Recipient Organization
UNIVERSITY OF NEBRASKA
(N/A)
LINCOLN,NE 68583
Performing Department
Agronomy & Horticulture
Non Technical Summary
Popcorn and sweet corn are highly consumed in the U.S. being nutritious snack and vegetable forms of the most highly grown U.S. crop, Zea mays. Breeding of popcorn has largely focused on improving profitability by maximizing flake expansion volume. Different flake types have been developed that best suit the mode of distribution and addition of various flavor components. Little attention has been given to investigating or improving the innate flavor, texture and nutritional characteristics of the popcorn itself. Sweet corn breeding has focused mostly on kernel sugar content and agronomic improvement but less attention has been paid to improving other macro- and micronutrients as well as aesthetic diversity of the kernels. There is considerable scope for combining genotypes and phenotypes between field corn, popcorn and sweet corn in order to improve both popcorn and sweet corn in terms of color diversity for enhanced consumer interest, macro nutrition in terms of essential amino acids, and micronutrition in terms of carotenoids and anthocyanins. Popcorn and sweet corn are both well suited to smaller-scale organic production and marketing of diverse varieties with improved nutrition, texture, flavor and aesthetics.To exploit popcorn and sweet corn diversity in developing new and exciting varieties, the goals of the project are as follows. First, the work will develop colored sugary-1 and shrunken-2 sweet corn varieties. This will explore the potential of sweet corn kernels to develop carotenoid and anthocyanin pigmentation by the prime eating stage and will test color combinations in established sweet corn hybrid combinations including Golden Cross and Iowa Chief sugary-1 and shrunken-2 hybrids. Second, the work will test the effects of opaque-2 induced high-lysine endosperm on eating stage sweet corn kernels. Sweet corn is a surprisingly good but incomplete protein source as a vegetable, but by rebalancing the proteome away from zeins and towards non-zein proteins, it will be established if sweet corn can be transformed into a more complete protein source. Third, the work will build on the knowledge generated by the recent development of elite Quality Protein Popcorn hybrids by generating an array for new, colored QPP varieties and testing their agronomic, biochemical, biophysical and consumer preference characteristics.
Animal Health Component
80%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
(N/A)
Goals / Objectives
In the broadest terms, the goals of this project are to breed new sweet corn and popcorn varieties with improved diversity for nutrition, taste and aesthetics. The project intends to develop products for small-scale organic production in a way that maximizes opportunities for undergraduates in the field and lab. The work leverages the knowledge and expertise of the PI in maize and popcorn breeding and undergraduate and graduate education as well as the infrastructure available at UNL for achieving the goals. The specific objectives are as follows:Breed colored sugary-1 and shrunken-2 sweet corn hybridsBreed and assess the potential of Quality Protein Sweet cornBreed novel Quality Protein Popcorn with diverse color and flavor
Project Methods
1. Breed colored sugary-1 and shrunken-2 sweet corn hybridsVarious Shrunken-2 (sh2) and Sugary-1 type sweet corn (su1) lines were acquired from the stock center and grown in the field at UNL East Campus in 2020. These included female and male parents in the sh2 Iowa chief hybrid (IA453 and IA5125) and the female and male parents in the su1 Golden Cross hybrid (P39 and P51) as well as the highly robust and large eared NE-EDR sh2 and su1 lines. In summer 2020, these and other sweet corn lines were crossed, in either direction, to series of dent and popcorn lines with various colored kernels. Color donors included dent and flint corns Coburns Early Red, Rainbow Flint Red, Bloody Butcher, Maize Azul, and Blue Indian Corn. Color was also mined from popcorn lines including Black Jewel, Red Popcorn, Glass Gem (many colors), Strawberry Popcorn, Cochiti Pueblo (Red, Blue), and Cherokee Long Ear (red, blue, purple). F1 kernels from all combinations obtained were planted in the greenhouse in the fall of 2020, self-pollinated and F2 ears show the predictable ¼ shrunken kernels. The F2 ears also segregate independently for the large array of reds, purples, blues and a large variety of lighter shades of mauve, pink and orange. Given the color diversity and the uncertainty of whether the various colors will develop by the sweetcorn eating stage, selection of mature, colored sweetcorn kernels will be done entirely by visual selection. Whole rows of selected colored sweetcorn F2 kernels will be planted and self-pollinated. F3 ears will be examined between 18 and 26 days after pollination to determine when colors first appear during the prime sweet corn eating stages. With the Golden Cross and Iowa Chief hybrid pairs, there is the possibility to make the colored hybrids from introgressions from the same or different colored parents thus expanding the possible color combinations.The anthocyanin and carotenoid pathways are responsible for a large repertoire of different colored pigments associated with beneficial antioxidant properties. The pathways are both complex involving multiple biosynthetic enzymes and transcription factors. All varieties used are naturally existing and so breeding with them is unlikely to result in unintended negative metabolic changes. However, colored sweet