GENETIC-ANALYSIS OF INBRED LINES AND THEIR CROSSES FOR RESISTANCE TO HEAD BLIGHT (FUSARIUM-CULMORUM, F-GRAMINEARUM) IN WINTER RYE

For genetic analysis of head blight in winter rye (Secale cereale) caused by Fusarium culmorum, six homozygous inbred lines from the Petkus gene pool were crossed in all combinations to obtain 15 diallel F1 crosses and the corresponding 15 F2 crosses. These materials and 10 additional inbreds were artificially inoculated in a 2-year field experiment. The inbreds were also tested with F. graminearum in a separate sub-experiment. Single disease rating, average disease rating, and yield components (grain-weight per spike, 1000-grain weight, kernel number per spike) relative to the non-inoculated treatment were significantly affected by Fusarium head blight in all material groups. The relative grain weight per spike ranged from 26% to 88%. Significant genotypic and genotype x year interaction variances were found throughout. Heritabilities were highest for homogeneous inbreds (h2 = 0.6-0.8) and lowest for heterogeneous F2 crosses (h2 = 0.4-0.6). Disease rating and relative grain-weight per spike were highly correlated for the inbreds and F2 crosses (r almost-equal-to 0.7, P less-than-or-equal-to 0.01), but lower for the F1 crosses (r almost-equal-to 0.6, P less-than-or-equal-to 0.05). Inter-annual correlation coefficients for disease ratings and relative grain-weight per spike ranged from r almost-equal-to 0.7 (inbreds) to r almost-equal-to 0.5 (F2 crosses). The diallel analysis showed significant GCA effects only for relative 1000-grain weight in 1990, but significant SCA and SCA x year interaction variances for most traits. The resistances of 16 inbreds to F. culmorum and F. graminearum were tightly associated for all traits (r = 0.96-0.97, P less-than-or-equal-to 0.01). In conclusion, only slow progress can be expected from selecting for Fusarium head blight resistance in rye due to the limited amount of additive genetic variance and the great importance of environmental factors.