Origins And Evolution Of Corchorus

Jute(Corchorus) is an annual herb plant of Tiliaceae, and it's the important fiber crop, as well as the important economic crop of China, India and Bangladesh. The researchers from different countries have different views about the origin and evolution of Corchorus. In order to make clear the origin and evolution of Corchorus,96 jute germplasm were studied used Sequence Related Amplified Polymorphism (SRAP), Inter-simple Sequence Related (ISSR), SRAP combined with ISSR and SRAP combined with morphology. The 96 jute germplasm included 9 relative wild species,9 wild olitorius species,13 wild capsularis species, 21 cultivated olitorius species and 44 cultivated capsularis species. The phylogenetic trees of Corchorus were constructed by MEGA and DPS software, and the divergence time of jute germplasm from different area was calculated. In order to reveal the evolution trend on cytology of Corchorus, the characters of chromosomes were also studied. The main results were as follow:1,The relative wild species located at the basic position of the dendrogram, and the divergence time of which was the longest, which indicated the relative wild species originated earliest and was the ancestors of cultivated jute. Among all the relative wild species in this study, the divergence time of C.tridens, C. trilacularis(19C) and C.pseudo-olitorius were longer than others, which widely distributed in Africa and Southeast Asia. Africa was the modern distribution center of Corchorus, which density and frequency of distribution were high. So a conclusion was drawn:Africa was the center of origin for Corchorus. The divergence time of C. trilacularis(21C), Zhangpu C.acutangularis and Nanyang C.acutangularis was the shortest among all relative wild species. These three species originated lately, were the newer biotypes originated from other relative wild species. Zhangpu C.acutangularis and Nanyang C.acutangularis were from China. Besides Africa and Indonesia, C. trilacularis(21C) also distributed in China. The above revealed China was the second original center of.Corchorus.2,Among all the olitorius species, the divergence time of wild and cultivated species from Africa was the longest, and cultivated species from India, Bangladish and China was longer. The average divergence time of species from other Asia Countries was the shortest. The above data indicated the olitorius species of Africa originated earliest, at the same time the wild and cultivated olitorius species were distributed widely in Africa. Some wild olitorius species were also distributed naturally in Yunnan-Guizhou Plateau, as well as in Guangxi,Guangdong and Fujian province of China, and there were abundant biotypes of cultivated olitorius species in South China. From above we can see, Africa was the center of origin for wild and cultivated olitorius species, while the areas which border on India, Burma and China was the second center of origin for cultivated olitorius species. After originated from its first and second center of origin, the cultivated olitorius species was spread to other countries and areas and cultivated widely, such as Viet Nam, Japan in Asia and Cuber in Aemrica.3,The wild capsularis species used in this study were from South China, Thialand and Nepal. Geographically, the region includes South China and Countries of South Asia and Southeast Asia which border on China. The divergence time of these wild capsularis species were longer, which indicated they originated earlier, were the ancestors of other capsularis species. The species "Hainan wild capsularis" from China was located nearest the cultivated capsularis at the evolutionary trees, which indicated it was the ancestor of cultivated capsularis, and cultivated capsularis was originated from it. Taken together, the divergence time of the cultivated capsularis species was shorter than other species, indicating this biotype originated later than olitorius species.Among 44 cultivated capsularis species, the divergence time of species from South China was longer than those from Countries border on China, such as Thailand, India and Japan. So the cultivated capsularis species of China were older biotypes, which originated earlier than other countries. Wild capsularis were distributed widely in South China, and cultivated capsularis were abundant in China, which also had a long cultivated history. Based on molecular biology, history of cultivating and distribution community, the conclusion was drawn that South China, South Asia and Southeast Asia which border on China were the centers of origin for wild capsularis. China was the center of origin for cultivated capsularis.4,Though all the ways used in this study could analized origins and evolution of Corchorus, and the conclusions were accordant, there were some differents each other. Judging from the total bands, polymorphic bands amplified by each primer and the evolutionary trees, SRAP molecular markers were better than ISSR molecular markers. Based on a comprehensive analysis of the position of Corchorus located on the evolutionary trees and average divergence time of Corchorus, SRAP molecular markers combined with morphology and SRAP molecular markers combined with ISSR markers were better ways to study the origin and evolution ofCorchorus, and they were better than other ways such as using SRAP and ISSR alone.5,The chromosomal characters of some species of Corchorus were studied. The results were as follow: the size of the chromosomes was different among jute species, and it varied regularly. The total and absolute chromosome longtitude of relative wild species was minimum, which of the cultivated olitorius species was midrange, and cultivated capsularis species had the maximum value. The variety of chromosome size was analyzed with the average divergence time to reveal the evolutionary trend of chromosome. It illustrated that the size of chromosomes of Corchorus became larger and larger through evolution. The size of chromosomes of species originated earliest had a minmum value, while which of the species originated lately was larger, and the species originated latest had a maxmum value. The evolutionary trend of chromosome was same as morphology, including the height of plant, the size of leaves and seeds. The karyotype of two cultivated species was 1A, which was symmetrical. Except C. pseudo-olitorius, the karyotype of most of the relative wild species was 2A, which was asymmetrical. The conclusion that the karyotype of Corchorus was from asymmetry to symmetry through evolution was deduced from above fact. The ratio of long and short chromosomal arm of Corchorus was different, which of species originated earlier was higher, while species originated lately was lower. It was concluded that the centromere position of Corchorus was from submedian centromere to median centromere.