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Leaf Emergence on Potato Stems in Relation to Thermal Time

Dep. of Agronomy, Nanjing Agric. Univ., Nanjing, Jiangsu 210014, China
Dep. of Horticulture, Univ. of Wisconsin, Madison, WI 53706

^* Corresponding author (Email: twt@calshp.cals.wisc.edu).

For simulation of foliar development of potato plants (Solanum tuberosum L.), it is necessary to quantify the responses of leaf emergence to major environmental factors. This study was conducted to determine the relationship of leaf emergence on potato stems to growing degreedays (GDD) under varied temperature patterns over different growth periods. In each of two duplicate experiments in controlled environments, potato plants were grown for 63 d after transplanting of tissue culture plantlets into 20-L pots containing peat-vermiculite mix. Four treatments were maintained, involving two constant temperatures of 17 and 22°C and two changed temperatures of 17-22-17 and 22-17-22°C over three 21-d periods under constant vapor pressure deficit of 0.60 kPa and photosynthetic photon flux density of 430 µmol m^–2 s^–1 fora 14-h photoperiod. The first period was the first 21 d of plant growth after transplanting, the second 21-d period coincided with plant enlargement and tuber initiation, and the third period coincided with tuber enlargement. Leaf numbers on main stems and uppermost apical branches were recorded every 2 to 3 d during the course of the experiments. This leaf number increased linearly with accumulated GDD over the whole experiment duration for each of the four treatments, whether the temperature was constant or changed. The phyllochron in GDD per leaf (6°C base temperature) was lowest at constant 17°C (19.2 GDD), highest at constant 22°C (22.8 GDD), and intermediate at the changed temperatures ( 21.3 GDD). Detailed analysis of the leaf emergence rates during each of the three 21-d periods indicates that the phyilochron at either 17 or 22°C was also slightly lower during the second 21-d period than during the first and third 21-d periods. The total leaf number increased with increasing total GDD among the treatments, primarily from varied leaf number on apical branches. The data suggest that a constant phyllochron for a given growth location and calendar time may provide sufficient accuracy for predicting leaf emergence on potato stems in the field environment.

Received for publication October 25, 1993.

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