Germination Ecology of Red Sprangletop:a Problematic Weed of Direct-Seeded Rice

Leptochloa chinensis L. commonly called red sprangletop is a new problematic weed of rice (Oryza sativa L.) sown under dry conditions in Pakistan and caused a drastic reduction in its yield and quality.Scientific inquiry was conducted concerning the germination ecology of this weed in directseeded rice.A series of laboratory experiments were conducted to determine the effect of pH, salinity, temperature, seed burial depth, and water ponding conditions on the germination of L. chinensis.In five different experiments, six variable pHs ranging from 5 to 10; six salinity levels viz.0 (Distilled water), 50 mM, 100 mM, 150 mM, 200 mM, 250 mM and 300 mM; six variable temperatures viz.20 o C, 25 o C, 30 o C, 35 o C, 40 o C and 45 o C; seven different burial depths viz.0 cm (on soil surface), 1 cm, 2 cm, 3 cm, 4 cm, 5 cm and 6 cm; and different water ponding depths viz.0 cm, 2 cm, 3 cm, 4 cm, 5 cm and 6 cm were kept as experimental treatments.The results revealed that within the pH range of 6-7 and 35 o C temperature, L. chinensis seeds attained the highest germination percentages (78% and 92%, respectively).A gradual significant decline in germination of L. chinensis was noted by the increase in NaCl concentration from 0 to 200 mM, sowing depth from 1 to 5 cm, and flooding depth from 0 to 4 cm.However, beyond 200 mM NaCl concentration, 5 cm sowing depth, and 4 cm flooding depth, no L. chinensis seed could germinate/emerge.According to the 3-parameters logistic model estimation, 50% germination of the maximum germination of L. chinensis occurred at 102 mM NaCl concentration, 1.56 cm burial depth, and 2.2 cm flooding depth.