Interspecific Cross-compatibility In Three Bearded Iris Species

In this experiment,Iris tigridia Bunge ex Ledeb.?I.bloudowii Ledeb.and I.germanica L.‘Gold boy' were carried out as test materials for interspecific hybridizations.The cross-compatibility was observed including stigma receptivity,pollen germination and tube growth in fluorescent microscope and embryo development.The seeds obtained from differentby hybridization were germinated and morphologically identified.The morphological characters of interspecific hybrids were also examined in this paper.The aim of this study is to clarify the mechanism of interspecific hybridization incompatibility,enrich the color of irises,and lay a theoretical foundation for overcoming the barriers of incompatibility and breeding new varieties.The main results were as follows:1.The flowering time of three species overlapped for 16 days.Their stigmas were all receptive and could be used as material for the following hybridization.2.The highest cross-compatibility was observed in I.tigridia × I.bloudowii in the comparison of the reciprocal crossings of the three Iris species.Its fruit-setting rate and the embryo rate were 59.01% and 64.42%,meanwhile,those of I.bloudowii×I.tigridia were50.59% and 86.75%,respectively.I.tigridia× I.germanica had the lowest fruit-setting rate and embryo rate,both were 0.3.The fruit-setting rate and the embryo rate of in different combinations of reciprocal crossing were significantly different.When I.germanica was as female parent,the fruit-setting rate was higher than their reciprocal cross,which was 45.83%,so did the embryo rate.Therefore,we should pay attention to the reciprocal difference of their interspecificcrossing.4.The rhythm of fruit growth was similar among self-fertility and cross-fertility of I.tigridia and I.bloudowii.The seeds were atrophied and mature around 23 days.In addition,the average fruit width of I.tigridia×I.bloudowii reached 12.168 mm at 27 days.On the other hand,the average fruit width of I.bloudowii×I.tigridia reached 11.015 mm at 27 days.The fruits of I.tigridia×I.germanica didn't expand any more after about 19 days,and started declining.On the contrary,the fruits of I.germanica×I.tigridia grew normally.5.By observing the pollen germination on the stigma and the growth of pollen tube,the incompatibility between I.tigridia×I.bloudowii reciprocal cross and I.tigridia×I.germanica reciprocal cross was similar.Most of the pollen grains of the four combinations can germinate on the stigma of the parent,but the pollen tube growth rate is slower than that of the parent,and there are abnormal phenomena such as fracture,entanglement,and callose in the pollen tube channel,etc.Each hybrid combination shows different degrees of pre-fertilizationbarriers,but finally the pollen tube can enter the ovary and combine with the ovule.6.After 9 days of pollination,the embryo of the pear-shaped embryo was formed by I.tigridia self-pollination,and the embryo developed and matured after 21 days.While the embryo of the I.tigridia×I.germanica formed scutellum-shaped embryo after 11 days of pollination,the endosperm began to deteriorate after 13 days of pollination,and the embryo completely disintegrated after 17 days of pollination.7.By comparing the seed morphological characteristics between different combinations,we found that the size and 1000-grain weight of seeds from interspecific combinations were different from those of self-crossing of the parents.The seed length,seed width and 1000-grain weight of I.tigridia×I.bloudowii were larger than the parents.However,those of I.bloudowii×I.tigridia were smaller than the parents.8.The highest seed germination rates of I.tigridia×I.bloudowii sowed in the incubator and substrate were 42.22% and 13.33%,respectively.Those of I.tigridia×I.germanica were36.67% and 6.67%.Both of the seed germination rates of I.bloudowii×I.tigridia and I.germanica×I.tigridia were 0.9.The flower pattern of the hybrid of I.tigridia×I.bloudowii resembled the mother,and it had the yellow hair which was unique to thefather..The color of the petals was light purple which was obviously different from that of the parents.