Study On Boll-Setting Of Cotton And Its Physiological Effect Regulated By Soil Drought Stress On During Blooming And Bolling Period

The pond experiment was carried out during flowering and boll-setting period .Effect of six water treatments on the cotton fruiting, dry matter production and transport about yield and its physiological mechanism was invested This experiment was conducted in the screened insectproof house of Nanjing Agricultural University with Jiangsu -popularized cultivars Nankang 7 from 2005.4 to 2006.11.Six soil water treatment were conducted from 7.8 to 9.15 as follow: Relative soil water content kept 70%～75% during treatment, relative soil water content kept 50%～55% during treatment,50%～55% relative soil water content lasted 10 days,20 days, 30 days and 20 days which spraying FA simultaneously, and then all rose to 70%～75% by irrigation again after blossoming, The results were as follows1.Cotton yield and its yield components were affected significantly by different soil drought durationThe result showed that, under drought condition in which kept on drought or relieved drought stress by irrigation again after 50%～55 % relative soil water content lasting more than 20 days after blossoming ,the drought effect would go down to 50 days after blossoming and badly restricted total velocity of dry matter accumulation at flowering and fruiting stages. Preponderance of dry matter accumulation tend to yield organs, but potential force of seed-cotton yield reduced. These led to number of bolls at different cotton positions descending 13.71%～24.05% and average per seed-cotton weight descending 4.03%～6.49%, and seed-cotton yield extent reducing greatly significantly, primarily because of reduction in number of bolls per-plant.When drought stress was relieved by irrigation again after drought lasting more than 20 days , increasing production in correlative parts was achieved ,because total velocity of dry matter accumulation resumed partly at 10th day after irrigating,and potential force of seed-cotton yield in yield organs also went up.When soil drought stress lasting 10 days was relieved after blossoming, it is propitious to dry matter accumulation of yield organs and potential increasing yield force of product organs at lower and inner during fruiting stages, number of bolls per-plant increased 2.83%, average per seed-cotton weight improved 0.45%, and then revealed no significance relativing to comparison.Lint percentage of boll at lower and inner improved greatly significantly under soil drought stress,and lint percentage of boll at middle branches and inner trended aggregately descending with soil drought continuing. Spraying FA during drought stress lasting 20 days could alleviate the harm to cotton, and showed the function of significantly increasing number of boll and boll weight,but it was lower than comparison and W1 treatment in yield.2.Colony structure of cotton yield formation was changed by different drought treatment.Soil progressive drought of 50%～55% relative soil water content restrained the growth of cotton nodes per-plant,increased the abscised velocity of squares and bolls per-plant after blossoming,and so the number of boll-setting was lower than comparison finally. Soil drought lasting twenty and thirty days led stress traits that the number of nodes per-plant increased slowly, and the abscised velocity of squares and bolls per-plant augmented and retained boll percentage reduced during the period of drought. When drought stress was relieved by irrigation again which drought lasting more than 20 days , the number of nodes per plant and its growth rate increased,but these could not compensate for reduction of output caused by drought stress,and so it was lower than comparison in yield . Spraying FA during 20 days drought intimidation could alleviate extent of harm to cotton, and showed the function of significantly increasing number of bolls and descreasing the abscised velocity of squares. When soil drought stress lasting ten days was relieved, the abscised velocity of squares and bolls increased later,but the number of nodes per-plant and retained boll percentage increased after a short time,compensating for loss of bud and boll desquamation caused by drought stress.At last,it showed highter than comparison in yield.3.Physiological responses to different progress soil drought stressThe results showed the SPAD values ,the stomatal conductance , the transpiration rate, the intercellular CO₂ concentration,apparent quantum yield,light saturation point photosynthetic rate of hight-effective leaf and sympodial leaf declined under soil drought of 50%～55% relative soil water content,while light compensation point ,pepitation rate,cell membrance permealility,the water potential,and proline content increased, the vegetative matter consumed rapidly . The physiological responses to drought stress relieved by irrigation were the same as progressive drought stress during drought stress period. The physiological indexes of drought stress lasting for 10days would snap back to comparison level after drought stress being relieved,while physiological indexes of drought stress lasting longer time come back slowly.