Search

In order to accurately model the flowering process, it is essential to determine which environmental factors are affecting development at any point in time. The purpose of this research was to determine when different soybean [Glycine max(L.) Merr.) genotypes first become sensitive to photoperiod and how long photoperiod continues to influence the appearance of the first flower under optimal temperature conditions. Controlled‐environment experiments were conducted in which plants were switched at intervals between emergence and flowering from long‐day (22 h) to short‐day (9 h) treatments and from short‐ to long‐day treatments. AH photoperiod chambers were maintained at 26 °C both day and night. Six cultivars from six maturity groups were used: ‘Dawson’, ‘Williams’, ‘Ransom’, ‘Forrest’, ‘Davis’, and ‘Jupiter’. Two nearly isogenic breeding lines differing in response to inductive conditions were also evaluated. All cultivars tested were sensitive to photoperiod by the time the unifoliolate leaf was fully expanded. The experimental line bred for a lengthened juvenile phase exhibited apparent insensitivity to photoperiod for 11 d longer than any of the other genotypes. After flowering was induced, further inductive nights hastened flowering. for all cultivars, photoperiod during the last 6.3 to 8.7 d prior to expression of the first flower had no effect on time to first flower. Thus, for modeling purposes, the interval between emergence and first flower can be divided into four phases: (1) a purely vegetative phase (absent in most of the cultivars tested); (2) a photoperiod‐sensitive inductive phase; (3) a photoperiod‐sensitive post‐inductive phase; and (4) a photoperiod‐insensitive post‐inductive phase.

Defoliation experiments were performed in order to provide information for development of a pest management simulation model for peanuts (Arachis hypogaeaL.). ‘Florunner’ peanut plants were defoliated uniformly and nonuniformly at 9, 12, and 16 weeks after planting and harvested 2, 4, or 6 weeks following treatment. All defoliations resulted in lower stem weight to length ratios, lower pod numbers and weights, and equal or higher leaf numbers and weights. Defoliation altered the normal partitioning of photosynthate between plant parts. The location of defoliation damage (either uniform throughout the canopy or confined to the outer portion of the canopy) affected plant response in that plants defoliated nonuniformly grew more leaves in the 2 weeks following treatment than those defoliated uniformly