Drought

Water Freedom System

Survive Global Water Shortages

Get Instant Access

Productivity gains in water-limited environments involve many traits (Fig. 5.1a) that tend to show a complex interaction with a number of environmental factors. Patterns of rainfall distribution across target regions as well as between seasons are unpredictable and their variance is expected to increase as climate changes (Jarvis et al., Chapter 2, this volume).

Drought-prone environments also exhibit wide variation in other climatic characteristics, biotic stresses and edaphic factors including micronutrient deficiency (like zinc) and mineral toxicity (such as boron, salinity and sodicity). With a few exceptions, combination effects have received scant attention, despite the fact that crop productivity is especially vulnerable when more than one abiotic stress is experienced (Mittler, 2006). The main implication for breeding will be a need to develop genetic combinations of traits that are robust to inter- and intra-seasonal variation in drought intensity - as well as the other exacerbating factors mentioned - while ensuring that such culti-vars remain responsive to favourable years. Because understanding of the physiological

Photoprotection (WUE)

• Leaf • Pigments morphology - chlorophyll a:b

- wax - carotenoids

- posture/rolling • Antioxidants'

YIELD = WU x WUE x HI (drought stress)

Transpiration efficiency (WUE)

• WUE of leaf photosynthesis

- low l2/13C discrimination

• Spike photosynthesis

• Heat tolerant metabolism

- delayed senescence (stay-green)

Partitioning (HI)

• Floret fertility

- flowering synchrony (maize)

- panicle extrusion (rice)

• Stem carbohydrate storage and remobilization

• Grain harvest index

- Rht alleles

Water uptake (WU)

Photoprotection (WUE)

• Leaf • Pigments morphology - chlorophyll a:b

- wax - carotenoids

- posture/rolling • Antioxidants'

Partitioning (HI)

• Floret fertility

- flowering synchrony (maize)

- panicle extrusion (rice)

• Stem carbohydrate storage and remobilization

• Grain harvest index

- Rht alleles

Water uptake (WU)

Ground cover - protects soil moisture

- early vigour

Access to water by roots

- cool canopy

- osmotic adjustment

Photoprotection (RUE)

• Leaf • Pigments morphology - chlorophyll a:b

- wax - carotenoids

- posture/rolling • Antioxidants

Photoprotection (RUE)

• Leaf • Pigments morphology - chlorophyll a:b

- wax - carotenoids

- posture/rolling • Antioxidants

Partitioning (HI)

• Floret fertility

• Stem carbohydrate storage and remobilization

• Grain harvest index

- Rht alleles

Efficient metabolism (RUE)

• Starch synthase

• Dark respiration rate

- CO2 concentrating mechanism

- Rubisco activase

- Rubisco specificity

Efficient metabolism (RUE)

• Starch synthase

• Dark respiration rate

- CO2 concentrating mechanism

- Rubisco activase

- Rubisco specificity

Partitioning (HI)

• Floret fertility

• Stem carbohydrate storage and remobilization

• Grain harvest index

- Rht alleles

Light interception (LI)

• Rapid ground cover

Water uptake (RUE)

• Access to water by roots

- vascular system to match evaporative demand

Water uptake (RUE)

• Access to water by roots

- vascular system to match evaporative demand

Fig. 5.1. Conceptual models for traits associated with adaptation to: (a) moisture-stressed environments grouped according to main drivers of yield under drought (yield = water uptake (WU) x water-use efficiency (WUE) x harvest index (HI) as defined by Passioura, 1977); (b) hot-irrigated environments grouped according to main drivers of yield without water limitation (yield = light interception (LI) x radiation-use efficiency (RUE) x harvest index (HI)). Spike photosynthsis may have higher WUE associated with recycling of respiratory CO2. Other traits presented are discussed in the text (and references therein); however, the list is not exhaustive, and while some of the traits have been successfully combined to achieve cumulative gene action for drought adaptation in wheat (Reynolds et al, 2009), traits cannot be assumed to be additive, or necessarily of equal value across a range of target environments because trait x environment interaction can be expected.

Fig. 5.1. Conceptual models for traits associated with adaptation to: (a) moisture-stressed environments grouped according to main drivers of yield under drought (yield = water uptake (WU) x water-use efficiency (WUE) x harvest index (HI) as defined by Passioura, 1977); (b) hot-irrigated environments grouped according to main drivers of yield without water limitation (yield = light interception (LI) x radiation-use efficiency (RUE) x harvest index (HI)). Spike photosynthsis may have higher WUE associated with recycling of respiratory CO2. Other traits presented are discussed in the text (and references therein); however, the list is not exhaustive, and while some of the traits have been successfully combined to achieve cumulative gene action for drought adaptation in wheat (Reynolds et al, 2009), traits cannot be assumed to be additive, or necessarily of equal value across a range of target environments because trait x environment interaction can be expected.

and genetic basis of adaptation to water-limited environments is incomplete, breeding progress will require empirical approaches such as multi-location testing (Braun et al., Chapter 7, this volume).

However, detailed characterization of target environments can help with the interpretation of adaptive responses, as well as germplasm deployment. Recent developments in the area of geographical information systems (GIS) make it more feasible than in the past to characterize target environments. For example, with GIS software, weather data can be interpolated across regions that may encompass relatively few weather stations, while databases permit additional information on soil properties and cropping systems to be entered and readily accessed (Hodson and White, Chapter 13, this volume). Such a database can be further enhanced by the calculation of stress indices (via crop simulation models) and summaries of weather variables coinciding with different stages of growth. When combined with phenotypic data from field trials, such indices and summaries of stress patterns can be applied in advanced statistical analyses to indicate the traits and genetic backgrounds associated with adaptation to specific environmental factors (see Crossa et al., Chapter 14, this volume). Molecular information can also be used to help explain genetic bases of genotype x environment interactions (Boer et al., 2007).

Was this article helpful?

0 0
Trash To Cash

Trash To Cash

This book will surely change your life due to the fact that after reading this book and following through with the steps that are laid out for you in a clear and concise form you will be earning as much as several thousand extra dollars a month,  as you can see by the cover of the book we will be discussing how you can make cash for what is considered trash by many people, these are items that have value to many people that can be sold and help people who need these items most.

Get My Free Ebook


Post a comment