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Increased Phytochrome B Alleviates Density Effects on Tuber Yield of Field Potato Crops¹

IFEVA, Faculty of Agronomy, University of Buenos Aires, Avenida San Martín 4453, 1417 Buenos Aires, Argentina (H.E.B., E.L.P., M.J.Y., R.A.S., J.J.C.); and Albrecht-v.-Haller Institute für Pflanzenwissenschaften Allgemeine und Entwicklungsphysiologie der Pflanze, Untere Karspüle 2, D–37073 Göttingen, Germany (C.G.)

The possibility that reduced photomorphogenic responses could increase field crop yield has been suggested often, but experimental support is still lacking. Here, we report that ectopic expression of the Arabidopsis PHYB (phytochrome B) gene, a photoreceptor involved in detecting red to far-red light ratio associated with plant density, can increase tuber yield in field-grown transgenic potato (Solanum tuberosum) crops. Surprisingly, this effect was larger at very high densities, despite the intense reduction in the red to far-red light ratios and the concomitant narrowed differences in active phytochrome B levels between wild type and transgenics at these densities. Increased PHYB expression not only altered the ability of plants to respond to light signals, but they also modified the light environment itself. This combination resulted in larger effects of enhanced PHYB expression on tuber number and crop photosynthesis at high planting densities. The PHYB transgenics showed higher maximum photosynthesis in leaves of all strata of the canopy, and this effect was largely due to increased leaf stomatal conductance. We propose that enhanced PHYB expression could be used in breeding programs to shift optimum planting densities to higher levels.

¹ This work was supported by the University of Buenos Aires (grant no. G 067 to J.J.C.), by the National Research Council of Argentina (Consejo Nacional de Investigaciones Científicas y Técnicas grant no. PID 888 to J.J.C.), and by the Fundación Antorchas (grant no. 14116–16 to J.J.C.).

^* Corresponding author; e-mail casal{at}ifeva.edu.ar; fax 5411–4514–8730.

Received July 2, 2003; returned for revision August 4, 2003; accepted September 9, 2003.

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