Productivity of Hybrid Rice: I. Vulnerability to Water Stress of Reproductive Development and Inhibition of RuBisCO Enzyme in Upper Leaves as Major Constraints to Yield

Abstract

Producing more rice (Oryza sativa L.) with less water is a formidable challenge for the food, economic, social, and water security. To achieve this, the knowledge of how plant water stress is transduced into plant performance is necessary. The objective of this research was to investigate in hybrid rice the impact of soil water deficit, especially on reproductive growth and photosynthetic activities that lead to the ultimate harvestable product—grains. The early reproductive growth period, encompassing tetrad-formation stage of meiosis (i.e., about 10–15 d prior to heading), was found to be the most sensitive and critical to water deficit resulting in up to 59% grain sterility that caused similar magnitude of yield reduction. As the grain formation progressed further, the early period of grain-filling was found to be more vulnerable to water stress than the late-milk stages. The behavior of upper leaves appeared to be conspicuously at variance under water stress in that the survival of flag leaf dropped from 81% at booting to 58% at heading, whereas in contrast, the second leaf registered the survival of only 30% at booting, which rose to 66% at heading stage. The drought-affected reduction in grain weight was attributable to the increased diffusive resistance of upper leaves during early hours of water stress (i.e., 2.5 s/cm in control plants), rose to 12 s/cm in stressed plants, restricting photosynthesis followed by 50%–70% decrease in the activities of carboxylating enzyme ribulose 1, 5-bisphosphate carboxylase/oxygenase (RuBisCO), and enhanced chlorophyll degradation during progressive water stress. Apparently, depending upon the time and intensity of the onset of water shortage, the grain number and its size both are likely to be affected adversely, leading to diminished productivity of hybrid rice. The present findings highlight the possibility of genetically engineering the variants of hybrid and transgenic rice having increased activities of RuBisCO enzyme for efficient photosynthesis under water stress. Further, from the practical point of view, an unplanned stress at flowering caused by a very high evaporative demand due to relatively dry or hot wind and/or inadequate irrigation may lead to high yield reductions. Water-management practices may, therefore, be directed and attempted accordingly to avoid losses in rice yield and to protect the plant from water stress during drought.

Keywords:

• desiccation injury
• hybrid rice
• leaf diffusive resistance
• meiosis
• photosynthesis
• relative water content
• ribulose 1
• 5-bisphosphate carboxylase/oxygenase (RuBisCO)
• water potential
• water scarcity

The authors sincerely thank Dr. S. P. Giri and Dr. M. K. Sharma of Narendra Deva University of Agriculture & Technology, Faizabad (U.P.), India, for supplying seeds of hybrid rice cultivar ‘NDRH-2’ used in these studies and conducting the statistical analysis of the data, respectively. The preparation of graphs by Mr. Raj Kumar, Lanka, Varanasi is gratefully acknowledged.