![\"\"](\"https:\/\/img.agropages.com\/UserFiles\/FCKFile\/zkc_2018-12-25_07-44-57_040.jpg\")
<\/div>\nRichard Trethowan, director of the Watson Grain Research Centre in New South Wales, is breeding temperature tolerance into wheat, chickpeas and fababeans. | University of Sydney photo \u201cWhat we realize is that for every degree rise in mean maximum temperature above the optimum for the season, there is a 250 to 400 kilogram per hectare (100 to 160 kg per acre) yield loss. It is really significant.\u201d<\/p>\n None of this bodes well for an expanding human population that increasingly depends on wheat, much of which is grown close to the equator where temperatures are rising faster, as is the population.<\/p>\n However, there have been recent breakthroughs in identifying genetic and molecular factors affecting heat tolerance in wheat. Plant breeders are moving ahead to improve heat tolerance using existing germplasm found in modern cultivars and indigenous species.<\/p>\n Excessive heat can damage cellular structure and affect metabolic pathways, especially those relating to membrane thermostability, photosynthesis and starch synthesis. This occurs through a molecular process called denaturation, in which proteins lose their natural structure because of an external force such as excessive heat.<\/p>\n This degenerative force increases levels of unsaturated fatty acids and disrupts water, ion and organic solute movement across cellular membranes. The increased cell membrane permeability inhibits cellular function, impacting photosynthesis.<\/p>\n Starch accumulation in wheat kernels is reduced by more than 30 percent at temperatures between 30 C and 40 C. Thus, the ability to synthesize, store and remobilize starch at high temperature is crucial to determination of grain sink strength.<\/p>\n Thylakoids are flattened sacs inside a chloroplast contained by pigmented membranes, upon which photosynthesis takes place. These sacs store the chlorophyll necessary for photosythesis.<\/p>\n Thylakoid membranes are the most easily damaged of all cell components. Membrane damage caused by excessive heat leads to chlorophyll loss. Thylakoid membranes under high temperature show swelling, increased leakiness and physical separation of the chlorophyll light harvesting complex.<\/p>\n Heat stress affects agronomic traits at every developmental stage. Short periods of high temperature at the pre-flowering and flowering stages reduce overall yield and kernel numbers per spike. This is attributed to pollen\u2019s lower ability to germinate and to the rate of pollen tube growth.<\/p>\n Yield losses during post-flowering are due to the abortion of grains and decreased grain weight. The early grain filling period is relatively more heat sensitive than later periods.<\/p>\n Australian researchers have found that variation in average growing season temperatures of 2 C can cut grain yield by as much as 50 percent, most of which is due to the leaves\u2019 rapid aging or deterioration when temperatures are above 34 C. Heat stress during the grain filling stages also has a negative impact on grain quality.<\/p>\n According to the September 2017 edition of the Australian magazine Grain Central, plant breeders in that country are responding to looming climate change by increasing their focus on breeding wheat lines with better yield potential under heat stress conditions.<\/p>\n \u201cAmong the Australian cultivars there is generally a degree of heat tolerance that has come from empirical selection in our environment. Breeders are making progress. There are lines like Mace that are one of the most heat-tolerant of all the Australian cultivars available,\u201d said Trethowan.<\/p>\n What can farmers do?<\/strong><\/p>\n But it\u2019s not all up to the plant breeders, said Trethowan. Farmers have to do their part too if they expect to achieve the best results with the new heat-tolerant lines. The new varieties need to be grown in conjunction with improved farming practices.<\/p>\n \u201cIf we are going to do something about the dips in yields in the difficult years, we have to sow crops on time,\u201d he said.<\/p>\n \u201cWe want a conservation agriculture system where you are retaining stubble. That gives you cooler soils, cooler roots and plants more able to deal with temperature shock.<\/p>\n \u201cConservation agriculture also reduces moisture stress. A plant under moisture stress is less able to deal with temperature shock. Weed control is very important. It\u2019s also a water use issue, and adequate nutrition. Plants that don\u2019t have adequate nutrition are less able to cope with temperature shocks.<\/p>\n Rebecca Thistlethwaite, a plant scientist at the University of Sydney, said Australian plant breeders are sourcing genetic material from lines that thrive in hot climates such as India, Mexico and Pakistan. In 2016 and 2017, the breeders looked at 4,200 heat tolerant lines from around the world.