Trigiano Robert N, Boggess Sarah L, Wyman Christopher R, Hadziabdic Denita, Wilson Sandra
Department of Entomology and Plant Pathology, Institute of Agriculture, University of Tennessee, Knoxville, TN 37996-4560, USA.
Department of Plant Sciences, Institute of Agriculture, University of Tennessee, Knoxville, TN 37996-4561, USA.
Plants (Basel). 2021 Jul 30;10(8):1565. doi: 10.3390/plants10081565.
Small, the whorled sunflower, is a perennial species only found at a few sites in the southeastern United States and was declared federally (USA) endangered in 2014. The species spreads locally via rhizomes and can produce copious seeds when sexually compatible genotypes are present. Vegetative propagation of the species via cuttings and the optimum conditions for seed germination have not been determined. To investigate asexual propagation via cuttings, stem sections were harvested in late May, June, and July in Knoxville, Tennessee (USA) and trimmed to a minimum of two nodes. The base of the cuttings was treated with either auxin or water, and grown in a Promix BX potting medium with intermittent mist and 50% shade for one month. Seeds were harvested from a population of multiple genotypes in Maryville, Tennessee and used to determine viability and the range of temperatures suitable for germination. A clonal population was developed and used for three years to assess sexual compatibility at three locations in Knoxville, Tennessee. Ninety-five percent of the cuttings from May rooted in two-to-three weeks and formed more than 20 adventitious roots per cutting with auxin and 18 with water treatments. The ability of cuttings to root decreased in June to about 20%, and none rooted in July with either water or auxin pretreatments. Pre-germination tetrazolium tests indicated that about 91% of seeds (achenes) were viable. Subsequent germination tests revealed high germination at varying temperatures (96 to 99% of seeds (achenes) germinated at 22/11, 27/15, and 29/19 °C), whereas germination was significantly inhibited by 33/24 °C. Fifty percent of the seeds germinated at 22/11 °C in 7.5 days, whereas only 2.0 to 2.5 days were required for 50% germination at 27/15, 29/19, and 33/24 °C. Seeds were not produced at any of the clonal planting locations during the three years. Vegetative propagation via rooted cuttings was successful in the mid-spring, seed germination was possible over a wide range of temperatures, and self-incompatibility was evident in this species. The results of this study will permit fast and efficient propagation of multiple and selected genotypes for conservation, commerce, and breeding of elite cultivars with disease resistance or other desirable attributes.
小轮生向日葵是一种多年生植物，仅在美国东南部的少数几个地点被发现，并于2014年被美国联邦政府宣布为濒危物种。该物种通过根茎在当地传播，当存在性兼容的基因型时，能够产生大量种子。通过扦插进行该物种的营养繁殖以及种子萌发的最佳条件尚未确定。为了研究通过扦插进行无性繁殖，于美国田纳西州诺克斯维尔市的5月下旬、6月和7月采集茎段，并修剪至至少有两个节。将插条基部用生长素或水处理，然后种植在含有间歇喷雾和50%遮荫的Promix BX盆栽基质中，持续一个月。从美国田纳西州玛丽维尔市的多个基因型群体中收获种子，用于确定种子活力以及适合萌发的温度范围。培育了一个克隆群体，并在田纳西州诺克斯维尔市的三个地点使用了三年，以评估性兼容性。5月份的插条中有95%在两到三周内生根，用生长素处理的插条每根形成20多条不定根，用水处理的插条每根形成18条不定根。6月份插条的生根能力下降到约20%，7月份无论用水还是生长素预处理，插条均未生根。发芽前的四唑试验表明，约91%的种子（瘦果）具有活力。随后的发芽试验显示，在不同温度下种子发芽率较高（在22/11、27/15和29/19°C时，96%至99%的种子（瘦果）发芽），而在33/24°C时发芽受到显著抑制。50%的种子在22/11°C下7.5天发芽，而在27/15、29/19和33/24°C时，50%的种子发芽仅需2.0至2.5天。在这三年中，任何克隆种植地点都没有产生种子。在仲春时节通过生根插条进行营养繁殖取得成功，种子在较宽的温度范围内都有可能发芽，并且该物种表现出明显的自交不亲和性。本研究结果将有助于快速高效地繁殖多个选定的基因型，用于保护、商业用途以及培育具有抗病性或其他优良特性的优良品种。
