Hot water treatments of carrot seeds: effects on seed-borne fungi, germination, emergence and yield

The effects of hot water treatments of carrot seeds on seed-borne fungi, ge rmination, emergence and yield were studied. Seeds infected with Alternaria dauci were hot water treated at temperatures ranging from 44 to 59 degrees C at intervals of 5 degrees C for periods of 5 to 40 minutes. Lots of diff erent grades of healthy carrot seeds were hot water treated at 50-55 degree s C. In some experiments seed treatments with Trichoderma harzianum, Strept omyces griseovirides or fungicides were included. Seed germination and surv ival of fungi were investigated in the laboratory and emergence was determi ned in a growth chamber test. Emergence and yield measurements under field conditions and postharvest evaluation of carrots were made in some experime nts. Hot water treatment of carrot seeds at 44, 49 and 54 degrees C general ly improved germination of infected seeds and reduced the incidence of A. d auci. Treatments at 54 degrees C for 20 minutes eradicated A. dauci without adversely affecting germination, emergence or yield. A significant correla tion (r=0.97) between the incidence of A. dauci and the occurence of abnorm al seedlings was found. Small seeds were more sensitive to hot water than l arger seeds. In two field experiments seed treatment with iprodione gave hi gher emergence and seedling weight than hot water treatment, possibly becau se iprodione may have reduced attack by soil-borne fungi whereas hot water treated seeds would not have been protected against such organisms. Hot wat er treatment of seeds and seed treatments with the biological control agent s had no effect on carrot yield and storage quality but reduced the inciden ce of the saprophyte Ulocladium atrum on the seeds. The germination percent ages found in the laboratory correlated well with the emergence percentages in the growth chamber. It is concluded that hot water treatment is an alte rnative to fungicides to eradicate seed-borne pathogens in carrots in organ ic farming systems.