corn inbreds and hybrids will be compared to their uncolored counterparts to detect any negative effects plant performance, ear size, kernel size, sugar content and consumer preference. Any lines that ultimately show desirable color accumulation as early as the prime eating stage, with be subjected to quantitative measurements of carotenoids and anthocyanin pigments using HPLC and spectrophotometric methodology.2. Breed and assess the potential of Quality Protein Sweet corn Though sweet corn is not a primary protein source in human diets, as a vegetable, it has one of the higher protein contents at around 3.5% fresh weight. It therefore has the potential to contribute to increasing human consumption of plant-derived protein. This potential could be increased if the limiting and essential amino acid lysine could be increased in both free- and protein-bound forms. Although the lysine-devoid zein protein are abundantly accumulating by the prime sweet corn eating stage (18-21 DAP), their relative proportion with non-zein proteins and their consequent effect on protein quality at that stage is unclear. We will thus investigate the potential for rebalancing the sweet corn proteome by reducing zeins and increasing non-zeins.In Summer 2020, two QPM lines, CML154Q and Tx807 were crossed with all the sweet corn lines described above including the Su1 Golden Cross Hybrid and Sh2 Iowa Chief Hybrid parents and NeEDR Su1 and Sh2. F1 plants have been selfed in the greenhouse and the F2 ears are being screened in the spring of 2021. All F2 ears clearly segregate for ¼ shrunken kernels in all the F2 ears so their selection for replanting is easy. Of these sweetcorn kernels, ¼ are QPM and carry the homozygous o2 mutation (1/16 of F2 kernels). Whole rows of sweetcorn F2 seed will be planted in the summer 2021 field and genotyped using SSR marker UMC1066 to find the QPM plants and only this fraction will be self-pollinated to generate F3 ears. These F3 ears carry both the sweetcorn allele and opaque2 allele specifying quality protein in homozygous form.Since the sh2 and su1 sweetcorn variants are well characterized and produce no starch and much reduced starch respectively, and they are homozygous by the F3, it will not be necessary to test for sugar content at this early stage. Since they are also opaque-2, they have a rebalanced proteome with less zeins and more (lysine-rich) non-zeins and are, by definition, high lysine. To confirm this, we will measure free and protein bound amino acids at 20-25 days after pollination (sweetcorn eating stage) kernels comparing opaque-2 (QPM) sweetcorn to regular sweetcorn kernels. To do this, kernels will be flask frozen, lyophilized and ground into a powder and amino acids analysis will be performed. If successful, later efforts will focus on determining agronomic performance and consumer preference compared to the parental hybrids.3. Breed novel Quality Protein Popcorn with diverse color and flavorPrevious work by the PI's lab has shown the potential of popcorn subspecies introgressed with the o2 mutation and modifier genes to produced fully popable and high-lysine, Quality Protein Popcorn. While selecting for a QPM-like proteome, key popcorn traits such as popability, kernel morphology, and kernel size were selected throughout the breeding program. Hybrids produced from these QPP inbreds performed comparably with elite commercial popcorn hybrids in terms of agronomic performance, yield and popcorn flake expansion volume while manifesting lysine contents similar to QPM dent corn. Recent consumer testing has indicated that QPP flakes possess a more diverse array of taste and texture profiles which, in many cases, are preferable to elite conventional popcorn flakes. This project seeks to take advantage of this diversity in taste and texture by using our knowledge and methodology to breed new QPP varieties using public popcorn and QPM germplasm. The colored popcorn lines selected will also add desirable aesthetic diversity to the products.The colored popcorn lines described in Aim 1 were crossed to CML154 QPM and Tx807 QPM in Summer 2020. F1 plants are being selfed in the green house to produce segregating F2 ears on which phenotypic selections will commence. Since crosses between dent corn and popcorn segregate for kernel dent and popcorn phenotypes as early as the F2, we will select popcorn phenotype F2 kernels bearing desirable colors for propagation. The 1/4 o2/o2 fraction of each introgression will be germinated for DNA extraction from seedling leaf tissue followed by PCR genotyping. Markers will first need to be tested to find ones showing polymorphisms between QPM and popcorn parents. Alternatively, biochemical selection using SDS-PAGE can be applied to the F3 kernels to identify ears that are 100% modified o2 (low alpha-zein and carrying the gamma zein duplication). The percentage popcorn genome will be increased by backcrossing to the recurrent popcorn parent or a different popcorn parent followed by selfing to again produce segregating F2s. BC2 and BC3 F4 ears have been shown to be 100% popable popcorn in our previous QPP work. Increasing the popcorn genome makes this aim more long term than aim 1 and 2 but should result in novel QPP inbreds within four years. Longer-term work will be to generate and test different QPP hybrid combinations, and assess their yield, flake type, texture, taste and color diversity. Since all hybrids will be derived from modified o2, they are all expected to have the same elevated lysine content. Work will be completed by the PI, graduate student and Plant Biology and other selected undergraduates.