Analysis of genetic and physiological factors governing water deficit and chilling stress effects on yield penalty in model cereal species

Developing crops with abiotic stress tolerance has moved ahead for many years by targeting the improvement of what could be considered survival traits. While important to plant growth, these traits have seldom proven to be good biological markers for the selection of lower yield penalty under abiotic stress. A major reason could be that these traits usually have a wide reaction norm while that of the complex trait that is being selected for, i.e. reproduction, typically does not. Reproductive transition requires that the intense cellular signaling that is characteristic of this stage of development not be perturbed. The cell differentiation processes that lead to floral organ formation are on very strict spatial and temporal programs. Therefore, improving the yield retention of food and fiber crops, while under reproductive stage stress, will require a better understanding of the physical and molecular processes that are tightly intertwined during reproductive differentiation. Therefore, current and future studies in food crop improvement should focus on characterizing the effects of suboptimal environments on the physical structures that undergird fruit formation (reproductive architecture) and on the molecular signals governing these processes. The literature on these types of studies is lacking but some researchers are realizing that the next generation of crops will have to be built (ideotype breeding) purposefully for reproductive resilience and not necessarily for survival. Our studies in rice and sorghum found that the reproductive stage of growth was critical for assessing tolerance to abiotic stress (chilling and water-deficit) with respect to yield penalty. Specifically, in rice, our findings showed that a gene network anchored by the DECUSSATE gene was pivotal for initiation of flowering (beginning at booting) before source strength became severely limited. In sorghum, our findings indicated that the panicle differentiation stage was sensitive to chilling stress with the later stages (SB1 and SB4) being the most sensitive as shown by the large grain yield penalties. These later stages represented differentiation of spikelet, spikelet pair, and floral meristems. Together, these case studies revealed the importance of reproductive stage resilience to abiotic stressors for lowering associated yield penalties.

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