Lecture 31
Papaya

Papaya: Carica papaya, Caricaceae

  • A tropical fruit, widely grown as a backyard tropical tree but increasingly important as a commercial fruit.
  • Family consists of two genera, Carica and Jacaratia.
  • Genera were so varied that they were hard to place, finally Caricaceae developed to include both genera.
  • A Venezuelan taxonomist, Bodillo, reduced the species to 57.
  • All are indigenous to the American tropics.

    		•  fig. 01

  • All dioecious except C. papaya which is polygamous (many sexual types).
  • All are single stemmed but C. goudatiana is free branching.
  • Only C. papaya is of economic importance but there have been attempts to commercialize C. pentagona
    • (babaco) a seedless, fruit from Ecuador with a sweet-tart taste.
  • Names include papaw (New Zealand), mamão = big breast (Brazil), lechoso = milky (Venezuela), fruita bomba = fruit bomb (Cuba).
  • The names refer both to the shape of the fruit and the milky exudate from the fruit skin which is the source of papain, a proteolytic enzyme and the source of Adolph's meat tenderizer.
  • Papain also used for certain delicate spinal cord surgeries.
  • While native to tropical America, perhaps the West Indies or Mexico, it spread rapidly to the Moluccas and India in the 19th century and was later imported to Hawaii.
  • The common Hawaiian cultivar called 'Solo' probably originated in Barbados.
  • Papaya is now cultivated in all tropical countries up to 32º latitude.

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    Babaco

    Babaco

    		 fig. 02

    Papaya, Puerto Rico

    Ecology

  • A tropical crop.
  • Moisture is important in papaya.
  • Total sugars however are higher under low irrigation.

    		•  fig. 03

    Phil Ito and Papaya species, Hawaii

    Papaya: 2001 World Production
    Continent 1000 tonnes Chief countries
    World 5,444  
    Africa 1,017 Nigeria (748), Congo (213), Mozambique (31)
    North America    778 Mexico (613), Cuba (40), Costa Rica (35)
    South America 1,987 Brazil (1,450), Peru (174), Colombia (114)
    Asia 1,642 India (644), Indonesia (470), Thailand (119)
    Oceania      20 Samoa (10), Australia (7), Fiji (2)

    Morphology

  • A large herbaceous, erect single stemmed tree and only occasionally lateral branches.
  • The main stem is hollow with prominent leaf scars.
  • The leaves are large, flat palmately lobed or entire.
  • As the leaves mature they dry off and fall, so the leaves are only found at the top of the tree.
  • Flowers are produced in the axils of the leaves.
  • The inflorescence is a modified cyme.
  • The type of inflorescence depends on the sex of the tree.
  • Hermaphroditic types are easily self pollinated but can be also cross pollinated.
  • Fruit are usually "melon shaped" but may be round, long pyriform or oval and usually has 5 carpels.
  • The fruit size varies from 0.5 to 15 pounds.
  • Flesh color ranges from pale orange to bright red.
  • There are many types of seed cavities, usually star-shaped to round.
  • The fruits have many hundreds of small seeds.
  • The crop is one of the few fruit crops planted from seed.

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    fig. 04 fig. 05
    fig. 06 fig. 07
    fig. 08 fig. 09
    fig. 11 fig. 12
    fig. 11 fig. 12

    Flower Type

    The flower type shows a relationship to fruit shape.

  • Type 1. Pistillate
    Has a functional ovary and no stamens.
    The petals are separate and fused only at the base.
    Fruits with only pistillate flowers (female trees) must be pollinated by an outside source.
    The fruit shape from pistillate flowers in 'Solo' is round and is not considered desirable in Hawaii because consumer thinks there is less flesh than a pyriform (pear-shaped) fruit.
  • Type II. Pentandria bisexual
    Contains 5 short stamens that occur in furrows in the pistil.
    The fruit is furrowed and considered unacceptable.
  • Type III. Intermediate or carpellodic bisexual
    Produces deformed fruit.

    		•  fig. 15

    Papaya flowers, Hawaii

  • Type IV. Elongata bisexual
    Produces pyriform fruit.
    Only this produces salable fruit in Hawaii.
    The pistil is long and cylindrical.
    Pistils have 5 carpels (range 1–10).
    Fruit shape changes with the number of carpels.
  • Type IV. Deviate type
    During certain season, Type IV fails to develop functional pistil, flower size is reduced.
    Appears to be intermediate between type IV and type V (staminate flower).
  • Type V. Staminate flower
    Corolla tube is slender and long.
    Flowers are borne on long cymes.
    No fruit is produced.
    Trees with all staminate flowers are considered male.

