Nutrient depletion in African soil, height-reducing genes boost drought resistance in wheat, sprouting wheat for better nutrition and the future of aphid control

Unbalanced nitrogen, phosphorus usage reducing African crop yields​

Despite increased use of nitrogen (N) and phosphorus (P) on African crops over the past few decades, unbalanced N-to-P ratios that see far more nitrogen being used are lowering crop yields, researchers say.

The researchers said that in order to meet intensifying agricultural needs in developing nations like Africa, nutrient inputs will need to be increased further; soils degraded by nutrient mining will have to be restored and nutrient applications of N and P need to be stoichiometrically balanced. The optimal N:P ration, they said, is 1:0.5 but current N inputs mean that to achieve this, P consumption would have to increase 2.3-fold to be optimal, and to increase 11.7-fold to close yield gaps.

There is a widespread problem of unbalanced fertilizer use across Africa - in some cases, overuse of nitrogen, and in other cases under-use, they wrote. Inefficient applications of N was sometimes caused by soil profiles that lost a lot of the applied nitrogen due to high mean annual precipitation, they explained, and over-use was sometimes a result of supply and price.

However, they said: "If the current trends are not reversed, the area of impacted cropland will expand over the coming decades."​

Researchers used crop response functions based on 741 FAO maize crop trials and EPIC crop modeling (which measures nutrient efficiency) across Africa to examine maize yield deficits resulting from unbalanced N to P applications under low, medium, and high input scenarios, for past (1975), current and future N-to-P mass ratios. At low N inputs (10 kg ha⁻¹​), current yield deficits amount to 10% but will increase up to 27% under the assumed future N-to-P ratio, while at medium N inputs (50 kg N ha⁻¹​), future yield losses could amount to over 40%.

The EPIC crop model was used to simulate maize yields across Africa, finding relative median future yield reductions at low N inputs of 40%, and 50% at medium and high inputs, albeit with large spatial variability. Dominant low-quality soils such as ferralsols, which are strongly adsorbing P, and arenosols with a low nutrient retention capacity, are associated with a strong yield decline, though arenosols show variable losses at low inputs. 

Source: Global Change Biology​
DOI: 10.1111/gcb.12481​
“African crop yield reductions due to increasingly unbalanced Nitrogen and Phosphorus consumption”​
Authors: Marijn van der Velde, Christian Folberth, Juraj Balkovič, Philippe Ciais, Steffen Fritz, Ivan A. Janssens, Michael Obersteiner, Linda See, Rastislav Skalský, Wei Xiong and Josep Peñuelas

Dwarfing genes may reduce drought impact in wheat​

Wheat DELLA-encoding height-reducing genes (Rht​) are associated with significant increase in grain yield, but could also be used to improve crops in drought conditions, find researchers.

Water deficiency is a major stress factor affecting plants at different developmental stages. Autumn-sown wheat frequently experiences early-season drought stress during seedling establishment, which can constrain the subsequent growth and development and lead to substantial yield reductions. 

A recent study sought to examine the effect of induced drought (six days at seedling stage) on leaf water content, level of oxidative stress, cell membrane stability, accumulation of osmoprotectants and activity of some antioxidant enzymes in wheat near-isogenic lines carrying the alleles Rht-B1b ​(semidwarfing) and Rht​-B1c​ (dwarfing) in comparison with the tall control Rht-B1a​.

The results indicated that plants carrying dwarfing alleles and, to a lesser extent, those carrying semi-dwarfing, perform better under stress compared with the control, 

These genes ensured more sustained membrane integrity, enhanced osmoregulation and better antioxidant defense in the induced drought, the researchers explained, findings that could be important to breeders when introducing Rht-B1​ alleles into wheat cultivars designed to be grown in drought prone regions. 

