Response to carbon monoxide by geographic variants in Acacia farnesiana.
A B S T R A C T Differences in degree of defoliation in CO-air mixtures were shown by geographic variants in Acacia farnesiana (L.) Willd., a widespread, weedy, pantropic, leguminous tree. Laboratorygerminated seedlings from MazatlAn (MAME-1), Sinaloa, Mexico, showed greater sensitivity to a CO gradient than plants from Point Tuna (PORO), Puerto Rico. Seedlings of both strains grown under a light intensity of 200 ft-c showed greater sensitivity to CO than those grown under 1,800 ft-c. When intact plants of 17 geographic variants grown at low-light intensities were exposed to 2%Fo CO in air, 11 strains (Mexico,8; Texas, 1; California, 1; Guatemala, 1) showed almost complete defoliation. The other six strains-from Brazil, Hawaii, Puerto Rico, 1Ttaly, Algeria, and Michoac4n, Mexico-showed defoliation averaging from 23 to 70%. The significance of the CO-defoliation response is difficult to explain in terms of the natural distribution of A. farnesiana. It is suggested that this response may be correlated with some biochemical process of adaptive significance. GEOGRAPHIC variants in Acacia farnesiana (L.) Willd. being studied at the Plant Ecology Research Laboratory differ in several parameters, but the most bizarre difference is one shown by exposure to low concentrations of carbon monoxide. While certain strains show nearly total leaf loss after 24-hr exposure to CO, other strains show little or no defoliation. First observed as a result of accidental exposure to CO, the geo
Stem Orientation in Two Populations of Acacia farnesiana from Mexico Under Controlled Environmental Conditions
The orientation of stem growth in upright plants from an inland population at Saltillo, Coahuila, and in prostrate plants from a beach population at Mazatlan, Sinaloa, was examined under several conditions of photoperiod, temperature, and light intensity. Prostrateness is enhanced by lower temperatures, shorter photoperiods, and higher light intensities in both populations but is induced to a greater degree and over a wider range of conditions in the naturally prostrate form. Under longer day lengths, 16 hr, and higher temperatures, 32-24 C, the prostrate form develops almost upright and is not significantly more prostrate than the naturally upright form. Regenerated stems produced under high light intensities were significantly more prostrate in the beach population than were stems of the inland population, but under low light intensities both populations produced upright stems. The results suggest that niche plasticity of the prostrate population offers selective advantage in a subtropical beach ecosystem.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.