Post-flowering photoperiodic effect on soybean reproductive efficiency.

NICO M; KANTOLIC A; MIRALLES DJ

Bento Goncalves

Congreso; 6th International Crop Science Congress; 2012

International Crop Science Society

The objective of the present work was to assess the role of post-flowering photoperiod on soybean reproductive efficiency. Previous results have shown that less-inductive daylengths extended post-flowering phases and increased seed number. It is hypothesized that the increases in seed number, due to an extended post-flowering phase, are mediated by an enhanced crop reproductive efficiency. Field experiments were conducted at Buenos Aires, Argentina during 2009 (late sowing) and 2010/11 (early sowing), without limitation in nutrient, water or biotic stress. Treatments were a factorial combination of genotypes (maturity group IV and V), incident radiation (control and shade) and photoperiod regimes (natural and artificially extended) installed after beginning bloom (R1). Reproductive growth rate was estimated from R1 to R8 on a thermal-days basis. Reproductive efficiency was estimated as the quotient between final seed number and reproductive growth rate. Photoperiod extension prolonged the pod production phase but its effects on crop growth rate and partition were not significant. Seed number showed a positive linear relationship with the reproductive growth rate across genotypes and radiation levels, but different relationships were adjusted depending on the experiment and photoperiodic regime. At a given reproductive growth rate, plants exposed to extended photoperiod produced more seeds than those exposed to the natural photoperiod condition. Similarly, yield per unit of reproductive growth rate was higher under lengthened photoperiod, although the magnitude of the response was lower than those of seed number, because plants exposed to extended day length had smaller seeds. Reproductive efficiency showed a positive relationship with the mean photoperiod explored during the post-flowering phase. Interestingly, mean photoperiod value in the extended photoperiod regime in the late sowing experiment was similar to the natural photoperiod explored in the experiment sown earlier (14:55 and 14:30 h, respectively) and had similar reproductive efficiencies (487.8 and 489.2 grains g-1 d m2, respectively). These results suggest that the promotion of seed number establishment by extended photoperiods is given not only by lengthening the phase of pod production and growth, but also by an increment on the reproductive efficiency, accepting the postulated hypothesis