Studies On Pathogens And Resistance To Crown And Root Rot In Alfalfa

1.Symptoms of Crown and Root Rot of Alfalfa. Crown and root rot of Alfalfa (CRRA) is a chronic disease throughout the world. Although there were some differences in symptoms caused by different pathogens, the symptoms were not always specific to any one of the pathogens. In Dingxi of Gansu province, infected plants displayed a 20 days late germination and decreased tillering capacity as well as slow growth. The disease is characterized by the presence of dark brown to black, wedge shaped necrotic lesions that spread from the affected crowns downward into root top. According to the investigation in mid-late May in Dingxi of Gansu province, field incidence of CRRA was between 20% and 40%.2. Identification of Pathogens of Crown and Root Rot of Alfalfa .The distribution, pathogenicity of Fusarium species associated with crown and root rot of alfalfa (Medicago saliva L.) were examined in DingXi, Gansu Province, China. Three dominant species have been discovered: (1) Fusarium oxysporum, average growth rate of cultures on PSA in 4 days was 2.35 cm. Myceleium was abundant with white color at first and became violet late on. Microconidia were generally abundant, cylindrical. Chlamydosporses were generally abundant and terminal or intercalary, formed in pairs or in chains. (2) E acuminaium, cultures had growth rate of 3.13 cm, Culture pigmentation was carmine red. Only macroconidia were produced. They were 3-7 septate often with an incurved elongation of the apical cell , and were produced from phialides. Chlamydospores were intercalary in knots. (3) E semitectum, growth rate was 3.35 cm. Culture pigmentation was peach changing to buff brown. Macroconidia displayed wedge shape foot cell , 0-5 septate, formed blastospores from polyblstic sympodial cell. Secondary macroconidia were typical heeled foot cell, 3-7 septate, formed from phialides usually grouped in sporodochia. Chlamydospores were often sparse, globose, intercalary, single or in chains. All of the species were the pathogenic to the disease.This paper happened to be the original study on pathogens of crown and root rot on Alfalfa in China. F. acuminatum and F. semitectum were the first record in alfalfa in China.3. Comparison of Pathogenicity among isolates from Fusarium spp and resistance among cultrvars in alfalfa. Twenty cultivars of alfalfa were artificially inoculated with seven isolates from Fusarium oxysporum, four isolates from F. acuminatum and five isolates from F.semitectum using a test tubes nutritivesolution method. All of the isolates originated from alfalfa in Dingxi of Gansu province, China. Inoculum was prepared from cultures by growing single conidia from each petri dish of potato sucrose agar (PSA) at 24 癈 for 10 days . Then myceleium and conidia spensions were inoculated into tubes that were culturing the alfalfa seedling in. Each test tube was inoculated by equal pathogen suspension. Numbers of surviving seedling was recorded after 7, 9, 11 days. Isolates from different species displayed different virulence. Different alfalfa cultivars differed hi resistance also. Some cultivars such as Verla, Derful , Ameristand 201,Caoyuan2 ,Sitel, Algongum, Tumu 2 , Gannong 2 expressed resistance to crown and root of alfalfa.4 The relationship between the peroxidase (POD) activity and cultivars resistance to crown and root rot in alfalfa. Peroxidase activities in seedling leaves and seedling roots of 16 alfalfa cultivars with different resistance to crown and root rot were determined. The results showed that there were significant difference hi peroxidase activity among 16 alfalfa cultivars both in the leaves and roots. The same results were obtained after inoculated seedling with Fusarium oxysporum. The POD activity decreased in the resistance cultivars but increased in susceptible cultivars after infected. Statistics analysis showed that the POD activity in leaves was positively correlated with their resistance. Perhaps the POD activity in seedling leaves of alfalfa can be used to evaluating the resistance to crown and root rot in alfa...