Effects Of Flower Bud Differentiation On Growth And Yield Of Cotton Under Early Drought And Density

Based on the development status of light and simplified cultivation,save costs and improve fiber quality in the Yellow River Valley,the effects of early drought and density on cotton growth and development were studied in this experiment.Using ’Nongda 601’as the experiment material.A two-factor split-plot design method was applied with main plot of two water treatments[full irrigation(CK)and drought(D)],and the sub-plot contained three density treatments(6×103 plants.hm-2,9×103 plants·hm-2 and 12×103 plants·hm-2)on the Qingyuan Experimental Plot of Hebei Agricultural University in 2019 and 2020.Through the observation and determination of the process of flower bud morphological differentiation and its main regulatory substances in the early stage of cotton,the observation of leaf structure in the middle stage of cotton growth,the determination of photosynthetic performance and physiological characteristics,the individual morphological characteristics,the dry matter accumulation and distribution,and the yield components of cotton population.The purpose of this study was to elucidate the effects of early drought and density on flower bud differentiation,population or individual growth and development of cotton in the Yellow River Valley.The main results are as follows:1.Through the observation of the microstructure of the shoot apical meristem of different leaf ages in cotton emergence stage.At 2-3 leaf stage,Under the same water treatment at the same leaf stage,the density of cells at the shoot apical meristem of cotton gradually flattened,and the height/length becomes smaller;the process of flower bud differentiation was accelerated in early drought treatment,and only sepals were differentiated in the control treatment at 25 days after seedling,while sepals and petal primordia were differentiated in early drought treatment,which made the bud nodes appear earlier.Compared with CK-6,the bud nodes of D-6 treatment were earlier.At the late stage of flower bud differentiation,the low density treatment had differentiated into stamens,while the high density treatment slowed down the process of flower bud differentiation,and then formed pistil and pistil primordia.Compared with CK-6,the budding node position of CK-12 was significantly higher by 0.87 node,and the first fruiting branch node was increased by 4.33 cm.2.The soluble sugar,soluble protein and endogenous hormones in the shoot apical meristem of cotton emergence were studied.At the 2-leaf stage,the content of soluble protein,soluble sugar and gibberellin(GA3)in the shoot apical meristem of cotton treated with D-6 was significantly higher than that of other treatments,with height/length and rapid differentiation rate.With the development of flower bud differentiation,the contents of soluble sugar,soluble protein,IAA,ZR and GA3 were important regulatory substances under early drought treatment,and the changes of density were irregular.3.Early drought and density had certain effects on the leaf structure,photosynthetic characteristics and regulatory substances of cotton at flowering and Bolling stage.The results showed that the mesophyll cells were elongated,the membrane was inward concave,the arrangement of cells was irregular,the gap was enlarged,the thickness of leaves was significantly increased,the thickness and area of xylem were significantly decreased,the number of chloroplasts was increased,and the SPAD value of chlorophyll was increased under early drought and low density treatment.The content of soluble sugar and soluble protein increased,the content of ABA and ZR increased,but the net photosynthetic rate did not decrease.Under the same water treatment,with the increase of density,the single mesophyll cell swelled and deformed,the edge depression deepened,the chloroplast structure deformation and number gradually decreased,which affected the relative content of chlorophyll,SPAD showed a downward trend.The decrease of soluble protein content and the increase of instantaneous water use efficiency were beneficial to the increase of net photosynthetic rate in late stage.4.The individual growth and development,dry matter accumulation and distribution of cotton population changed significantly under different treatments.Under early drought treatment,plant height and stem diameter decreased,leaf area index and total dry matter accumulation of cotton decreased,but there was no significant difference in dry matter distribution of reproductive organs.Under the same water treatment,with the increase of density,plant height increased and stem diameter decreased.In the rapid growth period of cotton,the leaf area index was higher and the total dry matter accumulation of population was higher under the condition of high density.It can be seen that higher density is easy to create a larger canopy structure in the vigorous growth stage of cotton,but the strong vegetative growth restricted the reproductive growth,resulting in a lower proportion of dry matter accumulation and distribution in the vegetative organs at the initial flowering stage compared with the other two densities(about 70 days after seedling)With the growth process,the difference between the distribution ratio and the other two densities decreased gradually.5.The speed of flower bud differentiation affects the position of budding node and the height of first fruiting branch,and regulates the leaf area index and dry matter accumulation and distribution in the middle growth stage,resulting in the influence of yield components and yield.Under different water treatments,the position of budding node,the height of first fruiting branch had a positive regulatory effect on leaf area index,total dry matter accumulation,autumn peach number and seed cotton yield.Under the early drought treatment,the flower bud differentiation speed was fast,the budding node position and the height of the first fruiting branch decreased,which had little effect on the number of bolls per plant and the weight of bolls per plant,the number of rotten bolls decreased,which changed the spatial distribution of cotton bolls,and the seed cotton yield decreased;under the same water treatment,with the increase of density,the ratio of autumn peach increased,the number of bolls per plant increased,the weight of bolls per plant had no significant change,and the seed cotton yield showed a significant increasing trend.