Studies On Morphology Basis Of Superior And Inferior Fruit In Hazelnut

Hazel(Corylus spp.)is one of the four important nuts,and has the nutritional and edible value.Therefore,hazel has demonstrated a huge market prospects.Hazel has a unique delayed fertilization characteristic.During early fruit developmental stage,frequent ovary abortion is obvious,and its detail process remains unknown.In this study,detail fertilization process of hazel was studied,and structure differences between developing and abortive ovary was compared.These studies results revealed the characteristics of fertilization in hazelnut,and the reason leading to ovary abortion was clarified.The main study results were listed as follows.(1)The results showed ovaries and ovules of hazel were invisible at the time of blooming.Early ovary and ovule primordium began to form from 15 and 20 days after blooming,respectively.Integument and mature embryo sacs differentiated from the nucellus on 40 th and 55 th day after blooming,respectively.Pollen tubes were retarded in the bottom of the style or the pollen tube cavity for about 26 days.Then,the pollen tubes were observed to leave the PTC and began to enter the ovary two days later.After that,a single pollen tube passed though vicinity of the micropyle.Finally,pollen tubes made a curve line to penetrate the embryo sac through the tissue of the chalaza instead of micropyle on 52 and 55 days after blooming respectively.The results of more in-depth information will be beneficial to better understanding of the delayed fertilization process in hazel.(2)The average number of pistillate flowers per inflorescence(ANP)and average number of fruit per cluster(ANF)of four hybrid hazel cultivars were 7.6-8.5 and 2.4-3.0 respectively;in C.heterophylla,its ANP and ANF was 5.8-6.2 and 3.5 respectively.The total drop varied from 50% to 67%.Ovary abortion in hazel initiated from about 30 days after blooming.The percentage of abortive ovaries in the four hybrid hazel cultivars ranged from 63% to 72%,and was significantly higher than that of C.heterophylla(29–42%).Only the abortive ovary ratio of C.heterophylla was significantly reduced after artificial pollination.Fruit number per cluster was positively and negatively correlated with yield and nut mass,respectively.In abortive ovaries,the diameter remained less than 2 mm during the entire fruit development,an integument seldom differentiated and a mature embryo sac never developed.In addition,pollen tube growth was arrested at the style base about40 days after blooming.Thus,fertilization of the ovule was precluded.Compared with abortive ovary,starch content in developing ovary of four hybrid hazel cultivars and C.heterophylla were significantly higher.Thus,this study shows the hazelnut has delayed fertilization trait,showing an obvious intermittent growthpattern.Its pollen tube growth process can be divided into three steps:(1)From the stigma to the PTC of the style outside the ovary.(2)From the PTC to the end of the style within the ovary.(3)From the end of the style within ovary to the integument,chalazal,and embryo sac.To conclude,abortive ovary was incapable to finish fertilization process due to the absence of mature embryo sac and arrested pollen tubes.For the four hybrid cultivars,abortive ovary was likely associated with insufficient resource availability to support fruit set by all flowers,whereas ovary abortion in C.heterophylla was at least partly determined by pollen availability.