Study of Dwarfing Wheat Sources Using Near Isogenic Lines

【Objective】Since the “green revolution” in the middle 20th century,in which wheat breeding was focused on dwarfing,wheat breeding in various countries of the world has been confined to a limited number of recessive dwarfing sources such as Rht1,Rht2 and Rht8. This study is intended to broaden the dwarfing sources of wheat so as to help the development of highly intensive varieties in wheat cultivation. 【Method】 Five known dominant dwarfing source genes(Rht3,Rht10,Rht12,Rht21 and Olesen) and 7 dominant dwarfing sources with moderate dwarfing ability developed and selected by the Wheat Breeding Laboratory of Southwest University (China),were incorporated into 4 mediums or tall-statured wheat varieties (F1B4 recurrent paternal parents) through back-crossing,thus establishing 4 sets of near isogenic lines of dwarfing genes. In 2005-2006,a multi-factor comparative experiment was conducted under non-competitive conditions of these near isogenic lines to investigate the effects of the genetic backgrounds of the drawfing genes and the recurrent paternal parents on the major agronomic characters. 【Result】 Under the unified genetic backgrounds of the present study,the plant height of all the 12 dwarfing sources ranged from 37.9～74.3cm,being in a significant correlation with their grain weight per plant (r=0.8884). Their grain weight per plant increased by 0.24 g as plant height increased by 1 cm. The agronomic characters of the NILs improved rapidly as their plant height increased and their dwarfing effect weakened. The productivity of a dwarfing source variety approached or exceeded its medium or tall-statured recurrent parent whenits plant height was raised to 60 cm or more. It,therefore,is possible to use such innovative dwarfing sources directly in hybridization breeding of wheat. In addition to such major effects,the 12 dwarfing genes showed pleiotropic effects of delaying the heading of the paternal recurrent parents and reducing their 1000-seed-weight,which,however,can be overcome by modifying the genetic backgrounds of the recurrent paternal parent. The experiment provides additional evidence that dwarfing source varieties with a plant height of 50 cm or less,with their high dwarfing effect,can hardly be employed directly in wheat breading due to their low biomass production;however,their plant height can be increased,to different extents,and some weak dwarfing source varieties may have an ideal plant height of 70-80 cm. This can be conducted through mutation of the major dwarfing gene(s) or the modification by special genetic background.【Conclusion】 Strengthening the research of weak dwarfing sources with increased plant height is a fundamental approach in application of dominant dwarfing sources in wheat hybridization breeding. It is recommended that the dominant weak dwarfing sources developed and selected in this study,i.e. SW07,SW05,YD Ai,SW02 and Rht21be utilized in “gene-designed” dwarfing breeding of wheat.