[01] Dennis Iorkor, Department of Plant Breeding and Seed Science, Joseph Sarwuan Tarkaa University, Makurdi, Nigeria. [02] Iyorkyaa Nater, Department of Plant Breeding and Seed Science, Joseph Sarwuan Tarkaa University, Makurdi, Nigeria. [03] Stephen Deborah Yage, Department of Biology, Ibrahim Badamasi Babangida University, Lapai, Nigeria.

A field and laboratory experiments were conducted in the Teaching and Research Farm and Plant Breeding and Seed Science laboratory both of Joseph Sarwuan Tarka University, Makurdi during the 2019 farming season to investigate the influence of planting date on physiological seed quality of soybean. The experiments consisted of three soybean varieties (TGX-1448-2E, TGX-1904-6F and TGX-1835-10E) obtained from the Seed Centre of Joseph Sarwuan Tarka University, Makurdi and five planting dates used were (22^nd June, 29^th June, 6^th July, 13^th July and 20^th July, 2019). The treatments of the field experiment were arranged in a Randomized Complete Block Design (RCBD) replicated three times and the laboratory experiment was laid out in a Completely Randomized Design (CRD) also with three replications. Physiological seed quality attributes evaluated included; germination percentage (G%), germination index (GI), germination rate index (GRI) and vigor index (I). The result from the Analysis of variance (ANOVA) revealed that early planting (22^nd June) significantly (p≤0.05) recorded the least germination percentage, germination index, germination rate index and vigor index. Whereas planting done 13^th July (mid-July) produced seeds with the highest germination percentage, germination index, germination rate index and vigor index. TGX-1448-10E and TGX-1904-6F produced seedlings with vigor index not significantly different from each other but were significantly inferior to seedlings of TGX-1835-10E. There was an increase in the germination percentage, germination index, germination rate index and vigor index from 22^nd June to 20^th July planting dates in all the three varieties studied. TGX-1835-10E when planted 20^th July recorded the highest germination percentage and germination index though not significantly different from TGX-1448-10E and TGX-1904-6F. TGX-1904-6F on the other hand recorded the highest germination rate index although not significantly different from TGX-1448-10E and TGX-1835-10E. Generally, physiological seed quality increased as planting was delayed with the highest quality recorded at 13^th July.

Physiological, Seed, Emergence, Quality, Vigor

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