Flowering and bolting in carrot. I. Juvenility, cardinal temperatures and thermal times for vernalization

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Abstract
Effects of temperature on flowering and bolting, measured as days to flower bud visibility and to internode extension (bolting) and as leaf number below the primary inflorescence, were studied in carrot cv. Chantenay Red Cored grown in controlled environments. Preliminary experiments showed juvenility to end when plants had initiated 8-12 leaves. Non-juvenile plants subjected to temperatures in the range 3 to 12°C for nine weeks or more flowered and bolted subsequently under warmer (16-20°C) conditions whereas those grown throughout at warm temperatures did not. Rates of bolting and flowering increased linearly with temperature from —1 to 5°C and declined linearly from 7 to 16°C. The linear relationship enabled the base, optimum and maximum temperatures for vernalization to be derived respectively as -1.0°C, 6.5°C and 16.0°C. The minimum ther- mal-time of vernalization for any bolting and flowering to occur in this cultivar of carrot was ca. 126°Cd and the minimum required for 90% bolting and flowering was ca. 336°Cd.

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