Location: Soybean/maize Germplasm, Pathology, and Genetics Research
2024 Annual Report
Objectives
Objective 1: Conduct research to develop genetic resource maintenance, evaluation, or characterization methods and, in alignment with the overall NPGS Plan, then apply them to avoid backlogs in maize genetic stock and information management.
Objective 2: Acquire, distribute, and maintain the safety, genetic integrity, health, and viability of maize genetic stocks and associated descriptive information.
Approach
We will phenotype maize genetic stocks to ensure their identity and trueness-to-type. For newly acquired stocks for which molecular data are available, we will work with submitters to confirm the presence of molecular phenotypes within increased materials. Kernel and ear traits will be evaluated on the cob and after the seeds have been shelled. Seedling traits will be evaluated in sand benches and shortly after germination in the field. Adult plant traits will be evaluated in an observation field. If homozygous viable, mutant plants will be marked for increase and these can be self- or sib-pollinated to generate seeds homozygous for the mutant. Unique quality control processes will be developed for novel stock types and traits. These processes will be customized to address the challenges that emerge, including procedures to avoid backlogs. Lethal recessive traits must be maintained as heterozygotes and screened each generation to determine which F2 ears carry the mutant trait. We will use appropriate conservation tools to maintain our genetic stock collection. We also will maintain a database of information about our stocks with tools that ensure information is provided to the public. We will develop database tools, in conjunction with the MaizeGDB team, to help users submit requests and help us determine which seed sources to use to fulfill these requests. Each spring, we will use our database tools to determine which stocks in our core collection need to be regenerated and propagated due to supply or age of seed. In all cases, seeds are hand planted to assure purity and all pollinations are done by hand using traditional methods of maize. To propagate stocks, we use appropriate genetic controlled crossing techniques (e.g., self or sib pollinations, outcrosses; seedling, adult or pollen observations) depending on the nature of the stock (e.g., dominant vs. recessive mutants; lethal vs. homozygous viable mutants; male-sterile vs. barren stalk vs. fully fertile, etc). To prepare for harvest, we take crossing notes to prepare labels that will be attached to harvested ears. We hand-harvest the crop as individual ears to ensure the integrity of the individual stocks. The seeds are then dried on the ear. After drying, we score for kernel and ear traits, after which we shell seeds from each cob and place each ear’s seeds into individual coin-type envelopes with the ear’s pedigree and phenotype noted on the envelope. We conduct sand-bench seedling tests to determine the presence of seedling mutant traits. For adult traits, we hold seeds for observation in the next growing season. Once the quality of an ear carrying the trait of interest is assessed, the seeds from that ear are entered into our inventory database and the seeds are stored in their envelope under low humidity cold storage conditions. Samples of genetic stocks that haven’t previously been backed up into long-term storage will be sent to the NLGRP in Fort Collins, CO to ensure that all maize mutants in our collection are preserved.
Progress Report
Five thousand three hundred forty-two seed samples, representing 5,077 different stocks, have been supplied in response to 266 requests. These include 134 requests received from 20 foreign countries. Approximately 4.5 acres of nursery were grown this summer at the Crop Sciences Research & Education Center located at the University of Illinois. Early season field conditions were excellent. We were able to plant in early and mid-May and germination for our crossing nurseries was good. Cool, dry weather took over in mid-May and persisted through harvest. For the second year in a row, near record low precipitation in June forced us to provide overhead irrigation twice. Corn smut was heavier than normal in the later planted nursery, particularly in weaker inbred lines. There were sufficient stands for a good increase in almost all instances. Donated stocks from the collections of three retired/retiring maize geneticists and one stock identified by staff at the Plant Introduction station were grown and recovered for preservation. In addition to our normal stock propagation activities, we conducted 124 allele tests with dwarf (d), brachytic (br) and rough endosperm (rgh) kernel mutants. We identified 14 new alleles of characterized dwarf genes and two new alleles of an uncharacterized seed mutant.
Accomplishments
1. Identified genes responsible for the albescent phenotype and determined their role in vitamin A biosynthesis. Vitamin A is an important nutrient for human and livestock health. This work sought to identify the sequences responsible for the albescent mutant trait (a bleaching of leaves and lack of carotenoid in the kernel). In collaboration with ARS researchers in Gainesville, Florida, and others, mutant alleles exhibiting the albescent1 phenotype were physically mapped to two tandemly duplicated genes encoding plastid terminal oxidase (ptox1 and ptox2). This enzyme plays an important role in carotenoid metabolism. Greater understanding of these genes may lead to improved beta-carotene (provitamin A) in maize.