Tom's Hardy Citrus

  The citrumelo is an old hybrid that crossed the Trifoliate orange with grapefruit in an early attempt to produce cold-hardy, edible citrus after disastrous freezes in Florida in the late 1890s.  The first citrumelos were produced by Dr. Walter T. Swingle of the United States Department of Agriculture.  Swingle was successful in producing several citrumelo cultivars.  He found that like most 50% hybrids of mainstream citrus (already complex hybrids) with Trifoliate orange (probably a pure species), the Trifoliate characteristics dominated the offspring.  This tendency worked to the advantage of retaining cold-hardiness, but was a definite disadvantage when trying to produce a fruit that could be used for anything more than a furniture polish. The citrumelo has proven itself over time to be a very reliable rootstock for grafting, and many citrus today are still grafted on citrumelo, which provides a robust root system and good cold tolerance to the scion.  Most of these cultivars by th

  Clem-Yuz 2-2 from Dr. Brown's original tree in Houston, TX. A very lemon-like Clem-Yuz from Augusta, GA. 'Yuzu Hybrid' from North Carolina An interesting class of citrus hybrids involving the Clementine mandarin was produced by the late Dr. John Brown of Houston, TX, back in the 1960s. Dr. Brown was a physician by profession but was an active and avid breeder of citrus, attempting to produce very cold-hardy, edible citrus. He succeeded in a number of areas, and some of his hybrids are just now getting the recognition they deserve. Many mainstream citrus are already complex hybrids involving two or more species of citrus, and this is true of the Clementine, which is probably a mandarin-orange hybrid (and the orange itself is probably a mandarin-pomelo hybrid). An interesting feature of citrus is that these hybrids produce seeds that are polyembryonic.   Each seed will contain two embryos, one produced sexually (zygotic), the other a nucellar clone of the seed parent.   O