Introductory Chapter: Advancements in Wheat Research

1. Introduction

Wheat is the most common food crop we grow. In 2018, it was grown on 214 million hectares, which is approximately 30% of the total land area sown to cereal crops. With an average yield of about 3.4 tonnes per hectare, 734 million tonnes of wheat were produced in 2018 [1]. Wheat’s role in human nutrition is another way to show how important it is. Approximately 20% of our protein intake and 20% of our carbohydrate intake come from wheat. Also, wheat represents our most traded cereal [2]. In 2018, over 118 mt of wheat was exported, which was 40% of all cereal exports. Australia, which is a major wheat producer, has average yields of less than 2 tons/ha, whereas yields in the UK are normally somewhere around 7 tons/ha and 8 tons/ha and are well more than 10 tons/ha in several zones [3]. Early in 2020, New Zealand had the maximum wheat yield ever observed: 17.4 t/ha. In many other places, it is hard to get more than 1 t/ha. The wide range of wheat yields shows how different the places where wheat is grown [4]. Due to variable environments, breeding programs usually concentrate on specific target areas. Breeding of wheat has been done mostly by the general public around the world, with help from governmental bodies or farmer groups. However, this has gradually evolved as profit incentive in breeding has grown, particularly in the EU and countries like Australia in which there is a clear way to make money from the benefits of improved varieties [5].

2. Recent developments in wheat for drought stress tolerance

Early on, the breeders realized that making wheat mature at right time for growing season was the most important adaptation trait that had to do with yield. The most important thing that affects yield, or more accurately, yield potential, is how much water is available. To get the most out of the crop, breeders look for patterns that mature and develop throughout the growth period. There is usually, although not always a proper relationship between both grain yield and biomass, growers try to time the development of the plant to coincide with when there is enough water. In cool climates, planting in the fall gives plants time to grow roots before the cold weather of winter, and then they grow quickly in the spring and early summer. If the winters are too cold and there is a chance of freezing damage, growers need to select varieties that can be planted after the danger has receded. They should also endeavor to extend the planting season as late as possible before drought and heat stress slow growth. This is different from hot season crops, whose growing season is cut short by killing frosts in temperate zones [6]. If there is enough irrigation water, the season can be extended into the summer. If there is not enough fertigation water, early maturing lines are needed. In Mediterranean-type climates, where it rains in the winter but is hot and dry in the summer, biomass can be built by planting in the fall and letting the plants grow over the winter. However, the plants need to be mature early enough to be harvested before every dry season.

It is well known how important it is to match maturity to the growing season, and so this attribute is usually well organized in existing projects by using genes and loci for earliness, vernalization, and photoperiod response. There might still be ways to change the various growth stages to better match the environment, but generally, the way elite varieties grow and develop makes sure that the crop could indeed take benefit of the times when there is enough water and then flower and have full seed before the end of the season. Even though adjusting development to the atmosphere has been important for increasing the yield of wheat, complications stem during unusual stages when the growth trajectory of elite varieties does not match the patterns of rainfall and temperature [7]. This problem is getting worse because the weather is becoming more unpredictable. Farmers know that some periods will be severe and that they may take a loss. However, good years can make up for this. The fact that bad years are happening more and more often is a big problem, and farmers are looking for varieties that will do well in good years but cause less damage in bad ones. Breeders try to solve this problem by looking for ways to use water more efficiently and reduce the effects of things that might make yield stability less stable.

3. Recent developments in wheat for high temperature tolerance

Wheat production is in danger from many environmental factors. For example, the last 10 years (2010–2019) were the warmest on record, and the steady temperature rise is thought to have caused many changes in the way the climate system works [8]. In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change said that by 2050, the average global temperature could rise by 2–5°C, or even more, and rain trends are likely to become less consistent [9]. “High confidence” says that these changes, like more frequent extreme events, are having an effect on food security. Food insecurity has effects that reach far and wide. Hagel, who used to be the head of the US Department of Defense, said that changes in climate “can add a lot to the problems of global instability, hunger, poverty, and war.” In 2018, climate was found to be a cause of “crisis-level acute food insecurity” in 26 of the 33 countries where it happened [10]. Since Russia, India, France, China, and the United States produce 50% of the world’s wheat, “any weather shock or external shock to production in these countries will have an immediate effect on global prices and price volatility.” Improving how efficiently food is made is seen as a key way to make food production more sustainable in the future. About half of the world’s wheat is affected by excessive heat, and 20 million ha or more often have too little water [11].

Models show that there is a chance that crops in global “breadbaskets” could fail at the same time because of heat or drought, and variation in rainfall and temperature (including drought) are indeed blamed for 40% of the variation in the production of wheat from 1 year to the next. By the end of this century, severe water shortages are predicted in approximately 60% of the world’s cereal growing regions, and each 1°C temperature rise is expected to decrease yield by a mean of 6% [12]. A few other research and modeling research shows that increasing the level of CO₂ in the atmosphere at least to some extent counteract the harmful effects of drought and heat stress, but the data are not constant [13]. Also, the models do not take into account the harmful effects of rising night-time temperatures, thermal shocks, unsteady rain patterns, and dietary components, which are not helped by higher CO₂ levels.

4. Recent developments in wheat for quality improvement

Wheat can be used for many different things, and each of these needs different qualities. The most important is GPC (grain protein content), which is a key factor how well a grain makes bread and pasta. Farmers usually get more money for grains that are high in protein. Content of protein is the most important quality trait, but the type of grain protein and a number of other qualities, such as grain hardness, also affect how the grain will be used [14]. There are several ways that heat and drought stress can change the quality. Extreme stress can stop starch from forming, which makes the grain smaller. Even mild stress can change the balance between gliadin and glutenin proteins, which changes the quality of the grain. But heat and drought have the most important effect on quality through their relationship to GPC. GPC is a complicated trait that is strongly affected by the environment but also has a clear genetic part. Breeders often choose plants based on how much protein they have since this is such a big part of how much the grain is worth [15]. Not surprisingly, the most important environmental factor that affects GPC is the amount of N fertilizer applied, but there is also a negative relationship between GCP and yield in many environments. GPD stands for “grain protein deviation,” which is a way that varieties can be different from the relationship between yield and GPC [16]. It has been suggested that breeders could use GPD as a selection target to get around or lessen the effect of the negative relationship. In a study done in Australia, the negative correlation was found to be the strongest in low-yielding environments that are stressed by heat and drought. Breeders in Australia seem to have chosen high-protein genotypes that do well in low-yield environments based on how well these genotypes limit biomass accumulation to save nitrogen for grain filling. Analysis of a large number of field trials in different environments has shown that breeders need to select under drought stress and limited N supply to maximize both yield and GCP in new varieties, and studies in Europe have shown that selecting based on GPD is also important [17].

5. Future prospects

Way forward in “Climate Change” conditions is to produce wheat cultivars having multiple favorable traits which may better mitigate the crop in stress environment. The wheat plants may be stronger to tolerate various biotic as well as abiotic stresses along with better nutritional value, as food security and safety are both equally important. What we need now is to produce wheat plants having temperature, drought, salinity tolerance as well as more protein contents so that plant may be grown healthy under adverse environments along with more nutrition in terms of protein, carbohydrates, etc. The breeders are highly recommended to include all possible factors contributing toward climate change in their breeding programs while developing new wheat cultivars.