California's cornucopia

• Citrus (Rutaceae) is the topic of Lecture 2
• Vegetative Parts


  • Roots
  • Stem
  • Leaves
• Tree terminology


  • Roots
  • Trunk
  • Crown (branches with leaves)
  • Shoot
• Reproductive Parts


  • Flower
  • Fruit
  • Seeds
• In flowering plants, seeds are always held in an organ called the FRUIT
• Flowering plants are called Angiosperms
• Fruits


  Have many shapes, forms and functions to protect and disperse seeds
• Strawberries


  • Fleshy part is called the receptacle
  • Achenes are supported by the receptacle
  • Achenes are fruits
  • Seeds are within the achenes
  • An achene is a small, dry one-seeded fruit that does not open to release the seed
• Life Cycle of a Flowering Plant (Angiosperm)

  1. Seed sprouts and develops into a flowering plant

  2. Pollen (with sperm) is transferred to the female part of the flower. Pollen germinates and fertilizes the egg

  3. Fertilized egg develops into an embryo

  4. Embryo becomes the seed (within the fruit)

  5. Seed germinates in soil
• Angiosperms have three reproductive organs
• In the early 1900s, Riverside was one of the wealthiest cities in the US, with wealth generated mainly from navel orange production
• Wealthy growers (from Midwest & England) recognized research could help them and lobbied state for financial aid to promote citrus
• History of the Citrus Experiment Research Station

  1. 1907 - 2nd UC campus, Citrus Experiment Station established at foot of Mt. Rubidoux

  2. 1917 - Citrus Experiment Station moves to Box Springs site

  3. 1954 - UCR's four-year "College of Letters & Sciences" opens to undergrads on the land of UC Citrus Experiment Station

  4. 1960 - Graduate Division added (PhD and MS degrees). College merges with Ag Experiment Station. UCR becomes a "general" campus

  5. 1966- UCR's carillon was dedicated

  6. 2023 - UCR is part of the AAU (American Association of Universities). Top 76 universities in the nation
• UCR has a world-renowned citrus research program (R'Citrus)

  
• Washington Navel Orange


  Seedless, flavorful & nutritious, easy to peel

  
• Citrus originated in South-east Asia (4000 BC)

  
• The travels of the "Selecta" orange


  1. A USDA fruit discoverer found "Selecta" oranges in Bahia, Brazil

  2. Hundreds of seedlings sent to Florida in 1873 and none survived

  3. By request, three Selecta plants were sent to Eliza Tibbets in Riverside in 1873

  4. With no water rights, she watered the trees with pan water. Two flourished in her yard

  5. The existing Washington Navel Orange "parent" tree might be the most important tree in citrus history

  
• The parent Washington Navel Orange tree will be 151 years old in 2024 and resides at the corner of Arlington and Magnolia

  
• Today the parent tree is tented to protect it from acquiring a deadly disease transmitted by the Asian Citrus Psyllid

  
• How the Washington navel orange got its name

  • Looks like a bellybutton (navel)
  • "Washington" acknowledges travel from Washington DC to Riverside
  • Due to a naturally occurring mutation, it is seedless and has a "navel". The navel is a small orange that did not develop

  
• Commercial Citrus Trees


  Created by grafting (asexual reproduction)

  
• Citrus trees are chimeras or hybrids


  • Citrus hybrids are a fusion of a rootstock and a scion (shoot)
  • Scion and rootstock sources must be certified as pathogen-free (UCR's Citrus Clonal Protection Program)

  
• To make a navel orange tree

  1. Scion = Navel orange

  2. Rootstock = A different citrus genotype grown from seed, chosen for ability to grow in a specific growing region (good performance in soil, resistance to pathogens)

  
• Clonal scions


  Cuttings from genetically identical trees, an example of asexual reproduction
• For a graft to 'work'


  1. The wound must heal (callus = C)

  2. The vascular systems (xylem and phloem) of scion and rootstock join
• More examples of citrus grafting

  • Sometimes multiple scions are grafted to a rootstock
  • A graft union in a mature tree

  
• California was the #1 state for total citrus production in 2023

  
• California is the #1 state for fresh market citrus

  
• California and Florida produce similar numbers of juicing oranges

  
• Where is Citrus grown in CA?

  • Central Valley (San Joaquin Valley)
  • Central Valley (Sacramento Valley)
  • Foothills
  • Coastal-Intermediate
  • Interior
  • Desert

  
• UCR's Citrus Variety Collection is one of the most diverse citrus collection in the world

  
• UCR's Citrus Variety Collection has two trees of ~1000 types within the genus Citrus and two trees of 27 of 33-related genera related to Citrus

  
• UCR's Citrus Variety Collection encompasses virtually all of the commercially important and historic citrus varieties of the world

  
• Florida's citrus industry is in crisis, with an 80% reduction in fruit yield in 20 years
• Reasons for the decline in Florida's citrus industry

  • Citrus greening disease begins to spread (2004)
  • Hurricane Irma (2017)
  • Hurricane Ian (2022)

  
• Citrus Greening Disease


  • Also known as Huanglongbing (HLB) or "Yellow dragon disease"
  • Vectored by the Asian Citrus Psyllid (ACP)
  • Causes leaf mottling, tree decline and mortality
• With no mechanism to cure Citrus Greening Disease, Florida focused on eliminating the insect vector (ACP) with insecticides and antibiotic treatment of trees to eliminate the bacterial pathogen
• Florida has both the ACP and the Citrus Greening Disease pathogen, leading to the rapid spread of the disease
• Citrus Psyllid (ACP)


  3 - 4 mm in length

  
• Citrus Greening Disease


  Causes leaf mottling and tree mortality