ROOT DEVELOPMENT AND AERENCHYMA FORMATION IN 2 WHEAT CULTIVARS AND ONE TRITICALE CULTIVAR GROWN IN STAGNANT AGAR AND AERATED NUTRIENT SOLUTION

Stagnant nutrient solution containing 0.1% agar and with an extremely low oxygen level ('stagnant agar solution') was used to simulate the g aseous composition and slow gas diffusion of waterlogged soils. Compar isons were made between the growth of two wheat cultivars (Triticum ae stivum, cvs. Gamenya and Kite) and one triticale cultivar (Triticoseca le, cv. Muir) grown in stagnant relative to aerated solution. For all genotypes tested, immersion of roots in stagnant agar solution resulte d in the death of the entire seminal root system and led to profuse br anching of the laterals of the nodal roots. In the stagnant agar solut ion aerenchyma, as a percentage of the total cross sectional area of n odal roots, was 18% for Muir, 14% for Kite and 12% for Gamenya; the ro ots of species with more aerenchyma also attained a longer maximum roo t length as predicted by the model of Armstrong (in: Woolhouse HW, ed. Advances in botanical research, vol. 7. London: Academic Press, 1979) . Muir also had a nodal root/shoot fresh weight ratio of 0.5 compared with 0.2-0.3 in Kite and Gamenya. The greater number and length of nod al roots of Muir did not lead to better shoot growth than in the other genotypes; one possible reason for this lack of improvement is a low efficiency of aerenchymatous roots in wheat. (C) 1998 Annals of Botany Company.