pH of the Pod-zone Affects Reproductive Growth of Groundnut

ABSTRACT

Most of the sandy soils that are suitable for production of groundnut (Arachis hypogaea L.) in the tropic and subtropics are acidic. Whilst effects of pH in the root zone have been studied, the effects of pod-zone pH on groundnut productivity remain relatively unknown. To develop appropriate soil management practices for groundnut production on acid soils, it is essential to understand how low pH affects reproductive growth of groundnut. Consequently, a glasshouse experiment was conducted in which attached groundnut gynophores were cultured in solution at pH ranging from 3.0 to 7.0. Low pH delayed pod initiation, and resulted in almost no pod expansion at pH 3.0. Only 12% and 55% of the cultured gynophores developed into pods at pH 3.0 and 4.0, respectively, compared with 91–95% at pH ≥ 5.0. Pods produced at pH 3.0 contained no seeds and those produced at pH 4.0 had a hollow, dark colored area in the cotyledon. Normal seeds and embryos were formed at pH ≥ 5.0, and plumule development was faster at solution pH ≥ 5.0 than at pH 4.0. Pod and kernel dry mass were optimised (90% of maximum) at pH 5.62–6.69 and 5.65–6.78, respectively. Septate and non-septate pod hairs were formed at all solution pH regimes, but were denser and more persistent at the higher pH. Kernel calcium (Ca) concentration decreased with decreasing pH, and was highly correlated with solution pH. Thus, pod-zone pH has important effects on the reproductive growth of groundnut, emphasizing the importance of managing pod-zone pH.

Keywords:

• Groundnut
• gynophore culture
• nutrient solution
• pod growth
• pod-zone pH

ACKNOWLEDGMENTS

The study was undertaken whilst the senior author was on study leave from the Department of Research and Specialist Services, Government of Zimbabwe, and was made possible by a fellowship from Rockefeller Foundation.