Studies On The Dwarfing Morphological And Mechanism And Genetic Characteristics Of Upland Cotton "Lu-ai 1"

Cotton is one of the most important economic crops in China.Plant height is not only an important agronomic traits of cotton,but also a major factor for field population structure and ecological structure.It is a main task that making ideal shapes and designing rational population structure by adjusting cotton plant height.Up to now,it has been paid much attention to using plant growth regulators(PGRs)and/or pruning artificially to control plant height,but the varieties improving,especially the breeding of dwarf varieties was neglected in a long time.With the developing harmoniously between social and environment,it has been required urgently for cotton production without environment pollution,higher efficiency and cost-saving.Consequently,it is very important to breed dwarf or semi-dwarf cotton-varieties replacing chemical regulators or manpower to modulate plant growth and development,form ideal population structure,enhance the utilizing efficiency of solar-thermal resources and potential productivity.On the other hand, the dwarf varieties with proper plant height had higher lodging resistance and a greater harvest index.This is also a new way for cost-saving in cotton production.So,it is important to exploit and investigate cotton dwarf traits for breeding cotton ideal plant type variety.A dwarf variety of cotton(Gossypium hirsutum L.)"Lu-ai 1" with better boiling and higher resistance to diseases,named temporarily,has been selected by Hunan Agricultural University from abroad cotton germplasm resources.In this study,dwarfing machnism of "Lu-ai 1" has been researched systematically from such respects as on morphology,anatomic structure,endogenous hormones content and the responses to exogenous hormones,the photosynthetical properties,genetic characters and molecular marking.The main results are as follows:(1)"Lu-ai 1" is a typical dwarf variety,which plant height is 91.0%and 72.5%shorter than that of TM-1 and 97004H(normal high statured varieties)respectively at boll opening stage.The dwarfing character of "Lu-ai 1" is stable,with the properties of smaller middle-upper leaves,shorter fruit-branches,harmonious ratio of vertical to horizontal, concentrative boiling(12-18 bolls per plant)and early maturing.(2)The key dwarfing period of "Lu-ai 1" comes into being in middle and late growth period.The elongation speed of intemodes and nodes differentiation speed in main stem of "Lu-ai 1" are similar to that of CK at seedling stage,however,the plant height of "Lu-ai 1" increases more slowly after squaring stage and stops increasing earlier.After full-flowering, the number of elongating internode increases no more,behaving determinate growth property,unlike indeterminate growth property of normal high-statured varieties.(3)The reason for that the plant height of "Lu-ai 1" is markedly lower than that of CK is caused by shorter internodes and less nodes together,of which the effect by shorter internodes,especially by shorter middle-upper internodes,is bigger.The total internode number of "Lu-ai 1" is 21.2%and 14.4%less than that of high-statured TM-1 and 97004H espectively,the average internode length of "Lu-ai 1" is 57.6%and 50.7%shorter than that of high-statured TM-1 and 97004H,respectively.(4)The shorter main stem internodes of "Lu-ai 1" is mainly due to its less cell number. The parenchyma cell of cortex and pith of 1^st～6^thinternode from top of main stem ranges more loosely in "Lu-ai 1" than in TM-1,and the total cell number in vertical of internodes is much less in "Lu-ai 1" than in TM-1.No significant difference of cell size is found in cortex and pith.(5)The secondary growth of main stem,the occurrence of secondary xylem and phloem and phellogen are all earlier and vascular bundle of main stem internodes develop faster in "Lu-ai 1" than in TM-1,the sites of cell fast elongation and stagnant elongation in cortex and pith of internodes are closer to apex in "Lu-ai 1" than in TM-1. The development process of "Lu-ai 1" is about 2 internodes development process earlier than that of TM-1.It suggests that too early and too fast secondary growth may affect the growth and differentiation of apex meristem significantly,and this effect results in more internode number,less cell number and the inhibition of plant height increasing.(6)The less promoting hormones and more inhibiting hormones in apical buds restrain the plant height increasing in "Lu-ai 1".During the key period for plant height formation while the plant height difference between "Lu-ai 1" and CK becoming more obvious,the GA₃ and IAA contents in apical buds are lower in "Lu-ai 1" than in TM-1 and in F₁, especially at full squaring stage when plant height increase fastest,the GA3 content in apical buds of "Lu-ai 1" is only about 28.37%and 31.04%of TM-1 and F1 respectively,at first squaring stage,the GA₃ content in apical buds of "Lu-ai 1" is only 68.4%of TM-1. Although the ABA content in "Lu-ai 1" decreases rapidly after full- squaring stage,still keep higher level compared with that of TM-1 and F₁,with 26.1%,32.4%,132.5%higher than that of TM-1,and with 129.1%,87.5%,37.4%higher than that of F₁ at full- squaring stage,first-flowering stage and full-flowering stage respectively.(7)The index of "plant height promoting rate by hormones"[(increased plant height by hormones - increased plant height of CK)/increased plant height of CK×100%]is used to estimate the sensitivity of "Lu-ai 1" to hormones.The sensibility of "Lu-ai 1" to exogenous GA₃ is higher than that of TM-1 and F₁,the GA3 promoting rate to plant height of "Lu-ai 1" reach up to 102.1%under 100mg/L GA3 concentration.ABA inhibit the plant height of all tested varieties significantly,especially under higher concentration(40mg/L), the inhibiting effect is extremely significant.The effect of IAA and KT to plant height of all tested varieties behaves promoting under lower concentration and inhibiting under higher concentration.When exogenous hormones are mixed to apply,ABA can counteract the promoting effect of GA₃ to a large extent,no significant effects by IAA and KT.From the results above,it can be considered that "Lu-ai 1" is sensible to GA₃.(8)There is no significant difference in total chlorophyll content among tested varieties, but,the photosynthesis rate" of "Lu-ai 1" is significantly lower than that of 97004H and TM-1,soluble sugar and starch content in "Lu-ai 1" are also lower than in 97004H and TM-1.The lower photosynthesis rate and soluble sugar and starch content in functional leaves is the result of hormones imbalance in "Lu-ai 1" and not the reason of dwarfing.(9)The dwarfing of "Lu-ai 1" behaves as quantitative genetic character.An SSR marker "BNL3034" which link with dwarfing is selected from 225 primers.Variance analysis indicates that the contribution rate of this mark to dwarfing is 17.11%.