Submitted to: Plant Cell and Environment
Publication Type: Review Article
Publication Acceptance Date: 8/1/2001
Publication Date: N/A
Interpretive Summary: Drought is, by far, the major environmental factor resulting in lost crop yields. An increasing amount of research has been committed to identifying genes and processes that lead to increased accumulation of organic compounds in plant cells to protect them against the damage of drought. This analysis, involving an ARS-USDA scientist at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, was undertaken to examine the putative benefit of the accumulation of these compounds in crops. It was argued that while the accumulation of these compounds could enhance plant survival to severe stress, this approach has little relevance in increasing crop yields under drought. First, conditions that are sufficiently serious to threaten crop survival almost invariably mean that the crop is an economic failure. Second, enhancement of crop yield necessarily requires additional water consumption by the crop so the only fundamental solution to drought is additional water. It is proposed that increased rooting depth, which might be stimulated by accumulation of organic compounds in root tips, into deep, wet soil appears to be the only clear mechanism for increasing crop yields under drought.
Technical Abstract: Osmolyte accumulation (OA) is frequently cited as a key putative mechanism for increasing yields of crops subjected to drought conditions. The hypothesis is that OA results in a number of benefits that sustain cell and tissue activity under water deficit conditions. It has been proposed as an effective tolerance mechanism for water- deficits, which could be enhanced in crops by traditional plant breeding, marker-assisted selection or genetic engineering. Field studies examining the association between OA and crop yield have, however, tended to show no consistent benefit. The few, often cited investigations, with positive associations were obtained under severe water deficits with extremely low yields. Under conditions where water deficits threaten crop survival, yields are so low that even large fractional yield gains offer little practical benefit to the grower. Indeed, the often-cited benefit of turgor maintenance in cells is likely to result in crop behavior that is exactly opposite to what is beneficial to crops. The one clear mechanism identified in this review for beneficial yield responses to OA is in the maintenance of root development in order to reach water that may be available deeper in the soil profile.