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Some Photo-Dependent Responses in Pisum. I. Physiological Behavior¹

Two new (G- and G2) and two previously known (K and I) photo-dependent response types of Pisum were compared in a phytotron after having been distinguished earlier under greenhouse conditions. In the first of two experiments the four response types were exposed to three photoperiods, 9, 12, and 15 hours, at a constant growth temperature of 17 C. Plants of the K-type exhibited a quantitative increase in nodes and days to flower in response to decreasing length of photoperiod, whereas I-type plants were day-neutral or insensitive to length of photoperiod. Flowering in G-type plants was either completely inhibited or sharply delayed at all three photoperiods. G2-type plants, like the I-type, were insensitive to daylength with respect to nodes to flower but, unlike the I-type, they exhibited a protracted period of apical growth, again at all photoperiods. The behavior of the G- and G2-types at the 15 hour photoperiod was atypical since under long day conditions in the field or greenhouse these types ordinarily do not show a response.

The response types were not discriminated under the conditions of a second experiment which included two levels of light intensity and two levels of growth temperature and a long (18-hour) photoperiod. Growth temperature had no influence on the number of nodes to flower but it had a marked influence on the number of days to flower.

Key Words: Photoperiodism • Light intensity • Growth temperature • Peas • Flowering response

² Associate Professor, Department of Vegetable Crops, New York State Agricultural Experiment Station, Geneva 14456.

Received for publication May 28, 1968.