Effects Of Grazing On Grassland Plant Disease In Eastern And Southern Gansu Province

Grazing is the most frequently measure in native grassland utilization, interactions between pasture and livestock, not only affect the grassland vegetation and soil, but also affect the occurrence and development of plant diseases. In this study, we choosed two separate sites which belongs to semi desert grassland and alpine grassland, the two sites were located at Huan county and Maqu county of Gannan,separately. The grassland plant disease occurrence under different grazing intensity of both sites were suveyed from the year 2013 to 2015, the relationship of the occurrence of plant disease and grazing intensity were analyzed. The main results obtained are as follows:1. A total of 35 fungal diseases has been found from 27 species of pasture plant which belong to 18 genera and 11 families in the two sites, the fungal pathogen belong to 25 species and 20 genera. Ten species and 8 general pathogenic fungi caused 17 disease occurred on 15 species of pasture plant in Huan Xian county, the diseased plants ranked from high to low were Leguminosae, Convolvulaceae, Gramineae, Compositae Rosaceae, Euphorbiaceae, Lamiaceae and Cruciferae, the most common diseases were rust disease(Uromyces lespedezae-procumbentis) of Lespedeza bicolor, leaf spot(Bipolaris stipicola) of Stipa bungeana. Eighteen fungal diseases occurred on 12 species and 12 generas and 8 families pasture plants were found at alpine grassland in Maqu, the most common diseases were rust disease and leaf spot, there were 9 and 4 kinds of plants infected, respectively. The diseased plants ranked from high to low were Compositae, Lamiaceae, Ranunculaceae, Gramineae, Polygonaceae, Leguminosae, Euphorbiaceae and Gentianaceae. The most common diseases were rust disease(Puccinia recondita) of Elymus nutans, leaf spot(Bipolaris sorokiniana) of Bipolaris sorokiniana.2. Among the 35 fungal diseases, ten species of the disease were first found in Gansu province. They are white rust(Albugo macrospora) of Ajuga lupulina, rust disease(Puccinia recondita) of Elymus nutans, rust disease(P.ustalis) of Lamiophlomis rotat, rust disease(P. rubigo-vera) of Thalictrum alpinum, powdery mildew(Erysiphe pisi) of Dracocephalum heterophyllum, powdery mildew(E. cruciferarum) of Neotorularia humilis, leaf spot(Bipolaris sorokiniana) of E. nutans, leaf spot(Cercospora chrysanthemi) of Saussurea hieracioides, leaf spot(B. stipicola) of Stipa bungeana, brown spot(Cercospora sp.) of Polygonum viviparum.3. The effects of grazing on plant diseases varied with the species of plant and plant diseases, the grazing treatments of Huan county are 0, 2.7, 5.3 and 8.7 sheep/hm2, the grazing treatments of Maqu county are 0, 2.7 and 5.3 sheep/hm2, intergrating the research results of two sites, the incidence and disease index of rust of L. bicolor and E. nutans and leaf spot of E. nutans was decreased with the increasing of stocking rates, the values were highest under 0 sheep/hm2 while lowest under 0 sheep/hm2, and the values were significantly lower under 8.7 sheep/hm2 and 5.3 sheep/hm2 compared with the treatment of 0 sheep/hm2(P<0.05). The incidence and disease index of leaf spot of S. bungeana was increased with the increasing of stocking rates, the values were lowest under 0 sheep/hm2 and highest under 8.7 sheep/hm2, the values of disease incidence and disease index were significantly lower under 0 sheep/hm2 and 2.7 sheep/hm2 than that under 5.3 sheep/hm2 and 8.7 sheep/hm2(P<0.05). However, the incidence and disease index of powdery mildew of Convolvulus arvensis and Neotorularia humilis have no significant relativity with the changing of stocking rates.4. The occurrence of major diseases significantly related to the coverage and density of host plants. The incidence and disease index of 3 pasture plant diseases includ rust of L. bicolor, E. nutans, leaf spot of S. bungeana and E. nutans, were significantly positively related to hosts coverage and density(P<0.05), the correlation coefficient were 0.923, 0.802 and 0.765, respectively. The relationship could be expressed by using the equations y=0.884x+23.40, y=2.465x-4.506 and y=1.625x+11.21, ―y‖means disease incidence, ―x‖ means plant density.In a summary, from the view of grassland plant diseases management, the 5.3 sheep/hm2 treatment and 2.7 sheep/hm2 treastments seems the most optimal grazing intensity in Huanxian and Maqu grassland respectively, which given the lowest disease incidence and disease index across the treatments.