Abstract
Crop plants grow, and then, they allocate resources to different structures, including seeds and fruits, which represent yield in most crops. We define the yield stability of a genotype as its ability to reduce the effects of temporal variation in resources and conditions on yield production, and we argue that yield stability can be understood in terms of two processes: (1) crop survival and growth (biomass production): the ability of the crop plants to survive and produce biomass under the range of conditions to which it is exposed and (2) the pattern of allocation of this biomass to yield across this range of conditions. Plant breeders and crop physiologists have focused on (1), but much less attention has been paid to (2). We hypothesize that (2) is primarily the result of reproductive allometry: the quantitative relationship between vegetative and reproductive biomass. Ecological theory and the allometric models we present predict a tradeoff between (a) the ability of a genotype to produce yield over a wide variety of conditions and (b) its ability to produce very high yields under optimal or near-optimal conditions. We reanalyze the data from two recent studies, and the results are consistent with this hypothesis. Yield stability in crops corresponds to bet-hedging in evolutionary ecological theory. It is the most appropriate strategy for smallholder farmers in developing countries, a group that comprises most of the farmers in the world. Researchers and crop breeders need to rethink their objectives if they want to develop optimal varieties for these farmers.
Highlights
One of the most important concepts in agronomy is yield stability, but there is not complete agreement on a definition of this important concept, whether it should be applied to geographical as well as temporal variability, and how to measure it statistically (Eberhart and Russell, 1966; Lin et al, 1986; Cleveland, 2001)
We define the yield stability of a genotype as its ability to reduce the effects of temporal variation in resources and conditions on yield production, and we argue that yield stability can be understood in terms of two processes: (1) crop survival and growth: the ability of the crop plants to survive and produce biomass under the range of conditions to which it is exposed and (2) the pattern of allocation of this biomass to yield across this range of conditions
We argue that yield stability can be understood and analyzed in terms of two processes: plant growth and allometric allocation
Summary
One of the most important concepts in agronomy is yield stability, but there is not complete agreement on a definition of this important concept, whether it should be applied to geographical as well as temporal variability, and how to measure it statistically (Eberhart and Russell, 1966; Lin et al, 1986; Cleveland, 2001). The plant does not always achieve this potential reproductive output because external factors, such as frost, pests, or disease can intervene and prevent this This allometric approach is especially relevant to annual crops, which generally follow the optimal reproductive allocation strategy first described by Cohen (1968): Plants allocate all resources to growth early in the season, and at some point, they switch to investing all resources into reproduction (yield formation). A review of R–V relationships in plants (Weiner et al, 2009) found two common patterns: A linear relationship, usually with a positive X-intercept, representing the minimum size for reproduction (Figure 1A), or a classical allometric relationship of the form Y = βXα, usually plotted and analyzed as log Y = log β + α log X to make it linear, but shown here on a linear scale (Figure 1B). There was a significant positive relationship between variation in yield and the allometric slope (exponent; Figure 3)
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