Early Maturity in Wheat for Adaptation to High Temperature Stress
Abstract High temperatures pose a serious threat to productivity maintenance and enhancement in wheat. A strategy that has come forward in the CIMMYT breeding program is the development of high yielding early maturing lines that are adapted to high temperature stress especially for South Asia. The high temperature stress in South Asia is classified into terminal high temperature stress where the high temperatures stress occurs during grain filling stages, and continual high temperature stress, where high temperature persists across the wheat growing season. The new high yielding, early maturing and heat tolerant CIMMYT wheat lines were evaluated for grain yield and adaptation across diverse locations in South Asia and Mexico. Trials were conducted for three consecutive years 2009–2010, 2010–2011, and 2011–2012. The results suggest that CIMMYT lines with high yields and early maturity, selected under normal and late sown condition in Cd. Obregon, Mexico, have the potential to adapt and outperform normal maturing check varieties under terminal and continual high temperature stress in South Asia. Earliness favored the plants to escape terminal high temperature stress and also promoted an efficient utilization of available resources under continual high temperature stress to achieve higher grain yield. The simultaneous enhancement of grain yield potential and heat stress tolerance of early maturing wheat lines is likely to be beneficial in enhancing productivity under high temperature stress across South Asia.
Keywords Early maturity • Heat stress • Heat tolerance • South Asia • Wheat
Temperature Stress and Wheat Production
Increasing variation in climate across the globe has become a serious concern to crop production. Wheat, a temperate crop, prefers a cooler climate for growth and reproduction. High temperatures during crop growth and grain filling stages are a major concern to its production. South Asia, comprising of India, Nepal, Pakistan and Bangladesh is one of the major wheat producing and consuming area in the world. This region suffers significant losses each year due to high temperature stress (Kumar et al. 2013). A recent study by World Bank predicts that a 2 °C rise in world average temperature may lead to extreme heat conditions in South Asia. With estimated losses of 6–20 % per degree rise in temperatures in South Asia, (Mondal et al. 2013; Lobell et al. 2008) high temperatures are a serious threat to wheat production.
The wheat producing areas in South Asia are grouped into mega environments (ME) based on the classification system developed by CIMMYT (Braun et al. 1992). ME1 is defined as the optimally irrigated highly productive environment where wheat grows in cool temperatures but suffers from terminal high temperature stress, such as North Western Gangetic Plain. ME5 is a rainfed, warm regions, where continuous high temperature stress is a major concern and comprises of eastern Gangetic plain, peninsular India, plains of Nepal and Bangladesh. ME1 has a cooler climate during crop growth which gradually increases during reproductive and grain filling stages in March and April. ME5 has warmer temperatures across the crop season. Similar trends are seen for maximum and minimum temperatures for ME1 and ME5 locations in South Asia (Fig. 26.1). Thus it is imperative to develop wheat varieties that are high yielding as well as tolerant to high temperature stress.