PLANT GROWTH UNDER CONTROLLED CONDITIONS. VIII. GROWTH AND FRUITING OF THE CHILI PEPPER (CAPSICUM ANNUUM)

Abstract

IN A SERIES of publications the response of tomato plants to external conditions has been described (Went, 1944, 1944a, 1945). It was found that the night temperature was the most critical single factor in their growth and fruit development, and a number of interactions between light, age, variety and temperature on the one hand and rate of stem elongation on the other were also found. Because of the fairly large size of tomato plants they could be grown in the air-conditioned greenhouses only up to the early fruiting stage. To see whether the conclusions drawn from the experiments with tomatoes have a wider application, a number of other plants must be analyzed in a similar way. In the present paper an investigation is reported in which the chili pepper (Capsicum annuum var. longum) was subjected to analysis.2 On the one hand the chili pepper is related to the tomato. On the other hand the pepper is a smaller plant, which usually stops growing once fruit set is heavy. Therefore it was possible to continue the investigation of the effect of environmental factors on development until complete maturity of fruit. The only similar studies which have been carried out with pepper plants are those by Cochran in 1936 discussed below. 1 Received for publication February 17, 1947. 2 This work was made possible through a research grant from Gentry Incorporated. Chili pepper plants of three varieties, the Mexicant Hungarian and California were grown in inert materials and watered daily with Hoagland's nutrient solution. The cultural conditions, which varied from experiment to experiment, are shown in table 1. When the plants were thoroughly established after transplanting into their containers, they were separated into a number of groups and the treatments in the air-conditioned greenhouses were started. VEGETATIVE GROWTH.-The pepper plant grows with a single stem, until 9-11 leaves have been formed. The main stem terminates with a flower. Two (or sometimes three) branches grow from the axils of the highest leaves. Each of these branches forms two leaves and terminates in a flower. Thus we get repeated seemingly dichotomous branching and the whole plant assumes an inverted conical shape. In contradistinction to the unlimited growth of most tomato plants, the growth of a pepper plant follows a sigmoid curve (fig. 4, 5). EFFECT OF TEMPERATURE.-The effect of temperature on the growth rate of peppers is very-much like that on the tomato plant. While they are young the optimal night temperature is at least as high as 300C., the highest controlled temperature tested. As they become older, the optimal night temperature progressively decreases. At 108 days the warm day plants had their optimal night temperature as