Breeding System Of Neem (Azadirachta Indica A. Juss)

Neem, botanical named Azadirachta indica A. Juss with great economic and ecologicalvalue, is a kind of multipurpose tree attached to Meliaceae. On one hand, the Azadirachtinextracted from A. indica can be used as highly active, low mammalian toxic andenvironment-friendly biotic pesticide. On the other, A. indica is widely planted for forestationand greening due to its good annidation, beautiful tree form, and ability of soil and waterconservation.Mastering the reproductive characteristics and bionomics of a species is the foundation offine variety breeding. And understanding the breeding system of A. indica provides basicevidence for the establishment of breeding technics. Both traditional methods and modernDNA marker were applied to study the component parts of breeding system of A. indicaoriginated from Myanmar which had been introduced to Yunnan, China. Morphologicalstructure of flowers, anthesis phenology, flowering pattern, species and visiting frequency ofpollinating insects, as well as foraging behavior of pollinators were observed. Furthermore, thetype of breeding system, outcrossing rate and gene flow were also tested by means ofoutcrossing index, pollen-ovule ratio, artificial pollination, bagging and Random AmplifiedPolymorphic DNA. Then the findings are as follows.1. The blooming period of a single flower is 5d; and the total blooming period of apopulation is 2 months, among which the stage of full bloom lasts for 1 month from Aprilto May. The tripping time of single flowers concentrate on 6-8a.m. and 8-10p.m. daily, and42.4％of the flowers start tripping at 6a.m. Flowers on anthotaxis bloom in turn during theanthesis. A. indica is protandrous, pollen viability lasts from mature buds to 9h afterblooming tested by TTC, while stigma reception lasts from 5h to 24h after blooming testedby benzidine and hydrogen peroxide. Scanning electron microscope shows that pollens areellipsoidal, with 4 germinal furrows and a pitted surface, and paraffin section indicates thatstyle is hollow with a stylar canal. During the whole flowering process, stigma and anthersare still on the same height. Flavor rises up right away after blossom and continues to 24h.2. The OCI is 4, and P/O is 921±70. According to OCI, P/O, bagging and RAPD, the breeding system of A. indica is outcrossing, partially self-compatible, and demand forpollinators. Moreover, self-pollination is not compatible, but geitonogamy is compatible.There is no parthenogenesis in A. indica.3. RAPD was used to estimate the outcrossing rate and gene flow of A. indica. The averageoutcrossing rate ofA. indica is 96.27％, with a high 95％confidence interval from 93.50％through 99.05％. The Daheigong population was used for a gene flow test. Two mothertrees, E and F, were maternal parents, and 96 trees around them were paternal parents. Twomethods, genetic exclusion and maximum likelihood, were used to estimate gene flow ofthe population.①Genetic exclusion: Compare DNA fragments among male parents, female parents and seedlings, if one specific fragment appears in one male parent of allpaternal trees and some sib code but not in female parent, then it shows that the maleparent with the specific fragments has distributed pollen to mother tree so that onepatemity is assured. With 12 primers, each of 2 paternal trees was confirmed to havedispersed pollen to E and F.②Maximum likelihood: Transform the fragments into 0/1data, then calculate the likelihood between paternal parents and sib code with the softwarePHYLIP V3.65. The most likely offspring and father trees would be clustered in the samegroup, so the most likely paternal trees of some seedlings are estimated. Results indicatethat 3 paternal trees have distributed pollen to maternal tree E, while 10 patemal trees havedistributed pollen to maternal tree F. According to the map, 52.9％of pollen dispersal is asfar as 30m-50m, and the amount of downwind distribution is not significantly distinct fromthe upwind.4. The natural fruiting rate of A. indica is very low and limited by pollinators. Thus A. indicais mainly pollinated by insects, such as bees, wasps, flies and ants. With highest visitingfrequency, the most important pollinating insect is Apis cerana subsp, cerana, whichworks at dawn. The activity of pollinating insects is apparently affected by the variation ofdaily temperature so that most pollinating occurs at dawn and dusk.5. Breeding bees and artificial xenogamy could improve fruiting and the yield of seeds inpractice.