紫花含笑传粉生物学初探

Pollination biology of Michelia crassipes

紫花含笑(Michelia crassipes)花色艳丽、花香浓郁,为解释其在自然条件下结实率低的原因和判断最佳杂交时期,该研究从传粉生物学入手,通过观察紫花含笑开花动态,运用异交指数(OCI)、花粉胚珠比(P/O)、花粉和柱头活性、人工授粉试验等方法对其繁育系统进行了检测,并记录访花昆虫的种类和行为。结果表明:(1)紫花含笑花期在4—5月,持续50 d左右,单花花期4~5 d。(2)雌雄同花,雌蕊先成熟,雄蕊空间位置高于雌蕊。(3)OCI等于4,P/O为2671±123。(4)套袋实验表明紫花含笑能进行少量的自花传粉,人工异花授粉结实率和种子质量显著高于人工自花授粉和自然条件下,且不存在无融合生殖。(5)开花后36 h雌蕊群弯曲分泌粘液时,与含笑(M.figo)杂交结实率最高达85.7%,为最佳授粉时期。(6)有效访花者主要有东方蜜蜂、黑纹食蚜蝇和独角仙,访花频率易受天气影响。综上说明,紫花含笑繁育系统以异交为主,部分自交亲和需要传粉者,存在一定近交衰退,自然条件下结实率低,主要受传粉昆虫和雌雄异熟限制,最佳授粉期的确定能够提高其杂交成功率。该研究结果为紫花含笑资源保护和杂交育种奠定了基础。

Michelia crassipes,a small tree to low shrub in Magnoliaceae,is a great ornamental plant with fragrant and dark purple flowers. It is a great ornamental germplasm resource for breeding Magnolia plants for container production. In order to explain the main reasons for the low natural seed rate of M. crassipes and determine optimum pollinating time for Magnolia cross breeding,the pollination biology of M. crassipes was studied. We attempted to study the floral character through field observation in Changsha. We also estimate the type of breeding system by out-crossing index( OCI),thepollen-ovule ratio( P/O),pollen viability and the stigma receptivity. And artificial pollination experiments were carried out. The visitors and their behaviors were observed and recorded. The results were as follows:( 1) The florescence of the M. crassipes was from mid-April to late May,lasting for approximately 50 d. Each flower opened for 4-5 d.( 2) M. crassipes was a typical species that monoecious with protogyny and herkogamy,and stamen was higher than pistil on spatial location. However,pistils were ready before stamens.( 3) The outcrossing index( OCI) was four and pollen/ovule ratio( P/O) was 2,671±123,which indicated that M. crassipes should be majorly classified as an allogamous plant.( 4) The artificial pollination revealed that spontaneous self-pollination phenomenon was existed and no apomixis phenomenon under field conditions. The fruiting rates and seed quality of artificial cross-pollination were significantly higher than that of natural and self-pollination.( 5) The optimal time to pollinate M. Crassipes with M. figo was 36 h after flowering when the gynoecium began to bend and secrete mucus,with the highest successful fruiting rate of 85.7%.( 6) The effective pollinators mainly were Apis cerana,Episyrphus balteatus and Allomyrina dichotoma whose frequency of pollination was low and easily affected by weather. In conclusion,the breeding system of M. crassipes was self-pollination,and mainly cross-pollination which requires pollinators. In addition,inbreeding depression was existed to some extent. And its fruitsetting rate was limited by pollinators and herkogamy under natural conditions. The success rate of hybridization could be raised by determining the optimum pollination time. The results can promote for protecting the resources M. Crassipes and hybridization of Magnolia.