CULTIVAR AND ENVIRONMENTAL-EFFECTS ON GROWTH AND DEVELOPMENT OF PEANUTS (ARACHIS-HYPOGAEA L) .2. REPRODUCTIVE DEVELOPMENT

Initiation of reproductive structures (pegs and pods) by spaced plants and distribution of dry-matter (DM) between vegetative and reproductive components of above-ground yield (tops and pods) were investigated for 16 peanut cultivars over 11 sowing dates in subtropical Australia. Assessments were made 35 (h1) and 65 (h2) days after first flower appearance. Cultivars showed a wide range in numbers of reproductive components and harvest index (HI) at both h1 and h2. These differences could be related to differing cultivar phenologies (both within and among botanical types) and also to differing patterns of assimilate partitioning between vegetative and reproductive components. Cultivars were grouped for sowing-date response for each of peg and pod number and HI. Cultivar groupings were quite similar for peg and pod numbers. At h1, Spanish cultivars were consistently in the group most responsive to sowing date, the single Valencia cultivar was consistently in the group least responsive to sowing date, and Virginia cultivars were generally intermediate. Cultivar groupings for HI did not follow simple botanical divisions, and also changed between h1 and h2. Peg and pod numbers and HI at both h1 and h2 were affected primarily by daylength during previous growth phases, although temperature was additionally important for some cultivars. Daylength effects differed in both sign (positive or negative) and the growth stage during which they were important. Reproductive development and HI at h1 were positively associated with daylength during the emergence-to-flowering period (the dominant effect) and, in addition, negatively associated with daylength during the flowering-to-h1 period for most cultivars. Reproductive development and HI at h2 were positively associated with daylength during the emergence-to-flowering or flowering-to-h1 (the dominant effect) periods, and generally negatively associated with daylength during the h1-to-h2 period. Daylength effects could not be separated into effects of photoperiod, irradiance or heat-unit accumulation, and further studies of this aspect are planned under field and controlled-environment conditions.