Root-invading Fungi Of Alfalfa And Their Pathogenicity In Different Ecologic Areas

The objective of this study was to explore the common root diseases of 41 different Alfalfa (Medicago sativa L.) varieties sampling roots in spring, summer and autumn growing seasons of the years 2006 and 2007 from three ecological zones in Henan province, China. Fungi were isolated from alfalfa rootlet and identified. The results showed that: (1) 10, 16 and 10 fungi were isolated from Anyang, Xuchang and Zhengzhou regions, respectively. The dominant species were different for three seasons. In Anyang, Alternaria alternate and Fusarium solani were the dominant fungi in three growing seasons, in addition, F. semitectum and F. oxysporum were also the dominant fungi in spring and summer, and F. acuminatum and Cylindrocarpon destructuns in autumn. In Xuchang, A. alternate and Rhizoctonia solani were the dominant fungi in three growing seasons, in addition, various dominant fungi appeared in three seasons: F. oxysporum and F. solani in spring, F. acuminatum and F. oxysporum in summer, Cylindrocarpon destructuns and F. acuminatum in autumn. In Zhengzhou, A. alternate, F. oxysporum and F. solani were the dominant fungi in three growing seasons, F. anthium in spring, grey colony in summer and autumn. (2) Root-invading fungi and their incidence in three growing seasons showed notable differences (P<0.05). The obtained from alfalfa rootlet was related to both growth seasons and alfalfa varieties. In spring, lower percentage of fungal isolation appeared and higher values in summer and autumn in Anyang and Xuchang. In Anyang, percentage of fungal isolation of Sitel, Farmers and Vernal were highest in spring, summer and autumn ,respectively. Varieties with higher mean percentage of fungal isolation are Sitel, Farmers, Phabulous, Flight No.4 and Hunter River in order. Varieties with lower mean percentage of fungal isolation are Alfaking, Affinity, WL-525HQ, Apex and Amerileaf 721 in order. In Xuchang, variety WL-525HQ showed the highest percentage of fungal isolation (100%) in spring, Alfaking et al in summer and Siriver et al in autumn. Varieties with higher mean percentage of fungal isolation are Alfaking, WL-525HQ, Sitel, Siriver and Aohan in order. Varieties with lower mean percentage of fungal isolation are Algonguin, Vernal, Golden-queen, Grandeur and THG-1 in order. In Zhengzhou, percentage of fungal isolation of Millennmium, Golden-queen and Amerimultileaf were highest in spring, summer and autumn respectively. Varieties with higher mean percentage of fungal isolation are WL-525HQ, Millennmium, Eureka, Golden-queen and Aohan in order. Varieties with lower mean percentage of fungal isolation are Alfasuper, Sitel, Affinity, Derby and Algonguin in order. It is very important was found that a new record: F. anthium was a new fungus isolated from alfalfa.Effects of inoculation with the isolated fungi on the seedling of 14 alfalfa varieties indicated that: (1) Nine isolations of F. semitectum had stronger pathogenic effects to alfalfa than control. (2) F. acuminatum isolated of different varieties showed notable inhibition on the root length, seedling length, disease indexes and germination rate for the same variety, however, various varieties responded differently to the inhibition. (3) Six isolates of F. solani, especially from variety LM400 had stronger pathogenicity, causing the disease indexes of 62.98. Root length and seedling length were reduced 63.01% and 51.50% after inoculation respectively. (4) Six isolates of R. solani also inhibited the root length of tested varieties significantly, most of which, R. solani from Golden-queen and Powerplant showed strongest inhibition on the root length. Accorging to integrated accessment of measurement including disease index, relative germination, relative root length and relative shoot length, fungi isolated from lucerne rootlet including nine isolations of F. semitectum, six isolates of F. solani, fifteen isolations of F. acuminatum and six isolates of R. solani were pathogenic to lucerne seed and seedling. Compared to resistance to those fungi among the 14 alfalfa varieties, Victoria, Vernal, Algonguin, Alfaking and Hunter river have more powerful resistance. However, Sandy, Amerileaf721, WL-323HQ, Phabulous and Sanditi have stronger susceptibility.To estimate the effect of variety, fungi and water content on the disease index, final survivals, root weight, seedling weight, root length and its weight, we found that significant effect of fungi and water content and their notable interaction(P<0.01). There is no difference in disease index between varieties; however, notable interaction was detected between variety and water content. Comparing with the control, higher disease index and lower survivals were found in the varieties inoculated with fungi especially with F. solani (P<0.05). Different fungi showed no influence on the root weight, however, indicating the significant interaction between the variety, fungi and water content (P<0.01). Inoculation with the fungi can reduce or improve the development of root. Seedling weight was also largely affected by variety, fungi and water content (P<0.01) and notable interaction was found between three factors. F. solani showed significant restriction on the seedling weight (P<0.05), however ,no obvious effect observed on the fungi separated from the variety“Xunlu”. Variety, fungi and water content showed observable influence on the seedling length(P<0.01)and notable interaction was observed between fungi and water content, however, no notable interactions between variety and fungi, variety and water content, fungi and water content. Reduced seedling lengths were found in three varieties inoculated with F. solani at three water content levels(P<0.05).Fungi, variety and water content showed the notable effect on the activity of POD, SOD, PAL (P<0.01). Clear interactions were observed between variety and fungi, fungi and water content. PPO activity in Algonguin after inoculation with F. solani was significant reduced comparied with Powerplant and Alfaking (P<0.05). After inoculation with F. solani, activity of POD followed clearly as the order: Algonguin﹥Powerplant﹥Alfaking. The order Powerplant﹥Algonguin﹥Alfaking occurred notably after inoculation with F. semitectum. Making a comparison among three water contents, the highest POD activity of Algonguin and Powerplant appeared at 50% (P<0.05). However, highest POD activity of Alfaking happened at 70% content, with lowest activity at 30% (P<0.05). At each water content, POD activity differed largely among varieties, but the touch down order were Algonguin﹥Powerplant﹥Alfaking at 30% and 50% water content and Algonguin﹥Alfaking﹥Powerplant at 70% level (P<0.05). After inoculation with fungi, SOD activity decreased for all varieties. Its activity in Alfaking was higher than in other varieties after inoculation with F. solani and F. semitectum. Comparing among three water contents, SOD activity of Algonguin and Powerplant was higher at normal level (50%) than at low (30%) and high (70%) levels, however, the lower activity of Alfaking appeared at high water content than other levels. At each water content, SOD activity of Powerplant was the lowest and of Alfaking highest. PAL activity of Algonguin and Powerplant were higher at normal level (50%) than at low (30%) and high(70%)levels, however, the lower activity of Alfaking appeared at low water content than other levels. After inoculation, PAL activity of Algonguin and Powerplant increased to a degree but insignificantly.