EFFECTS OF ABIOTIC VARIABLES ON THE RESPONSE OF CARNATION CULTIVARS TO FUSARIUM-OXYSPORUM F SP DIANTHI

The effects of abiotic variables on the response of carnation cultivar s to Fusarium oxysporum f.sp. dianthi (F.o. dianthi) were examined in experiments conducted under semi-controlled environments. The abiotic variables examined were solar radiation intensity, temperature and gro wth substrate. Temperature was not controlled, but differed markedly a mong experiments, thus, its effect was not determined quantitatively. Disease incidence and disease severity varied significantly among the experiments (due mainly to differences in temperature), among the sola r radiation treatments and among the cultivars tested. The three-way i nteraction term (i.e. cultivar x shade treatment x experiment) was hig hly significant (P < 0.001) when both disease incidence and disease se verity were considered, indicating that no single variable was predomi nant in determining disease intensity. The effects of the growth subst rate on disease progress was examined in plants grown in tuff or in tu ff mixed with peat (1:1 and 1:3) substrates. The growth substrate had a potent effect on disease development in the less susceptible cultiva rs. Severe epidemics developed in all cultivars when they were grown i n the tuff/peat mixture, although some were resistant when grown in tu ff alone. These results led to the conclusion that the carnation respo nse to F.o. dianthi is substantially influenced by the environmental c onditions of the test.