Quick screening of cowpea genotypes for manganese tolerance during vegetative and reproductive growth

In cowpea (Vigna unguiculata) genotypical differences in Mn tolerance during vegetative growth are due to differences in Mn tolerance of the plant tissue, especially of the leaves. Mn applied to the petioles of fully expanded leaves induces the same toxicity symptoms on the leaf blades as Mn absorbed by the roots. There is a good agreement between the rankings of the different genotypes for Mn tolerance according to the depression of shoot dry matter production by Mn excess in long term pot experiments and the appearance of toxicity symptoms after application of Mn to the petioles. However, Mn tolerance during vegetative growth is not necessarily correlated with Mn tolerance during reproductive growth as no close relation exists between reduction by Mn excess of dry matter and of grain yield. Application of Mn to the peduncles two days after flowering causes the same toxicity symptoms on the pods as Mn adsorbed by the roots. The application of Mn to the petioles allows a very simple, quick and non-destructive screening of cowpea genotypes for Mn tolerance during vegetative growth. Application of Mn to petioles and peduncles looks promising as a screening technique of Mn tolerance in vegetative and reproductive growth.