The Genetic Diversity Of Paddy Rice In Traditional Rice-fish-duck System In Congjiang County Of Guizhou Province

Traditional agricultural systems not only contribute to the food and livelihood security for people throughout the world,but also have maintained a rich diversity of genetic resources.These abundant genetic resources play an important role in crop production stability and crop breeding.As the rapid development of modern agriculture that often adopts high-yielding and genetically uniform varieties,many traditional agricultural systems along with local genetic resources and indigenous technical knowledge are progressively abandoned and disappeared.Thus,before the traditional agriculture is lost due to agriculture modernization,it is urgent to study how traditional agricultural practices can preserve a high level of genetic diversities.The"rice-fish-duck system",which has been practiced by local farmers in Congjiang,Guizhou,China for more than 1200 years,it was listed as an Globally Important Agricultural Heritage Systems(GIAHS)in 2011.In this study,I first conducted a field and farmer survey to investigate the rice varieties in the"rice-fish-duck system".Then,combining with the field experiments,I used the morphological and molecular methods to analyze the genetic diversity and genetic structure of rice.The main findings of the study were as follows:1 Rice varieties in“Rice-fish-duck system”The"rice-fish-duck system"has been widely practiced by local farmers in Congjiang county,Guizhou province,in which a large number of local rice varieties were grown by the local farmers.In the 13 villages that we surveyed,a total number of 107 rice varieties were grown in paddy fields.2 Analysis of genetic diversity of Congjiang riceFifteen-pairs of Simple Sequence Repeats(SSR)primers were used to detect the genetic diversity of the rice variety samples.The percentage of polymorphic loci was100%.A total of 97 alleles were detected.The allele amplitude of each locus ranged from 2 to 15 and the average number of alleles was 6.5.The average number of effective alleles was 2.305.The range of genetic diversity index was 0.587~1.352.The average diversity index was 0.837.The average expected heterozygosity was0.493.The frequency of allelic variation of SSR ranged from 0.0029 to 0.6971.There were more high frequency alleles,62.86%with allelic frequency?0.05,and 94.29% with frequency?0.01.By using non-spatial Bayesian cluster procedure in STRUCTURE,there were four genetic groups in Congjiang rice local varieties,and no relatively independent genetic structure was formed among the groups.AMOVA analysis showed that 95%of the genetic variation came from within the population.The Mantel test showed that there was a low correlation between geographical distance and genetic distance,indicating that the population structure in this area is subject to the"IBD"model and the population gene flow is limited by geographic isolation.3 Analysis of phenotypic diversity of Congjiang riceMorphological analysis on the whole samples from Congjiang county showed that there were four types of rice based on the the grain characteristics.They were broad-oval-grain and short-awn,long oval and without awn,oval-grain and long awn,oval-grain and middle-length of grain awn.The variation of awn length was high,up to 265.08%.On the whole,the differentiation degree of grain length and width were low(0.0606,0.0174),but the diversity indices of shape,length and width of grains were high among varieties.The average diversity indices of shape,length and width of grains was 1.3748.The variation of morphological traits(e.g.plant height,length of flag leaf and inverted two leaf)was low(CV=4.52%~15.73%)except that the variation of awn length was high(CV=148.02%)among the rice varieties.The diversity of morphological traits was high with an average diversity index of 1.8447.There was agreat differentiation between the traits(average 0.3941).Based on Nei's differentiation index(D_r),the morphological traits had high D_r value(average 0.3941).Cluster analysis showed that the sampled rice varieties can be classed into five groups.Group ?had characteristics described as semi-dwarf straw,broad-oval-grain and middle-length of grain awn.Group? had high plant height,broad-oval-grain and without awn.Group ? had dwarf straw,oval-grain and without awn.Group ? had high plant height,long flag leaf and second leaf,broad-oval-grain n and without awn.Group? had high plant height,broad-oval-grain and long awn.