Diallel Analysis for Scab Resistance Using Winter and Spring Genotypes.

Fusarium head blight (FHB), caused by Fusarium graminearum, is an important disease of wheat in South Dakota.  The study was conducted to determine combining ability and gene effects in FHB resistance.  Six parents consisting of winter wheat ‘Nekota’, ‘2137’ and ‘Harding’, spring wheat  ‘ND2710’ and ‘BacUp’ and facultative wheat ‘Ning7840’ were crossed in a partial diallel mating design.  F_4:5 lines were hand transplanted in May 2006 and 2007 and screened for FHB resistance under mist-irrigated field conditions.  Artificial inoculation consisted of corn spawn spread at jointing and inoculum suspension spray at flowering stages.  Disease index (DI) percentage (incidence percentage * severity percentage/100) of the crosses was analyzed using Griffing’s method 4 and model 1.  General and specific combining abilities were highly significant (P < 0.01) for both years.  The result showed that both additive and non-additive gene effects were involved in the of FHB resistance.  The ratio of combining ability variation components [2σ²_GCA/(2σ²_GCA+ σ²_SCA)] was 0.85 and 0.81 in 2006 and 2007, respectively.  The homogeneity of the data over two years was tested.  The calculated F-value for the ratio of error variances (F = larger error MS/smaller error MS) for two years was 1.09 (P = 0.10, Df_num = 846, Df_den = 867).  The test of homogeneity indicated that the two years data could be pooled.  The pooled analysis showed that general combining ability was significant (P < 0.01) but not the specific combining ability (P = 0.17).  GGE biplot software was also used in the pooled diallel data set to graphically display the GCA and SCA effects of the parents and performance of the crosses.  Both the individual and pooled analysis showed that additive gene effects were more important than non-additive gene effects.  Thus, progress in developing resistance in wheat can be made by selection.