Differential susceptibility of two varieties of cowpea (Vigna unguiculata (L) Walp) to phosphorus-induced zinc deficiency

Summary In a soil pot culture experiment conducted under greenhouse conditions, two varieties of cowpea (Vigna unguiculata (L) Walp) were found to be differentially susceptible to phosphorus-induced zinc deficiency. Although phosphate application, in the absence of applied zinc, caused growth disorder in both the varieties, the symptoms were more virulent, appeared early and were induced with both 25 and 75 ppm phosphorus in variety HFC-42-1, as against FOS-1, in which case zinc deficiency symptoms appeared under P₇₅Zn₀ treatment only. Contrary to the expectation the more susceptible variety was found to have higher zinc concentration in its shoots and thus the differential susceptibility of these varieties of cowpea could not be related to their zinc absorption characteristics. High phosphate application caused efflux of zinc during 16–32 day growth in both the varieties. However, higher sensitivity to phosphorus-induced zinc disorder in variety HFC-42-1, appeared to be due to nearly 2 times higher P concentration in this variety as against FOS-1. The results indicate that variety HFC-42-1 has a greater need for zinc because of its inherent capacity to accumulate more phosphorus. Dry matter yield and phosphorus and zinc content in the varieties were also differentially affected by the applications of both phosphate as well as zinc. re]19760504