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EFFECT OF COMBINED NITROGEN ON GROWTH AND NODULATION OF TWO MUNGBEAN (VIGNA RADIATA [L.] WILCZEK) CULTIVARS
Botany Division, Institute of Pure and Applied Biology, Bahauddin ZaKariya University, Multan, Pakistan.
Abstract: Two mungbean (Vigna radiata [L.] Wilczek) cultivars, NM-51 and NM-92, were compared for plant growth and root nodulation during development at different nitrogen regimes (0, 2, 5 and 10 mM) in sand cultures. Dry weight of plants, after 5, 8 and 10 weeks of sowing, increased in both cultivars at all the nitrate levels. The maximum increase in dry weight, however, occurred at 5 mM nitrate for NM-51 and at 2 mM nitrate for NM-92. The two cultivars were comparable in reproductive growth since number of flowers per plant, number of pods per plant and fresh weight of pods per plant generally increased with increasing nitrogen levels. Nodule development in both the cultivars was stimulated in the presence of 2 mM nitrate but was increasingly depressed by the higher levels of nitrate. Nitrate levels of 5 and 10 mM decreased nodule number and nodule fresh weight. Cultivar NM-92 showed increased growth and nodulation at all nitrate levels compared to NM-51. Also, nodulation of NM-92 was more tolerant to nitrate compared with NM-51.
Keywords: Biological nitrogen fixation, combined nitrogen, growth, mungbean, nodulation, Vigna radiate.