Studies On Intergeneric Distant Hybridization Between Brassica Species And Orychophragmus Violaceus And New Germplasm Creation

Orychophragmus violaceus L. is a species of Cruciferae. It was cultivated in someplaces as an ornamental plant. O. violaceus has attracted increasing attention of therape-breeders, owing to its good agronomic characters. This paper has made somestudies on the ovary culture, the compatibility and pollen-stigma interaction betweenBrassica species and O. violaceus and others such as the morphological character,cytology and SSR molecular identification of intergenetic hybrids and so on.Theresults were as follows:(1) Crosses were made between B.species and O. violaceus. Total 15117 stigmaswere pollinated and 6034 ovaries were cultured,and 231 pods, 238 pollinated seeds and12 F₁ hybrid plants were obtained.(2) The crossing-compatibility were studied between B. species and O.violaceus,and the results showed that there were higher incompatibilities between themand it was very difficult to get intergeneric hybrids, the number of hybrid seeds wasrelated to the parental genotype and crossing types.The crossing-compatibilities werehiger when B. species were used as the maternal parents than when O. violaceus asmaternal, which indicated that the maternal parent had obvious influence oncrossing-compatibilities. More seeds could be obtained through ovary culture.(3)The pollen-stigma interaction between B. species and O. violaceus wereobserved under fluorescent microscope. The results showed that the incompatibilityand rejection responses had occurred between B. species and O. violaceus in a certainextent, and were obvious on stigma. The binding degree and germinating rate of pollengrains were weakened when B. species respectively was pollinated with O.violaceus.The pollen grains of O.violaceus was hardly ever observed binding to the stigma ofB.species which was respectively used as female parent. The callose could be foundeasily depositing in papillose cells in these combinations.Germinated pollen tubes grewslowly on the stigma and gave rise to the distortion of pollen tubes,and swelled of theirtops, Thus, the quantities of germinating tubes on the stigmas and of penetrating stigma were reduced. Sometime, a few of pollen tubes could enter into styles throughstigmas. In addition, the binding degree and germinating rate of pollen grains varied inthese combinations, in other words,there were different degrees of compatibilitybetween the pollen grains of O. violaceus and the stigmas of the different B. species.Thecompatibility between the pollen grains of O. violaceus and the stigmas ofB.juncea(Sichuanhuanzi) was higher than those of B.napus (Xiangyou15)×O.violaceus and B.campestris (Lilinbaicai)×O. violaceus. It was suggested that theincompatible reaction caused by pollen-stigma interaction could be the one of mainbarriers of intergeneric crosse between B. species and O. violaceus.(4) Using Brassica napus, B. campestris,B. juncea and O. violaceus asexperimental material, crosses were made to produce intergeneric hybrids through ovaryculture techniques. It showed that ovary culture was more effective in terms of seedsobtained when ovaries were in vitro culture at the 7th day after bud pollination. Amongthese cross combinations,the number of hybrid seeds(F₁) obtained from differentcombinations varied and the ratio of setting seeds of the combination of Hongyejie×O.violaceus was highest and 12.20 seeds per 100 ovaries were obtained. The number ofhybrid seeds obtained from derect cross and reciprocal cross combinations is alsoobviously different,more seeds could be obtained by selecting the female parent withhigh cross-compatibility. Of the media studied, MS media supplemented with variousplant hormones,such as 6-BA,NAA was better than B₅ media also supplemented withthe same plant hormones, while MS media supplemented with 2.0mgL^-16-BA+0.2mgL^-1NAA+500 mgL^-1casein+0.5% actived carbon showed the best response to allcross combinations. The results of the treatments on maternal stigma indicated thatGA₃,Gly and NaCl solution can't improve cross-compatibility between B. species and O.violaceus.(5) Morphological characters of hybrids (F₁) were investigated and the resultsrevealed that a majority of F₁hybrids showed the same morphological characters as theirfemale parents,a minority of them had an intermediate morphology between the twoparents,such hairy leaves, serrated leaves and purple petioles et al as in the male parentO.violaceus and a few showed new morphological characters which both parents didn't. For example, petal colour of hybrid (F₁) from the combination of 742×O. violaceuswhich were ivory-white and leaf shape of hybrid(F₁) from the combination of Younensi×O. violaceus were obviously distinguished from those of the two parents.(6) The pollen fertility of F₁ hybrids were observed between B. species and O.violaceus and the results showed that the ratios of fertile pollen were different amongthese cross combinations and the range of pollen fertility of F₁ hybrids centred around0-21% by pollen stainability, two plants from the cross combinations of 742×O.violaceus and Younensi×O. violaceus were male sterility.(7) SSR analysis from 4 primer pairs selected from 55 primer pairs wasemployed to identify the 192 F₁ plants obtained from cross combinations betweenB.species and O. violaceus and the results indicated that 12 F₁ plants had characteristicSSR segments of both parents or lost one of the characteristic SSR segments of femaleparent,thus, these F₁ plants were true intergeneric hybrids.The results also suggestedthat the SSR molecuar marker technique is accurate,simple,fast and efficient in hybrididentification.(8) The remarkable genetic variation presented in the intergeneric hybridssuggested intergeneric cross between B.species and O. violaceus could be apromising way to create new germplasm.