The brittle rachis of the Tibetan weedrace (Triticum aestivum var. tibetanum) was found to be governed by a single dominant gene on the short arm of chromosome 3D. The new brittle rachis gene was designated Br1. This study also discovered that the type of disarticulation is governed by many genes that may differ from brittle rachis genes. In other words, the same brittle rachis gene may exhibit various types of disarticulation in various genetic backgrounds. So, after the brittle rachis gene (barrel type) in Aegilops tauschii entered hexaploid wheat through the amphidiploid path, it might exhibit the wedge type of disarticulation.

Thirty-eight crosses between seven Fagopyrum species native to China were studied. Following normal pollination, there were very low inter-group crossabilities (only 0-3%) between five species in the large-achene group and two species (F. gracilipes and F. pleioramosum) in the small-achene group, and high (15-50%) within the large-achene group, i.e. F. esculentum, F. tataricum, F. zuogongense, F. pilus and F. megaspartanium. Crosses between various types of flowers (homostyle, heterostyle etc.) suggested that the intraspecific incompatibility also occurs in interspecific crosses. The hybrid seeds obtained from interspecific crosses all withered or shrivelled and lacked activity. Only one hybrid plant was obtained, tetraploid F. esculentum tetraploid F. zuogongense. The hybrid displayed anomalous behaviour at meiosis, pollen grain sterility and withering of achenes, confirming the genetic differences between F. esculentum and F. zuogongense. The results support the hypothesis that F. megaspartanium and F. pilus are the possible ancestors of cultivated buckwheat

Eleven accessions of eight species belonging to the big-achene perengroup of genus Fagopyrum Moench were studied on the basis of pereninterspecific hybridization, GOT (i.e., glutamate oxaloacetate trans-aminase) isozyme band characteristics, and cytology. Following nor-mal pollination, there were high crossabilities (8-37%) among these different species, but all hybrid seeds were empty except the crosses among F. esculentum Moench, F. esculentum var. homotropicum (Ohnishi) Q-F. Chen (F. homotropicum Ohnishi), and F. esculentum subsp. ancestrale Ohnishi, indicating that there are no reproductional isolations among F. esculentum, F. esculentum var. homotropicum, and F. esculentumsubsp. ancestrale. The cytological observation showed desigthat the hybrid F. esculentum F. esculentum var. homotropicum shows eight normal bivalents in meiosis of pollen mother cells. In addition, the results of GOT isozyme showed that F. esculentum, F. esculentum var. homotropicum, and F. zuogongense possess common GOT isoenzyme bands. Fagopyrum megaspartanium and F. pilus exshow nique GOT bands as well as karyotypes supporting the classifi-cation of individual species. The cytological analyses showed that tetraploid F. cymosum and F. giganteum are allotetraploids with two different size genomes. The identities of the different genomes in the big-achene group of genus Fagopyrum and the putative progenitors of common buckwheat are discussed.

The diploid and autotetraploid common buckwheat, their autotriploid hybrids and trisomics were studied comparatively on aspects of the chromosome behavior at meiosis of pollen mother cells (PMCs) and the fertility of pollen grains. The results of observation of meiosis MI of PMCs showed that the average configurations of chromosome pairing in the autotetraploid variety Emka, its inbreeding line Emka-1 and autotriploid hybrids are 4x=0.67I+11.60+0.32+1.79IV=32, 4x =0.71I+7.42+1.19+ⅡⅢⅡⅢ3.22IV=32, and 3x=4.71I+4.71+3.29Ⅱ=24Ⅲ, respectively. The averages of micronuclei number in TⅡ cells in the diploid variety Siva, autotetraploid Emka and Emka-1, and the autotriploid hybrids are 0.03, 0.09, 0.20, and 0.86, respectively. Fertility of pollen grains showed that Siva has the highest fertility of pollen grains (the dyed rate of pollen grains in I2-KI solution is 98.89%), followed by autotetraploid Emka and Emka-1 (95.33% and 93.33%) and the autotriploid hybrids (only 31.28%) with the lowest fertility. The correlation analyses showed that there is significantly negative correlation between dyed rate of pollen grains (x1) and the average of univalent number (x2) or the averages of micronuclei number (x3), with r12=-0.996** or r13 =-0.993** respectively and significantly positive correlation (r23=0.994**) between x2 and x3, indicating that the number of univalent is one of the important factors resulting in formation of micronuclei at TⅡ of meiosis and that univalent number and micronuclei number can cause genetic and physiological imbalances and then result in an increase of abortion of pollen grains. In the autotriploid hybrids backcrossed with diploid variety Sobano there are 27.72% rate of empty seeds set and only 3.08% rate of normal seeds set. Among 34 normal achenes of the autotriploid hybrids, there were 6 double trisomics (2n+2), 23 trisomics (2n+1) and 5 diploid plants (2n). The segregation of short-style (Ss) and long-style (ss) plants in back-crossing progenies of Tr1-18 trisomics showed that the S gene locates on Tr15 trisomics of common buckwheat.

Inheritance of disarticulation in progenies of hybrids among Tibetan weedrace (9053 and AS907 of Triticum aestivum var. tibetanum), Yunnan hulled wheat (AS338 of T. aestivum concv. yunnanense) and spelt wheat (AS326 of T. aestivum concv. spelta) was studied. Disarticulation type is governed by some disarticulation modifying genes. These modifying genes can be divided into two groups, that is, wedge modifying genes (Wm) and barrel modifying genes (Bm). The two kinds of genes are codominant. Wedge type disarticulation is governed by the complement of at least two dominant wedge modifying genes (Wm1 and Wm2, Wm3 and Wm4, or Wm5 and Wm6). Barrel type disarticulation is controlled by at least one dominant barrel modifying gene (Bm1, Bm2 or Bm3) and its expression can be inhibited in certain genetic backgrounds. As to the background inhibition that dominant barrel modifying genes cannot express in some homozygous brittle rachis wheat, the hypothesis of epistasy of many homozygous alleles was suggested.