Breeding Of Genic Male Sterile Line And Studies On Sterile Mechanism In Pepper

Pepper, one of the major often cross-pollinated vegetable crops in the world, is born withsignificant heterosis in maturity, yield, quality, and disease resistance. At present hybridvarieties originated from conventional cultivars or self-bred lines have been dominantpositions in China’s pepper production. However, artificial emasculation must be carried outbecause of the monoclinous flower during the hybrid seed production, which brings aboutboth high cost and poor seed purity. For now male sterility has been applied to hybrid seedproduction at home and abroad, which plays a promoting role in improvement of seeds purityand reduction of seeds cost. The key issue appearing in the pepper breeding lies in the poorgermplasm resources of male sterility accompanying with poor agronomic and economiccharacters. In order to solve this problem, we have created a new male sterile germplasmresource named MS4by means of wide crosses and artificial mutation since2002. Based onthe inheritance of this original strain, a new genic male sterile line HW58AB was developedthrough hard working for7years. Studies on main agronomic characters, cytology,physiology and biochemistry and molecular biology were conducted for the sake ofexploration of the mechanism of male sterility to take advantage of this new genic male sterileline preferably in pepper breeding.1. A new male sterile strain MS4was obtained by use of wide crosses and artificialmutation with three cultivated species: Capsicum. annuum、C. chinense and C. peruvianum.The male sterile plants had malfunctioned anther that came about almost no or inactive pollengrain, but the pistil developed normally and had fertilization ability. The plants of F1generation were all fertile by biparental cross and the segregation ratio of F2generationcomplied with Mendel’s single gene inheritance model. In the offspring population by sibcross, the number of sterile plants was equal to fertile plants in statistics. The result alsoshowed that the plants of F1generation from MS4crossed by six high generation inbred lineswere all fertile by paired cross, which indicated the strain MS4was related to genic malesterility without finding maintainer lines among all tested materials.2. A new genic male sterile line HW58AB that had malfunctioned anther and abortivepollen with genetic stability was developed by use of sib cross within segregating populationthrough hard working for7years. The line had the conical fruits and presented goodresistance to pepper Phytophthora blight. Further more, we transferred male sterile characterto sweet pepper inbred line CK15so as to provide the breeding materials for furtherinvestigation to the mechanism and heterosis utilization of male sterility in pepper. 3. Observed through paraffin section and electronic microscope, microspore abortion ofthe genic male sterile line occurred at the telophase of microspore mother cell stage whentapetal cells excessively expended with considerable vacuolation resulting in the occupationof the loculi, then the microspore mother cells began to autolyze merged with tapetum layerso that the meioses of pollen mother cells couldn’t process to form the tetrad.4. The changing trend and equilibrium relationship of endogenous hormones includingIAA, ZRs, GA3and ABA between sterile and fertile buds in genic male sterile line werestudied by way of ELISA. The result showed that the buds of sterile plants had lower contentsof IAA, ZRs and GA3, but higher ABA than fertile plants in different microsporedevelopmental stages. Nevertheless, the ratios of IAA/ABA, ZRs/ABA, GA3/ABA of sterilebuds were all less than fertile buds except for ZRs/GA3, which meant that equilibriumrelationship of endogenous hormones changed that it seemed to be a reciprocal reactionbetween the IAA and ABA. The maladjustment of IAA, ZRs and GA3caused male sterility.5. Total93transcript-derived fragments differentially expressed from buds in differentmicrospore developmental stages were screened between sterile and fertile plants by use ofcDNA-AFLP. The result showed that these transcript-derived fragments had high homologywith genes of cell wall biosynthesis and trans-membrane action, electron transport or energymetabolic, defense and stress response, general metabolic and unknown or putative protein.About27and10transcript-derived fragments specifically expressed in the fertile and thesterile buds respectively, which indicated that some gene silence in sterile buds occurredduring microspore developmental staged so that pollen grain became completely abortive.6. The temporal and spatial expression patterns of representative transcript-derivedfragments were analyzed by RT-PCR. The result showed that transcript-derived fragmentsconcerning pectate lyase, acyl-CoA synthetase, arginine decarboxylase specifically expressedor had higher expression level in fertile buds, and other transcript-derived fragments related toperoxidase and proline dehydrogenase specifically or up-regulated expressed in sterile buds.Combination of this result with the content of IAA and activity of peroxidase in budsillustrated that over expression of peroxidase could bring about a lack of IAA, which inhibitedthe elongation of microspore mother cell. In addition, the reduction of free proline because ofthe over expression of proline dehydrogenase could induce the breakdown of membranesystem, which mainly gave rise to microspore abortion.