John A. Biernbaum

Irradiance and temperature effects on time of development and flower size in chrysanthemum

Abstract The effects of day temperature (DT), night temperature (NT) and photosynthetic photon flux (PPF), on rate of development and flower size were studied in chrysanthemum ( Dendranthema grandiflora Tzvelev. cultivar ‘Bright Golden Anne’). DT and NT ranged from 10 to 30°C and PPF from 1.8 to 21.6 mol day −1 m −2 . Flower initiation did not occur after 100 short days (SD) at low PPF levels (1.8 mol day −1 m −2 ) in combination with high DT or NT (30°C). The number of days to flower varied from 58 to 140 days among plants grown under environmental conditions allowing flower initiation within 100 SD. The time to flower from start of SD decreased nonlinearly as PPF increased. Increasing PPF by 9.9 mol day −1 m −2 at 20°C accelerated flowering 20 days when the initial PPF was 1.8 mol day −1 m −2 , but only 10 days when the initial PPF was 11.7 mol day −1 m −2 . The DT and NT for most rapid flower development were estimated from a model predicting time to flower. Independent of PPF in the range from 2 to 20 mol day −1 m −2 , the optimum DT was 17°C and the optimum NT was 18°C. Total flower area per plant varied from 14 to 310 cm 2 . The flower size increased linearly as PPF increased from 1.8 to 21.6 mol day −1 m −2 at a constant temperature of 20°C. The optimum DT NT combination for largest flower size changed from 21 14° to 20 18° C as PPF increased from 5 to 20 mol day −1 m −2 .

A simulation model of the spread of Botrytis leaf blight of onion and its effect on onion yields

Abstract A computer model was constructed which simulated build-up and spread of Botrytis leaf blight of onion using inputs of daily averages of vapor pressure deficit, humidity and temperature. Destruction of leaf tissue and resulting effects on onion yields were modeled using data from several sources and a previously constructed model of growth of the onion plant. Effects of fungicide sprays as a disease control agent were incorporated in the model. The model was quite realistic when compared with research data collected from the field.