Better yields have long been the focus of crop scientists, but now researchers have their work cut out. Climate change means that droughts and flooding will become commonplace, and decreased soil quality is also an issue. Poor harvests in some regions have already led to higher food prices globally. Thankfully, tougher crops resilient to environmental stresses are now beginning to make their way from field trials to farmers. In addition to genetic modification techniques, gene banks and wild species often hold the key to crops better suited to more challenging conditions.
Environmental stresses continuously influence plants growth and development. Stressors are either biotic, including weeds, pests or diseases, or abiotic, such as heat, salt, drought or light. Abiotic stresses can cut yields by up to 50%. These stressors affect the plants energy balance. Many plants then stop or slow down their fruit formation or grain development as they devote considerable resources to expressing genes that could help them defend from drought or other stresses. Reducing energy lost this way helps plants better withstand stress in the short-term, as well as increasing both yield stability, and the types of land where crops can be planted.
Poly(ADP-ribose)polymerase or PARP proteins are major energy consumers in stress conditions. Gene silencing is one technique that can be used to down-regulate PARP, so that plants devote less energy to creating proteins as part of their repair response. This genetic shock-absorberâ creates more stress-tolerant plants. Bayer CropScience has shown that oilseed rape (canola) with silenced PARP genes performs well under stress, with yields over two-thirds higher in these strains when compared to controls. The company is also researching abiotic stress in cotton, rice and corn, with a view to making new crops available to farmers within the next ten years.
Plant lines that have conservative responses to stress requiring minimal energy expenditure are of interest for breeding, according to Kay Simmons, national program leader for plant genetics and grain crops, US Agricultural Research Service (ARS). Those plants spend less energy in responding to drought and also less energy in resuming growth when the drought stress ends. Simmons explains, so when it rains again the plants can efficiently resume growth and often have higher yields than plants that over-react to drought. For example, slow wilters in soybean are a type of germplasm that we are hoping to identify and use in genetic improvement projects.
ARS researchers are working to discover genes that help plants better protect themselves from weather stress. Particularly, we are identifying useful genes that help plants use water and nitrogen more efficiently under water limiting conditions, says Simmons. Researchers are also looking for traits that help plants tolerate other types of weather stress, especially heat and cold stress, which sometimes accompany drought. One of the most valuable contributions we can make is to identify new germplasm sources for weather stress tolerance for crop breeders to use, says Simmons. ARS researchers are systematically screening accessions in the US national seed collections for lines that are drought tolerant. The information is entered into germplasm databases and combined with other data on quantitative trait loci (QTLs) and molecular maps and markers for stress tolerance. Both the seeds and the genetic data are made broadly available to plant breeders and other researchers worldwide. Our scientists are striving to develop new, high throughput screening methods to reliably identify germplasm and advanced breeding lines with any useful form of genes that confer drought protection. As well as looking for fast and accurate tests to screen for drought-tolerant plants, the ARSÂ Â is exploiting new genome sequence information developed by the US National Plant Genome Initiative notably for corn and soya bean sequences.ARS researchers are also developing new statistical methods, informatics tools and software that plant breeders might exploit. Some breeding experiments could take place by computer simulation or be accelerated using a rapid laboratory or field test.
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