| Orchardgrass (Dactylis glomerata L.) is one of the most commonly used forage species in the world, exhibiting prominent social and ecological benefits in many countries. Chinese orchardgrass genetic resources are diverse but few varieties were released. Most varieties were introduced from abroad with low adaptability. Hybridization can pyramid beneficial genes for the hybrids to have higher adaptation and production than their parents. But, reports on orchardgrass hybridization breeding are limited and no hybrid variety was released in China. Therefore, twelve tetraploid orchardgrass F1hybrid combinations, four diploid orchardgrass F1hybrid combinations and six tetraploid orchardgrass F2hybrid combinations were used in this study to analyze their agronomical and genetic variation and relationship between parents and progenies. The main results were listed as follows:1) Nine agronomic traits were evaluated on orchardgrass F1hybrid combinations which were length of flag leaf, width of flag leaf, length of second leaf, width of second leaf, culms diameter, length of culm, length of internode, tiller number and individual yield. The results showed that different extents of heterosis existed in hybrid F1. Highest hybrid vigor was found in width of flag leaf both in tetraploid and diploid orchardgrass F1hybrid. Tetraploid orchardgrass had higher parent heterosis in culm diameter, tiller number and individual yield, whereas, diploid orchardgrass had lower hybrid vigor than tetraploid. Moreover, the rust resistance ability was enhanced in hybrid F1, such as heat tolerance ability and disease resistance ability. Some combinations with strong heterosis were selected and kept to study their hybrid F2, such as BaoxingxYA02-116, YA02-116X Baoxing, Chuandong X Baoxing, Baoxing×Chuandong, Baoxing×Kaimo and Kaimo×Baoxing. The multiple comparisons of9agronomic traits showed that significant differences existed in reciprocal crosses.2) Twelve tetraploid orchardgrass F1hybrid combinations and four diploid orchardgrass F1hybrid combinations were used to analyze the genetic difference based on SSR markers. The results showed that most F1progenies possessed much more genetic diversity than their parents. The average percentage of polymorphic loci (Pp) of tetraploid hybrid was72%, the average Nei’s gene polymorphism (H) was0.29and the average Shannon genetic diversity index (I) was0.42. The The Pp of diploid orchardgrass was45%, the H was0.21and the I was0.30. The correlation of genetic distance and heterosis were calculated and it was concluded that only the heterosisi of tiller numbers (r=0.869, P<0.05) and the length of culm (r=-0.892, P<0.05) could be predicted by parents genetic distance. 3) Six F2reciprocal hybrids combinations were chosen out for their well performances in F1to make further study. The coefficient of variation (CV) was compared between F1and F2hybrids. Only the the BaoxingxYA02-116(F2) had higher CV than F1in length of flag leaf, length of culm and individual yield which was12.9%,1.8%and0.3%, respectively. No significant differences of culm triats were found between F1and F2hybrids. F2hybrids had higher length of culm, tiller number and individual yield than their F1. But the multiple comparisons between F1and F2showed that the significant differences of reciprocal crosses in9agronomic traits were decreased in F2.4) Six F2crosses were amplified through SSR marker. After the band analysis, the amplified results showed that F2had higher mutual band of parents with progenies but lower non parents band than F1. Especially, F2had more specific bands than F1. The change of band types between generations indicated that the hybrid F2still retained parts of heterozygosis but prone to be a steady population. The F2average percentage of polymorphic loci was decreased with a range of4.5-37.5%. The average Nei’s gene polymorphism was0.23and the average Shannon genetic diversity index was0.33, lower than their hybrid F1progenies. The genetic distance between F2reverse and inverse crosses was larger than the F1reciprocal crosses. |
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