Soybean adjusts pods after simulated reproductive damage.

Soybeans have the ability to compensate for damage caused by Helicoverpa zea When tissue loss occurs early in the reproductive cycle, this compensation varies according to the growth habit of the cultivar. Indeterminate growth varieties adjust pod types and seed weight differently than determinate varieties. This conclusion results from a field experiment conducted in North Carolina, USA, simulating damage between stages R1 and R3.

The insect Helicoverpa zeaThe corn earworm, known as the corn earworm, feeds on the leaves, flowers, and pods of soybeans. Attacks on reproductive organs can reduce yield components. Management recommendations in the southeastern United States are largely based on determinate cultivars. This study evaluated whether indeterminate cultivars, which maintain vegetative growth after flowering, better compensate for this type of damage.

Two cultivars

Researchers compared two commercial soybean cultivars, both from maturity group 5. One cultivar exhibited determinate growth, while the other exhibited indeterminate growth. The experiment took place over two growing seasons, 2020 and 2022, at the Rocky Mount experimental station. The plots received three treatments involving manual removal of flowers and small pods: 0%, 50%, and 100% of the reproductive tissue.

The removal simulated the attack of Helicoverpa zea The study was conducted during the period between the beginning of flowering and the start of pod formation. This interval coincides with the pest's preferred oviposition period. In each plot, ten plants were marked and subjected to the treatment. Harvesting occurred after physiological maturity. The researchers evaluated average seed weight, total number of pods per plant, and distribution of pods with one, two, three, and four grains.

Average seed weight

The average seed weight varied between years and growth habits. In 2020, indeterminate growth plants produced heavier seeds than determinate plants. In 2022, this difference did not appear. The percentage of reproductive tissue removal did not consistently alter the average seed weight across the two years.

The total number of pods per plant responded to partial removal of reproductive tissue. On average, the treatment with 50% removal generated more pods than the treatments with no removal and with total removal. This effect was most evident in 2022. Total removal reduced yield components, while moderate damage allowed for compensation.

Different strategies

The cultivars exhibited distinct strategies for adjusting yield components. Indeterminate growth plants produced more pods with one grain and more pods with four grains under certain conditions. Determinate growth plants, on the other hand, concentrated their compensation on increasing the number of pods with three grains. The number of pods with two grains varied little between treatments, years, or growth habits.

The complete removal of reproductive tissue between R1 and R3 did not prevent seed formation until harvest. This indicates a capacity for compensation even after severe losses in this initial period. However, compensation did not occur uniformly across years, suggesting the influence of environmental conditions.

The authors tested the hypothesis of greater compensatory capacity in indeterminate cultivars. The results did not consistently confirm this hypothesis. The observed differences depended on the yield component evaluated and the agricultural year. The study used only one cultivar of each growth habit, which limits generalizations.

The data reinforces the fact that soybeans naturally abort a large portion of their flowers. Therefore, flower loss at the beginning of flowering tends to have less impact on final yield. Removing pods at later stages usually generates greater losses, as pointed out by previous studies cited by the authors.

The study did not evaluate productivity at the plot level, only yield components in individual plants. Thus, heavier seeds do not, in isolation, indicate increased productivity. The authors highlight the need for further studies with more cultivars, different environments, and direct yield measurement.

More information at doi.org/10.1016/j.cropro.2025.107325