Photosynthetic Activity Increase and Genetic Improvement of Crop Yield ?.

Crop physiology points out that yield is limited by photosynthetic input, more so at some stages of development than others. Generally in the past however, direct selection for increase in photosynthetic activity at the leaf level (P max, µmoles CO₂ m^-2 s^-1) has not led to associated yield increase , nor has Pmax been found to increase with genetic improvement of yield. There have been some past reports contradicting the above generalization, and in the last decade, a number of studies of the most recent varieties have revealed increased Pmax. Often Pmax increases were determined during grain filling, when sink strength in terms of grain number may be the underlying cause. But in other reports Pmax (and radiation use efficiency, RUE) increases were measured before and around flowering, a period which may better reflect inherent photosynthetic capacity. The presentation will review data available on this subject and concludes that seeking and exploiting natural genetic variation to further increase inherent Pmax in crop plants is a plausible way forward in breeding for greater yield. However, how this (or any other physiological trait selection) is executed within

modern breeding programs moving towards increased use of molecular markers remains an

intriguing question.