Breeding of Vegetable, Spice and Tuber crops (2+1)

The pollination process

• Monoecious plants have both male and female flowers on the same plant. Dioecious plants have only one sex of flower per plant.

• Both monoecious and dioecious plants generally require cross-pollination. When a pollen grain lands on a receptive stigma, it forms a pollen tube down the style to the ovary.
• Male genetic material passes down the pollen tube and fertilizes an ovule. Ovules become seeds and the surrounding ovary develops into the fruit.

 

• Cucurbit plants, for example, have separate male (staminate) and female (pistillate) flowers. Male flowers generally appear on the plants several days before female flowers.
  
• The female flower is easily recognized by the presence of a miniature fruit below the flower petals. (Fig.1) Pollen from the male flower must be transferred to the female flower for pollination and subsequent fruit development to occur.

Female flowers on cucurbit plants have a miniature fruit below the petals

• Many insects visit flowers to collect pollen and nectar as food.
  
• These insects spread pollen grains among flowers, accomplishing pollination.
  
• Many flowers offer sugary liquid nectar as an added enticement for these pollinating insects.
• Among insect pollinators, bees are especially efficient because they eat pollen and nectar exclusively, visit many flowers of the same species during a single trip and have hairy bodies that easily pick up pollen grains.
• Cucurbit flowers open shortly after sunrise and remain open until late afternoon or early evening, so each flower is open for only a few hours.
  
• The honeybee is the most common and effective cucurbit pollinator. Honeybee activity closely coincides with the period when the flower is open.
• Honeybees begin to visit flowers an hour or two after sunrise and continue to visit until mid-afternoon. If temperatures are very warm, bee activity may decline about noon. When bees are active, spraying pesticides should be avoided.
  
• Research on watermelon in Florida showed that the number of bee visits was more important than the length of time that each bee stayed on the flower. Well-shaped, fully-expanded fruit developed after eight bee visits to a female flower.
  
• Fruit set was significantly reduced when bees only visited two to four times. Misshaped or undersized fruit could be the result of poor or incomplete pollination.
  

Misshaped or small fruit may result from poor or incomplete pollination

• The formation of seed in more complex plants depends on sexual reproduction in the flower. This process can be quite complex and is of fundamental interest to plant breeders.
• It is important that plantings be sufficiently separated when crossings are not wanted.
• Home gardeners who want to save seed from vegetable plants can expect Group 1 to contain less than five percent mixed seed.
• When seeds are saved from Groups 2, 3 and 4 and more than one variety of the same species is grown in the garden, gardeners should use special care to prevent crossing.