INTRODUCTION CHAPTER 1

Transcription

1 INTRODUCTION CHAPTER 1

2 INTRODUCTION Globally, maize (Zea mays L., 2n= 10) is the number one cereal crop in the world (FAOSTAT, 2011). Being a C 4 crop, it is most versatilee in terms of wide adaptability and highh potential productivity, which is grown over a range of environmental conditions around the world. Diversity of the environments under which maize is grown is unmatched with any other crop. It is grown up to 58 o N in Canada and the Russian Federation to up to 40 o S in Chile and Argentina, and from below sea level in Caspian plain up to 4000 meters in the Andean mountains (Goldworthy, 1974). Globally, maize is classified into three distinct agro-ecologies, depending on the latitude and environment, viz tropical maize, grown between the equator and 30 o N and 30 o S, sub-tropical maize, grown between 30 o and 34 o latitudes and temperate maize, grown in cooler climate beyond 34 o N and 34 o S. Tropical maize is further classified into three sub-classes, i.e. lowland, mid-altitude and highland tropical maize (Dowswell et al., 1996). A large proportion (over 100 million hectare) of the total world maize is grown in developing countries in Asia, Latin America and Africa (Figure 1). Asia 28% America 54% Euroupe 11% Africa 7% Oceania 0% Figure 1. Maize Production share by region (FAOSTAT 2010). Out of this, about 80% of the maize areas come under lowland tropical, mid-altitude and sub-tropical environment. More than 90% of the maize produced in industrialized countries is grown in temperate production environments. This stands in sharp 1 Introduction...

3 contrast to the developing world, where only about 20% of the maize is grown in temperate environments, most of which are found in China and Argentina, and the rest is grown under tropical ecology. According to International Grain Council report 2012, during , maize cultivated in 167 million tonnes hectares (ha) leading to a production of 860 million tonnes globally. During 2011, global maize area and production reached a historical high of 167 million ha and 860 million tonnes, which is 21 per cent and 43 percent, increase in area and production, respectively compared to USA, China, Brazil, Mexico, Argentina and India together accounts for 75 percent of the world maize production. 4 3 % Annual growth rate Africa America Asia Europe Oceania Area Harvested Production Yield 1 2 Figure 2. Per cent annual growth rate in areaa harvested, production and yield of maize in different regions (FAOSTATT 2010). According to FAO statistics for the year 2010, Asian maize production touched upon mt with an average of 53.7 mha and average productivity of 4.8 t ha - 1 (Figure 2). According to recent statistics of the Ministry of Agriculture, Govt. of India, a total of mt maize was produced from mha area harvested during Yet, to maintain self sufficiency, maize production in India needs to grow annually by 6%, to reach to the figure of 26.2 million tons in 2020 (Maize Report, 2008, The Associated Chambers of Commerce and Industry in India). Given the limited opportunities for increasing maize area, future output growth must come from 2 Introduction...

4 expanding maize areas in marginal and less favourable environments, and from intensifying the production on current maize land. In India, maize has a pride of place in food grain scenario of the country, which contributes more than 8% in the national food basket. In addition to staple food for human being (25%) and quality feed for poultry (49%) and animals (12%), it serves as a basic raw material for the industry (12%) for production of starch for textile, pharmaceutical, cosmetic industries, high quality corn oil, protein, alcoholic beverages, food sweeteners etc. It is used as an ingredient in more than 3000 products. Maize is also grown for other purposes such as QPM (Qualitative protein maize) for human nutrition, alleviation of malnutrition and quality feed for poultry and animals, baby corn and sweet corn for vegetable and other table purposes, including different value-added products. Increasing demand from poultry sector is likely to substantially hike maize consumption to go over 30 million tonnes by 2020 due to which its production has started growing at faster pace since maize is key ingredient in poultry ration [Maize Report 2008 of The Associated Chambers of Commerce and Industry of India (ASSOCHAM)]. Area under maize was static at 6.0 million ha since 1970, but has shown increasing trend during last decade and presently it is grown on 7.89 mha (about 4.5% of the gross cropped area). In the Vision 2025 of the Directorate of Maize Research, it is projected that another 3.2 mha will be added to the current maize area, by replacing upland rice in the Eastern & Central Indian states, winter rice in South India, and from classical rice-wheat system in Indo-Gangetic plains(igp). However, most of these expansions are expected in the winter season maize, which has a limited scope (presently represent about 13.2% of total maize acreage in India) due to low temperature during winter season in most parts of the country, except in South India. Maize has many divergent types, and therefore, is grown over a wide range of climatic conditions. The bulk of maize is produced between o latitude around the world, and relatively little is grown at latitude higher than 47 o. Maize is a warm humid weather (not hot dry) crop and has a cold limit. Daytime temperature, solar radiation and relative humidity are the factors significantly determining effectiveness of the rainfall a maize crop has received. When temperature and solar radiation are high and relative humidity is low, more water evaporates from soil and from maize 3 Introduction...

