REDUCTION IN THE FROST-RESISTANCE AND WIN TER HARDINESS OF WINTER-WHEAT VARIETIES AS THE RESULT OF BUNT INFECTION

Investigations were made in the artificial infection nursery between 1 991 and 1993 on the susceptibility of registered wheat varieties to bu nt (Tilletia foetida, T. caries) and on the year effect. This was foll owed by the phytotronic frost testing of healthy and artificially infe cted wheat plants in 1995 and field testing in boxes between 1993/1994 and 1995/1996 to determine the effect of bunt infection on the frost resistance and winter hardiness of the varieties and the combined effe ct of biotic (bunt infection) and abiotic (frost damage) stress. Of th e 9 varieties examined, Martonvasari 17 was resistant, Fatima 2 was mo derately resistant, Martonvasari 16, Martonvasari 18 and Martonvasari 23 were moderately susceptible and the remainder were susceptible. Gen otype-dependent differences were also found for the year effect. The f rost resistance of the varieties examined was lower as the result of b unt infection than for healthy plants. For the majority of varieties t he higher killed plant rate observed after infection was correlated wi th the degree of susceptibility to bunt. The close (r=0.89) correlatio n observed between the susceptibility of the varieties to bunt and the increased killed plant rate as the result of infection suggests that the chemical substances (e.g. sugars, carbohydrates, lipid composition of the membranes) involved in hardening are consumed during the devel opment of the disease. Consequently, a severe infection will lead to a reduction in the concentration of the cell solution, with a resulting increase in frost sensitivity.