Ecophysiological Yield Components In Wheat Cultivars Under Variable Phosphorus Availability
Abstract
Effects of P deficiency and interactions Cultivar x P available , on wheat yield and ecophysiological components were analysed, considering that the grain number m-2 is the product of the length of spike growth period, crop growth rate during this phase, the proportion of growth for spikes (partitioning) and spike fertility (grain number produced per unit of spike dry weight). Four cultivars with different strateg y to generate yield (i.e. combinations of ecophysiological yield components) were compared with and without P fertilization, during two years in Azul, Buenos Aires, Argentina. The soil was moderately P deficient (7 -9 mg P kg-1 soil) and P fertilization tre atments (50 kg P ha-1) were established at sowing. P deficiencies affected yield and most of its components, the exceptions were: partitioning to spike, spike growth period and radiation use efficiency. The interaction Cultivar x P fertilization was not si gnificant in all cases. The lack of interaction between cultivar and P level suggest that improvements in any crop physiological component will express in both, moderately deficiencies or high P environment.
Keywords
Download Options
Introduction
The Phosphorus (P) is one of the most limiting macronutrients for crop production (Ziadi et al., 2013) and today, in many areas of the world it is one of the highest-cost inputs used by farmers to achieve profitable crop yields (Ryan et al., 2012). Under current production conditions there is concern about making a more rational use of P fertilizer application (Ryan et al., 2012). The development of P-efficient crop varieties that can grow and yield better with low P supply is a key in improving crop production. However, current conventional breeding strategies are mainly implemented through yield selection under high fertility soils. Wissuwa et al. (2009) concluded that modern varieties have often been selected under high nutrient input conditions in order to obtain high yield. These varieties may not be the most suitable for conditions of low P supply.
On the other hand, wheat cultivars have different strategies (i.e. combinations of yield crop physiological components) to generate yield. The differences between cultivars would be attributed to a grain number m-2 (GN) and/or grain weight. According to Fischer (2007) the GN is a direct function of spike dry weight (SDW) and spike fertility (SF). The SDW is defined as the product of spike growth period (SGP) and the spike growth rate (SGR). The spike growth rate is defined by product of the crop growth rate (CGR) and the proportion assigned to spike (partitioning). Finally, the CGR is the product between the intercepted solar radiation and the radiation use efficiency. Differences between cultivars have been found in: (1) partitioning (Fischer & Stockman, 1986), (2) spike fertility (Abbate et al., 1998; Lázaro & Abbate, 2012), (3) CGR (Montenegro, 2001), (4) RUE (Shearman et al., 2005) and (5) grain weight (Sayre et al., 1997). However, the relative impact that P deficiencies, has on these yield components in different genotypes is not well known. Various authors (Rosa & Camargo, 1991; Manske et al., 2000; Egle et al., 1999 and Manske et al., 2001) found differences in the absorption and utilization of P using different cultivars, but they did not explore the yield components in detail. Gutheim et al. (2001) in the Pampas region of Argentina and Batten et al. (1984) in Australia analyzed the responses to P fertilization of wheat genotypes and did not find genotype x P level fertilization interaction for yield.
These authors observed that modern semi-dwarf cultivars had higher yield in both, high and low P, and that these increases were due to a greater GN. However, these studies do not show whether this behaviour is due to a high stability of all GN ecophysiological components or only to some strong interactions cultivar x P availability. On the other hand, Lázaro et al. (2010) and Sandaña & Pinochet (2011) studied the effects of P deficiencies in ecophysiological components but they used only one cultivar. Previous investigations have not analysed in depth whether the effects of P deficiencies differ between wheat cultivars that have different strategies (combinations of yield crop physiological components) to generate yield. Knowing the stability of physiological attributes to different stress situations, such as P deficiency, can contribute to germplasm improvement, since that can help choose physiological attributes that have an advantage in cropping situations to be transferred to top lines.
This study evaluated whether cultivars with different strategies to generate yield respond similarly to P status, i.e. if yield and crop physiological components are stable to changes in P availability. It should be clarified that stability refers to a dynamic agronomic concept, where the adaptability of a genotype depends, largely on a linear response to environmental variables (Flores et al. 1998). Therefore, a cultivar is stable if its yield is parallel, respect at mean yields of all cultivars in a range of environments of availability P.
Conclusion
Phosphorus deficiencies operated in similar way on cultivars with different strategies to generate yield. Responses to P deficiencies are negative for PARi, CGR, SGR, SDW and GN, while the other components remained unchanged (RUE, partitioning, duration of SGP and grain w eight) and even SF increased slightly. All variables analyzed (yield, weight per grain, GN and components) are very stable among cultivars under contrasting P availability, since the interactions cultivar x P were not significant, moreover none of the interactions involving P was important. Only interaction cultivar x year was significant in some few cases (GN, SGP, PARi) and stability between cultivars was different because they responded differently to year effects but not to P effects. The results support the idea that breeding programs in high or low P availability can be developed, and that any ecophysiological component can be improved under any condition since cultivar x P interactions were low in all components .
