Wind tunnel analysis of cereal crop lodging

Lodging impedes the successful cultivation of cereal crops in the upper midwestern United States.  Lodged cereals not only possess reduced grain yields, but also decreased grain quality from diminished sunlight and pathogen exposure. Lodging is a quantitative trait with substantial environmental effects that make discovering morphologies that confer lodging resistance difficult.  To better identify promising trait targets for breeding and selecting lodging resistance in cereal crops, we subjected a diverse panel of 38 cereal cultivars (oat, wheat, barley) to replicated testing in a wind tunnel. Each replicate received identical regimes of wind acceleration and deceleration, with wind and atmospheric data recorded through a pressure transducer that was synchronized to video recordings of the plant responses. Through subsequent video analysis we quantified drag coefficients, the proportion of the drag force resisted by the plant in the airstream (Coefficient of lodging resistance, CLr), stem bending, and lodging angles. Drag coefficients did not differ significantly among cultivars of diverse morphologies, indicating similar aerodynamic behavior among common cereal crops. However, significant differences among cultivars (p<0.001) were found for CLr values, with some cultivars resisting almost 7 times the drag forces of others. CLr values were also positively correlated (r = 0.41, p<0.001) with more upright lodging angles in the wind tunnel.  These and other trends from the wind tunnel point to a cereal ideotype of low total biomass, high stem strength, and high stem elasticity that together should confer increased lodging resistance.
 

Using Unmanned Aerial Vehicle (UAV) Technology to Explore Physiological Traits in Wheat Breeding

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Remote sensing has been widely used as an indirect approach to study the agronomic and physiological traits of plants. Remote detection and assessment of plant diseases, estimation of yield and better understanding of other physiological traits can be important to increase yield and improve quality of wheat varieties. This study investigates the potential use of low-cost Unmanned Aerial System (UAS), equipped with RGB and multispectral sensors as a high-throughput field phenotyping tool in wheat breeding. Multiple band (RGB, Red Edge, and Near Infrared) images were acquired by flying rotary wing UAS over wheat fields located at Castroville, College Station and Bushland, Texas. Canopy Surface Model (CSM) and several Vegetation Indices (VIs) were developed to assess the foliage disease severity and study the season long variation in VIs. Further processing of imagery data helped to discover additional phenotypic features such as canopy volume, canopy area, and stand density. These extracted features were then used to estimate yield, and evaluate genotypes in terms of biotic and abiotic stress severity. Significant differences in genotypes were observed in most of the traits and we were able to separate the genotypes that were diseased and were low producing. The results shows that this technique can be beneficial to understand the physiological basis of wheat improvement in terms of yield and overall quality.
 

Breeding for tastier tomatoes: Eliminating negative flavor volatiles

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Tomato is one of the highest value crops worldwide with 177,042,359 tons of production from 11,818,422 acres of harvested area in 2016. Commercially produced tomatoes in large retail grocery stores have often lost their flavor compared to heirlooms and other older varieties that are locally produced. Strong selection for alleles favoring weight, yield and shelf life resulted in the cumulative loss of superior alleles affecting volatiles, deteriorating flavor over many breeding cycles. Identification of genes associated with negative flavor traits would assist in selection against them in initial breeding stages leading to early crop improvement while retaining good flavor. Propyl acetate, guaiacol, and methyl salicylate are three major negative flavor volatiles identified in tomatoes. We have identified novel genes associated with the production of these negative volatiles through Genome-Wide Association Study (GWAS) of 167 Solanum lycopersicum var. lycopersicum, S. lycopersicum var. cerasiforme and S. pimpinellifolium accessions. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/ CRISPR-associated protein-9 nuclease (Cas9) constructs for the identified candidate genes were prepared and transformed into tomato plants through an Agrobacterium-mediated transformation to confirm the candidate gene and understand gene function. The mutants created will be carefully analyzed and studied for developmental and biochemical pathways related to the negative volatiles. We will also perform a functional analysis of the biochemical pathways that control the negative flavor volatiles identified from our study. In addition to confirming the identified candidate genes, the study aims to identify the entire pathway regulating the volatiles under study.

Nutritional breeding in watermelon can improve both plant and human health

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Watermelon fruit (Citrullus lanatus) is a natural source of phytonutrients including lycopene, citrulline, and arginine, all of which offer benefits to both plant and human health. Two segregating, outcrossed watermelon populations, NC High Yield (NCHYW) and NC Small Fruit (NCSFW), were evaluated for these traits and for indicators of ripeness (pH and soluble solids content). Parents tested in 2015 were sampled for the above and offspring were tested in 2016 if the sampled fruit of the parents were of qualifying ripeness (SSC≥8, pH 5.5-6.5), resulting in 251 families (NSF = 72, NHY = 175). Narrow-sense heritability was estimated in each of the populations using the methods of parent-offspring regression and variance of half-sibling family means. Heritability for citrulline NCHYW was moderate in both parent-offspring and half-sibling estimations (38% and 43%), as was arginine (40% and 44%) and lycopene (46% and 47%, respectively). Estimates for these traits in NCSFW were considerably different, with parent-offspring and half-sibling estimations for citrulline (65% and 22%), arginine (9% and 20%), and lycopene (44% and 68%). Lycopene was significantly and weakly correlated to citrulline (0.22), but was not correlated to arginine (0.06). Similar correlations were found in NCSFW; SSC was significantly correlated to citrulline (0.24), arginine (0.18), and their combination (0.23), while lycopene was slightly correlated to citrulline (0.15) and not significantly correlated to arginine. Based on these heritabilities and phenotypic correlations, tandem selection for high lycopene and citrulline content may be accomplished, benefiting both the health of the plants themselves in addition to humans.