Haploid induction in tropical supersweet corn and ploidy determination at the seedling stage

The objective of this work was to determine the possibility of haploid induction in tropical supersweet corn (Zea mays L. var. saccharata) using a maternal inducer, as well as to identify alternative methods for haploid selection. A single-cross hybrid of field corn and 11 tropical supersweet corn populations were crossed with the haploid inducer. The haploids were pre-selected using the R1-navajo marker and were differentiated into haploids or false positives at the V2-V3 stage, based on the color of the first leaf sheath and on the length of stomata guard cells. The obtained results are indicative of the possibility of inducing maternal haploids in populations of tropical supersweet corn. However, a large number of false-positive haploids were incorrectly selected by the R1-navajo marker. The color of the first leaf sheath was efficient for haploid identification in supersweet corn populations, and the method based on stomata morphometry can be used when there is no color distinction on the first leaf sheath.

Testers in supersweet corn lines

ABSTRACT: The purpose of this study was to evaluate the discriminatory capacity of tester lines for tropical corn lines converted to supersweet shrunken (sh2) gene, for the development of hybrids adapted to tropical conditions. Lines were used as female parents in crosses with three testers: open-pollinated mixed variety; supersweet line L4; supersweet commercial hybrid Tropical Plus. Four trials were carried out to evaluate topcrosses in Maringá - PR e Sabáudia - PR, Brazil in the main growing season of 2015/16. The following traits were evaluated: total ear weight (TEW, in kg), commercial ear weight (CEW, in kg) and total soluble solids (TSS, in °Brix). The GCA estimates for TEW and CEW were highest for L4. The lines Balu-114 and UEM-25 were selected based on the effects of g ̂ ifor the traits studied and should be used in the establishment of base populations for the breeding of superior lines. The s ̂ ijvalue for TEW was highest for cross BALU-182 x Tropical, while for CEW was the highest value for cross BALU-94 x Mista.

Plantability and moisture content of naked and pelleted seeds of supersweet (Sh2) corn during cold storage conditions

The supersweet (Sh2) corn seeds have a thin tegument and an irregular shape, which hinder the sowing procedure. As a function of those factors, the significance of using the pelleting process to improve sowing and standardize the stand of plants in the field without the need of thinning within the row is emphasized. Although this technique has already been known for many years, little has been studied on the effect of such procedure on the plantability and on the moisture content of the supersweet corn seeds. Therefore, this research work aimed at evaluating the effects of pelleting on the moisture content of the seeds along the storing process, on the occurrence of gaps on seed deposition and on the dropping of double seeds, with the aid of a testing seeder. Other physical attributes of seeds and pellets were also evaluated through tests of fragmentation, screen retention, mass of a thousand seeds and apparent volume. Results have shown an increase on the mass and on the volume of the pelleted seeds that presented highly resistance to cracks and breaking. The pelleting was efficient on the reduction of gaps and on the deposition of double seeds at sowing, thus providing highly satisfactory results for these attributes. An increase on the seed moisture content was also observed as a function of storage with a significant reduction on this factor after the pelleting procedure. Results allow concluding that the pelleting process reduces seed moisture content and improves plantability, positively affecting the efficiency of the sowing process.

Stalk Senescence, Sugars, Proteins, and Minerals in Stalks of a Supersweet Corn at Developmental Stages

Senescence and levels of minerals, sugars, and proteins were determined in stalk internodes of corn (Zea mays L.) cv. Illini Gold, a shrunken2 hybrid, from from mid-whorl (V9; internodes completely juvenile) to fresh-market maturity (FM; internodes exhibiting stages of senescence). Senescence was rated in internodes near the base of the stalk (I7), below the ear (I9), and between the ear and tassel (I11). Tissues were extracted and analyzed by carbon-nuclear magnetic resonance spectroscopy (C-nmr) and SDS-PAGE electrophoresis. Senescence rating increased from V9 to FM. Through silk emergence (R1) C-nmr carbohydrate spectra were similar, regardless of internode, with chemical shifts between 61 and 104 ppm, mostly of glucose, fructose, and sucrose. At FM, additional lines were found that were not associated with a saccaride. The highest concentration of sucrose was at R1, fructose at tasseling (VT), and R1, and for glucose from VT to FM. The protein profile present through R1 in I7 was not present at FM. In I9, the protein profile was similar throughout. In I11, numbers, or density, of protein bands decreased through FM. Mineral concentrations did not change, decreased, or fluctuated. Levels of N, Cl, or Na at VT, R1, and FM, respectively, were negatively correlated with senescence. In I7 and I9, senescence ratings were negatively correlated with levels of Mg, NO–3, or SO2–4. Senescence appears to be associated with concentrations of some minerals, a reduction in levels of sucrose, and with the presence or absence of some proteins; however, cause and effect remains to be established. This research was hosted by USDA/SCARL at Lane, Okla., and made use of NMR equipment provided through USAF/AFOSR Grant F49620-95-1-0316 and NIH/NIGMS Grant GM 08003.