TOLERANCE OF WHEAT (TRITICUM-AESTIVUM CVS GAMENYA AND KITE) AND TRITICALE (TRITICOSECALE CV MUIR) TO WATERLOGGING

Responses of two genotypes of wheat (Triticum aestivum cvs. Gamenya and Kite) and one genotype of triticale (Triticosecale cv. Muir) were evaluated in stagnant solution culture and in waterlogged soil, using 23- to 36-d-old plants. Stagnant nutrient solutions decreased shoot fresh weight of Gamenya by 21% compared with aerated plants, while shoot fresh weight of Muir was unaffected. Reductions in nodal root fresh weight under stagnant conditions were also less for Muir than Gamenya. Aerenchyma in nodal roots of stagnantly grown plants accounted for 6.7 and 12.7% of the root cross sectional area for Gamenya and Muir, respectively. Oxygen supplied via this aerenchyma was substantially greater for Muir than Gamenya, and greatest for nodal roots of Kite. Elongation rates of stagnantly grown nodal roots in an O2-free medium reflected the amount of O2 supplied via the aerenchyma, and were 0.11, 0.17 and 0.27 mm h-1 for Gamenya, Muir and Kite, respectively. Waterlogging in soil decreased the redox potential from +600 to -200 mV after 35 d. Waterlogging decreased shoot fresh weight of Gamenya, Kite and Muir by 63-82% compared with drained plants, with similar reductions in growth of seminal roots. Nodal root growth was little affected by waterlogging in soil, although Muir had a 1.6-2.4-fold greater nodal root mass than Gamenya and Kite. Furthermore, after two cycles of 7 d waterlogging and 7 d drainage the seminal roots of Muir were at least double the length of Gamenya and Kite. Under the same waterlogged conditions, the shoot growth of rice (Oryza sativa cv. Calrose) was much greater than for wheat and triticale, and this reflected differences in morphology and anatomy of the root systems. Nodal root/shoot ratios indicated the major factor limiting shoot growth of wheat was the small mass of nodal roots per plant. However, a possible additional factor is the poor function of nodal roots of wheat and triticale in waterlogged soil.