Molecular and physiological approaches to maize improvement for drought tolerance

Abstract

Average maize yields have increased steadily over the years in the USA and yet the variations in harvestable yield have also markedly increased. Much of the increase in yield variability can be attributed to (1) varying environmental stress conditions; (2) improved nitrogen inputs and better weed control; and (3) continuing sensitivity of different maize lines to the variation in input supply, especially rainfall. Drought stress alone can account for a significant percentage of average yield losses. Yet despite variable environments, new commercially available maize hybrids continue to be produced each year with ever-increasing harvestable yield. Since many factors contribute to high plant performance under water deficits, efforts are being made to elucidate the nature of water-stress tolerance in an attempt to improve maize hybrids further. Such factors include better partitioning of biomass to the developing ear resulting in faster spikelet growth and improved reproductive success. An emphasis on faster spikelet growth rate may result in a reduction in the number of spikelets formed on the ear that facilitates overall seed set by reducing water and carbon constraints per spikelet. To understand the molecular mechanisms for drought tolerance in improved maize lines better, a variety of genomic tools are being used. Newer molecular markers and comprehensive gene expression profiling methods provide opportunities to direct the continued breeding of genotypes that provide stable grain yield under widely varied environmental conditions.

Identification of Quantitative Trait Loci That Regulate Arabidopsis Root System Size and Plasticity

“…Assessing the benefits of RSS and developmental plasticity: Having an intrinsically large and deep root system is thought to be one of the most important factors allowing crop plants to survive drought conditions (Price and Courtois 1999;Bruce et al 2002;Tuberosa et al 2003). Other studies have indicated that the ability to regulate root system morphology in response to environmental cues can give plants a selective advantage (reviewed in Malamy 2005).…”

Differential expression of dehydrin genes in hull-less barley (Hordeum vulgare ssp. vulgare) depending on duration of dehydration stress

“…These responses are not only dependent on the severity and duration of the water deficit, but also on the developmental stage and morphological/anatomical parameter of the plants (Ludlow and Muchow 1990;Smith and Griffiths 1993). The interface between the expression of stress responsive genes and plant stress is critical for translating molecular genetics into advances in crop production under stress conditions (Bruce et al 2002).…”

Analysis of Physio-Genetic Traits for Drought Tolerance in Maize (Zea mays L.)

“…Generally however, the slow growth of the ear prior to silking is reflected in slow growth and small size of ovules, weak silk growth and a failure to set grain even when pollinated with adequate amounts of fresh pollen. The numbers of kernels set filled under drought stress accounts for most of the variation in maize grain yield under drought (Bruce et al, 2002), and directly affects HI. Highly significant per se performance for harvest index was reported in the lines L 1 , L 4 and L 5 whereas among the testers T 1 recorded significant value when compared with their respective mean.…”