5 leaves (high evapo-transpiration). Maize can survive brief exposures to adverse temperatures, such as temperatures ranging from near 0 o C to over 40 o C. However, the optimal temperatures for growth vary between day and night, as well as over the entire growing season for example, during day-light hours, the optimal ranges between o C, while night temperatures range between o C. Temperature above 35 o C for a long period is considered to be unfavorable for maize and over 40 o C may cause irreversible damage to maize crop. High-temperature stress during ear formation, reproduction and grain filling is normally detrimental to yield. Under rainfed conditions, maize usually begins to stress when air temperatures exceed 35 o C during the tasseling, silking and early grain filling stages. Global climate change effects are likely to increase the incidence of heat and drought in many established maize growing areas. The impact of climate change on agricultural production will be greatest in the tropics and sub-tropics, with South Asia projected to be particularly vulnerable from multiple stresses and low adaptive capacity (IPCC, 2007; Rodell et al., 2009; Niyogi et al., 2010; ADB, 2009). Many climate modeling studies suggest that high day- and night-time temperatures will become more common in the future and may represent a tremendous environmental hurdle to global food production (Lobell et al., 2011a; Stebbins, 2011; Cairns et al., 2012). Maize is particularly vulnerable to the reproductive stage heat stress (Cairns et al., 2012). A recent study showed that each degree day spent above 30 C reduced the final yield of maize by 1% under favorable growing conditions and 1.7% under drought stressed environments (Lobell et al., 2011b). A record drop in maize production due to heat waves have already been reported globally (Ciais et al., 2005; Van der Velde et al., 2010). The US Environmental Protection Agency (EPA, 1998) predicted decrease in maize yields under conditions of future climatic change of 4-42% due to temperatures rising above the range of tolerance for the maize crops. In maize, the extended period of high temperature during grain filling affects kernel growth, composition, and the starch, protein and oil contents (Wilhelm et al., 1999). Increased heat stress is expected for maize crops in Asian tropics. Maize yields may drop by 17%, wheat by 12%, and rice by 10% in irrigated areas in South Asia because of climate change induced heat and water stress, if current trends persist by 2050 (IFPRI, 2009). This will be compounded by heat stress, with temperatures expected to increase by an average of 2 C across Asia, with an increase in annual precipitation 4 Introduction...

6 and extreme weather events (IPCC, 2007; ADB, 2009; IFPRI, 2009). Mean temperature of India will rise at a greater rate than the global mean, which is expected to rise by 2-3 o C by 2050 and this will double the number of heat-shock days during the same periods. Studies have indicated that each degree temperature rise will increase irrigation water requirements for maize and other crops by 2% (Zaidi and Singh, 2005). Figure 3. Heat stress in South East Asia. (Source: D. Hodson. CIMMYT GIS unit) During , maize production increased annually by 6% in Asia, as compared to 5% in Latin America, and 2.3% in sub-saharan Africa (FAOSTAT, 2010). However, between now and 2050, the demand for maize in the developing world will double, and by 2025 maize will become the crop with the highest production in the developing world (Rosegrant et al., 2009). This has particular implications to Asia, where an array of factors contributing to a sharp increase in maize demand, including growth rate in per capita GDP (gross domestic product), changing diets, and a significant rise in feed use that is driven largely by rapidly growing poultry sector (Prasanna, 2011; Shiferaw et al., 2011). Although demand for maize is significantly rising in South Asia, over 80 per cent of maize growing area in this region is rain-fed and highly vulnerable to extreme weather events (Prasanna, 2011). Therefore, the major challenge is to keep pace with unprecedented increase in maize demand by 5 Introduction...