Source: Journal of Agronomy and Crop Science​
DOI: 10.1111/jac.12047​
“Changes in Water Status, Membrane Stability and Antioxidant Capacity of Wheat Seedlings Carrying Different Rht-B1 Dwarfing Alleles under Drought Stress”​​
Authors: K. Kocheva, V. Nenova, T. Karceva, P. Petrov, G. I. Georgiev, A. Börner and S. Landjeva

Sprouting process makes for more nutritional wheat​

Sprouting significantly improves the nutritional value and antioxidant capacity of wheat grains, find researchers.

Published in the Journal of Food Science & Technology, ​researchers found that sprouting ups the levels of tocopherols, niacin, riboflavin and free and bound phenolic compounds. The results found that sprouted wheat is a rich source of bioavailable phytochemicals, and can improve the nutritional quality of food.

For the study, wheat grains were immersed in distilled water and steeped for 24 hours at room temperature. A portion of imbibed wheat grains were incubated in the dark at 50% humidity for five days before they were air-dried to remove the moisture of approximately 11%. Untreated whole wheat grains were used for the control sample. All samples were milled into whole-grain flour.

After sprouting for five days, the content of total phenolics, flavonoids and ferulic acid calculated as the sum of its fractions was increased by 9.9, 30.7 and 21.6%, respectively. The content of α-, β+γ- and δ-tocopherols was increased for 3.59-fold, 2.33-fold and 2.61-fold respectively, while the content of niacin, as predominant B vitamin, was increased for 1.19-fold after sprouting. The total antioxidant capacity of untreated, steeped and sprouted whole wheat grains was 19.44, 20.37 and 22.70 mmol Trolox Eq/kg, respectively.

Despite challenges of processing whole sprouted flour, it should be considered as a food ingredient that could provide positive health effects, the authors wrote. 

Source: International Journal of Food Science & Technology​
DOI: 10.1111/ijfs.12397​
“Can the sprouting process applied to wheat improve the contents of vitamins and phenolic compounds and antioxidant capacity of the flour?”​​
Authors: Slađana Žilić, Zorica Basić, Vesna Hadži-Tašković Šukalović, Vuk Maksimović, Marijana Janković and Milomir Filipović

Seeking new, diverse sources of aphid resistance​

Despite advancements in crop production, aphids continue to damage major world food and fiber crops through direct feeding and transmission of plant viruses. The development of aphid-resistant crops over the past century have greatly improved global food production from both an ecological (reduction in insecticides and better-quality water) and economic (via millions in savings to the ag industry) standpoint.

Aphid-resistant cultivars have been repeatedly shown to slow the spread of aphid-vectored viruses. Phenotypic characters have been successfully used to map aphid resistance genes. Often inherited as a dominant trait, aphid resistance is also polygenic and inherited as recessive or incomplete. Two aphid resistance genes have been cloned to date: Mi-1.2 (from a wild tomato) and Vat, an NBS-LRR gene (from a melon). Virulence to aphid resistance genes of plants occurs in 17 aphid species—more than half of all the arthropod biotypes exhibiting virulence. Given the recurring incidence of aphid virulence, new and diverse sources of resistance to delay or prevent biotype development are needed.

Tolerance resistance to aphids, though understudied, is attractive because it delays the need for insecticidal control and rarely elicits virulence. Tolerance resistance to many aphid species has existed for several decades in cultivars of alfalfa, barley, maize, rice, rye, sorghum and wheat.

Genomic tools such as genetic linkage maps can provide insights into the structure, function and location of aphid resistance and aphid-vectored virus resistance genes, and could be used in high-throughput, mass data analysis techniques for rapid identification of aphid- and virus-resistant crops. Still, the lack of development and use of large-scale plant genomic analyses for both aphid and virus resistance present major obstacles to the development of more durable aphid- and virus-resistant crops.

Source: Pest Management Science​
DOI: 10.1002/ps.3689​
“Plant resistance to aphid feeding: behavioral, physiological, genetic and molecular cues regulate aphid host selection and feeding”
Authors: C Michael Smith and Wen-Po Chuang