Response of five wheat cultivars to early drought in the Pampas

Wheat production in the Pampas of Argentina is frequently reduced because o f early drought occurring during vegetative growth. The plant morphological and physiological traits required to resist such an early drought and to p roduce substantial grain yields is still controversial. In this study we ha ve investigated the behaviour of five wheat cultivars in terms of their veg etative growth, water use, phenological development, biomass accumulation a nd grain yield, under irrigated and water-stressed treatments. When looking at the vegetative growth, we pointed out that some cultivars were favoured by high tillering capacities and apparent vigorous root system, even in ir rigated treatments. Others developed adaptive capacities when submitted to drought, such as production of second generation of tillers after the water stress period or enhancement of the rooting front. Among yield components, it appeared that the two most favourable traits were a long grain filling period and/or a high harvest index. The investigated cultivars exhibited va rious strategies to achieve this. Some strategies correspond to a specific physiological functioning. This is the case of the durum wheat cultivar, wh ich showed a high level of late growth rate. Some other strategies correspo nd to adaptation of plants to limited water supply, such as developmental p lasticity. An important finding is that vegetative drought resistance did n ot infer the final grain yield. Moreover, luxuriant vegetative growth appea red to be a disadvantage for grain yield.