Adjust Mechanisms Of Creeping-rooted Character In Alfalfa (Medicago Sativa L.)

Creeping-rooted character in alfalfa (Medicago sativa L.)was the character which can originate a shoot from the root system, and provide the plant with a rhizome-like ability to regenerate in stands. This habit of spreading by means of root proliferation provides alfalfa with a form of vegetative spread and multiplication.Through 6 years(2003-2007) experiments of the alfalfa germplasm evaluation and new variety breeding project,the mechanism of creeping rooted character's ontogene and performance was systematically studied.The results are as following:1. Root system type of three years old alfalfa materials was investigated in Xianghuang banner of inner Mongolia,Travois ,Ladak, Teton and Xinjiang big leaf were selected for representing the root system type of Creeping-rooted (CR), Branch rooted( BR ), Rhizomatous rooted( RR), and Tap rooted (TR) type respectively. Based on it, the genetic character, yield and nutrition character were analyzed between the 4 rooted types.,Which showed that CR is the important genetic resource in breeding for the drought-resistant, high quality and high quantity new varieties . AHP analysis method were used to analyzed the drought resistant of different root system types and the drought resistance ability at the Seedling Stage. Results showed that CR alfalfa has the gene from yellow followered alfalfa,and performed excellent in the steppe district. The synthetic evaluation values of the different experimental root type material showed that the drought dolerent ability in seeding stage is :CR>TR>BR>RR.2. Rooted system of thecreeping rooted plant were investigated in the whole growth period.Thus the ontogenesis and performance of the creeping-rooted character including 5 stages: creeping rootedt swellon stage,creeping rooted bud stage,creeping rooted shoots stage,ceeping rooted clusters stage and further creeping rooted stage。The first 2 stages representated the ontogenesis stage,and the rest 3 stages as the performance stage.Anatomical research on CR character ontogenesis showed that the buds of root shoots grow originally from meristematic tissue of phellem cambium in root and after developing aboveground internodes, parts of its underground tissues put up root character, and then developing the offspring plant which will having the independent growth and developing function. Research on the dynamic change of root assimilation product of CR showed that the root soluble sugar content was probably related with the overgroud growth. .Starch content of CR alfalfa was higher than NCR and this could conclude that starch accumulation in root was the material basic to CR thrait happening. After bud germinating, soluble protein content changed evidently, this might be related with the synthesis of specific protein.3. Based on the investigation and statistic of CR percentage rate and its expressional trait of different habitat in inner Mongolia and Beijing area, it was showed that percentage of creeping rooted plants of 3 years old materials was about 80%,and there was no evident difference in this two areas in the same plant age.The influence of the marginal effect on the performance of the creeping rooted character but has no effect on the ontogenesis of creeping rooted character.4.Research on the root system structure of CR alfalfa indicated that the ontogenesis of CR was related to the third class root number in the 10~20cm soil layer, and the root number of each class in 0 ~10 cm was related to the expression of CR, which showed that the function of different root system in different soil layers was different.The function of different class of root in different soil layer. the studing also showed that with the increasing of CR trait, the root neck diameter had a decreased trend.Soil water content was positive correlated with the first class root number in the 0 ~ 20cm soil layer of CR alfalfa, and soil volume had evidently negative correlation with the third class root number in 10 ~ 20 cm soil layer.5. Endogenous hormone including GA3,IAA,ABAand (Z+ZR) content in different part of the horizontal root in CR,NCR and the TR plant were measured by the method of HPLC. Result showed that endogenous hormone had different effect on the overground and underground character of the CR alfalfa: IAA and (Z+ZR) had the positive correlation with the plant height, CR cluster number and CR stem number, while GA had the negative correlation with this three characters; ABA content had the prominence positive correlation with the amount of the root, while had the prominence negative correlation with the creeping rooted extent and CR stem number. ABA of 3 types in Xianghuangqi spot were higher than that of the Beijing spot, and the content ranked as TR>NCR>CR,which was reverse to the Beijing spot. It showed that the CR alfalfa endured less drought stress in the aridity district than the TR and NCR alfalfa due to this character.6. Through the starch gel electrophoresis of the monomeric allozymes LAP-2 alleles are found in the CR,NCR and medicago falcate populations .the results showed that the LAP-2 was a polymorphic loci。The allele frequencies of LAP-2100in the CR and NCR populationg were 91.0% and 99.9%respectively,nearly possessed by all the experimental materials。While the allele frequencies of LAP-298.0 in the CR and NCR population were 6% and 0% respectively.In the population of medicago falcate,the llele frequencies of LAP-295.5 is 10%,so this allele could be predicted as the medicago falcate gene,which originaled from the medicago falcate,and relatived with the CR character.