Screening Of Resistant Mutants To Continuous Cropping Obstacles In Strawberry And Resistance Evaluations Of Their Regeneration Plants

Strawberry is a crop intolerant to continuous cropping. Continuous cropping obstacles restrict sustainable development of strawberry production, which is the most important issues in agricultural production that need to be solved urgently. At present, one of the most effective prevention methods is to cultivate resistant cultivars to continuous cropping obstacles. The resistant mutants to wilt disease (DA-1, TZ-1, TZ-2, SE-1 and SE-2) were selected from the stress of crude toxin of Fusarium oxysporum f. sp by Liu Xuejing. On the bases, the theme is on allelopathic autotoxicity and pathogenicbacteria. for For this paper, It starts with the cause of strawberry continuous cropping obstacles, and includes the following experiments: Screening 4-Hydroxybenzoic acid (PA) tolerant mutant using tissue culture, mutagenesis technique and RAPD identification, evaluation of their growth, differentiation, disease resistance and physiological and biochemical property compared with CK were explored. This study reveals the mechnism of continuous cropping obstacles, creates new sources to improve the breeding efficiency and provides a theoretical basis and technical support for further studying to reduce obstacles as well as for achieving effective control of the obstacles as soon as possible.The main results were summarized as follows:1. Soil samples, as 0-15cm layers, were collected from five continuous cropping strawberry fields, with different cultivation times (2, 3, 5, 7 and 9 years, respectively). The amount of 4-Hydroxybenzoic acid in soil increased with the increasing of continuous cropping years.2. Establishment of direct regeneration system of strawberry under the treatment of PA mutagen was focused firstly. The death rate of buds increased as the concentration of PA increased gradually. The result showed that the PA concentration of 0.24g/L was considered as the selection pressure of resistant mutants, TZ-1 and TZ-2, but the selection pressure of DA-1 was 0.32g/L. The resistance of mutants to PA could be improved as the concentration increased gradually and subculture times. The differentiation of buds of mutant cultivated by PA was not as well as CK, but it was better than wild type. The treatment of PA reduced the index of wild type strawberry, such as height, root length and dry weight. The index of mutants was higher than that of the wild type after being treated by PA. The result of resistance identification indicated that the resistant levels of strawberry mutants to PA were increased compared with their parents. Ten different resistant buds were obtained, named TZ-125, TZ-126, TZ-128, TZ-158, TZ-189, DA-131, DA-133, DA-142, DA-186 and DA-192 respectively. The level of DNA molecules existed differences among mutant plants and wild-type plants, such as DA-1, DA-133 and DA-142, but which of these polymorphisms and anti-toxicity related needs further identification.3. Three different resistant strawberry cultivars (DA, DA-1 and DA-133) were used to evaluate for their resistance to continuous cropping obstacles and the mechanism of their resistance under F. oxysporum inoculated or autotoxins-4-Hydroxybenzoic acid stress was studied with a pot culture experiment. The growth, the dynamic activities of protective enzymes (including PPO, POD and CAT), malondialdehyde (MDA), cytoplasm osmoticum were determined. The result indicated that the dynamic activities of protective enzymes in leaves of regenerated mutants were enhanced significantly. The changes of CAT and POD activities have the similar tendedcy. They increased at the beginning, and then decreased after the regenerated and their parents were treated with the combination stress. The activities of CAT and POD in leaves of regenerated mutant DA-133 were higher than those wild type DA and resistant mutant to wilt disease DA-1. The content of MDA of DA-133, DA and DA-1 increased after treated with the combination stress and the growth of DA-133 was higher than that of DA and DA-1. The root activity of DA, DA-1 and DA-133 plants treated with all stresses declined as time goes on, and DA-133 was highest among wild type DA, DA-1 and DA-133. The change of root electrolyte leakage was opposite to the root activity change. It decreased after different treatment, but DA-133 was lowest among DA, DA-1 and DA-133.