| Since the mid-20th century, maize breeders at home and abroad have approved that tropical and subtropical maize germplasm with abundant genetic variation should be used to widen germplasm base of genetic improvement and maize heterosis.It is important to utilize tropical and subtropical maize germplasm to improve and widen existing germplasm with narrow genetic base in China. Tropical and subtropical maize germplasm are unadapted to be grown in temperate, such as silking and anthesis uncoordinated and barrenness and son on. Most of them can not be used directly to select lines because of photoperiod sensitivity, so they need to be improved for adaptation in temperate. Compared with other ways of population improvement, Mass selection can not only preserve genetic variance within populations, but also prevent from inbreeding depression. Many tropical and subtropical maize germplasm made a great progress by mass selection. Institute of Crop Sciences, Chinese Academy of Agricultural Sciences (i.e.former institute of Crop breeding and cultivation) has improved successfully two gene pools (POOL33and POOL34) of subtropical quality protein maize. Improved gene pools was named respectively as Zhongqun13 and Zhongqun14.Original populations of two tropical maize populations (POB4 and SUWAN-1)and sub-tropical populations (POB69and POB70) and their improved populations of different cycles by mass selection controlling bi-parents were conducted in two locations during 2006-2007.The experiment was based on comparisons with POOL33,POOL34 and their improved populations (Zhongqunl3 and Zhongqun14).The objective of this experiment was to analyze selection response of anthesis and other agronomic traits in the process of adaptation improvement and genetic diversity variance of different cycles of every population by SSR molecular marker, in order to determine improvement effect of genetic variance and adaptation of tropical and sub-tropical populations among different cycles, as an academic basis for further improvement and utilization in breeding.Most traits were not significantly different among different cycles within population in tropics (Hainan), but most traits such as anthesisi were different significantly (or extremely significantly) in temperate (Beijing).Most traits were correlated significantly with mass selection, as follows:Anthesis showed a trend to earlier and ASI became shorter for the tropical populations (POB43 and SUWAN-1).Days to silking decreased from 99.2d to 79.5d and 90.7d to76.2d respectively, averaged 4.9d and 3.6d per cycle. Days to anthesis reduced from 90.8d to 76.7d and 70.8d to 74.7d respectively, averaged 3.5d and 0.8d per cycle.ASI showed an obvious trend to short from 8.3d to 2.8d and 12.8d to 3.5d respectively, averaged 1.4d and 2.3d per cycle.For two sub-tropical populations (POB69å’ŒPOB70), Days to silking became shorter from 78.3d to 69.2d and 81.8d to 69d respectively, averaged 2.3d and 3.2d per cycle;ASI shortened from 7.3d to 1.7d and 9.3d to 2.7d respectively, averaged 1.4d and 1.7d per cycle.Days to silking and days to anthesis responded differently. ASI shortened because anthesis showed less degree to reduction than silking data. Traits response to cycle in anthesis and RD value decreased with increasing cycles.Plant and ear height showed a trend to reduction. For the tropical populations (POB43 and SUWAN-1),plant height reduced from 378.8cm to 334.1cm and 310.0cm to 301.2cm respectively, averaged 11.2 and 2.2cm per cycle.Ear height reduced from 213.1cm to 176.1cm and 179.6cm to 166.2cm respectively, averaged 9.3cm and 3.4cm per cycle. For the sub-tropical populations (POB69 and POB70), plant height decreased from 301.2 cm to 270.3cm and 287.5cm to 263.2cm respectively, averaged 7.7cm and 6.1cm per cycle. Ear height decreased from 144.8cm to 131.9cm and 142.cm to 131.6cm respectively, averaged 3.2cm and 2.7cm per cycle.Grain yield, shelling percentage and resistance to barrenness presented a great trend to improvement. For the tropical populations (POB43,and SUWAN-1),shell percentage increased from 62.8% to 81.1% and 81.4% to 80.7% respectively, averaged 4.58% and-0.81% per cycle.Resistance to barrenness improved from 36.1% to 85.1% and 71.0% to 85.0% respectively, averaged 12.3% and 4.4% per cycle. Grain yield increased from 1232.1kg/ha to 6228.2kg/ha and 3693.7kg/ha to 5726.9kg/ha. For the subtropical populations (POB69 and POB70),shelling percentage increased to 82.7% respectively from 77.7% and 79.4%, averaged 1.25% and 0.83% per cycle respectively. Resistance to barrenness increased to 82.7% respectively from 68.1% and 58.6%; averaged from 4.7% and 8.6% respectively. Grain yield increased from 3419.3kg/ha to 4559.0kg/ha and 2642.8kg/ha to 4624.3kg/ha respectively, averaged 284.93kg/ha and 508.30kg/ha per cycle.Ear Traits were correlated with other agronomic traits, which varied with different populations.Anthesis showed a trend to earlier and ASI became shorter for the testcrosses also and Grain yield of testcrosses presented a great trend to improvement also.DNA samples of 24 maize populations were amplified using 40 pairs of SSR primers, and then tested by SSR fluorescent markers of DNA genetic analyzer automatically.40 pairs of SSR primers presented polymorphism in all tested materials.343 allele variations were detected. Every pair of SSR primer can test 3-17 alleles, averaged 8.575 per site. Variance range of polymorphism information content (PIC) of every pair of SSR showed 0.257-0.899, averaged 0.747.Shannon-weaver index distributed at the range of 1.038-2.494,averaged 1.657.The resulted documented compared with original populations, genetic diversity of improved populations did not change significantly.Tested genes in improved generations C4 of POOL33,POOL34, POB43,SUWAN-1, POB69 and POB70,showing 104,111,105,107,108 and 101 respectively, were no significant differences than in their original generations CO (98,114,87,88,106 and 102 respectively) by 40 pairs of primers.Means of PIC of six populations was calculated.means of the improved generations C4 of POOL33,POOL34,POB43,SUWAN-1,POB69,POB70 was 0.411,0.400,0.395, 0.394,0.423 and 0.366 respectively, all of which was was no significant differences than means of their original populations CO (0.346,0.420,0.333,0.359,0.422 and 0.363 respectively).Means of genetic diversity index of six populations was calculated.means of the improved generations C4 of POOL33,POOL34,POB43,SUWAN-1,POB69,POB70 was 1.287,1281,1.286,1.283,1.284 and 1.279 respectively, all of which was was no significant differences than means of their original populations CO(1.284,1.287,1.285, 1.281,1.287 and 1.274 respectively).According to the genetic similarity coefficient of each original and improved population, genetic similarity coefficient distributed in 0.755-0.843 among circles of POB43,0.732-0.848 among circles of SUWN-1,0.700-0.793 among circles of POB69 and 0.726-0.819 among circles of POB70, respectively.24 populations were clustered according to genetic similarity coefficient. The dendrogram showed that the original populations (CO) and the improved populations Cl-4 of POB43,SUWAN-1,and POB69 were in the same group; the original population of POBB70 and its improved population C1-3 were in the same group(not improved population including C4).Conlusion:their adaptability to temperate enhanced, ASI shortened, plant and ear height reduced, resistance to barrenness and grain yield increased,and abundant genetic variance were maintained for the tropical and temperate populations improved by mass selection controlling bi-parental, as a basis for improving genetic variance and heterosis utilization of temperate maize.
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