<\/p>\n Rebecca Thistlewaite has taken on a post-doctoral role to continue her work on breeding heat tolerant wheat at the University of Sydney. | University of Sydney \u201cWe have found there is significant genetic diversity both within the Australian and international germplasm,\u201d said Thistlethwaite.<\/p>\n \u201cThere have been two particularly promising lines from Australian cultivars: EGA Gregory and Livingston were the two best,\u201d she said.<\/p>\n \u201cThose that did better than the commercial varieties were international germplasm, mainly from Mexico and India.\u201d<\/p>\n Thistlethwaite said another part of the project at Narrabri was developing phenotyping protocols for the best heat tolerance germplasm. In modern wheat, breeders are usually selecting genes on the best yield. Because of that, the genetic base of wheat has been narrowed.<\/p>\n It\u2019s important to broaden the genetic base, and wild wheat ancestors can contribute a lot. Emmer wheat, the first domesticated wheat, contains immense variation, contributing to tolerance of high temperature and drought.<\/p>\n Stay-green capacity is another factor. When a crop is under stress, genotypes with long stay-green ability continue with photosynthesis for very long periods, thus contributing to grain filling.<\/p>\n Heat helps nitrogen<\/strong><\/p>\n There may be a slight benefit to high heat events. Australian scientists found that in some situations, extreme heat actually increased nitrogen content.<\/p>\n The researchers know they can\u2019t help a wheat plant by turning down the oven or making it rain. But if they better understand how heat waves impact wheat, they will be better prepared for whatever the future brings. To assist in this endeavor, they are entering real time field observations into software models to perhaps help Australian grain growers deal with rising temperatures.<\/p>\n The scientists study the impact of heat on soil microbial activity, soil structure, soil moisture, air around the plants and of course the wheat plants themselves. Knowing how these factors affect crops might help farmers protect their plants against the negative impact of heat waves, said James Nuttall, a scientist with Australia\u2019s federal agriculture department.<\/p>\n \u201cHeat waves greatly reduce wheat yields. Computer modelling helps find strategies to limit the impact of extreme weather and climate change. This can specifically come in handy during the sensitive periods of crop flowering and the grain filling phase,\u201d said Nuttall, who is working with the Soil Science Societies of America.<\/p>\n Nuttall and his team performed three sets of heat stress studies looking at timing, intensity and duration:<\/p>\n \u201cWe have data from three experiment sets on the response of wheat to a range of acute high-temperature treatments for 35 C, 37 C and 42 C. It includes one day, three days and five days of exposure,\u201d Nuttall said.<\/p>\n \u201cResults showed that high temperatures five days before the wheat began to flower reduced the number of wheat kernels on a plant. Also, a high-temperature event while the grain of wheat was growing reduced the grain size.<\/p>\n \u201cWe developed algorithms they called \u2018heat sum,\u2019 which encompassed temperature, duration in hours and plant stage at which the stress occurred. Some of their findings showed that high temperature five days prior to anthesis reduced kernel numbers and overall grain yield, but individual kernel weight and nitrogen concentration increased.<\/p>\n \u201cFor extreme high temperature after anthesis, grain yield and individual kernel weight decreased but nitrogen concentration increased. Water availability prior to anthesis helped wheat respond positively to high temperature.\u201d<\/p>\n They put all the results together into a computer simulation model, which allowed them to predict how broad acre wheat crops in the future will be affected by heat waves of different intensity and duration.<\/p>\n Scientists studying climate change are now delving more deeply into plants\u2019 response to carbon dioxide levels, temperature and rainfall. This crop model allows them to test combinations of these factors on growth and yield.<\/p>\n \u201cThese computer models help predict how wheat will react to extreme heat so we can try to prevent negative effects in advance,\u201d Nuttall said.<\/p>\n \u201cSuch algorithms contribute to developing strategies for crop adaptation to climate change.\u201d<\/p>\n With a population of only 24 million, Australia does not account for a big piece of the human pie and they don\u2019t consume much of the wheat they grow. But Australia is in a semi-arid zone and it does grow about 32 million tonnes of wheat annually, so wheat plant survival in severe heat is a matter of great concern Down Under.<\/p>\n
\n<\/em><\/p>\n![\"\"](\"https:\/\/img.agropages.com\/UserFiles\/FCKFile\/zkc_2018-12-25_07-45-40_322.jpg\")
<\/div>\n
\n<\/em><\/p>\n\n
Source<\/strong>:\u00a0THE WESTERN PRODUCER<\/a><\/span><\/h4>\n<\/div>\n