PNAS 89 (20) 9794-9798 (Oct 15, 1992)
The Path of Carbon in Photosynthesis: Improved Crop Yields with Methanol
AM Nonomura and AA Benson

Foliar sprays of aqueous 10-50% methanol increased growth and development of C3 crop plants in arid environments. The effects of low levels (<1 ml per plant) of methanol were observed for weeks after the brief time necessary for its rapid metabolism. Within several hours, foliar treatment with methanol resulted in increased turgidity. Plants treated with nutrient-supplemented methanol showed up to 100% increases in yields when maintained under direct sunlight in desert agriculture. In the shade and when winter crops were treated with methanol, plants showed no improvement of growth. When repeatedly treated with nutrient-supplemented methanol, shaded plants showed symptoms of toxicity. Repeated methanol treatments with glycine caused increased turgidity and stimulated plant growth without injury under indirect sunlight, but indoors with artificial illumination, foliar damage developed after 48 hr. Addition of glycerophosphate to glycine/methanol solutions allowed treatment of artificially illuminated plants indoors without injury. Plants with C4 metabolism showed no increase in productivity by methanol treatment. Plants given many applications of aqueous methanol showed symptoms of nutrient deficiency. Supplementation with a source of nitrogen sustained growth, eliminating symptoms of deficiency. Adjustment of carbon/nitrogen ratios was undertaken in the field by decreasing the source of nitrogen in the final application, resulting in early maturation; concomitantly, irrigation requirements were reduced.

Our preliminary tests on roses with high concentrations of iron showed that iron EDTA at 0.9 g/liter in methanol was phytotoxic, but 0.08 g/liter in methanol was the maximum concentration tolerated by young rose foliage. A very high C/N ratio was achieved in the final foliar application because no urea was added. When treated with methanol, cultivars Rotary Rose, Paul Harris, Miss All-American Beauty, Blue Girl, Tiffany, Mr. Lincoln, John F. Kennedy, Joseph's Coat, Peace, Lowell Thomas, and Queen Elizabeth grew to bud and bloom within 62 days of placement in the greenhouse. Treated cultivars Angel Face, First Prize, and Tropicana required ~70 days to reach bud and bloom. In the control greenhouse, all varieties required 75-80 days to achieve bud and bloom maturity. Treated roses showed fuller foliage and blooms than controls. 'Miss All-American Beauty' flowers, for example, averaged 26 g compared with 18 g for controls. At the time of first bloom, treated 'Paul Harris' plants averaged eight fully opened flowers. Controls later averaged four fully opened flowers. Plants remained healthy and pest-free.