Pg. 8-10 Evaluating the Success of Cross-Pollinating Techniques in Litchis (Litchi chinensis Sonn)

Single inflorescences of litchi trees produce several hundred flowers each. The sexes are separated on different flowers and male, female and male flowers are produced successively on a given inflorescence. Self-pollination occurs commonly since pollen shed overlaps with receptivity of the female flowers. Two methods, daily physical removal of the male flowers prior to hand pollination, and the use of a pollen dispenser attached to a beehive inside an encaged tree were used to produce directed crosses as part of a litchi breeding programme. The success of the two methods was investigated with isozyme analysis of the parents and progeny. Both methods resulted in the production of a satisfactory percentage of hybrid progeny. Physical removal of the male flowers followed by hand pollination is, however, the preferred method since it resulted in a minimum of 75% hybrid progeny.

Summary:

• Litchi trees produce inflorescences with several hundred flowers, with male, female, and male flowers produced successively on the same inflorescence, enabling possible self-pollination due to overlapping pollen shedding and female receptivity.
• Two cross-pollination methods were tested in a breeding program:
  • Daily physical removal of male flowers before hand pollination.
  • Use of a pollen dispenser attached to a beehive inside an encaged tree.
• Isozyme analysis (phosphoglucoisomerase-PGI) was used to evaluate the success of these methods in producing hybrid progeny.
• Results showed both methods produced a satisfactory percentage of hybrid progeny, with hand pollination via removal of male flowers yielding a minimum of 75 hybrids, making it the preferred method.
• The litchi is naturally an outcrossing diploid species with strong preference for cross-pollination between different cultivars.
• Large quantities of viable pollen can be collected and stored for several days at room temperature or weeks at 4°C.
• Hand pollination involved covering inflorescences in paper bags, removing male flowers daily, and brushing pollen onto receptive female flowers.
• Crosses showed varying progeny genotypes, with some evidence of self-fertilization but predominantly hybrid offspring.
• The pollen dispenser with bees also resulted in hybrid progeny but is considered less practical.
• Genetic analysis revealed complexities such as two-locus inheritance patterns and some unexplained genetic observations requiring further research.
• The study concludes hand pollination after male flower removal is an effective and practical breeding technique for directed crosses in litchis.
• The pollen dispenser method may produce hybrids but is not recommended due to practical inconveniences.
• The research supports genetic improvement in litchis through controlled cross-pollination, facilitating better selection and breeding strategies.
• This summary encapsulates the main points of the research and experimental findings regarding cross-pollination techniques in litchis.