for spring maize. Stem breaking mainly occurred in the third node section, which accounted for about 56.44% of stem breaking recorded, and then followed by the fifth(16.83%), the second(12.87%), the fourth(11.88%), stem breaking in the other internodes was extremely rare.5. Maize plant gravity height(GH), stem bending strength(BS) and dry weight per unit(DWPU) could be as general indices for evaluating lodging resistance of spring corn during growth period. In addition, basal internode length(IL) can be used as major indicators of lodging resistance assessment during flowering stage; with ear height(EH),stalk rind penetration strength(RPS) cross section area(CSA), rind thickness(RT) and xylogen content of basal internode used as secondary indicators. Stem water content can be used as the major indicator in later grain filling stage. In addition, comparing the sensitivity to maize planting density variation of the above mentioned indicators will be more scientific, but the key is the selection of reference varieties.6. Our study revealed significant differences in grain filling characteristics with varieties of different lodging resistance genotypes. Varieties of susceptible lodging types such as XY335 and HY33 have higher intensity of grain filling rate and grain filling duration showed 1-2 days shorter than resistant lodging type of maize DK516 and NH101. Our results also showed that maize of susceptible lodging type had larger dry matter transportation ratio of stem and higher allocation proportion of dry matter to grain, which could be one of the most important mechanisms responsible for reduced maize stem lodging resistance.7. Maize lodging resistance during growth period could be evaluated by the model of “Safety Factors”. It was showed significant correlation between Safety Factors Value and maize lodging index, and has been verified by the field experiment, Safety factors value could be accurately estimated by plant lodging index in grain filling stage, and we derived the following equation: Y=3.9503e-0.26 LI. In addition, we proposed characteristic of ideal plant type with high lodging resistant based on the result of our study.8. The maize grain yield, biomass, harvest index and lodging scores were significantly affected by PGRs(T), Hybrids(H),Year(Y). Grain yields and lodging scores were also affected by T×Y, H×Y interaction. The increase of HI as a result of the decreased lodging rate was an important way to improve maize grain yield in the study.9. The maize lodging–related characters of EH and GH were decreased. The internodes can became more shorten and widen and is an important mechanism of morphological target for the improvement of the stalk and lodging resistance. The PGRs has strong effect on the internode 2 and 3 above the ground and it can significantly improve the lodging–related characters, such as the DWPU, the content of structural carbohydrate of the lignin and BS. This serves as an important mechanism of the biological development for the enhancement of stalk lodging resistance.The maize grain yield increased significantly in a high lodging year, but had no corresponding rise or low reduction in grain yield for a low lodging year. Therefore, once the time of PGRs is sprayed at a jointing stage for general year, or sprayed at joint age, and bell stage separated during a very serious lodging season, it can serve as an important measure cultivation and production of the spring corn in Jilin province. |
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