Study On Histopathology Of Strawberry Roots Infected By Fusarium Oxysporum F. Sp. Fragariae Under Autotoxin Stress

The sustainable development of strawberry production has been severely restricted bythe replant diseases of strawberry. In this paper, the paraffin section technology of roots oftwo strawberry cultivars (’Toyonoka’ and ’Tutela’) was optimized on dehydrating, waxing,dewaxing and dying, and the lateral root development process was observed with theoptimization technique. Experiment on potted plants of strawberry were conducted todetermine the effect of4-Hydroxybenzoic acid, an allelochemical in the root exudates ordecomposed liquid, and Fusarium oxysporum f.sp. fragariae in continuous croppingobstacles of strawberry. The histopathological changes of roots of two different strawberrycultivars infected by F.oxysporum f.sp.fragariae after inoculating pathogen under autotoxinstress were defined. The main results were summarized as follows:1. After being fixed by FAA liquid, the strawberry roots were dehydrated in70%,85%,95%alcohol for50minutes, respectively, and then hyalined after dewatering twice in100%ethanol for30minutes each time; the pure wax should be replaced for three timeswith every6hours at58℃before being embedded and sectioned. After being dewaxedwith xylene for40minutes, the roots should be dyed with sarranine and solid green, andthen the strawberry root sections were obtained with clear dying and completedorganization.2. The development process of lateral root was about72hours. At first, somepericyclic cells in primary roots began to divide with a periclinal growth; after24hourspericycle cell layers unevenly increased; after48hours, pericycle cells broke through thecells into the cortex and formed lateral root primordia; root primordia elongated graduallyand passed through the cortex and epidermal cells after60hours;72hours later, the cellnumber of lateral root primordial increased sharply and the meristem formed the lateralroots in the end.3. With the elongation of the time, the infection rates of hyphae in strawberry rootstissue inoculated with F. oxysporum f.sp. fragariae under autotoxin stress were faster thanthose of hyphae in strewberry roots tissue inoculated with the pathogen alone. After inoculation24days, catheter infection rates of ’Toyonoka’ and ’Tutela’, were62.2%and50.0%, respectively, significantly higher than those treated with of pathogen alone.4. The destruction degrees of epidermal, cortical, stele cells and duct walls afterinoculating F. oxysporum f.sp. fragariae under autotoxin stress both were more seriousthan those treated on both cultivars with the pathogen alone to the both cultivars. At thelate stages, epidermal and cortical cells had broken or fallen off, and the inclusions incatheters had blocked the parts of catheters after inoculating F. oxysporum f.sp. fragariaeunder autotoxin stress. But, the roots structure treated with F. oxysporum f.sp. fragariaealone were more integrated. At the same time, the destruction degree of cells in ’Toyonoka’roots was severer than that of ’Tutela’.5. With the elongation of the inoculation time, the inclusions in catheters were bothincreasing continuously in two cultivars. The infection rates of catheter in roots of’Toyonoka’ and ’Tutela’ after inoculating F. oxysporum f.sp. fragariae under autotoxinstress, were22.5%and15.8%, respectively, higher than those8.9%and12.1%of F.oxysporum f.sp. fragariae treatments. The rate of catheter containing jelly of ’Tutela’, was26.3%after inoculating F. oxysporum under autotoxin stress, higher than that of’Toyonoka’(16.3%) at the same conditions and that of ’Tutela’(17.5%) after inoculating F.oxysporum f.sp. fragariae.The rate of catheter containing tylosis of ’Tutela’ afterinoculating F. oxysporum f.sp. fragariae was1.6%,higher than that of ’Toyonoka’ at thesame conditions and ’Tutela’ after inoculating F. oxysporum f.sp. fragariae under autotoxinstress, respectively, were1.0%and1.2%.