    		•  fig. 16

    Papaya cavity types

    Genetics of Sex Determination

  • Pistillate = m
  • Hermaphroditic = M2
  • Staminate = M1
  • Pistillate tree = mm
  • Hermaphroditic tree = M2m
  • Staminate tree = M1m

  • Note: M1M1, M1M2, and M2M2 are lethal combinations.
  • Pistillate tree (mm). Produces type I flower. This is a stable type and requires pollination.
  • Continually fertile hermaphroditic tree (M2m).
  • From July to December type IV flower is produced in terminal position to produce pyriform fruit.
  • In some seasons Type II and III flowers are produced.
  • Thus abnormal fruit may be produced in some seasons.
  • The hermaphroditic types of sex expression shifts with temperature.
  • Low temperature gives a shift to femaleness, high temperature gives a shift to maleness.
  • Staminate (or male) tree (M1m) A counterpart of the pistillate tree.

    		•

    Sex Determination Inheritance

    Dioecious types

    mm (pistillate) × M1m (staminate) ­> 1 mm : 1 M1m

  • Thus, when seed is planted half the plants are pistillate and half are staminate.
  • But of course only staminate types bear fruit.
  • Approximately 5 to 10% of trees should be staminate to insure adequate pollination.
  • This is usually controlled by planting three seeds per hole and if possible, leaving only one pistillate tree, determined when the trees flower.
  • One eight of holes with 3 plants will be all staminate (1/2 × 1/2 × 1/2 = 1/8) (Note: This is the same probability of a couple having three sons.) Eliminating two trees will leave one staminate tree. Seven eighths of holes will have at least one pistillate tree.
  • Thus a field planted with 3 seed from a dioecious cross and thinned to obtain at least one pistillate plant will contain 12.5% staminate trees or 87.5 % pistillate trees.
  • If 4 plants are left per hole, 6.5% will have four staminate plants; if 5 plants are left the number of holes with all staminate plants with be 3.125%.

    		•

    Hermaphroditic types

    In this case seed from intercrossed M2m types are planted; plants can self or cross pollimate.
    M2m selfed (M2m × M2m)
                                        1 M2M2 (lethal) : 2 M2m (hermaphroditic) : 1 mm (pistillate).

  • The M2M2 seeds abort so the effective ration is 2 hermaphroditic to 1 pistillate.
  • Now in the case of 'Solo' the mm pistillate type has unacceptable round fruit so these types are eliminated.
  • If one plant per hole is planted 2/3 or 66.7% of the plants will be hermaphroditic and 1/3 or 33.3% will be the undesirable pistillate types.
  • If two seeds per hole are planted and thinned to obtain at least one hermaphroditic plant, 1/3 × 1/3 = 1/9 or 11.1% of the holes will have two undesirable pistillate plants.
  • With three seeds only 1/27 (1/3 × 1/3 × 1/3) or 3.7% will be all pistillate and so forth.

    • Proportion of expected desired sex with thinning

    No. of plants per hole % pistillate (dioecious types) % hermaphrodites (hermaphroditic types)
    1 50.0 66.7
    2 75.0 88.9
    3 87.2 96.3
    4 93.8 98.7
    5 96.9 99.9

    At the present time there is no way to pre-select seedlings for sex. A technique using molecular markers should be possible but has not been reported.

    Spacing

  • Usually papaya is planted 10 × 10 or 8 × 10 feet; 10 feet minimum between rows is usually maintained to accommodate tractors.
  • Trees get too close if planted too close.
  • 'Solo' usually requires 50 nodes for first flower, but some strains flower after 25 nodes.
  • To keep orchards low, growers start plants in cans to produce short internodes but of course as plant grow crop gets higher and higher.

    		•
    fig. 17 fig. 18

    Diseases

  • The greatest problem in papaya is tomato ringspot virus.
  • At the present time Florida cannot successfully produce papaya because of the virus problem.
  • Research on genetic transformation to induce virus resistance is underway in Hawaii.

    		•
    fig. 19

    Papaya, Phytophthora damage

    		 fig. 20

    Papaya plantation, Phytophthora

    Commercialization

  • The 'Solo' papaya is becoming the major world cultivar because the size is suitable and the quality is high.
  • 'Solo' papaya is often available in most supermarkets in the United States.
  • Red-fleshed mutants are available which are very attractive.
  • 'Solo' is now very popular in Brazil.
  • However in Mexico many high quality, large-fruited types from dioecious cultivars are produced and recently these have also been imported into the United States.

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    Packing Papaya
    fig. 22

    Papaya

    		 fig. 23

    Henry Nagasone, short compact leaved Papaya
    fig. 24

    Long Peduncle Papaya

    		 fig. 25

    Long Peduncle Papaya
    fig. 26

    Segregation: long peduncle, short peduncle

    		 fig. 27

    Papaya, multiple fruiting

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