Cytological Study On The Sterility Of F1 Hybrids Between Indica And Japonica Rice

The partial spikelet sterility of intersubspecific hybrids has been a major barrier forutilization of the strong heterosis expressed in hybrids between Oryza sutivu ssp.indcicaand O.sativa ssp.japonica. At present, many investigation revealed that it is caused bymale gamete abortion, female gamete abortion, the unkindness between the pollen and thestigma and so on. But the impregnating process report are really few, also about thecytology characterisitic and reason of the male and female gamete abortion there is noaccordant viewpoint. So the systemic observational study from the female and maleoccuring to the impregnation overing has the vital practical significance to verifies thesubspecies hybrid sterile mechanism.In this study, we used Oryza sativu ssp.indcica (Nanjing 11, IR36), Oryza sativussp.Japonica (Balilla, Nipponbare) and WCV(Dular, 02428) to compound sevencombinations: Balilla /Nanjing11 and Nanjing11/Balilla, Nipponbare/IR36 and IR36/Nipponbare, Balilla/Dular, Nanjing 11/02428 and as well as Nanjing 11/IR36 (CK). Inorder to observe the male and female development and the impregnating process of theseven F₁ hybrids, we have observed large numbers of stamens, pistils and 8h fertilizationovaries by paraffin section and staining with Ehrlich's hematoxylin. Meanwhile, we haveobserved the adsorption and germination of pollens by scanning electron microscope, andthen further discussed the relativity among various factors and the main reason of thesterility of intersubspecific hybrids, the results we had were stated as the follows:1. The four intersubspecies hybrids have been observed abortion from megasporestage to mature embrysosacs stage. By investigating the mature embrysosacs, we foundthat: in the intrasubspecies hybrids Nanjing11/IR36, 5.32% unnormal sacs aborted after8-nucleus stage, and in the hybrids with WVC, almost 99.00% embrysosacses werenormal, but in the subspecies hybrids, 55.88% embrysosacs didn't development normalmature embrysosacses. And there was no obviously difference between the crosses withthe same parents, but the abortiong ratio was obviously different among the hybrids withdifferent parents.2. The two hybrids Nanjing11/Balilla and Balilla/Nanjing11 appeared obviousabortion from the mid-microspore stage to the mature pollen stage, and the abortion ratiorespectively was 77.29% and 66.85%. But in the other two combinations the developmentof the male gamete was almost normal as same as the CK and the crosses with WCV.ByI₂-KI stainability and FDA stainability, we examinated mature pollen fertility and enzyme vigor. The I₂-KI stainability of Nanjing11/Balilla and Balilla/Nanjing11 were both muchtoo lower, respectively 10.53% and 19.96%. The pollen enzyme vigor was also very weak,the accounts of I kind (active pollen ) was 10.01% and 23.49%.3. Observing the amount of pollen adhension on per stigma and the situation of thepollen sproutting, we discovered that, Every stigma of the CK(Nanjing 11/IR36) and thehybrids with WCV (Nanjing11/02428,Balilla/Dular) had many pollen attached, theaverage number is above 20 grains, also the pollen tube elongates quite normally. But theinster-subspecies Nanjing11/Balilla and it's con cross had less than 10 grains per stigma,including 36.00% stigmas attached without pollen.And also massive pollen could't sprout,or the sproutted pollen tube appeared many abnormal phenomenon: short, curving, coarsesurface and so on, some stigmas formed callose stratum on the place where the pollenattached to, and prevent the pollen tube out the stigma surface. But another two hybrids(Nipponbare/IR36 and IR36/Nipponbare) still had the certain proportion stigma with nopollen adhension, and the ratio respectively was 5.56% and 11.76%.4. In the Nanjing 11/IR36 and the hybrids with WVC (Nanjing11/02428, Balilla/Dular), 90% ovaries that have blossomed 8h later have finished double fertilization,formed zygote or been carrying on the first fission, and the primary endosperm nucleushad split many times. But in the four inter-subspecies hybrids, excluding the abortionalfemale and male gamete and the unkindness between stigma and poolen, still had certainratio ovaries which couldn't complete the fertilization.5. From the fructification rate examination, the intersubspecies hybrids were so lowto 15.27% and 17.82% in Balilla/Nanjing11 and Nanjing11/Balilla, and the blighted grainrate is 1.55% and 1.81%. Though Nipponbare/IR36 and IR36/Nipponbare had more highfructification rate, aboved 50%, but the blighted grain rate is high 10.6%, 13.4% and theblighted grain equably distrubit the entire panicle differently from the CK and the hybridswith WCV.6. The relevant analysis between the influence factors ivestigeted and thefructification rate show that: the embryso sacs sterility 0.9765, the pollen sterility 0.8822,the stiga with pollen adhension ratio 0.9238, normal fertilized rate 0.9902. Although allthe coefficients were extremely remarkable correlation, after ananlyzed the effect amongthe factors, we thought the embryso sacs abortion was the main reason leading lowfructification rate.