Effect Of Seed Aging On Change Of Genetic Integrity In Maize, Barley And Wheat Germplasm Accessions

The effect of seed aging on genetic integrity changes of stored seeds in genebank is an urgent task to be clarified for germplasm preservation. It is of great significance for a safe conservation of germplasm resources. Working on seeds of maize (ZeamaysL.) , barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) , the effect of seed viability decline on the alteration of genetic integrity was analyzed with morphological markers, cytological markers, biochemical markers and DNA molecular markers, so as to provide scientific and theoretical basis for making a germination-rate-based criteria for regenerating germplasm resources. Main results found were as the following.1. Genetic alterations of maize landrace cv. Tiaohuanuo populations having different germination levels were analyzed by using agronomic traits and SSR markers. It was shown that change measured as the percentage of polymorphic bands, the number of alleles (na), effective number of alleles (ne) , Nei's gene diversity index (h) and Shannon's information index (I) and so on, were lower in artificially aged population with lower germination percentage than in CK population with higher germination percentage. This indicated that the genetic diversity was lower in aged population than in CK population. The proportion of plant with light-purple gemmule sheath decreased with the decline of germination percentage. When seed germination percentage declined to 32%, there was no light-purple plant. This result indicated that alternation of the genetic composition from light-purple plant to no light-purple plant could occur in regenerating population if the seed germination percentage declined to 32%. On the other hand, the proportion of light-purple leaf sheath plant increased while the white leaf sheath plant decreased, when seed germination percentage declined. This result also indicated that a low germination percentage standard for regeneration is disadvantageous for maintaining the genetic integrity of heterogeneous accessions.2. The hereditary characters of barley landrace cv. Punaiganmu were analyzed using botanical cell chromosomal and A-PAGE methods. The result showed that there was no significant difference in seed chromosomal aberration ratio in root tip cells between populations with different germination percentage. By the use of A-PAGE, four biotypes differing in the hordein spectra have been determined, biotype ratio varied with the decline of germination percentage. One "biotype" disappeared while seed germination percentage declined to 34%. The result indicated that the loss of seed viability and differential survival of the biotypes resulted in selection and genetic shifts in germplasm accessions, and also indicated that the A-PAGE could be used to detect genetic integrity change in barley accessions.3. A same set of 30 wheat accessions from two sources, one set was from seeds stored in the National Long-term Genebank, and the other was from seeds stored in the mid-term Genebank. On growthduration and other agronomic traits studies, no significant differences were found between two sets except on panicle length. Chromosomal aberration percentages in root tip cells of 20 wheat accessions which were stored in mid-term genebank and had lower viabilities were averaged as 4.41%, which was obviously higher than the value of 0.49% calculated from cells of wheat accessions which were stored in long-term genebank and had higher viability. Seed chromosomal aberration proportion in root tip cells was negatively correlated with seed germination percentage. There was no significant correlation between seed germination percentage and storage time for seeds no matter they were stored in the mid-term or long-term genebank. Studies on 9 wheat accessions newly regenerated also showed that there was no significant difference on the chromosomal aberration in root tip cells between seeds stored in mid-term genebank and long-term genebank.