EFFECT OF DIFFERENT NUMBERS OF BACKCROSS ON IMPROVING AGRONOMIC CHARACTERS IN WHEAT

Nine crosses were studied from 1980 to 1984.The main results are shown as following:1.Short culm plants with early maturity,which have some donor traits could be selected in the BC2 generation.2.The main economic traits of the recurrent parent could be basically recovered in BCz or BC1F1(BC2F1)generations.3.Selection effects for traits in backcrossed generations depends upon the rate of homozygosity advance which should show the same trend as narrow heritability and gene effects for traits.4.The net increment of homozygosity proportion in BC2 fitted in with the theoretical results calculated by formula and thus the number of genescontrolling the traits could be calculated.The proportion homozygosity of some traits in BC1F1 are about 1/2-1/3 of BC1 progenies.5.High heritability traits such as grain number per panicle and weight per thousand grains can be improved synchronously by limited backcrossing in breeding procedures.Based on strict selection of recurrent parents,new varieties which maintain(or surpass)the main desirable traits of the original varieties and have short or semishort culm,early maturity and big panicles can be selected by limited backcrossing in a shorter breeding period.The results showed that limited backcrossing can shorten the breeding period and is an effective technique.