Abstract
Management and transmission of four seed-borne pathogenic fungi namely,Colletotrichum trifolii, Rhizoctonia solani, Fusarium equiseti and F. incarnatum were investigated on alfalfa plants. The pathogenicity test on alfalf plant showed that R. solaniand C. trifolii caused high percentages of rotted seeds and seedlings mortality (26.45, 26.1% and 31.6, 21.1% , respectively). However, no significant differences were observed between the treatments with F. equiseti and F. incarnatum when compared with the control treatment. Transmission of the pathogenic fungi from seed to mature plant of alfalfa was investigated in this study. Results indicate that the recovery percentages of the tested pathogens gradually decreased from root apex up to the first internodes below the shoot tip, but did not reach to the shoot apex. In order to control these fungi, different concentrations of sodium metabisulphite (SM), sodium salicylate (SS) and hydroquinone (HQ) were tested in vitro. Treatment with SM at 10 mM completely inhibited the growth of all isolated fungi. Under greenhouse conditions, soaking alfalfa seeds in a water solution of hydroquinone at 12mM showed to be the most effective treatment in reducing seed rot and seedling mortality percentages and increasing seedling survival percentages. Application of the tested treatments presented significant increases in growth parameters, photosynthetic pigments (chlorophyll a and b and carotenoids) in leaves and total phenol in alfalfa plants. This study therefore recomended the use of HQ and SM as potential and promising antifungal agents in the protection of alfalfa plants against the tested seed-borne fungi. Key words: Pathogenicity, Colletotrichum trifolii, Rhizoctonia solani, Fusarium equiseti, F. incarnatum, transmission, hydroquinone, sodium metabisulphite and sodium salicylate.
Highlights
Alfalfa (Medicago sativa L.) is the oldest and most important forage crop in the world
Following-up the growing-on-test two months later, results indicated that, most tested fungi caused mild to severe infection in alfalfa plants.C. trifolii and R. solani showed the highest percentages of rotted alfalfa seeds (31.6 and 26.45%, respectively), followed by F. equiseti (17.45%) and F. incarnatum (15.7%), which is not significant as compared to the check (1.6%)
Pathogenicity test indicated that R. solani and C. trifolii were the most devastating fungi causing 26.45, 26.1%, seed infection and 31.6, 21.1% seedling mortality, respectively
Summary
Alfalfa (Medicago sativa L.) is the oldest and most important forage crop in the world. In Saudi Arabia, it is widely cultivated and comes to be the first cultivated forage crop and occupies more than 30% of the cultivated area (Al-Askar et al, 2012). In 2012, the cultivated area under alfalfa in Saudi Arabia was 122,563 hectares, which produced 2,528441 tons. Cultivation is mainly in Riyadh (62879 ha) area of the Kingdom with an average production of 1,264579 tons Seed-borne disease refers to the particular plant diseases that are transmitted by seed. In some cases the transmission on seed is insignificant compared to the population of disease organisms that exist in soil or on weed species. The transmission on seed is the primary means by which a disease spreads. Seed transmission studies help to confirm the seed to plant transmission to prove the pathogenicity and to design the
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