7 enhancing the overall productivity and production, and at the same time, adapt and mitigate the climate change effects such as global warming. Since opportunities are limited for further expansion of maize area, future increases in maize supply to meet future food, feed and other demands, will have to be achieved through commercialization and intensification of current maize-production systems, including expansion of maize area in Spring season, where crop is prone to face severe heat stress. Not only during Spring season, heat stress has emerged as a major challenge for main season crop, i.e. Kharif maize. Though, studies have been done on heat stress tolerance in maize, largely on temperate maize (Wilhelm et al., 1999; Monjardino et al., 2005), information on heat stress tolerance in tropical maize is very meagre and fragmentary. Rinco-Tuexi et al. (2006) found that heat stress significantly reduced biomass accumulation, grain yield, grain number per ear and harvest index, except test weight. Wilhelm et al. (1999) determined the effect of an extended period of high temperature during grain filling and found that heat stress lengthened the duration of grain filling but an over compensatory reduction in kernel growth rate resulted in an average kernel dry weight loss by 7%. Breeding methods can be utilised to improve genetic improvement for heat tolerance in tropical maize. Several research groups have attempted to address this issue, particularly focusing on flowering stage heat-stress tolerance. Shabala et al. (1996) suggested that measurement of leaf temperature kinetics is a convenient procedure for estimating plants adaptive ability to high temperatures. Karim et al. (2000) suggested that LER and Pn measured at high temperature conditions can be regarded as good indicators of thermo-tolerance for tropical maize at the seedling stage. Yu et al. (2002) determined physiological indices of leaf near cob (LNC) at different times after silking at high temperature. Correlation analysis indicated a significant positive correlation between leaf dry weight near cob at silking stage and crude protein content in kernels. While studying the response of male flowering of temperate maize hybrids under heat stress. Schoper et al. (1987a) found that anther emergence on the central tassel spike decreases differentially among the hybrids at a high temperature (38 o C). However, anther emergence and pollen viability did not always have similar response to high temperature, and therefore, should be studied as 6 Introduction...

8 separate traits for heat tolerance. Frova et al. (1995) suggested that pollen viability could serve as a trait in selection to improve at least some gametophytic and sporophytic components for thermo-tolerance in maize. Under the Cereal System Initiative for South Asia (CSISA) project, systematic efforts to develop tropical maize cultivars with high temperature tolerance have only recently been initiated. Initial experiments undertaken by the CIMMYT-Asia team to identify heat stress tolerant tropical maize lines among the elite, drought tolerant (DT) maize germplasm developed in Mexico, Asia and Africa revealed: (a) high vulnerability of most of the tropical maize germplasm, including commercial cultivars to reproductive stage heat stress; and (b) poor correlation between drought and heat tolerance, indicating that physiological mechanisms that contribute to heat stress tolerance in maize may be different from those that contribute to drought tolerance (Zaidi and Cairns, 2011; Cairns et al., 2012). With-in the CSISA project the present study focussed on identification of most susceptible growth stage(s), secondary traits associated with heat stress tolerance in tropical maize, and identification of available genotypic variable among Asia adapted tropical maize germplasm for heat stress tolerance. The present study is planned with the following major objectives: OBJECTIVES 1. To assess the stage susceptibility for heat stress tolerance in tropical maize. 2. To identify the available genotypic variability for heat stress tolerance in tropical maize. 3. To identify the secondary traits associated with heat stress tolerance in tropical maize. 4. To develop the screening protocol for identifying genotypic variability for heat tolerance in tropical maize. 7 Introduction...