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The Reproductive Efficiency of Cultivated Peanuts. IV. The Influence of Photoperiod on the Flowering, Pegging, and Fruiting of Spanish-Type Peanuts¹

The time of flowering and pegging during the early development of the peanut plant are heritable and correlated This research was designed to determine the effects of photoperiod on the periodicity of flowering and subsequent peg growth within specific portions of the life cycle of the peanut plant. A Spanish-type peanut, Arachis hypogaea L., C2 (PI 262000), was used in the investigations.

Plants exposed to long-day treatments (light interrupted 15-hour dark period) in growth chambers of the North Carolina State University Phytotron Unit, produced 1.84 times more flowers per plant than those grown in 9 hour photoperiods. Plants in short-day treatments reached flowering peaks earlier than those in long-day chambers and produced 134.4 shellable fruit per plant in contrast to 34.1 fruit per plant for long-day treatments.

The reproductive efficiency, relative to other plant traits, was also enhanced by growing the plants in short-day photoperiods. Twenty-seven percent of the flowers on plants grown under short days produced shellable fruit resulting in 106.5 g of seed per plant. Only 3.8% of the flowers on plants in long-day chambers produced shellable fruit resulting in 12.1 g of seed per plant. The proportion of seed weight to plant top weight was 59.6% in short-day regimes compared to 3.0% in long-day regimes.

The peanut, unlike other plants, has three distinct steps in the reproductive process. These are the flowers, the peg, and the fruit. To measure the responses of the plants in each of these reproductive steps to changes in photoperiod, seven different sequences of photoperiods were applied to the plants over three 36-day growth periods. The stage most sensitive to changes in photoperiod was found to be that period when the plant was between 36 and 72 days of age. Substituting short days for long days during this growth caused increased numbers of pegs, increased peg growth, increased fruit numbers, increased fruit weight, increased seed weight, and increased seed weight per plant weight. Plant weight was decreased by the same substitution.

The dramatic changes in flowering periodicity and increased rates of growth for reproductive traits when plants are exposed to shortday growth periods will serve as selection criteria in segregating populations of crosses between Spanish and Virginia-type peanuts. The latter are large-seeded and later maturing than lines used in this study.

Key Words: Flowering • Fruiting • Pegging • Light Treatments • Groundnuts • Arachis hypogaea L.

² Professor of crop science and honors research undergraduates in 1978 and 1976, respectively, North Carolina State Uni., Raleigh, NC.

Received for publication December 25, 1979.